Thermal pericyclic tandem reactions

FULL PAPER

Thermal Pericyclic Tandem Reactions^[‡]

Henning Hopf*^[a]and Joachim Wolff^[a]

Keywords: Acetylenes / Claisen rearrangement / Cope rearrangement / Domino reactions / Pericyclic reactions / Thermal

isomerizations

Gas phase thermal isomerizations of twelve acetylenic sys-

hydrogen-shift processes were employed as the pericyclic

tems, all of which can in principle undergo two successive steps from which the tandem processes were composed. The

pericyclic steps, are described. The substrates, the syntheses

and spectroscopic properties of which are presented, are

formal derivatives of but-2-yne, with different functional

compositions of the pyrolysates obtained were determined

over broad temperature ranges, and the mechanisms of the

individual steps producing the pyrolysis products are discus-

groups in the 1- and the 4-positions. The Cope, Claisen, sed.

Claisen ester, retro-ene, 1,5-hydrogen shift, and 1,5-homo

Introduction

kcal·mol^Ϫ1).^[6]In the other characteristic type of reaction

Ϫ addition Ϫ in which acetylenes normally participate, the

thermodynamically less favorable π-bonds are replaced to-

tally or partially by σ-bonds, and a countless number of

inter- and intramolecular addition reactions involving

acetylenes are known.^[7]Finally, acetylenes are attractive as

starting materials or intermediates in organic chemistry be-

cause they are often very easily available. By exploitation of

the acidity of terminal alkynes, all types of functional

groups may be introduced and chain extensions of different

complexity can readily be carried out.

In this paper we present a comprehensive study of the

thermal isomerization of various acetylenic systems, all of

which can in principle undergo two pericyclic steps in tan-

dem fashion. In these substrates the triple bond serves two

functions: on the one hand it is the ‘‘energy reservoir’’ and

‘‘molecular fuse’’ for the isomerization under consideration,

and on the other it ‘‘holds together’’ the two pericyclic

steps.

In the current discussion on improvement of the effici-

ency of chemical transformations, concepts such as atom

economy,^[2]tandem and domino reactions,^[3]solvent-free

processes,^[4]and catalytic transformations with high stereo-

selectivities^[5]play important roles. While it would probably

be very difficult to design chemical reactions involving all

of these features, it is attractive to develop processes incorp-

orating at least several of them. As far as atom economy is

concerned, two types of chemical reactions clearly stand

out: isomerizations and additions. Whereas the molecular

masses of starting material and product are identical in the

former transformations, the mass of the product in the lat-

ter is the sum of the masses of the reaction partners, as no

atoms are lost in the process. The second and the third

points on the above list are often encountered in thermal

processes, and when these proceed according to a pericyclic

mechanism they often also take place in highly stereoselec-

tive fashion. During the course of our work on the pyrolytic

behavior of alkynes, allenes, and cumulenes, we have ob-

served several thermal isomerizations (see below), which

may best be described as tandem reactions composed of

several pericyclic steps. That acetylenes and/or their iso-

meric allenes are particularly prone to participation in these

processes is not surprising; they are energy-rich substrates,

which may experience considerable stabilization as a result

of redistribution of their π-electrons over the σ-framework:

i.e., isomerization. A simple example illustrating this ‘‘de-

localization’’ of π-electrons over a more extended σ-skel-

eton is provided by the heats of formation of the three C₄H₆

isomers but-1-yne (∆H°_f(g)ϭ 33.9 kcal·mol^Ϫ1), buta-1,2-di-

ene (33.2 kcal·mol^Ϫ1), and buta-1,3-diene (20.7

Results and Discussion

Selection of Substrates to be Studied

The different acetylenes we wished to subject to gas

phase (i.e., solvent-free) pyrolysis are summarized in

Scheme 1. This reaction matrix begins with deca-1,9-dien-

5-yne (1), a hydrocarbon that can undergo two successive

Cope isomerizations, and the thermal conversion of which

into 3,4-bismethylenehexa-1,5-diene (‘‘2,3-bisallyl-1,3-buta-

diene’’) we already described many years ago (see below).^[8]

Proceeding along the first row of the scheme, we next arrive

at the enolether 2, in which a succession of Claisen and

Cope steps (or vice versa, see below) appears feasible. Entry

number 3 allows for the combination of the Cope process

with a Claisen ester isomerization, entry number 4 that of

a Cope with a retro-ene step (i.e., in this latter case we are

losing some of the atoms of the substrate). To combine a

[‡]

Thermal Isomerizations, XXXI. Ϫ Part XXX: ref.^[1]

[a]

Institut für Organische Chemie, Technische Universität

Braunschweig,

Hagenring 30, 38106 Braunschweig, Germany

Fax: (internat.) ϩ 49 (0)531/391-5388

E-mail: h.hopf@tu-bs.de

Eur. J. Org. Chem. 2001, 4009Ϫ4030

WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001

1434Ϫ193X/01/1121Ϫ4009 $ 17.50ϩ.50/0

4009

H. Hopf, J. Wolff

FULL PAPER

Scheme 1. A selection of substrates for tandem reactions involving disubstituted alkynes

1,5-hydrogen shift process with a Cope rearrangement, we substrates and simplicity of performing chemical trans-

proposed to study the hydrocarbon 5 as a model system, formations with them are concerned. In the following sec-

while with the cyclopropane derivative 6, allowing the inclu- tions we describe the preparation and gas phase pyrolysis

sion of a 1,5-sigmatropic homo hydrogen shift reaction, our of 12 of the 21 derivatives presented in Scheme 1, systems

combinatorial scheme grows still further. The remaining particularly well suited in our opinion to demonstrate the

entries in the scheme are self-explanatory.

scope and limitations of the sequential processes.

It is also of interest to include cyclopropane rings in some

of the substrate molecules, because the ring strain of the

three-membered ring results in the energy content of the

starting material being increased still further. We had al-

ready previously demonstrated that the subsystem cis-1-

ethynyl-2-methylcyclopropane readily undergoes the an-

ticipated hydrogen shift process.^[9]Although the concept of

using highly unsaturated starting materials that also contain

a strained ring is attractive for the design of systems capable

of undergoing multiple pericyclic tandem reactions, the syn-

thesis of these doubly activated starting materials could be-

come a problem in certain cases. Cyclopropane and cyclo-

butane chemistry has experienced phenomenal growth in

the last two decades,^[10]but it still cannot compete with

Preparation of Starting Materials

From the retrosynthetic viewpoint, it is advantageous to

cleave the molecules collected in Scheme 1 between the

triple bonds and a neighboring carbon atom, since the re-

sulting six building blocks 22؊27 (Scheme 2) have all been

described in the chemical literature.

Scheme 2. Starting materials for the synthesis of the acetylenes

acetylene chemistry as far as (commercial) availability of shown in Scheme 1

4010

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Thermal Pericyclic Tandem Reactions

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Of these, the cyclopropylacetylene 27 was the most diffi-

cult to prepare at the outset of our studies, the others being

available by published procedures (see Exp. Sect.). The

cyclopropane 27 had originally been obtained as a mixture

of isomers by cyclopropanation of pent-2-en-4-yne with di-

azomethane/cuprous chloride.^[9]However, the yields of this

reaction were so low that it was impossible to synthesize

the hydrocarbon in amounts large enough for subsequent

steps. The route presented in Scheme 3, arrived at after

much optimization work, finally furnished trans-27 in mul-

tigram amounts.

Scheme 4. Preparation of the methyl propargyl ethers 4, 9, 18, and

the but-3-enylalkyne 6

The acetylenes, obtained in 30Ϫ40% yields, were stable,

colorless liquids that could be purified by vacuum distilla-

tion; they were characterized by the usual spectroscopic and

analytical methods (see Exp. Sect.). In principle, 22, 24, and

27 could also be used as starting materials for other derivat-

ives shown in Scheme 1 for 2, 7, and 11 by use of bromome-

thyl vinyl ether as the trapping reagent, for example. Since

this compound is not readily available, however, the corres-

ponding coupling reactions were not attempted.

trans-1-Hex-5-en-1-ynyl-2-methylcyclopropane (6): When

acetylides are treated with a non-activated electrophile, such

as 4-bromobut-1-ene (35), much harsher reaction condi-

tions are necessary. In fact, this process was only used for

the synthesis of 6, since this hydrocarbon could not be ob-

tained by any other route (Scheme 4). When the reaction

was carried out in THF solution, no coupling of 27 with 35

could be accomplished; only when HMPT was added as

more polar co-solvent was the cyclopropylacetylene derivat-

ive produced, although only in poor yield (10%). The

reason for this disappointing result can be seen in the low

reactivity of 35 and its high tendency to undergo dehy-

drobromination in the presence of base, to give buta-1,3-di-

ene.

Scheme 3. Preparation of trans-1-ethynyl-2-methylcyclopropane

(trans-27)

The synthesis began with the alkylation of ethyl ace-

toacetate (28) with propylene oxide (29), a process de-

scribed in the literature,^[11]and which provided 3-acetyl-5-

methyldihydro-2-furanone (30) in one step in acceptable

yield (50%). When the ring-opening of this lactone was car-

ried out with a mixture of dichloromethane/conc. hydro-

chloric acid under phase-transfer conditions (PTC), 5-chlo-

rohexan-2-one (31) was obtained in 42% yield. Subsequent

ring-closure of 31 under the conditions reported in the liter-

ature with sodium amide provided trans-1-acetyl-2-methyl-

cyclopropane (32), but the yields were disappointing. When

potassium tert-butoxide was employed as base, however,

compound 32 was isolated in yields between 70 and 80%.

Chlorination of 32 to give the dichloride 33 was problem-

atic,^[12]and in our hands yields in the 40% range could not

be exceeded. Under the drastic reactions conditions used

(see Exp. Sect.), ring-opening to 2,5-dichlorohex-2-ene (in-

ter alia) was observed. The final dehydrochlorination step

with potassium tert-butoxide in ether to give trans-27 could

again be carried out in acceptable yield (61%).

Enynes 5, 10, 17, and 20: These conjugated enynes were

prepared by Hagihara coupling of 22, 24, 25, and 27 with

1-bromoprop-1-ene (36, mixture of isomers, Scheme 5).

Scheme 5. Preparation of the conjugated enynes 5, 10, 17, and 20

The yields of these reactions were acceptable (40Ϫ50%),

and since 36 was employed as a (E)/(Z) mixture the enynes

were also produced as mixtures of diastereomers. In most

cases the coupling provided decidedly more of the (Z) iso-

mer. Separation was achieved by preparative gas chromato-

graphy, allowing full spectroscopic identification of the dif-

ferent enynes.

Trapping of the acetylides prepared from 22؊27 with dif-

ferent electrophiles permits most of the alkynes summarized

in Scheme 1 to be prepared. These derivatives fall into two

categories: unsymmetrically and symmetrically substituted

acetylenes.

7-Vinyloxyhept-1-en-5-yne (2): As mentioned above, since

bromomethyl vinyl ether is not a readily obtainable reagent,

a) Unsymmetrically Substituted Acetylenes

Methyl Propargyl Ethers 4, 9, and 18: These three methyl its direct coupling with terminal acetylenes was not a viable

propargyl ethers were prepared by coupling the lithium option for preparation of propargyl vinyl ethers. Since,

salts of 22, 24, and 27, respectively, with bromomethyl moreover, the addition of alcohols to acetylenes can be qu-

methyl ether (34), as shown in Scheme 4.

ite demanding from the practical viewpoint,^[13]we decided

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H. Hopf, J. Wolff

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Scheme 6. Preparation of the unsymmetrical propargyl vinyl ether 2

to use a procedure originally proposed by Brandsma for the

synthesis of 24^[14]to prepare the propargyl vinyl ether 2. As

shown in Scheme 6, compound 22 was first chain-elongated

to afford the propargyl alcohol 37, which was subsequently

converted into 7-(1-chloroethoxy)hept-1-en-5-yne (38) by

treatment with paraldehyde in the presence of hydrogen

chloride.

In this conversion, the initially produced hemiacetal re-

acted further, to give 38 by a nucleophilic substitution.

When 38 was added to hot N,N-diethylaniline, dehydro-

chlorination took place and 2 was formed in approximately

40% yield, the product having to be removed from the reac-

tion flask immediately on formation.

Scheme 8. Preparation of the diester 12 and the divinyl ether 7

b) Symmetrically Substituted Acetylenes 19 and 12, and

also 7

Pyrolyses

For acetylenes bearing two identical substituents, the best

starting materials are acetylene and but-2-yne-1,4-diol (42,

see Scheme 8). As shown in Scheme 7, the bis-Grignard re-

agent derived from acetylene, 39, reacted with propanal to

give the expected diol 40 (mixture of diastereomers), which

yielded the vinylacetylene 41, as a mixture of isomers, on

treatment with phosphorous tribromide in pyridine (yield

50%, Z/E ratio 2:1).

Pyrolysis experiments were carried out in a conventional

tubular furnace equipped with an empty quartz tube con-

nected on one side to an evaporation system (kugelrohr

oven with evaporation flask) and on the other to a cold

trap cooled with liquid nitrogen. This set-up allowed experi-

ments to be performed both in the mg range (product ana-

lysis by GC or GC/MS analysis) and also on a preparative,

gram scale (product analysis after gas chromatographic sep-

aration by conventional spectroscopic methods). Contact

times were estimated as several seconds, and in all experi-

ments a complete temperature profile was determined: the

reaction temperature at which isomerization was just begin-

ning to occur was determined, as was the highest temper-

ature at which the starting material was fully consumed.

The temperature increase was carried out in 25Ϫ30-degree

steps.

The first sigmatropic tandem isomerization of simple

acetylene derivatives were studied by us as early as 1985

and involved the hydrocarbon 1 and the ester 3.^[8]The pro-

totype for the thermal isomerization of 1 was the propargyl

Scheme 7. Preparation of octa-2,6-dien-4-yne (19)

With diazabicycloundecane (DBU) in DMSO, compound Cope rearrangement^[15]of hex-1-en-5-yne (22) to hexa-

41 underwent the second dehydrobromination step and fur- 1,2,5-triene (45), studied extensively by Huntsman and co-

nished the dienyne 19 as a mixture of isomers [(Z,Z)/(Z,E)/ workers^[16](Scheme 9).

(E,E) ϭ 3:5:17, GC analysis] in 39% yield; the hydrocarbons

could be separated by preparative gas chromatography and cess more and more became accompanied by an irreversible

were fully characterized spectroscopically (see Exp. Sect.). cyclization reaction producing 3- and 4-methylenecyclopen-

As pyrolysis temperatures increased, this reversible pro-

1,4-Diacetoxybut-2-yne (12) is easily made by ester- tene (47 and 48). The cyclization was initiated by a 1,5-C,C-

ification of 42 with acetyl chloride in dichloromethane bridging step, which generated the diradical 46; this species

(70Ϫ80% yield). When compound 42 is first esterified with that underwent 1,2-hydrogen shifts in two different direc-

formic acid in toluene, the resulting diester 43 was con- tions to furnish the dienes 47 and 48. Incorporation of a

verted in 26% yield into 1,2-bis(vinyloxy)but-2-yne (7) on second butenyl substituent into 22 created the prerequisites

treatment with TebbeЈs reagent (44) (Scheme 8).

for a tandem Cope rearrangement process, and when 1

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Thermal Pericyclic Tandem Reactions

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3, was of particular interest. Its thermal isomerization be-

tween 190 and 500 °C is represented by the yield vs. temper-

ature diagram in Figure 1.

Scheme 9. Tandem pericyclic reactions of 1 and 3

was heated to 410 °C compound 1 indeed isomerized to

give 4,5-dimethyleneocta-1,7-diene (50). The primary iso-

merization product, the allene intermediate 49, could not

be isolated under the reaction conditions. An increase in

the pyrolysis temperature to 470 °C caused the formation

of 3,4-dimethylenecyclooctene (51), presumably through an

intramolecular ene reaction. Thus, compound 1 experienced

three consecutive pericyclic steps in total, and since the re-

sulting cross-conjugated triene, a cyclic [3]dendralene deriv-

ative,^[17]is set up for a DielsϪAlder addition, even a fourth

pericyclic step appears feasible in principle. Because the ac-

tivation energies of allyl ester rearrangements are higher

than those of pure Cope isomerizations (see below), it has

been argued^[8]that an allene intermediate should be isolable

if one of the allyl subsystems of 1 were replaced by an ester

function. This was indeed the case. At 460 °C the allene 52

was obtained from 3 as the primary product, and when the

temperature was raised to 540 °C the expected tandem

product 55 was formed, accompanied by the five-membered

ring compound 54. This latter ester was produced since the

harsher reaction conditions necessary for the 52 Ǟ 55 iso-

merization to take place also induced five-membered ring

formation by way of 53. That the conjugated isomer of 54,

corresponding to 47, could not be isolated under these con-

ditions might well be the result of still another

[3.3]sigmatropic shift. This would produce 1-acetoxy-2,3-di-

methylenecyclopentane, which, with its now exocyclic con-

jugated diene system, could participate in cycloaddition re-

actions to afford higher molecular weight material.

Figure 1. Temperature profile for the pyrolysis of 7-vinyloxyhept-

1-en-5-yne (2)

The rearrangement set in at a comparatively low temper-

ature (see the other isomerizations described below), and at

300 °C the substrate had been fully converted. The primary

product was the allene 59, which reached its peak concen-

tration of 41% at 290 °C. Beginning at ca. 250 °C, 3,4-di-

methylenehept-6-enal (62) was produced, and reached its

maximum concentration (87%) in the product mixture at

350 °C. As well as these two main isomerization products of

2, up to 12% of 3-methyl-4-methylenehept-6-enal (60) was

produced. At higher temperatures (400Ϫ500 °C), increasing

amounts of 2-methyl-3-methylenehexa-1,5-diene (56) could

be detected; this hydrocarbon was the main pyrolysis prod-

uct above 450 °C. Up to 400 °C these products were the

only ones produced, but at higher temperatures the reaction

becomes increasingly complex, yielding numerous other iso-

merization and fragmentation products as shown by GC/

MS analysis. Altogether the process constitutes a preparat-

ively useful route to the trienal 62. The sequence of events

during the pyrolysis of 2 is charted in Scheme 10.

The initial [3.3]sigmatropic rearrangement of the sub-

strate can follow either a Cope or a Claisen path. Since

neither the product of the former process (58) or its cycliza-

tion product (61), which might be produced through the

intermediate 57 in analogy to the 52 Ǟ 54 cyclization, could

be detected in the pyrolysate, the Claisen process evidently

won the competition in this first step. Actually this is not

surprising, since a CϪO double bond is generated in this

isomerization (see below). Intermediate 59 then underwent

1. Pyrolyses of the Hex-1-en-5-yne Derivatives 2, 4, 5, and 6

a) Pyrolysis of 7-Vinyloxyhept-1-en-5-yne (2): In view of the expected Cope process to furnish the main product, 62.

the above complex thermal behavior, the pyrolysis of the To account for the other identified pyrolysis products we

vinyl ether 2, more highly oxidized than 1 but less so than propose that 62 then enolized, resulting in the generation

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H. Hopf, J. Wolff

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As can be seen from the diagram, this substrate was ther-

mally more stable than 2. Whereas 4 was still the predomin-

ant component of the pyrolysate at about 400 °C, no 2 sur-

vived under these conditions. The only product generated

from 4 up to this temperature was the allene 64, produced

in ca. 40% yield. From there on, essentially three products

were formed: 3-methylenehexa-1,5-diene (65), 3-methoxy-

methyl-4-methylenecyclopentene (66), and 2-methylfulvene

(70); at ca. 500 °C these were present in roughly equal

amounts. Above this temperature, aromatization set in, and

benzene and toluene were chiefly formed from the above

precursors. The formation of 64 and 65 is self-explanatory

(Scheme 11): the former is the result of a Cope rearrange-

ment that clearly requires less energy (see below) than the

ene reaction producing the latter product.

Scheme 10. Tandem pericyclic processes in the pyrolysis of 2

of the cross-conjugated enol 63, which was converted into

60 by way of a 1,5-hydrogen shift. Finally, the triene 56

could be produced by decarbonylation of 60 and/or 62, car-

bon monoxide loss being a well established process at

higher temperatures.^[18]

b) Pyrolysis of 7-Methoxyhept-1-en-5-yne (4): Proceeding

from 2 to 4, we now encountered a rearrangeable system

that for the first time contained a subunit that could be split

off during the cascade process. This was disadvantageous

from the point of view of atom economy, but it could in

principle result in a simpler product mixture composition.

Actually, this was not the case for 4, at least not at higher

reaction temperatures. The temperature profile for the pyro-

lysis of this ether between 200 and 600 °C is shown in Fig-

ure 2.

Scheme 11. Tandem pericyclic processes in the pyrolysis of 4

Higher temperatures favored five-membered ring forma-

tion, and 64 was converted into 66 by way of 67 through a

mechanism similar to the one discussed above. The simplest

route to the fulvene 70 could involve loss of methanol from

68 to give the [3]dendralene^[17]69, which would stabilize

itself in turn by a hydrogen shift. The thermal cleavage of

unsaturated methyl ethers to dienes and methanol is a

known process that takes place in high yield.^[19]

It was again surprising that the conjugated isomer of 66,

the ether 68, was missing from the pyrolysate, although it

could in principle easily have been generated through a 1,2-

hydrogen shift. Derivative 68, however, meets the prerequi-

sites for undergoing retro-ene cleavage to give 71 (loss of

formaldehyde). To reach 70 from this diene intermediate,

though, would require hydrogen loss. 1,2-Bismethylenecy-

clopentane (71) could not be detected among the pyrolysis

products.

c) Pyrolysis of Nona-1,7-diene-5-yne (5): In this hydrocar-

bon the initial isomerization step could be either a Cope

rearrangement or a 1,5-hydrogen shift. Since both processes

Figure 2. Temperature profile for the pyrolysis of 7-methoxyhept-

1-en-5-yne (4)

4014

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Thermal Pericyclic Tandem Reactions

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occur with comparable activation energies (see below) it was

difficult to predict the outcome of this primary competi-

tion. When a mixture of cis/trans-5 was pyrolyzed between

300 and 500 °C, essentially three products were formed

(Figure 3), two of them Ϫ 1-allyl-3-methyl-2-methylene-

cyclobutene (73) and 2-allylcyclohexa-1,3-diene (75) Ϫ cle-

arly being intermediates, and the other, benzene (76), being

produced as a final product. It was shown by GC analysis

that thermal equilibration between the diastereomers of the

starting material took place.

Scheme 12. Tandem pericyclic processes in the pyrolysis of 5

valence isomer lies completely on the side of the open-chain

product. If, however, one of the double bonds of the diene is

replaced by an allene group, the situation begins to reverse,

because the high endothermicity of the allene grouping can

overcome the ring strain of the cyclobutene ring. Thus, an

equilibrium between penta-1,2,4-triene (vinylallene) and 3-

methylenecyclobutene is established when these hydrocar-

bons are heated to approximately 170 °C in a static re-

actor.^[23]The vinylallene derivative 72 cyclized analogously

to 73, with the additional double bond presumably contrib-

uting to the ring-forming process. Note that no methylene-

cyclopentene derivative was produced from 72, although the

structural prerequisites were fulfilled (see above); probably

the cyclization temperature was too low for this process to

compete.

Figure 3. Temperature profile for the pyrolysis of nona-1,7-dien-5-

yne (5)

At the relatively high temperature of 450 °C, about 60%

of the substrate still survived, whereas 75 made up 26% of

the pyrolysate. While 73 was vanishing from the product

mixture (ca. 2%), 76 was beginning to become detectable

(ca. 2%). In interpretation of the formation of these hydro-

carbons we propose that the initial step of this tandem se-

quence was the formation of the Cope product 72. With its

hexa-1,2,4-triene substructure it was able to participate in

the expected 1,5-hydrogen shift, which would produce 3-

vinylhexa-1,3,5-triene (74) as a reactive intermediate. 1,5-

Hydrogen shifts of this type have been investigated thor-

oughly by Okamura and co-workers, who used them in their

extensive studies on novel routes to Vitamin A and D deriv-

atives.^[20]Conjugated trienes are known to electrocyclize be-

tween 350 and 400 °C,^[21]and the ring-closure of 74 to the

cyclohexadiene 75 hence comes as no surprise (Scheme 12).

The aromatization of cyclohexa-1,3-diene at temperatures

above 500 °C by radical processes is well known,^[22]and

since 75 had to eject a (resonance-stabilized) allyl radical

during this process, benzene (76) formation was already act-

ive at lower temperatures. Unexpected in view of the reac-

tion matrix (Scheme 1) was hydrocarbon 73. It should be

kept in mind, though, that the number and type of peri-

cyclic processes were deliberately restricted when this

scheme was composed. Had other pericyclic reactions, such

as the important electrocyclizations, been included, the

scheme would, of course, have been more complex. Cyclo-

butene 73 is indeed an electrocyclization product. Normally

d) Pyrolysis of trans-1-Hex-5-en-1-ynyl-2-methylcyclopro-

pane (6): The pyrolysis of the cyclopropylacetylene 6 com-

pleted the prototype tandem processes summarized in the

first row of Scheme 1. As shown in the conversion diagram

(Figure 4), trans-6 was stable up to 300 °C under flow con-

ditions.

Figure 4. Temperature profile for the pyrolysis of 1-(hex-5-en-1-

ynyl)-2-methylcyclopropane (6)

At ca. 310 °C, small amounts of 3-(2-methylcyclopro-

the equilibrium between a 1,3-butadiene and its cyclobutene pyl)hexa-1,2,4-triene (77) were formed. Increases in the

Eur. J. Org. Chem. 2001, 4009Ϫ4030

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H. Hopf, J. Wolff

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temperature in small steps caused an increase in the yield,

near 20% conversion being attainable at 430 °C. At that

point a veritable explosion of complexity set in, resulting in

at least 20 different products, all of them isomers of the

starting material 6 as shown by GC/MS analysis. Needless

to say, separation of this mixture was impossible. In the

hope of reducing the number of isomerization products, the

pyrolysis was repeated at 200 °C in a static system. In addi-

tion to 6 (78%) and 77 (8%, GC analysis), the same complex

pyrolysate was generated again. Whether 6 really preferred

the Cope process over the 1,5-homo hydrogen shift, which

would produce the C₁₀H₁₄hydrocarbon 78, could not be

determined. The activation energy of the conversion of 1-

ethynyl-2-methylcyclopropane to hexa-1,2,4-triene is un-

known^[9](Scheme 13).

Figure 5. Temperature profile for the pyrolysis of 1,4-bis(vinylox-

y)but-2-yne (7)

Scheme 13. Tandem pericyclic processes in the pyrolysis of 6

al (81) were produced. Clearly, the reaction had taken place

as expected, as a tandem Claisen rearrangement to yield the

desired 80 (Scheme 14).

From what we have learned so far, it is obvious that both

77 and 78 could serve as entries for other thermal intercon-

versions. For example, they could both participate in a sub-

sequent pericyclic step that would produce 4-vinylocta-

1,4,7-triene or Ϫ as allylallenes Ϫ they could form methyl-

ene cyclopentane-1,3-diyl intermediates (see above). Other

reaction channels could be opened up from either of these

species, yielding still further C₁₀H₁₄isomers. Clearly, this

thermal process of a hydrocarbon without a built-in point

of fracture is preparatively useless (see below).

Scheme 14. Tandem pericyclic processes in the pyrolysis of 7

This dialdehyde, however, was unstable under the reac-

tion conditions, and it was decarbonylated to the aldehyde

81. Looking back to Figure 5, it is apparent that the reac-

2. Thermal Isomerization of the Enol Ethers 7, 9, and 10

The second row of Scheme 1 displays a collection of enol tion is not a ‘‘clean’’ one; side products were already being

ethers. Comparing these substrates with those of row 1, we formed at ca. 250 °C and dominated the reaction above

note that the allyl group in 2Ϫ6 has been replaced by a 310 °C. According to GC/MS analysis, these (unidentified)

vinyloxy substituent. In the section below, the pyrolyses of products were either isomers of 7, 79, and/or 80 or cleavage

the model systems 7, 9, and 10 are discussed. Since CC products. Before judgment is passed on the preparative

double bonds are converted into carbonyl groups in all value of the 7 Ǟ 80 isomerization, it should be kept in mind

these processes the driving force for the respective isomeriz- that 2,3-difunctionalized buta-1,3-dienes are difficult to

ations should be high.

prepare by other routes, fulgenic acid (buta-1,3-diene-2,3-

a) Pyrolysis of 1,4-Bis(vinyloxy)but-2-yne (7): As seen in dicarboxylic acid) and its anhydride being particularly well

Figure 5, and in line with expectations, the isomerization known examples.^[24]

set in at very low temperatures (Ͻ 180 °C), and at 280 °C

b) Pyrolysis of 1-Methoxy-4-vinyloxybut-2-yne (9): The

none of the starting material remained. Unfortunately, the pyrolysis of 9 was a remarkable process: it was clean (no

primary product, produced in approximately 60% yield at side products), and it yielded only two products (Figure 6).

240 °C, could not be isolated by preparative gas chromato-

Surprisingly, however, these were not the expected prod-

graphy because of its low stability. By GC/FT-IR analysis, ucts (see below), but 2-methoxymethylbuta-1,3-diene (83)

however, it could be identified as 3-vinyloxymethylpenta- and isoprene (86, Scheme 15).

3,4-dienal (79), its intense allene band at 1969 cm^Ϫ1being

If it is postulated that 9 should prefer the Claisen process

of particular diagnostic value.

over the retro-ene cleavage (see above), the initial pyrolysis

Between 280 and 320 °C the main product of the iso- product should be 82, not the allene vinyl ether 84. If 82

merization was 3,4-dimethylenehexane-1,6-dial (80), separ- were subsequently to fragment by a retro-ene process, the

able by preparative gas chromatography and identified by dienal 85 should result. Neither 82 nor 85 were isolated,

the usual spectroscopic methods (see Exp. Sect.). Beginning however, although we should at least expect 85 not to be

at 280 °C, small amounts of 4-methyl-3-methylenepenten-4- particularly sensitive. After all, the dialdehyde 80 is an isol-

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Figure 6. Temperature profile for the pyrolysis of 1-methoxy-4-vi-

nyloxybut-2-yne (9)

Figure 7. Temperature profile for the pyrolysis of 6-vinyloxyhex-2-

en-4-yne (10)

The main product obtained up to this temperature was

the cyclohexadienyl acetaldehyde 94. It was produced in

60Ϫ70% yield between 300 and 400 °C, making this process

an attractive preparative route to this diene system. As a

side product, 3-(prop-1-enyl)penta-3,4-dienal (90) was gen-

erated. Above this temperature the thermolysis became

more and more intricate and the product mixture was in-

creasingly composed of degradation products. Among

these, the cross-conjugated hydrocarbon 3-methylenehexa-

1,4-diene (95), benzene (76), toluene (96), and 3-methylene-

cyclohexene (97) could be found, the aromatic products be-

Scheme 15. Tandem pericyclic processes in the pyrolysis of 9

able product in the pyrolysis of 7. Intermediate 82 by- coming Ϫ as expected Ϫ more and more important as the

passed retro-ene cleavage by splitting off carbon monoxide temperature increased. The formation of all of these prod-

to produce 83, the main pyrolysis product. For this latter ucts can be interpreted by the transformations summarized

ether, only one reaction path was open. This was the retro- in Scheme 16.

ene cleavage to 86, evidently the most energy-demanding

The tandem sequence began with the Claisen isomeriz-

step in the whole cascade. Interestingly, Jung and Zimmer- ation of 10 to the aldehyde 90, which subsequently evidently

man observed a similar process during flash vacuum pyro- underwent the expected 1,5-hydrogen shift. The anticipated

lysis of methyl 4-vinyloxybut-2-ynoate (87), which initially isomerization product, 91, however, did contain a hexa-

resulted in the allene ester 88.^[25]At higher temperatures, 88 1,3,5-triene subsystem and so could readily undergo electro-

was converted into methyl 2-methylene-but-3-enoate (89) by cyclization to give the cyclohexadiene derivative 94. Since

decarbonylation, in a fragmentation process involving hy- 90 and 94 are both aldehydes, we should not be surprised

drogen transfer from the formyl substituent to the central to see them suffer decarbonylation as the temperature is

carbon atom of the allene group by way of a five-membered increased. Whereas the cleavage product from 94 (hydrocar-

transition state.

bon 97) was indeed isolated, the intermediate produced

c) Pyrolysis of 6-Vinyloxyhex-2-en-4-yne (10): The pyro- from 90 (the vinyl allene 93) still had several steps ahead of

lysis of this substrate, carried out between 100 and 600 °C, itself before it could reach a stable situation. Through a 1,5-

produced one of the most complex product mixtures en- hydrogen shift, a process known to take place in methyl-

countered in this study. As shown in Figure 7, isomerization substituted vinyl allenes,^[20]it rearranged to its linearly con-

of the vinyl ether set in at low temperatures, and conversion jugated isomer 92, which again fulfilled the prerequisites for

of 10 was already complete at 300 °C.

a 1,5-hydrogen shift and isomerized in turn to the [3]den-

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Figure 8. Temperature profile for the pyrolysis of 1,4-bis(acetoxy)-

but-2-yne (12)

Scheme 16. Tandem pericyclic processes in the pyrolysis of 10

dralene 95. Remarkable in these latter processes are the ob-

servations that the vinyl allene 93 did not cyclize to a

methylenecyclobutene derivative (see above) and that the

trans isomer of 95 was formed, the cis diastereomer being

the expected isomerization product. In view of the relatively

high temperatures it seems reasonable to assume that both

93 and 95 preferred their thermodynamically more stable

isomers under the conditions of their generation. Finally,

aromatization and cleavage of 97 to give toluene (96) and

benzene (76) is a known high temperature process.^[26]

Scheme 17. Tandem pericyclic processes in the pyrolysis of 12

3. Thermal Isomerization of 1,4-Diacetoxybut-2-yne (12)

The butadiene 99 was also able to lose ketene (100) to

furnish 103, in a process similar to the one described by

Allan and co-workers^[27]for the vinyl ester of acetic acid

(101), which on heating between 500 and 550 °C in the gas

phase fragmented into acetaldehyde (102) and ketene (100).

In this third category (row three in Scheme 1) we had so

far studied only the pyrolysis of the diester 12; this, how-

ever, is a relative of the monoester 3, the thermal behavior

of which was already discussed in the introductory chapter.

Although 12, with its two ester groups as the only re-

arrangeable substituents, was expected very probably to re-

quire high isomerization temperatures and so presumably

yield complex product mixtures, it was not expected that

its pyrolysis would give such disappointing results as were

actually observed (Figure 8).

4. Thermal Isomerization of the Methyl Propargyl Ethers

17 and 18

a) Pyrolysis of 6-Methoxyhex-2-en-4-yne (17): The ether

17 (mixture of isomers) represented an attempt to couple a

As shown in this diagram, 12 was indeed thermally very retro-ene process to a 1,5-hydrogen shift. Although results

stable. Significant conversion of starting material only set in of preparative significance were not expected (see below),

at approximately 450 °C, a temperature at which numerous the compound was pyrolyzed between 300 and 650 °C to

products were also beginning to be formed in small concen- add another piece to our increasingly complete mosaic of

trations. As the only isolable and identifiable product, 3- thermal pericyclic tandem processes. As shown in Figure 9,

acetoxybut-3-en-2-one (103) was obtained in 25% yield at the ether was thermally very stable. Significant isomer-

550 °C. To explain these results we postulate that the inten- ization was observed only above 450 °C and gave only one

ded tandem process from 12 to 99 by way of 98 did occur product: 1,3-cyclohexadiene (107). This constituted ca. 60%

as anticipated, but that both intermediates fragmented un- of the pyrolysate at 600 °C. The only other product formed

der the harsh reaction conditions (Scheme 17).

was benzene (76), which became the major component

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crease in the pyrolysis temperature caused increased toluene

production, accompanied above ca. 570 °C by rising quant-

ities of benzene (76) (Figure 10).

Figure 9. Temperature profile for the pyrolysis of 6-methoxyhex-2-

en-4-yne (17)

Figure 10. Temperature profile for the pyrolysis of 1-(3-methoxy-

prop-1-ynyl)-2-methylcyclopropane (18)

Altogether, the pyrolysis was not very ‘‘clean’’ and many

other products were produced in small yields (Scheme 19).

At ca. 450 °C the sum of these ‘‘impurities’’ amounted to

25Ϫ35% of the pyrolysate. The most interesting products in

these experiments were the five-membered ring compounds

111 and 112. All the other components of the thermolysis

mixture could be accounted for by mechanisms similar to

those already presented several times in this study. In other

Scheme 18. Tandem pericyclic processes in the pyrolysis of 17

above 650 °C. Scheme 18 effortlessly explains these observa- words, 18 entered into the isomerization sequence by con-

tions. version into 108 (1,5-homo hydrogen shift). By a retro-ene

In a manner comparable to a knightЈs move in chess, the process this lost formaldehyde to provide hepta-1,3,6-triene

triene 106 was produced either by a retro-ene process fol- (113), which rearranged by a 1,5-hydrogen shift into its con-

lowed by a 1,5-hydrogen shift, by way of 104, or by the jugated isomer 114. The most likely thermal reaction path

reversed sequence of these steps, via 105. Since neither 104 available for this hydrocarbon was its cyclization to toluene

nor 105 accumulated during the process, the activation en- (96) and benzene (76). Obviously, 113 could also be reached

ergies of both pericyclic steps appear to be quite similar (see from 18 by way of 110. The primary product was a deriv-

below). Although both 104 and 105 are vinylallene derivat- ative of allylallene (45, see above) and, as such, prone to

ives, neither cyclized to a methylenecyclobutene at these intramolecular cycloaddition (by 1,5-carbon bridging) to

high temperatures, as discussed previously. The cyclization yield the diradical 109. Like the parent system 46, 109 was

of 106 to 107 was expected, as was its aromatization to 76 able to undergo 1,2-hydrogen shift reactions in two different

(see above).

directions, furnishing the nonconjugated diene ether 111 or

b) Pyrolysis of trans-1-(3-Methoxy-prop-1-ynyl)-2-methyl- its conjugated isomer 112 as a mixture of diastereomers.

cyclopropane (18): With its multifarious structural features, As methyl allyl ethers, both of these pyrolysis products in

we would expect a varied thermal behavior for the cyclopro- principle could in principle participate in further pericyclic

pylacetylene 18. This was indeed the case, although, unfor- reactions, and this may be part of the reason why the com-

tunately, at no temperature was one single pyrolysis product position of the product mixture is so complex in this case.

favored over its isomers or cleavage products. The tandem

process was triggered relatively late (at ca. 400 °C) and first 5. Thermal Isomerization of the Enyne Hydrocarbons 19

produced small amounts of 7-methoxyhepta-1,4,5-triene and 20

(108). From 450 °C onwards three additional products were

This study began with the presentation of the pyrolytic

generated; these were cyclopentenes 111 and 112 (formed behavior of a hydrocarbon, deca-1,9-dien-5-yne (1), and we

as a mixture of (E)/(Z) isomers that could not be separated also wish to end it with the description of the behavior of

by gas chromatography) and toluene (96). A further in- two hydrocarbons under flash vacuum conditions: octa-2,6-

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Scheme 19. Tandem pericyclic processes in the pyrolysis of 18

dien-4-yne (19) and 1-methyl-2-(pent-3-en-1-ynyl)cyclopro- six-membered isomerization products, all of which could be

pane (20). degraded to 76 and 96. Clearly, the initiation step in this

a) Pyrolysis of Octa-2,6-dien-4-yne (19): Although this di- transformation produced such an energy-rich intermediate

vinylacetylene in principle had many interesting options to that no discrimination between the ensuing isomerizations

undergo sequential reactions after an initial 1,5-hydrogen and/or fragmentations could take place any longer.

shift had converted it into octa-1,3,4,6-tetraene, these pos-

sibilities evidently could not be seized under the prevailing

reaction conditions. As shown in Figure 11, the substrate

was essentially stable up to 500 °C.

b) Pyrolysis of trans-1-Methyl-2-(pent-3-en-1-ynyl)cyclo-

propane (20): Replacement of one of the double bonds in

19 by a cyclopropane ring gives hydrocarbon 20. Since this

is clearly more strained than the divinylacetylene 19, one

would expect it to isomerize under milder conditions and

hence engage in a more specific pericyclic tandem sequence.

On the other hand, because of the numerous isomerization

possibilities ‘‘built’’ into 20, we might expect a rather com-

plex composition of the pyrolysis mixture. By and large

these assumptions were born out by experiment. The re-

arrangement began at ca. 320 °C, 100 degrees lower than

that of 19, and at 460 °C all of the starting material had

been transformed. Depending on the temperature, three hy-

drocarbons were obtained: 2-vinylcyclohexa-1,3-diene (75),

3-but-2-enylidenecyclopentene (119), and benzene (76),

which constituted ca. 50% of the pyrolysate at 500 °C (Fig-

ure 12).

Preparatively, the tandem process is of very limited use,

since these three hydrocarbon products are Ϫ as shown by

GC/MS analysis Ϫ accompanied by numerous other prod-

ucts formed in yields too low to enable separation and char-

acterization. Note also that four diastereomers of 119 are

possible. Since the GC fraction containing this hydrocarbon

could not be further separated, the structure assignment

shown must remain speculative. A mechanistic scheme ac-

counting for the formation of 119, 75, and 76 is shown in

Scheme 20.

Figure 11. Temperature profile for the pyrolysis of octa-2,6-dien-4-

yne (19)

Above this temperature, only two (unremarkable) prod-

ucts were produced: toluene (96) and benzene (76). Since

not a trace of any intermediate could be isolated in this case

it appears futile to speculate on the pathways producing

these simple aromatics. The primary divinylallene men-

tioned could in principle give rise to acyclic four-, five-, and

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Thermal Pericyclic Tandem Reactions

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other cyclohexadiene isomers through a succession of 1,5-

hydrogen shifts.

Discussion

In this study we have investigated the flash vacuum pyro-

lyses of 12 substrates with the common feature that they all

possess a core unit derived from but-2-yne. These acetylenes

can in principle all undergo tandem isomerizations com-

posed of various sigmatropic steps. These pericyclic pro-

cesses belong to six different categories: the Cope, Claisen,

Claisen ester, retro-ene, 1,5-hydrogen shift, and 1,5-homo-

hydrogen shift rearrangements. Before the above tandem re-

actions are discussed and compared, it is appropriate to re-

call the activation parameters for the partial steps out of

which the sequential processes are composed. Although not

known for all these model reactions, detailed kinetic investi-

gations have been performed for some of them. Further-

more, comparison with the corresponding model com-

pounds in which the triple bond has been replaced by a

double bond should turn out to be helpful.

Figure 12. Temperature profile for the pyrolysis of 5-(2-methyl-

cyclopropyl)pent-2-en-4-yne (20)

As a first glance at Scheme 21 (which lists the activation

parameters for thermal pericyclic reactions of pertinent ol-

efinic and acetylenic substrates) shows, many more kinetic

data have been reported for the olefinic model reactions.

Comparing the entries of the left half of this collection,

we note that the Cope and the Claisen rearrangements pos-

sess the lowest Arrhenius activation energies and A factors.

Hydrogen shifts, whether of the 1,5- or 1,5-homo-type,

come next. In the latter case there is a pronounced differ-

ence between the cis and the trans isomers of 1-methyl-2-

vinylcyclopropane (last entry, left half of Scheme 21).

Whereas the activation parameters for the cis compound

indicate a concerted process (symmetry-allowed homodi-

enyl-1,5-hydrogen shift or retro-ene rearrangement), the iso-

merization of the trans isomer to the diene, which requires

more drastic conditions, is thought to be triggered by a

transǞcis isomerization through

a diradical interme-

diate.^[37]Finally, the highest activation energies were found

for the Claisen ester rearrangement and the retro-ene cleav-

age. Because of the linearity of the triple bond, one would

intuitively expect that replacement of a CC double bond by

a CC triple bond in any of the model systems (see right half

Scheme 20. Tandem pericyclic processes in the pyrolysis of 20

Compound 20 was converted into 118 either through a of the scheme) should result in an increase in the activation

1,5-homo hydrogen-shift/1,5-hydrogen shift tandem se- energies. After all, this functional group interchange should

quence, or by the reverse sequence of these steps, passing increase the distance between the terminal atoms of the re-

through intermediates 115 and 117 en route. As an allyl acting system. As has been known for a long time, however,

allene, 115 was able to participate in the cyclization step so this rate retardation is not observed.^[16]Acetylenes are

characteristic of this arrangement of double bonds, to pro- known to participate in many pericyclic reactions, with

vide 119 by way of the diyl 116. Since 118 is the linear rates usually of the same order as those of their olefinic

isomer of the branched tetraene 74 (2-allylhexa-1,3,5-triene) counterparts, and sometimes isomerize even faster. The

discussed above in the pyrolysis of 5 (20 and 5 are both reason can be found in the considerable deformability of

C₉H₁₂hydrocarbons), we would expect comparable be- the triple bond, a fact also illustrated by the generation of

havior in this intermediate. This was the case, both com- cycloalkynes such as cyclopentyne and cyclohexyne.^[42]Ob-

pounds first cyclizing to 2-allylcyclohexa-1,3-diene (75), viously, the geometric and stereochemical properties and re-

which subsequently fragmented to become 76 by loss of an quirements of the transition states of the olefinic and acetyl-

allyl radical Ϫ presumably after having equilibrated to ene processes will differ considerably, but both systems can

Eur. J. Org. Chem. 2001, 4009Ϫ4030

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H. Hopf, J. Wolff

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Scheme 21. Activation parameters for olefinic and acetylenic pericyclic processes

achieve bonding between the termini of the reacting systems acetylenic Claisen and Claisen ester isomerizations have so

with comparable ease. The entries of the ‘‘acetylenic half’’ far been reported, the observed rearrangement temper-

of Scheme 21 illustrate these generalizations clearly. Re- atures, 250 and 630 °C, respectively, are in accordance with

placement of a double bond in hexa-1,5-diene by a triple a prediction based on the thermal behavior of the respective

bond (generation of 22) influences the activation para- olefinic substrates. Agreement between the activation para-

meters only slightly. Even with a second ethynyl group the meters for retro-ene processes of the two classes of com-

corresponding hydrocarbon, hexa-1,5-diyne, shows the typ- pounds is again excellent. And although the known and

ical Cope parameters. Although no quantitative data for calculated activation energies for 1,5-hydrogen shifts in

4022

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Thermal Pericyclic Tandem Reactions

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relative reactivity of the former with a high degree of con-

fidence. We can hence postulate the following reactivity or-

der: Claisen Ն Cope Ͼ 1,5-hydrogen shift Ͼ retro-ene Ͼ

Claisen ester. For the 1,5-homo-H shift, the position within

this series is determined by the stereochemistry of the sub-

stituents at the three-membered ring: closer to the high-re-

activity end for the cis isomer and closer to the retro-ene

and ester end for the trans isomer.

Can the above considerations also be used to account for

the thermal behavior of the tandem processes described in

this study? By and large, the answer is yes. Since no kinetic

experiments have so far been carried out for any of the

coupled isomerizations summarized in Scheme 1, our ex-

planations must obviously remain qualitative. In Scheme 22

we list the 12 acetylenes studied here according to the tem-

perature at which half of the substrate has been isomerized

(‘‘50%-T’’).

The clear ‘‘winners’’ in this table are the Claisen and the

Cope processes: the first four entries all incorporate the vi-

nyloxy function. The ‘‘losers’’, on the other end of this list,

possess ester functions and have to undergo 1,5-hydrogen

shifts involving acetylenes. The center positions are occu-

pied by the three cyclopropane derivatives 20, 6, and 18.

These react relatively slowly because of the trans arrange-

ment of the substituents at the three-membered ring. It

would have been interesting to study a cis-substituted cyclo-

propane able to participate in a Claisen or Cope process,

but we have unfortunately been unable to prepare the re-

quired substrates.

From the preparative viewpoint, some of the above tan-

dem processes are useful (1 Ǟ 50, 2 Ǟ 62, 4 Ǟ 64,

10 Ǟ 94). Whether higher selectivity Ϫ i.e., less complex

pyrolysis mixtures Ϫ might on occasion be achievable by

introduction of functional groups into the above model

compounds is an open question.

Experimental Section

General Remarks: All moisture-sensitive reactions were carried out

in flame-dried glassware under nitrogen or argon. Commercially

available reagents and solvents were purified and dried when neces-

sary by standard methods immediately prior to use. Ϫ IR: Nicolet

320 FT-IR spectrometer. Ϫ UV/Vis: HP 8452A Diode Array spec-

trophotometer. Ϫ ¹H and ¹³C NMR: Bruker AC 200 or Bruker

DRX 400 at 200.1 and 50.3 or 400.1 and 10.6 MHz, respectively;

chemical shifts refer to TMS as internal standard. Ϫ MS: Finnigan

MAT 8430. Ϫ GC/MS: Carlo Erba HRGC 5160 combined with a

Finnigan 4515 mass spectrometer. Ϫ HRMS: Finnigan MAT 8430

using the peak matching method. Ϫ Elemental analyses: Institute

of Inorganic and Analytical Chemistry of the Technical University

Scheme 22. Temperatures at which half of the substrate had been

consumed

acetylenic and allenic substrates are considerably higher

than those of their olefinic counterparts, the pericyclic pro-

cesses in these cases also require higher activation than, for

example, a Cope or Claisen process. Finally, the scarce data of Braunschweig. Ϫ 1-Hexen-5-yne (22),^[43]3-vinyloxypropyne

available for trans-2-ethynynl-1-methylcyclopropane (trans-

27) also seem to indicate that this diastereomer prefers a

(24),^[14]and 3-methoxypropyne (25)^[44]were prepared according to

published procedures.

radical route over a concerted one, for which a far lower

isomerization temperature would be expected. It appears,

then, that in those acetylenic cases for which no detailed

kinetic studies have been carried out, we can employ the

Preparation of the Building Block trans-1-Ethynyl-2-methylcyclopro-

pane (27): Although both 27 and its precursors have been described

previously,^[11]we describe the synthesis of this intermediate in full,

since the reported spectroscopic data are incomplete. a) 3-Acetyl-

corresponding data for their olefin pendants to estimate the 5-methyldihydro-2-furanone (30): Anhydrous ethanol (2.5 L) was

Eur. J. Org. Chem. 2001, 4009Ϫ4030 4023

H. Hopf, J. Wolff

FULL PAPER

placed in a 4-L three-necked flask, and sodium (108.0 g, 4.7 mol) Ϫ UV (acetonitrile): λ_max(log ε) ϭ 194 nm (3.75). Ϫ GC/MS

was slowly added. The resulting solution of sodium ethoxide in (40 eV): m/z (%) ϭ 98 [M^ϩ] (10), 83 (28), 55 (27), 53 (5), 43 (100).

ethanol was cooled to 0 °C and ethyl acetoacetate (28) (650 g, 5.0

d) trans-1-(1,1-Dichloroethyl)-2-methylcyclopropane (33): Com-

pound 32 (12.8, 0.13 mol) was added at 0Ϫ5 °C to a suspension of

phosphorous pentachloride (52 g, 0.25 mol) in 150 mL of carbon

tetrachloride. After the reaction mixture had been stirred for 5 h at

mol) was added rapidly. Propylene oxide (29) (290 g, 5.0 mol) was

added over 30 min, and the solution was stirred for 18 h. The eth-

anol was distilled off in a rotary evaporator, keeping the temper-

ature below 50 °C. Glacial acetic acid (315 g, 5.25 mol) was added

this temperature, the solution was poured into ice-cold aqueous

to the syrupy residue, followed by ice-water (500 mL). The oily

sodium bicarbonate solution. The mixture was neutralized by addi-

layer was separated and the water phase was extracted with ether.

tion of further sodium bicarbonate, the aqueous phase was separ-

The combined organic phases were neutralized with sodium bicar-

ated and carefully washed with ether, and the organic phases were

bonate solution and dried with MgSO₄, and after the solvent had

combined and dried with MgSO₄. The organic solvents were re-

been removed by rotary evaporation the remaining oil was fraction-

moved in vacuo and the remaining oil was fractionated by using a

ated. At 95Ϫ97 °C (0.3 mbar), 355 g (50%) of 30 distilled as a col-

orless liquid. Since the lactone was produced as a mixture of dias-

spinning-band column. At 38Ϫ39 °C (25 mbar), compound 33

(7.7 g, 38%) was obtained as a colorless liquid.^[12,46]

(400.1 MHz, CDCl₃): δ ϭ 1.10 (d, J ϭ 5.4 Hz, 3 H, CH₃), 0.50,

0.93, 1.13, 1.38 (m, 4 H, 1-H Ϫ 3-H), 2.13 (s, 3 H, CH₃CCl₂). Ϫ

¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 13.30 (d, C-2), 13.33 (t, C-3),

Ϫ

¹H NMR

tereomers, the NMR spectra showed two sets of signals. Ϫ ¹H

NMR (400.1 MHz, CDCl₃): δ ϭ 1.42/1.45 (d, ³J ϭ 6.1 Hz, 3 H,

CH₃), 2.38/2.40 (m, 2 H, 4-H), 2.43/2.47 (s, 3 H, Ac), 3.78/3.80 (m,

1 H, 5-H), 4.62/4.69 (m, 1 H, 3-H). Ϫ ¹³C NMR (100.6 MHz,

CDCl₃): δ ϭ 19.04/20.97 (q, CH₃), 29.11/29.61 (q, Ac), 31.22/31.80

3

17.83 (q, CH₃), 36.03 and 37.05 (d and q, C-1 and CH₃CCl₂), 91.79

Ϫ1

˜

(s, C-4). Ϫ IR (film): ν ϭ 3023 cm (w), 3003 (m), 2959 (s), 2932

(t, C-4), 54.36/54.77 (d, C-5), 75.64/76.82 (d, C-3), 172.12 (s, C-2),

(m), 2871 (m), 1455 (m), 1378 (s), 1183 (s), 1116 (s), 1070 (s), 1036

(m), 691 (vs). Ϫ UV (acetonitrile): λ_max(log ε) ϭ 192 nm (3.11).

Ϫ1

˜

199.90/200.10 (s, C-6). Ϫ IR (film): ν ϭ 2983 cm (m), 1767 (vs),

1655 (m), 1455 (s), 1423 (m), 1361 (s), 1273 (m), 1181 (m), 1122

(s), 1055 (m), 951 (s). Ϫ UV (acetonitrile): λ_max(log ε) ϭ 254 nm

(2.67).

e) trans-1-Ethynyl-2-methylcyclopropane (trans-27): 18-Crown-6

(1.32 g, 0.005 mol) and compound 33 (23.20 g, 0.15 mol) were ad-

ded to a suspension of potassium tert-butoxide (50.5 g, 0.45 mol)

in pentane (600 mL). The mixture was stirred at room temp. for

18 h and then hydrolyzed with ice water until the solid residue dis-

solved. The pentane phase was separated and carefully washed with

water to remove the tert-butyl alcohol formed. After drying

(MgSO₄) and removal of the solvent, the remaining oil was purified

by distillation with a spinning-band column. At 69Ϫ71 °C trans-

b) 5-Chlorohexan-2-one (31): Concd. hydrochloric acid (500 mL)

was added to a solution of 30 (113.7 g, 0.8 mol) and benzyltriethyl-

ammonium chloride (18.2 g, 0.08 mol) in dichloromethane

(500 mL), and the reaction mixture was stirred at room temp for

18 h. The aqueous phase was separated and extracted with di-

chloromethane. The combined organic layers were neutralized with

sodium bicarbonate solution and dried with MgSO₄. The solvent

was removed in vacuo and the residue was purified by fractional

27 (7.3 g, 61%) of trans-27 distilled as a colorless liquid.^[9,12,45]

Ϫ

¹H NMR (400.1 MHz, CDCl₃): δ ϭ 1.07 (d, ³J ϭ 4.0 Hz, 3 H,

CH₃), 0.53, 0.85, 0.91, 1.09 (4 ϫ m, 4 H, 1-H Ϫ 3-H), 1.78 (d, ⁴J ϭ

2.0 Hz, 1 H, HCϵC). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 7.11

distillation: 44.1 g (42%) of 31, colorless liquid.^[11]

Ϫ

¹H NMR

(400.1 MHz, CDCl₃): δ ϭ 1.53 (d, ³J ϭ 6.1 Hz, 3 H, 6-H),

1.85Ϫ2.09 (m, 2 H, 4-H), 2.18 (s, 3 H, 1-H), 2.67 (m, 2 H, 3-H),

3.96 (m, 1 H, 5-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 25.45

(q, C-6), 30.03 (q, C-1), 33.68 (t, C-4), 40.37 (t, C-3), 58.08 (d, C-

(d, C-1), 16.24 (t, C-3), 16.62 (d, C-2), 18.13 (q, CH₃), 63.58 (d,

Ϫ1

˜

HCϵC), 87.36 (d, HCϵC). Ϫ IR (film): ν ϭ 3301 cm (s), 3314

(vs), 3083 (w), 3022 (w), 3007 (m), 2959 (s), 2933 (m), 2901 (m),

2115 (s), 1463 (m), 1445 (m), 1037 (m). Ϫ UV (acetonitrile): λ_max

(log ε) ϭ 192 nm (3.37).

5), 207.71 (s, C-2). Ϫ IR (film): ν ϭ 2929 cm^Ϫ1(m), 2873 (m), 1739

˜

(vs), 1414 (m), 1380 (m), 1359 (m), 1271 (m), 1189 (m), 966 (w). Ϫ

UV (acetonitrile): λ_max(log ε) ϭ 248 nm (2.00). Ϫ GC/MS (40 eV):

m/z (%) ϭ 136 [M^{ϩ 37}Cl] (2), 134 [M^{ϩ 35}Cl] (6), 119 (5), 98 (4), 58

(74), 56 (17), 55 (23), 43 (100), 41 (18).

General Procedure for the Preparation of the Methyl Propargyl

Ethers 4, 9, and 18: n-Butyllithium in hexane (15.7 mL, 0.025 mol

of a 1.6  solution) was added over 15 min to a cooled (Ϫ40 °C)

solution of the 1-alkyne (0.025 mol) in 25 mL of anhydrous ether.

A solution of bromomethyl methyl ether (34) (3.12 g, 0.025 mol) in

10 mL of anhydrous ether was added, the temperature of the reac-

tion mixture was slowly allowed to rise to room temp., and after a

further 1 h stirring, 50 mL of ice-water was added. The aqueous

phase was extracted with ether, the organic phases were combined,

and, after removal of the solvent by rotary evaporation, the residue

was purified by vacuum distillation.

c) trans-1-Acetyl-2-methylcyclopropane (32): Potassium tert-butox-

ide (37.0 g, 0.33 mol) was suspended in anhydrous ether (600 mL)

in a 1-L three-necked flask, equipped with mechanical stirrer and

reflux condenser. The mixture was stirred and 31 (44.1 g, 0.33 mol)

was added at such at rate that the ether refluxed gently. The reac-

tion mixture became increasingly viscous during the addition, re-

quiring vigorous stirring. After addition of the chloride was com-

plete, stirring was continued for 15 min, followed by addition of ice-

water until the solid residue had dissolved completely. The aqueous

phase was separated and washed thoroughly with water. The com-

a) 7-Methoxyhept-1-en-5-yne (4): Preparation from 22, colorless li-

bined ether extracts were dried (MgSO₄), the solvent was removed quid, 0.95 g (31%), b.p. 33Ϫ34 °C (4 mbar).

by rotary evaporation, and the remaining residue was purified by (400.1 MHz, CDCl₃): δ ϭ 2.23Ϫ2.45 (m, 4 H, 3-H, 4-H), 3.37 (s,

fractional distillation by using a spinning-band column. At 58Ϫ59 3 H, CH₃), 4.18 (t, ⁵J ϭ 1.9 Hz, 2 H, 7-H), 5.03 (dd, ²J ϭ 1.5, ³J ϭ

Ϫ

¹H NMR

2

3

°C (85 mbar), 23.5 (73%) of 32 was obtained as a colorless li-

quid.^{[45] 1}H NMR (400.1 MHz, CDCl₃): δ ϭ 1.12 (d, ³J ϭ 5.86 (ddt, ³J ϭ 10.5, ³J ϭ 17.1, ³J ϭ 6.4 Hz, 1 H, 2-H). Ϫ ¹³C

6.0 Hz, 3 H, CH₃), 0.73, 1.24, 1.40, 1.68 (4 ϫ m, 4 H, 1-H Ϫ 3- NMR (100.6 MHz, CDCl₃): δ ϭ 18.50 (t, C-4), 32.71 (t, C-3), 57.28

10.5 Hz, 1 H, 1-H), 5.18 (dd, J ϭ 1.5, J ϭ 17.1 Hz, 1 H, 1-H),

Ϫ

H), 2.22 (s, 3 H, Ac). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 18.02 (q, CH₃), 60.07 (t, C-7), 76.13 (s, C-5), 86.22 (s, C-6), 115.56 (t, C-

(q, CH₃), 19.27 (t, C-3), 19.96 (d, C-2), 30.22 and 30.27 (d and q, 1), 136.77 (d, C-2). Ϫ IR (film): ν ϭ 3295 cm^Ϫ1(w), 3080 (w), 2240

˜

C-1, C-5), 208.30 (s, C-4, Ac). Ϫ IR (film): ν˜ ϭ 2303 cm^Ϫ1(w), (w), 1639 (s), 1618 (s), 1449 (m), 1360 (m), 1270 (s), 1136 (m), 1094

2960 (w), 1697 (vs), 1438 (w), 1403 (s), 1345 (m), 1177 (s), 855 (m). (m), 944 (w), 871 (m). Ϫ UV (acetonitrile): λ_max(log ε) ϭ 192 nm

4024

Eur. J. Org. Chem. 2001, 4009Ϫ4030

Thermal Pericyclic Tandem Reactions

FULL PAPER

(3.96), 262 (2.46). Ϫ GC/MS (40 eV): m/z (%) ϭ 124 [M^ϩ] (2), 123 2 H, 4-H), 5.02 (dd, J ϭ 1.6, J ϭ 10.3 Hz, 1 H, 1-H), 5.09 (dd,

(24), 109 (24), 93 (22), 92 (14), 91 (60), 81 (22), 79 (87), 77 (48), 65

²J ϭ 1.6, ³J ϭ 17.1 Hz, 1 H, 1-H), 5.47 (dq, ³J ϭ 15.8, ⁴J ϭ 1.9 Hz,

(17), 53 (49), 52 (29), 51 (21), 45 (100), 41 (45). Ϫ C₈H₁₂O (124.18): 1 H, 7-H), 5.86 (ddt, ³J ϭ 10.3, J ϭ 17.1, J ϭ 6.6 Hz, 1 H, 2-H),

2

3

calcd. C 77.38, H 9.74; found C 77.36, H 9.70.

6.06 (dq, ³J ϭ 15.8, ³J ϭ 6.9 Hz, 1 H, 8-H). Ϫ ¹³C NMR

(100.6 MHz, CDCl₃): δ ϭ 18.37 (q, C-9), 19.12 (t, C-4), 32.96 (t,

C-3), 79.50 (s, C-6), 87.50 (s, C-5), 110.91 (d, C-7), 115.46 (t, C-1),

136.99 (d, C-2), 138.15 (d, C-8). Ϫ IR (film): ν˜ ϭ 3080 cm^Ϫ1(m),

3028 (m), 2981 (m), 2936 (s), 2914 (s), 2851 (m), 1642 (m), 1441

(m), 1362 (m), 1331 (m), 981 (m), 953(s), 915 (m), 722 (s). Ϫ UV

(acetonitrile): λ_max(log ε) ϭ 192 nm (3.68), 226 (4.08), 234 (sh,

4.00). Ϫ GC/MS (40 eV): m/z (%) ϭ 120 [M^ϩ] (65), 105 (47), 93

(39), 91 (76), 79 (100), 78 (47), 77 (74), 66 (17), 85 (18), 53 (14). Ϫ

C₉H₁₂(120.19): calcd. C 89.94, H 10.16; found C 89.88, H 9.97.

b) 1-Methoxy-4-vinyloxybut-2-yne (9): Preparation from 24, color-

less liquid, 0.8 g (28%), b.p. 69Ϫ70 °C (8 mbar). Ϫ ¹H NMR

2

(400.1 MHz, CDCl₃): δ ϭ 3.38 (s, 3 H, CH₃), 4.13 (dd, J ϭ 2.4,

³J ϭ 6.7 Hz, 1 H, ϭCH₂), 4.14 (t, ⁵J ϭ 1.7 Hz, 2 H, 1-H), 4.31

2

3

5

(dd, J ϭ 2.4, J ϭ 14.3 Hz, 1 H, ϭCH₂), 4.44 (t, J ϭ 1.7 Hz, 2

H, 4-H), 6.45 (dd, ³J ϭ 6.7, ³J ϭ 14.3 Hz, 1 H, -CHϭ). Ϫ ¹³C

NMR (100.6 MHz, CDCl₃): δ ϭ 55.94 (t, C-4), 57.51 (q, CH₃),

59.69 (t, C-1), 81.02 (s, C-3), 83.02 (s, C-2), 88.24 (t, ϭCH₂), 150.29

Ϫ1

˜

(d, -CHϭ). Ϫ IR (film): ν ϭ 2934 cm (m), 2908 (m), 2879 (m),

2824 (m), 1639 (s), 1620 (s), 1450 (m), 1356 (s), 1320 (s), 1271 (m),

1189 (vs), 1153 (s), 1123 (s), 1098 (vs), 1059 (s), 988 (m), 960 (m),

949 (m). Ϫ UV (acetonitrile): λ_max(log ε) ϭ 194 nm (3.81). Ϫ GC/

MS (40 eV): m/z (%) ϭ 126 [M^ϩ] (7), 97 (8), 96 (8), 95 (8), 94 (10),

83 (19), 82 (18), 81 (45), 68 (30), 55 (43), 53 (100), 52 (40), 51 (38),

50 (18), 45 (45). Ϫ C₇H₁₀O₂(126.15): calcd. C 66.65, H 7.99; found

C 66.51, H 8.02.

b) 6-Vinyloxyhex-2-en-4-yne (10): Preparation from 24, colorless li-

quid, 3.2 g (52%), b.p. 57Ϫ58 °C (8 mbar). According to GC ana-

lysis a (Z)/(E) mixture in 2:1 ratio was obtained; the pure diastereo-

mers were obtained by preparative gas chromatography (Car-

1

bowax, 3 m, 120 °C). Ϫ (E)-6-Vinyloxyhex-2-en-4-yne [(E)-10]: H

3

4

NMR (400.1 MHz, CDCl₃): δ ϭ 1.79 (dd, J ϭ 6.8, J ϭ 1.7 Hz,

2

3

3 H, 1-H), 4.12 (dd, J ϭ 2.3, J ϭ 6.8 Hz, 1 H, ϭCH₂), 4.31 (dd,

²J ϭ 2.3, J ϭ 14.3 Hz, 1 H, ϭCH₂), 4.49 (d, ⁵J ϭ 1.7 Hz, 2 H, 6-

3

c) 1-(3-Methoxyprop-1-ynyl)-2-methylcyclopropane (18): Prepara-

tion from trans-27, colorless liquid, 1.2 g (37%), b.p. 50Ϫ51 °C

H), 5.52 (dtq, ³J ϭ 15.9, ⁴J ϭ 1.9, ⁵J ϭ 1.7 Hz, 1 H, 3-H), 6.20

3

(dq, J ϭ 6.8, J ϭ 15.9 Hz, 1 H, 2-H), 6.46 (dd, J ϭ 6.8, J ϭ

14.3 Hz, 1 H, 7-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 18.56

(q, C-1), 56.64 (t, C-6), 81.71 (s, C-4), 85.74 (s, C-5), 88.17 (t, ϭ

CH₂), 109.87 (d, C-3), 140.88 (d, C-2), 150.44 (d, -CHϭ). Ϫ (Z)-

1

(8 mbar). Ϫ H NMR (400.1 MHz, CDCl₃): δ ϭ 0.54, 0.84, 0.94,

3

1.08 (4 ϫ m, 4 H, 1-H Ϫ 3-H), 1.07 (d, J ϭ 1.0 Hz, 3 H, CH₃),

3.35 (s, 3 H, OCH₃), 4.04 (d, ⁵J ϭ 2.0 Hz, 2 H, CH₂). Ϫ ¹³C NMR

(100.6 MHz, CDCl₃): δ ϭ 7.43 (d, C-1), 16.41 (t, C-3), 16.73 (d,

1

6-Vinyloxyhex-2-en-4-yne [(Z)-10]: H NMR (400.1 MHz, CDCl₃):

C-2), 18.18 (q, CH₃), 57.26 (q, OCH₃), 60.16 (t, CH₂), 71.28 (s, C-

δ ϭ 1.88 (dd, ³J ϭ 6.8, J ϭ 1.6 Hz, 3 H, 1-H), 4.14 (dd, J ϭ 2.3,

4

2

Ϫ1

˜

5), 89.93 (s, C-6). Ϫ IR (film): ν ϭ 3004 cm (m), 2989 (m), 2957

³J ϭ 6.8 Hz, 1 H, ϭCH₂), 4.33 (dd, ²J ϭ 2.3, ³J ϭ 14.3 Hz, 1 H, ϭ

(s), 2932 (s), 2900 (m), 2872 (m), 2844 (m), 2821 (m), 2242 (m),

2225 (m), 1463 (m), 1448 (m), 1379 (m), 1357 (m), 1187 (s), 1098

(vs), 1067 (s), 1001 (m), 898 (m), 849 (m). Ϫ UV (acetonitrile): λ_max

5

3

4

CH₂), 4.55 (d, J ϭ 1.9 Hz, 2 H, 6-H), 5.51 (dtq, J ϭ 10.7, J ϭ

3

1.6, ⁵J ϭ 1.9 Hz, 1 H, 3-H), 6.02 (dq, 1 H, J ϭ 6.8, J ϭ 10.7 Hz,

2-H), 6.48 (dd, ³J ϭ 6.8, ³J ϭ 14.3 Hz, 1 H, 7-H). Ϫ ¹³C NMR

(100.6 MHz, CDCl₃): δ ϭ 15.94 (q, C-1), 56.63 (t, C-6), 83.69 (s,

C-4), 87.99 (s, C-5), 88.23 (t, ϭCH₂), 109.20 (d, C-3), 139.67 (d,

(log ε) ϭ 192 nm (3.49). Ϫ GC/MS (40 eV): m/z (%) ϭ 124 [M^ϩ

]

(46), 123 (29), 109 (67), 95 (29), 93 (36), 91 (74), 82 (25), 81 (48),

79 (81), 78 (28), 77 (100), 66 (24), 65 (31), 53 (55). Ϫ C₈H₁₂O

(124.18): calcd. C 77.38, H 9.74; found C 77.30, H 9.84.

C-2), 150.40 (d, -CHϭ). Ϫ IR (film): ν ϭ 3031 cm^Ϫ1(w), 2970 (w),

˜

2218 (w), 1639 (vs), 1618 (vs), 1448 (m), 1372 (s), 1359 (s), 1319

(s), 1268 (m), 1189 (vs), 1152 (vs), 1077 (m), 1056 (s), 1029 (m),

985 (s), 957 (s). Ϫ UV (acetonitrile): λ_max(log ε) ϭ 194 nm (4.01),

226 (4.08). Ϫ GC/MS (40 eV): m/z (%) ϭ 122 [M^ϩ] (1), 107 (20),

91 (2), 79 (50), 78 (14), 77 (100), 69 (11), 53 (14), 51 (20). Ϫ C₈H₁₀O

(122.17): calcd. C 78.65, H 8.25; found C 78.89, H 8.34.

General Procedure for the Preparation of the Enynes 5, 10, 17, and

20: Copper(I) iodide (760 mg, 4.0 mmol) was added to a solution

of 1-bromo-1-propene (36, 1:1 mixture of the (E) and (Z) isomers

according to ¹H NMR analysis, 8.46 g, 0.07 mol), the 1-alkyne

(0.05 mol), and tetrakis(triphenylphosphane)-palladium(0)

(230 mg, 0.2 mmol) in diethylamine (60 mL). The mixture was

stirred for 3 h at room temp., hydrolyzed with 100 mL of ice-water,

and thoroughly extracted with pentane. The combined organic

phases were filtered through a short alumina column, the solvent

was removed in vacuo, and the remaining oil was fractionated by

vacuum distillation.

c) 6-Methoxyhex-2-en-4-yne (17): Preparation from 25, colorless li-

quid, 3.1 g (47%), b.p. 38 °C (10 mbar). According to GC analysis

a (Z)/(E) mixture in 4:1 ratio was obtained; the pure diastereomers

were obtained by preparative gas chromatography (Carbowax, 3 m,

100 °C).

Ϫ

(Z)-6-Methoxyhex-2-en-4-yne [(Z)-17]: ¹H NMR

3

4

(400.1 MHz, CDCl₃): δ ϭ 1.89 (dd, J ϭ 6.9, J ϭ 1.6 Hz, 3 H, 1-

a) Nona-1,7-dien-5-yne (5): Preparation from 22, colorless liquid,

2.46 g (40%), b.p. 52Ϫ53 °C (8 mbar). According to GC analysis,

a (Z)/(E) mixture in 2:1 ratio was obtained; the pure diastereomers

H), 3.41 (s, 3 H, OCH₃), 4.27 (d, ⁵J ϭ 1.9 Hz, 2 H, 6-H), 5.52 (dtq,

³J ϭ 10.8, J ϭ 1.6, J ϭ 1.9 Hz, 1 H, 3-H), 6.00 (dq, J ϭ 10.8,

4

5

3

³J ϭ 6.9 Hz, 1 H, 2-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ

were obtained by preparative gas chromatography (Carbowax, 3 m, 15.87 (q, C-1), 57.40 (q, OCH₃), 60.37 (t, C-6), 85.02 (s, C-4), 91.12

1

120 °C). Ϫ (Z)-nona-1,7-dien-5-yne [(Z)-5]: H NMR (400.1 MHz, (s, C-5), 109.41 (d, C-3), 138.96 (d, C-2). Ϫ (E)-6-Methoxyhex-2-

3

4

1

CDCl₃): δ ϭ 1.85 (dd, 3 H, J ϭ 6.9, J ϭ 1.9 Hz, 9-H), 2.30 (dt, en-4-yne [(E)-17]: H NMR (400.1 MHz, CDCl₃): δ ϭ 1.79 (dd, 3

2 H, J ϭ 6.6, J ϭ 6.8 Hz, 3-H), 2.44 (t, J ϭ 6.8 Hz, 2 H, 4-H), H, J ϭ 6.8, J ϭ 1.9 Hz, 1-H), 3.38 (s, 3 H, OCH₃), 4.19 (d, ⁵J ϭ

3

4

5.04 (dd, ²J ϭ 1.6, ³J ϭ 10.3 Hz, 1 H, 1-H), 5.10 (dd, ²J ϭ 1.6, 1.8 Hz, 2 H, 6-H), 5.51 (dtq, J ϭ 15.8, J ϭ 1.9, J ϭ 1.8 Hz, 1

3

4

5

³J ϭ 17.1 Hz, 1 H, 1-H), 5.47 (dq, ³J ϭ 15.8, J ϭ 1.9 Hz, 1 H, 7- H, 3-H), 6.18 (dq, ³J ϭ 15.8, J ϭ 6.8 Hz, 1 H, 2-H). Ϫ ¹³C NMR

H), 5.89 (m, 2 H, 2-H, 8-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃):

(100.6 MHz, CDCl₃): δ ϭ 18.50 (q, C-1), 57.40 (q, OCH₃), 60.30

δ ϭ 15.64 (q, C-9), 19.35 (t, C-4), 33.07 (t, C-3), 77.52 (s, C-6), (t, C-6), 85.02 (s, C-4), 91.12 (s, C-5), 110.08 (d, C-3), 140.23 (d,

4

3

Ϫ1

˜

93.96 (s, C-5), 110.22 (d, C-7), 115.54 (t, C-1), 136.97 (d, C-2), C-2). Ϫ IR (film): ν ϭ 3030 m (m), 2990 (m), 2937 (s), 2916 (s),

137.07 (d, C-8). Ϫ (E)-Nona-1,7-dien-5-yne [(E)-5]: ¹H NMR 2894 (s), 2821 (s), 2190 (w), 1465 (m), 1448 (s), 1399 (m), 1376 (s),

3

4

(400.1 MHz, CDCl₃): δ ϭ 1.76 (dd, J ϭ 6.9, J ϭ 1.9 Hz, 3 H, 9-

1357 (vs), 1279 (m), 1187 (vs), 1151 (vs), 1135 (vs), 1099 (vs), 1000

H), 2.27 (dt, 2 H, ³J ϭ 6.6, ³J ϭ 6.8 Hz, 3-H), 2.37 (t, ³J ϭ 6.8 Hz, (m), 952 (s), 905 (s). Ϫ UV (acetonitrile): λ_max(log ε) ϭ 226 nm

Eur. J. Org. Chem. 2001, 4009Ϫ4030

4025

H. Hopf, J. Wolff

FULL PAPER

(4.02) Ϫ GC/MS (40 eV): m/z (%) ϭ 110 [M^ϩ] (56), 95 (79), 79 ing to NMR analysis, the liquid consisted of 38 and the target

(67), 77 (100), 67 (60), 53 (23), 51 (41). The ether has been described molecule 2. This mixture was added slowly to N,N-diethylamine

in the literature;^[47]however, the reported spectroscopic data are in-

complete.

(10 mL) heated to 95Ϫ105 °C. When the addition was complete,

the reaction mixture was stirred for 30 min at this temperature. The

flask was connected to a distillation apparatus and the vinyl ether

formed was distilled off directly at 33 °C and 0.7 mbar: 1.56 g

(38%) of 2, colorless liquid. Ϫ ¹H NMR (400.1 MHz, CDCl₃): δ ϭ

d) 5-(2-Methylcyclopropyl)pent-2-en-4-yne (20): Preparation from

trans-27, colorless liquid, 1.5 g (48%), b.p. 39 °C (5 mbar). Accord-

ing to GC analysis a (Z)/(E) mixture in 4:1 ratio was obtained; the

pure diastereomers were procured by preparative gas chromato-

graphy (Carbowax, 3 m, 120 °C). Ϫ (Z)-5-(2-Methylcyclopro-

pyl)pent-2-en-4-yne [(Z)-20]: ¹H NMR (400.1 MHz, CDCl₃): δ ϭ

2

3

2.24Ϫ2.35 (m, 4 H, 3-H, 4-H), 4.11 (dd, J ϭ 2.3, J ϭ 6.8 Hz, 1

H, H₂CϭCHO), 4.29 (dd, ²J ϭ 2.3, ³J ϭ 14.3 Hz, 1 H, H₂Cϭ

CHO), 4.37 (t, ⁴J ϭ 2.1 Hz, 2 H, 7-H), 5.03 (dd, ²J ϭ 1.5, ³J ϭ

2

3

17.1 Hz, 1 H, 1-H), 5.08 (dd, J ϭ 1.5, J ϭ 10.4 Hz, 1 H, 1-H),

3

0.58, 0.97, 1.08 (3 ϫ m, 4 H, 6-H Ϫ 8-H), 1.09 (d, J ϭ 4.1 Hz, 3

3

5.85 (ddt, J ϭ 10.4, J ϭ 17.1, J ϭ 6.4 Hz, 1 H, 2-H), 6.45 (dd,

³J ϭ 6.8, ³J ϭ 14.3 Hz, 1 H, H₂CϭCHO). Ϫ ¹³C NMR

(100.6 MHz, CDCl₃): δ ϭ 18.53 (t, C-4), 32.55 (t, C-3), 56.46 (t,

C-7), 75.01 (s, C-5), 87.15 (s, C-6), 88.03 (t, H₂CϭCHO), 115.68

(t, C-1), 136.65 (d, C-2), 150.46 (d, H₂CϭCHO). Ϫ IR (film): ν˜ ϭ

3118 cm^Ϫ1(m), 2982 (m), 2289 (w), 2225 (w), 1638 (m), 1374 (s),

1270 (s), 1154 (s), 1128 (s), 989 (m), 944 (s), 871 (s), 630 (s). Ϫ UV

(acetonitrile): λ_max(log ε) ϭ 192 nm (4.04), 262 (2.52). Ϫ GC/MS

(40 eV): m/z (%) ϭ 136 [M^ϩ] (1), 121 (5), 107 (10), 93 (28), 91 (78),

81 (10), 79 (28), 78 (27), 77 (100), 65 (39), 55 (17), 53 (29). Ϫ

C₉H₁₂O (136.19): calcd. C 79.37, H 8.88; found C 79.38, H 8.95.

H, 9-H), 1.83 (dd, ³J ϭ 6.8, ⁴J ϭ 1.6 Hz, 3 H, 1-H), 5.42 (dq, ³J ϭ

4

3

10.6, J ϭ 1.6 Hz, 1 H, 3-H), 5.85 (dq, J ϭ 10.6, J ϭ 6.8 Hz, 1

H, 2-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 8.34 (d, C-6),

15.66 (q, C-1), 16.96 (t, C-7), 17.24 (d, C-8), 18.31 (q, C-9), 72.71

(s, C-5), 97.78 (s, C-4), 110.23 (d, C-3), 136.79 (d, C-2). Ϫ (E)-5-(2-

1

Methylcyclopropyl)pent-2-en-4-yne [(E)-20]: H NMR (400.1 MHz,

CDCl₃): δ ϭ 0.58, 0.97, 1.08 (3 ϫ m, 4 H, 6-H Ϫ 8-H), 1.09 (d,

3

4

³J ϭ 4.1 Hz, 3 H, 9-H), 1.74 (dd, J ϭ 6.8, J ϭ 1.6 Hz, 3 H, 1-

H), 5.44 (dq, ³J ϭ 10.6, ⁴J ϭ 1.6 Hz, 1 H, 3-H), 6.03 (dq, ³J ϭ

15.7, J ϭ 6.8 Hz, 1 H, 2-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃):

3

δ ϭ 8.12 (d, C-6), 15.66 (q, C-1), 16.68 (t, C-7), 17.24 (d, C-8),

18.40 (q, C-9), 74.62 (s, C-5), 91.34 (s, C-4), 110.92 (d, C-3), 137.98

Octa-2,6-dien-4-yne (19). ؊ a) 6-Bromo-oct-2-en-4-yne (41): Phos-

phorous(III) bromide (35.2 g, 0.13 mol) was added at Ϫ20 °C over

30 min to a solution of oct-4-yne-3,6-diol (40, prepared by addition

of propanal to acetylene bis-Grignard 39 according to ref.,^[48]

22.0 g, 0.15 mol) and pyridine (4.0 g, 50 mmol) in anhydrous ether

(400 mL). The reaction mixture was stirred for 2 h at room temp.

and hydrolyzed by addition of ice-water (200 mL). The aqueous

phase was separated and washed carefully with ether, and the com-

bined organic phases were neutralized with bicarbonate solution

and finally dried with MgSO₄. The solvent was removed in vacuo

and the remaining oil was fractionated by distillation through a

40 cm Vigreux column; at 60Ϫ62 °C and 0.6 mbar 20.3 g (50%) of

41 was obtained as a colorless liquid. According to GC analysis

the mixture consisted of (Z)- and (E)-41 in 2:1 ratio. For analytical

purposes the pure diastereomers were separated by preparative gas

chromatography (Carbowax, 3 m, 150 °C): (Z)-6-bromo-oct-2-en-4-

yne: ¹H NMR (400.1 MHz, CDCl₃): δ ϭ 1.12 (t, ³J ϭ 7.3 Hz, 3 H,

Ϫ1

˜

(d, C-2). Ϫ IR (film): ν ϭ 3081 cm (w), 3026 (s), 3005 (m), 2958

(vs), 2930 (m), 2913 (m), 2869 (m), 2213 (m), 1619 (w), 1460 (m),

1444 (m), 1362 (m), 1067 (m), 1034 (m), 952 (m), 932 (m), 848 (s),

720 (s). Ϫ UV (acetonitrile) λ_max(log ε) ϭ 192 nm (3.70), 230

(3.95), 238 (3.95). Ϫ GC/MS (40 eV): m/z (%) ϭ 120 [M^ϩ] (100),

105 (85), 103 (33), 91 (80), 79 (75), 78 (28), 77 (84), 65 (25), 63 (24),

52 (25). Ϫ C₉H₁₂(120.19): calcd. C 89.94, H 10.06; found C 90.70,

H 10.38.

6-(trans-2-Methylcyclopropyl)hex-1-en-5-yne (6): n-Butyllithium so-

lution (1.6  in hexane, 32 mL) was added at 15Ϫ20 °C to a solu-

tion of trans-27 (4.0 g, 50 mmol) in anhydrous THF (40 mL). The

mixture was stirred for 10 min and a solution of 1-bromo-3-butene

(35) (6.7 g, 50 mmol) in HMPTA (30 mL) was added. After 3 h of

additional stirring at 15Ϫ20 °C, ice-water was added for hydrolysis.

The aqueous phase was separated and washed carefully with ether,

and the organic phases were combined and dried with MgSO₄. The

solvents were removed in vacuo and the remaining oil was fraction-

ated at 42Ϫ45 °C and 0.3 mbar: 0.7 g (10%) of 6, colorless liquid.

3

8-H), 1.88 (dd, ³J ϭ 6.8, ⁴J ϭ 1.8 Hz, 3 H, 1-H), 2.06 (dq, J ϭ

3

5

6.0, J ϭ 7.3 Hz, 2 H, 7-H), 4.72 (dt, J ϭ 6.0, J ϭ 1.8 Hz, 1 H,

3

4

5

6-H), 5.53 (ddt, J ϭ 10.7, J ϭ 1.8, J ϭ 1.8 Hz, 1 H, 3-H), 6.03

1

Ϫ H NMR (400.1 MHz, CDCl₃): δ ϭ 0.46, 0.75, 0.88, 0.90 (4 ϫ

3

(dq, J ϭ 6.8, J ϭ 10.7 Hz, 1 H, 2-H). Ϫ ¹³C NMR (100.6 MHz,

CDCl₃): δ ϭ 11.72 (q, C-8), 15.98 (q, C-1), 33.18 (t, C-7), 39.92 (d,

C-6), 83.87 (s, C-5), 92.23 (s, C-4), 109.25 (d, C-3), 139.84 (d, C-

3

m, 4 H, 7-H Ϫ 9-H), 1.05 (d, J ϭ 5.5 Hz, 3 H, CH₃), 2.21 (m, 4

H, 3-H, 4-H), 5.00 (dd, ²J ϭ 1.5, ³J ϭ 16.9 Hz, 1 H, 1-H), 5.05

2

3

(dd, J ϭ 1.5, J ϭ 10.1 Hz, 1 H, 1-H), 5.84 (ddt, J ϭ 10.1, J ϭ

1

2). Ϫ (E)-6-bromo-oct-2-en-4-yne: H NMR (400.1 MHz, CDCl₃):

16.9, J ϭ 6.4 Hz, 1 H, 2-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃):

3

δ ϭ 1.12 (t, ³J ϭ 7.3 Hz, 3 H, 8-H), 1.80 (dd, ³J ϭ 6.8, ⁴J ϭ 1.8 Hz,

3 H, 1-H), 2.06 (dq, ³J ϭ 6.3, ³J ϭ 7.3 Hz, 2 H, 7-H), 4.65 (dt,

δ ϭ 7.65 (d, C-7), 16.25 (d, C-9), 16.41 (t, C-8), 18.28 (q, CH₃),

18.62 (t, C-4), 33.29 (t, C-3), 75.05 (s, C-6), 83.44 (s, C-5), 115.23

(t, C-1), 137.19 (d, C-2). Ϫ IR (film): ν˜ ϭ 3080 cm^Ϫ1(m), 3003

(m), 2979 (m), 2956 (s), 2928 (s), 2869 (m), 2245 (w), 2231 (w),

1642 (m), 1469 (m), 1444 (m), 1068 (m), 1034 (m), 913 (s). Ϫ UV

(acetonitrile): λ_max(log ε) ϭ 192 nm (3.78), 240 (3.20). Ϫ GC/MS

(40 eV): m/z (%) ϭ 143 [M^ϩ] (3), 119 (23), 106 (18), 105 (24), 93

(10), 92 (16), 91 (100), 79 (13), 78 (20), 77 (79), 65 (24). Ϫ C₁₀H₁₄

(134.22): calcd. C 89.49, H 10.51; found C 89.61, H 10.53.

³J ϭ 6.3, J ϭ 1.8 Hz, 1 H, 6-H), 5.53 (ddt, J ϭ 15.8, J ϭ 1.8,

5

3

4

3

⁵J ϭ 1.8 Hz, 1 H, 3-H), 6.19 (dq, J ϭ 6.8, J ϭ 15.8 Hz, 1 H, 2-

H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 11.72 (q, C-8), 18.60

(q, C-1), 33.18 (t, C-7), 40.09 (d, C-6), 85.56 (s, C-5), 92.98 (s, C-

4), 109.94 (d, C-3), 141.03 (d, C-2). Ϫ IR (film): ν˜ ϭ 3031 cm^Ϫ1

(m), 2974 (vs), 2938 (s), 2914 (s), 2877 (m), 2204 (w), 2180 (w),

1737 (m), 1671 (m), 1462 (m), 1363 (s), 1171 (vs), 1087 (s), 722 (vs),

665 (s), 598 (s), 577 (s). Ϫ UV (acetonitrile): λ_max(log ε) ϭ 194 nm

(3.93), 236 (3.13). Ϫ GC/MS (40 eV): m/z (%) ϭ 188 [M^{ϩ 81}Br] (4),

186 [M^{ϩ 79}Br] (4), 107 (100), 91 (72), 79 (39), 78 (29), 65 (16). Ϫ

C₈H₁₁Br (187.08): calcd. C 51.36, H 5.93; found C 51.22, H 5.81.

7-Vinyloxyhept-1-en-5-yne (2): Gaseous hydrochloric acid was

passed for 1 h at Ϫ5 °C through a mixture of hept-6-en-2-yn-1-ol

(37, from 22 by treatment of its lithium salt with paraldehyde,

3.36 g, 30.5 mmol) and paraldehyde (1.52 g, 0.12 mol). The reac- Ϫ b) Octa-2,6-dien-4-yne (19): DBU (14.3 g, 0.09 mol) was added

tion flask was placed in a cooling bath (Ϫ70 °C), and after a short to a solution of (E/Z)-41 (17.5 g, 0.07 mol) in anhydrous DMSO

time a solid layer (conc. HCl) had formed. The supernatant phase (120 mL). The reaction temperature increased to 45Ϫ50 °C, and

was carefully decanted and dried with magnesium sulfate. Accord-

the solution was stirred until it had reached room temp. again.

4026

Eur. J. Org. Chem. 2001, 4009Ϫ4030

Thermal Pericyclic Tandem Reactions

FULL PAPER

˜ ϭ 3118 cm^Ϫ1

After hydrolysis with aqueous HCl (400 mL, 0.05 ), the aqueous (d, -CHϭ). Ϫ IR (film): ν

(w), 3060 (w), 1960 (w),

phase was separated and extracted with pentane. The organic

phases were combined, washed carefully with saturated ammonium 986 (m), 826 (m). Ϫ UV (acetonitrile): λ_max(log ε) ϭ 194 nm (4.23).

chloride solution, and dried with MgSO₄. The pentane was re-

Ϫ GC/MS (40 eV): m/z (%) ϭ 138 [M^ϩ] (1), 109 (3), 95 (25), 81

moved in a rotary evaporator and the residue was fractionated by (9), 67 (32), 65 (25), 52 (37), 53 (26), 41 (100). Ϫ C₈H₁₀O₂(138.16):

1639 (s), 1620 (w), 1357 (m), 1320 (s), 1188 (s), 1152 (s), 1061 (m),

vacuum distillation, using a 40 cm Vigreux column. At 45Ϫ47 °C

and 8 mbar, 2.7 g (39%) of a colorless liquid distilled. This was

shown by GC analysis to consist of (Z,Z)-, (Z,E)-, and (E,E)-19 in

3:5:1 ratio. For analytical purposes the pure diastereomers were

separated by preparative gas chromatography (Carbowax, 3 m, 120

°C). Although these hydrocarbons are known, the spectroscopic

data are incomplete and not readily available.^[49]Ϫ (Z,Z)-19: ¹H

calcd. C 69.55, H 7.29; found C 69.60, H 7.32

Pyrolysis Experiments: Pyrolyses were carried out as described in

the main section. At the beginning of each experiment, the com-

pound to be pyrolyzed was frozen out in the evaporation flask and

the whole apparatus was evacuated to about 0.1 mbar by con-

necting the (receiving) cold trap to a high vacuum line. Air was

removed from the substrate and the apparatus by carrying out sev-

eral freeze-pump-thaw cycles. For the analytical runs, about

20Ϫ30 mg of the starting material was pyrolyzed and the progress

of the reaction was monitored by GC and GC/MS analysis. In this

manner the various temperature profiles shown in the main section

were established. For preparative runs, ca. 0.5Ϫ1.0 g of the starting

material was pyrolyzed, the product mixture was taken up in pent-

ane, and the pyrolysis products were separated for spectroscopic

identification by preparative gas chromatography on a Carbowax

column. The spectroscopic properties of the main and/or novel

pyrolysis products are described below; spectroscopic data for

simple pyrolysis products such as benzene (76), toluene (96), 1,3-

cyclohexadiene (107), etc. are not given; those products were identi-

fied by comparison with the authentic compounds. Pyrolysis ex-

periments exclusively yielding such simple compounds are not de-

scribed.

3

4

NMR (400.1 MHz, CDCl₃): δ ϭ 1.91 (dd, J ϭ 6.9, J ϭ 1.6 Hz,

3

4

3 H, 1-H, 8-H), 5.65 (dq, J ϭ 10.8, J ϭ 1.6 Hz, 1 H, 3-H, 6-H),

6.00 (dq, ³J ϭ 10.8, ³J ϭ 6.9 Hz, 1 H, 2-H, 7-H). Ϫ ¹³C NMR

(100.6 MHz, CDCl₃): δ ϭ 15.93 (q, C-1, C-8), 91.56 (s, C-4, C-5),

1

110.30 (d, C-3, C-6), 137.69 (d, C-2, C-7). Ϫ (E,E)-19: H NMR

3

4

(400.1 MHz, CDCl₃): δ ϭ 1.80 (dd, J ϭ 6.9, J ϭ 1.6 Hz, 3 H, 1-

H, 8-H), 5.60 (dq, ³J ϭ 15.8, ⁴J ϭ 1.6 Hz, 1 H, 3-H, 6-H), 6.10

(dq, ³J ϭ 15.8, ³J ϭ 6.9 Hz, 1 H, 2-H, 7-H). Ϫ ¹³C NMR

(100.6 MHz, CDCl₃): δ ϭ 18.66 (q, C-1, C-8), 68.34 (s, C-4, C-5),

1

110.90 (d, C-3, C-6), 138.93 (d, C-2, C-7). Ϫ (E,Z)-19: H NMR

3

4

(400.1 MHz, CDCl₃): δ ϭ 1.82 (dd, J ϭ 6.9, J ϭ 1.6 Hz, 3 H, 8-

H), 1.89 (dd, ³J ϭ 6.9, J ϭ 1.6 Hz, 3 H, 1-H) 5.59 (dq, J ϭ 15.8,

4

3

⁴J ϭ 1.6 Hz, 1 H, 6-H), 5.67 (dq, J ϭ 10.8, J ϭ 1.6 Hz, 1 H, 3-

3

4

H), 5.95 (dq, ³J ϭ 10.8, ³J ϭ 6.9 Hz, 1 H, 2-H), 6.15 (dq, ³J ϭ

3

Ϫ1

˜

15.8, J ϭ 6.9 Hz, 1 H, 7-H). Ϫ IR (film): ν ϭ 3080 cm (m),

3028 (m), 2981 (m), 2936 (s), 2914 (vs), 2851 (m), 2227 (w), 2205

(w), 1642 (s), 1441 (s), 1362 (m), 1331 (m), 991 (m), 953 (m), 915

(vs), 722 (s). Ϫ UV (acetonitrile): λ_max(log ε) ϭ 234 nm (3.95). Ϫ

GC/MS (40 eV): m/z (%) ϭ 106 [M^ϩ] (100), 105 (18), 91 (65), 79

(28), 78 (24), 77 (33), 65 (20), 63 (12), 52 (13), 51 (24).

a) Pyrolysis of 7-Vinyloxyhept-1-en-5-yne (2). ؊ 2-Methyl-3-methyl-

enehexa-1,5-diene (56): Spectral data are identical with data re-

ported in ref.^[52]Ϫ 3-(But-3-enyl)penta-3,4-dienal (59): ¹H NMR

3

(400.1 MHz, CDCl₃): δ ϭ 2.08 (dt, J ϭ 6.5, J ϭ 6.5 Hz, 2 H, 7-

3

5

3

H), 2.20 (tt, J ϭ 6.5, J ϭ 3.0 Hz, 2 H, 6-H), 2.99 (dt, J ϭ 2.5,

1,4-Bis(acetoxy)but-2-yne (12): The diester was prepared according

to,^[50]by esterification of but-2-yne-1,4-diol (42) with acetyl chlor-

ide; its spectroscopic data have all been reported in the chemical lit-

erature.

⁵J ϭ 3.0 Hz, 2 H, 2-H), 4.82 (tt, J ϭ 3.0, J ϭ 3.0 Hz, 2 H, 5-H),

5.01 (dd, ²J ϭ 1.5, ³J ϭ 17.1 Hz, 1 H, 9-H), 5.08 (dd, ²J ϭ 1.5,

³J ϭ 10.4 Hz, 1 H, 9-H), 5.83 (ddt, ³J ϭ 10.5, ³J ϭ 17.1, ³J ϭ

6.5 Hz, 1 H, 8-H), 9.68 (t, ³J ϭ 2.5 Hz, 1 H, 1-H). Ϫ IR (film):

ν˜ ϭ 3081 cm^Ϫ1(w), 3004 (m), 2999 (m), 2981 (m), 2917 (m), 2839

(m), 2256 (m), 1724 (vs), 1667 (m), 1641 (m), 1598 (m), 1440 (m),

1386 (m), 1191 (m), 1134 (m), 1096 (m), 1038 (m), 998 (m). Ϫ GC/

5

1,4-Bis(vinyloxy)but-2-yne (7): Titanocene dichloride (9.00 g, 0.036

mol) was placed under nitrogen in a flame-dried 250 mL three-

necked flask, and a toluene solution of trimethyl aluminum (2.0 

solution, 52 mL, 0.104 mol) was added by syringe. The dark red MS (40 eV): m/z (%) ϭ 136 [M^ϩ] (1), 135 (6), 121 (16), 107 (22),

solution was stirred for 3 days at room temp. The resulting solution

of Tebbe’s reagent 44 was then added by syringe over 30 min to

94 (35), 93 (35), 92 (21), 91 (50), 81 (39), 79 (39), 77 (42), 41 (100).

Ϫ 3-Methyl-4-methylenehepta-2,6-dienal (60): NMR

¹H

3

a solution of 1,4-bis(formyloxy)but-2-yne (43, prepared from 42 (400.1 MHz, CDCl₃): δ ϭ 2.32 (s, 3 H, 8-H), 3.07 (ddd, J ϭ 6.5,

according to,^[51]2.51 g, 18 mmol) in anhydrous THF (80 mL) at

Ϫ40 °C. The reaction mixture was stirred for 30 min at this temper-

ature and then slowly warmed to room temp. After additional stir-

⁴J ϭ 1.3, ⁴J ϭ 1.3 Hz, 2 H, 5-H), 5.06 (dd, ²J ϭ 1.5, ³J ϭ 17.1 Hz,

2

3

1 H, 7-H), 5.09 (dd, J ϭ 1.5, J ϭ 10.4 Hz, 1 H, 7-H), 5.37 and

5.63 (2 ϫ s, 2 H, 9-H), 5.82 (ddt, ³J ϭ 10.5, ³J ϭ 17.1, ³J ϭ 6.5 Hz,

ring for 2 h, THF (50 mL) was added, the temperature was lowered 1 H, 6-H), 10.18 (d, ³J ϭ 7.4 Hz, 1 H, 1-H). Ϫ ¹³C NMR

to Ϫ10 °C, and aqueous sodium hydroxide solution (15%, 40 mL)

was added carefully (vigorous gas evolution). While the temper-

ature was kept at Ϫ10 °C, a solid precipitate formed, the color of

(100.6 MHz, CDCl₃): δ ϭ 14.59 (q, C-8), 37.64 (t, C-5), 116.89 and

119.48 (2 ϫ t, C-7, C-9), 126.68 (d, C-2), 135.37 (d, C-6), 146.53

Ϫ1

˜

(s, C-4), 155.87 (s, C-3), 192.08 (d, C-1). Ϫ GC/IR: ν ϭ 3091 cm

which changed from orange to blue, and finally disappeared. The (w), 3014 (w), 2981 (m), 2950 (m), 2934 (m), 1795 (s), 1696 (vs),

residue was removed by filtration and carefully washed with pent-

ane. The combined organic phases were concentrated in vacuo until

1635 (w), 1593 (m), 912 (s). Ϫ GC/MS (40 eV): m/z (%) ϭ 136 [M^ϩ

] (3), 135 (15), 121 (19), 108 (41), 107 (53), 106 (27), 105 (28), 95

an orange red toluene solutions was obtained. When pentane (77), 93 (48), 91 (88), 79 (51), 77 (63), 65 (41), 41 (100). Ϫ 3,4-

(300 mL) was added to this solution, an orange solid precipitated

Dimethylenehept-6-enal (62): ¹H NMR (400.1 MHz, CDCl₃): δ ϭ

and was removed by filtration through a short alumina column. 3.06 (ddd, ³J ϭ 6.5, ⁴J ϭ 1.3, ⁴J ϭ 1.3 Hz, 2 H, 5-H), 3.31 (dd,

4

The resulting solution was fractionated at 34 °C/0.2 mbar, furnish-

³J ϭ 2.5, J ϭ 0.9 Hz, 2 H, 2-H), 5.10 (m, 6 H, 7-H Ϫ 9-H), 5.86

ing 0.65 g (26%) of 7 as a colorless liquid. Ϫ ¹H NMR (400.1 MHz, (ddt, J ϭ 10.5, J ϭ 17.1, J ϭ 6.5 Hz, 1 H, 6-H), 9.59 (t, J ϭ

3

CDCl₃): δ ϭ 4.14 (dd, ²J ϭ 2.6, ³J ϭ 6.8 Hz, 2 H, ϭCH₂), 4.33 2.5 Hz, 1 H, 1-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 37.93

2

3

(dd, J ϭ 2.6, J ϭ 14.3 Hz, 2 H, ϭCH₂), 4.44 (s, 4 H, 1-H), 6.45

(t, C-5), 49.45 (t, C-2), 114.98, 116.44, 117.55 (3 ϫ t, C7 Ϫ C-9),

(dd, ³J ϭ 6.8, ³J ϭ 14.3 Hz, 2 H, -CHϭ). Ϫ ¹³C NMR (100.6 MHz, 136.04 (d, C-6); the quaternary carbon atoms could not be de-

Ϫ1

˜

CDCl₃): δ ϭ 55.90 (t, C-1), 81.80 (s, C-2), 88.41 (t, ϭCH₂), 150.26 tected, due to their low intensity. Ϫ GC/IR: ν ϭ 3097 cm (m),

Eur. J. Org. Chem. 2001, 4009Ϫ4030

4027

H. Hopf, J. Wolff

3013 (w), 2925 (m), 2809 (m), 2715 (m), 1745 (vs), 1643 (m), 1596 (t, C-1), 104.89 (s, C-3), 115.57 (t, C-6), 136.02 (d, C-5), 204.95 (s,

FULL PAPER

Ϫ1

˜

(m), 1390 (m), 1037 (m), 909 (s). Ϫ GC/MS (40 eV): m/z (%) ϭ 136 C-2). Ϫ GC/IR: ν ϭ 3071 cm (s), 3001 (vs), 2962 (vs), 2931 (s),

[M^ϩ] (1), 121 (8), 117 (12), 107 (45), 93 (68), 92 (43), 91 (100), 79 2912 (s), 2901 (s), 2884 (s), 1959 (m), 1948 (m), 1646 (m), 1454 (m),

(71), 77 (67), 41 (73).

1439 (m), 1141 (m), 914 (s), 888 (s), 851 (s). Ϫ GC/MS (40 eV): m/

z (%) ϭ 134 [M^ϩ] (62), 119 (93), 117 (28), 115 (18), 105 (23), 91

(100), 79 (20), 78 (62), 77 (24).

b) Pyrolysis of 7-Methoxyhept-1-en-5-yne (4). ؊ 3-(Methoxyme-

thyl)hexa-1,2,5-triene (64): ¹H NMR (400.1 MHz, CDCl₃): δ ϭ

5

2.80 (m, 2 H, 4-H), 3.33 (s, 3 H, 8-H), 3.94 (t, J ϭ 3.2 Hz, 2 H, e) Pyrolysis of 1,4-bis(vinyloxy)but-2-yne (7). ؊ 3-Vinyloxymethyl-

7-H), 4.80 (tt, ⁵J ϭ 3.2, ⁵J ϭ 3.2 Hz, 2 H, 1-H), 5.04 (dd, ²J ϭ 1.5, penta-3,4-dienal (79): GC/IR: ν ϭ 3074 cm (w), 3058 (w), 3027

Ϫ1

˜

³J ϭ 17.1 Hz, 1 H, 6-H), 5.09 (dd, J ϭ 1.5, J ϭ 10.4 Hz, 1 H, 6- (m), 2885 (w), 1969 (m), 1811 (s), 1780 (m), 1427 (m), 1395 (m),

2

3

H), 5.85 (ddt, ³J ϭ 10.4, J ϭ 17.1, J ϭ 6.4 Hz, 1 H, 5-H). Ϫ ¹³C

1145 (s), 1058 (s), 1027 (vs), 995 (s), 869 (s). Ϫ GC/MS (40 eV): m/

3

NMR (100.6 MHz, CDCl₃): δ ϭ 33.71 (t, C-4), 57.54 (q, C-8), z (%) ϭ 110 [M^ϩϪ CO] (2), 94 (13), 82 (14), 81 (100), 69 (11), 66

72.74 (t, C-7), 75.79 (t, C-1), 98.67 (s, C-3), 116.12 (t, C-6), 135.25 (52), 65 (30), 55 (14), 54 (13), 53 (43), 52 (12), 51 (23). Ϫ 3,4-

(d, C-5), 216.96 (s, C-2). Ϫ GC/IR: ν˜ ϭ 3070 cm^Ϫ1(w), 2993 (s), Dimethylenehexanedial (80): ¹H NMR (400.1 MHz, CDCl₃): δ ϭ

3

2931 (s), 2900 (s), 2868 (m), 2830 (s), 1956 (m), 1181 (s), 1100 (vs), 3.39 (d, J ϭ 2.5 Hz, 4 H, 2-H, 5-H), 5.28 and 5.32 (2 ϫ s, 4 H, 7-

998 (m), 917 (s), 849 (s). Ϫ GC/MS (40 eV): m/z (%) ϭ 124 [M^ϩ

]

H, 8-H), 9.63 (t, ³J ϭ 2.5 Hz, 2 H, 1-H, 6-H). Ϫ ¹³C NMR

(1), 123 (6), 109 (14), 91 (26), 79 (37), 77 (15), 51 (10), 45 (100), 41

(100.6 MHz, CDCl₃): δ ϭ 49.17 (t, C-2, C-5), 119.05 (t, C-7, C-8),

Ϫ1

˜

(11). Ϫ 3-Methylenehexa-1,5-diene (65): Spectral data are identical 138.01 (s, C-3, C-4), 199.56 (d, C-1, C-6). Ϫ GC/IR: ν ϭ 2966 cm

to those reported in ref.^[53]Ϫ 3-Methoxymethylene-4-methyl-

(w), 2942 (m), 2389 (m), 2831 (s), 1670 (vs), 1608 (m), 1393 (s),

1

enecyclopent-1-ene (66): H NMR (400.1 MHz, CDCl₃): δ ϭ 3.10 1322 (s), 1227 (s), 1079 (m), 1038 (m), 885 (s). Ϫ GC/MS (40 eV):

(m, 2 H, 5-H), 3.38 (s, 3 H, 7-H), 3.40 (m, 3 H, 3-H, 6-H), 5.07 m/z (%) ϭ 138 [M^ϩ] (1), 120 (10), 109 (100), 95 (30), 91 (31), 82

(m, 2 H, 8-H), 5.82 (m, 2 H, 1-H, 2-H). Ϫ ¹³C NMR (100.6 MHz, (29), 79 (25), 77 (15), 67 (72), 65 (25), 53 (40), 41 (59). Ϫ 4-Methyl-

CDCl₃): δ ϭ 39.01 (t, C-5), 50.00 (d, C-3), 58.92 (q, C-7), 76.81 (t, 3-methylenepent-4-enal (81): ¹H NMR (400.1 MHz, CDCl₃): δ ϭ

C-6), 107.64 (t, C-8), 130.35 and 132.07 (2 ϫ d, C-1, C-2), 150.04 1.99 (s, 3 H, CH₃), 3.32 (d, ³J ϭ 2.3 Hz, 2 H, 2-H), 4.98, 5.08, 5.19,

Ϫ1

3

˜

(s, C-4). Ϫ GC/IR: ν ϭ 3074 cm (m), 2989 (m), 2931 (s), 2904

5.40 (4 ϫ s, 4 H, ϭCH₂), 9.60 (t, J ϭ 2.3 Hz, 1 H, 1-H). Ϫ GC/

(s), 2878 (s), 2835 (s), 1192 (m), 1125 (vs), 888 (s), 720 (m). Ϫ GC/ IR: ν˜ ϭ 2808 cm^Ϫ1(m), 2715 (m), 1745 (s), 1701 (w), 1601 (w),

MS (40 eV): m/z (%) ϭ 124 [M^ϩ] (3), 94 (8), 91 (38), 79 (72), 78 1419 (m), 1034 (m), 912 (m). Ϫ GC/MS (40 eV): m/z (%) ϭ 110

(20), 77 (52), 66 (25), 45 (100). Ϫ 1-Methylpentafulvene (70): Spec-

[M^ϩ] (3), 95 (4), 82 (81), 79 (15), 67 (100), 65 (14), 54 (28), 53 (28),

51 (11), 41 (54).

tra are identical to those reported in ref.^[54]

c) Pyrolysis of Nona-1,7-dien-5-yne (5). ؊ 1-Allyl-3-methyl-4-

f) Pyrolysis of 1-Methoxy-4-vinyloxybut-2-yne (9). ؊ 2-(Methylme-

methylenecyclobutene (73): ¹H NMR (400.1 MHz, CDCl₃): δ ϭ thoxy)buta-1,3-diene (83): The spectroscopic data of this pyrolysis

3

1.18 (d, J ϭ 6.9 Hz, 3 H, 8-H), 2.87 (m, 2 H, 5-H), 3.14 (m, 1 H, product are incomplete in ref.^[55]Ϫ ¹H NMR (400.1 MHz, CDCl₃):

3-H), 4.45 and 4.59 (2 ϫ s, 2 H, 9-H), 5.05 (dd, ²J ϭ 1.5, ³J ϭ δ ϭ 3.36 (s, 3 H, CH₃), 4.11 (s, 2 H, 5-H), 5.16 (dd, ²J ϭ 1.5, J ϭ

3

2

3

17.1 Hz, 1 H, 7-H), 5.12 (dd, J ϭ 1.5, J ϭ 10.8 Hz, 1 H, 7-H), 11.0 Hz, 1 H, 4-H), 5.25 (s, 2 H, 1-H), 5.30 (dd, ²J ϭ 1.5, ³J ϭ

3

5.88 (ddt, ³J ϭ 6.8, J ϭ 10.8, J ϭ 17.1 Hz, 1 H, 6-H), 6.40 (m, 1 17.7 Hz, 1 H, 4-H), 6.38 (dd, J ϭ 11.0, J ϭ17.7 Hz, 1 H, 3-H).

H, 2-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 17.33 (q, C-8), ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 58.00 (q, CH₃), 72.27 (t,

Ϫ

31.96 (t, C-5), 42.48 (d, C-3), 94.67 (t, C-9), 116.12 (t, C-7), 134.72 C-5), 114.29 (t, C-1), 117.20 (t, C-4), 136.49 (d, C-3), 142.34 (s, C-

(d, C-6), 141.55 (d, C-2); the quaternary carbon atoms could not 2). Ϫ GC/IR: ν˜ ϭ 3097 cm^Ϫ1(w), 2993 (m), 2931 (s), 2910 (s), 2835

Ϫ1

˜

be detected, due to their low intensity. Ϫ GC/IR: ν ϭ 3075 cm

(m), 2823 (m), 1592 (m), 1194 (m), 1118 (vs), 993 (m), 906 (vs). Ϫ

(s), 2981 (m), 2916 (vs), 2870 (s), 1620 (m), 1141 (m), 891 (m), 853 GC/MS (40 eV): m/z (%) ϭ 98 [M^ϩ] (2), 96 (33), 94 (20), 81 (37),

(m). Ϫ GC/MS (40 eV): m/z (%) ϭ 120 [M^ϩ] (65), 105 (47), 92 (39),

19 (100), 78 (48), 77 (70), 66 (22), 65 (23). Ϫ 2-Allylcyclohexa-1,3-

67 (11), 66 (11), 65 (19), 53 (11), 51 (18), 45 (100), 43 (12).

g) Pyrolysis of 6-Vinyloxyhex-2-en-4-yne (10): A (Z)/(E) mixture

of 10 (ratio 2:1) was employed in the pyrolysis experiments. Ϫ 3-

1

diene (75): H NMR (400.1 MHz, CDCl₃): δ ϭ 2.18 (m, 4 H, 5-H,

6-H), 2.82 (t, ³J ϭ 6.3 Hz, 2 H, 7-H), 5.04 (dd, ²J ϭ 1.5, ³J ϭ

1

Propenylpenta-3,4-dienal (90): H NMR (400.1 MHz, CDCl₃): δ ϭ

2

3

17.1 Hz, 1 H, 9-H), 5.09 (dd, J ϭ 1.5, J ϭ 10.3 Hz, 1 H, 9-H),

5.80 (m, 4 H, 1-H, 3-H, 4-H, 8-H). Ϫ ¹³C NMR (100.6 MHz,

CDCl₃): δ ϭ 23.23 and 26.24 (2 ϫ t, C-5, C-6), 41.71 (t, C-7),

116.15 (t, C-9), 119.46, 123.86, 124.56 (3 ϫ d, C-1, C-3, C-4),

136.54 (d, C-8); C-2 could not be detected because of low signal

intensity. Ϫ GC/IR: ν˜ ϭ 3086 cm^Ϫ1(m), 3040 (s), 298 (m), 2929

(vs), 2861 (m), 1843 (m), 1621 (m), 1443 (m), 1408 (m), 1366 (m),

1333 (m), 988 (m), 918 (s), 718 (m). Ϫ GC/MS (40 eV): m/z (%) ϭ

120 [M^ϩ] (56), 105 (38), 92 (31), 91 (67), 79 (100), 78 (37), 77 (67),

65 (16).

2

3

1.81 (dd, J ϭ 1.7, J ϭ 6.9 Hz, 3 H, 8-H), 3.13 (d, J ϭ 2.9 Hz, 2

H, 2-H), 4.98 (m, 2 H, 5-H), 5.51 (dq, 1 H, ³J ϭ 15.4, ³J ϭ 6.9 Hz,

3

7-H), 6.00 (d, J ϭ 15.4 Hz, 1 H, 6-H), 9.64 (t, J ϭ 2.9 Hz, 1 H,

1-H). Ϫ GC/IR: ν ϭ 3042 cm^Ϫ1(w), 2929 (m), 2805 (m), 2712 (m),

˜

1942 (m), 1746 (vs), 1032 (m), 962 (s), 855 (s). Ϫ GC/MS (40 eV):

m/z (%) ϭ 122 [M^ϩ] (6), 121 (12), 107 (45), 94 (24), 93 (13), 91

(31), 79 (84), 78 (20), 77 (100), 65 (24), 53 (25), 52 (16). Ϫ 2-Cyclo-

1

hexa-1,3-dienyl-acetaldehyde (94): H NMR (400.1 MHz, CDCl₃):

δ ϭ 2.20 (m, 4 H, 5-H, 6-H), 3.09 (d, ³J ϭ 2.6 Hz, 2 H, 2-H),

3

5.50Ϫ6.00 (m, 3 H, 4-H, 7-H, 8-H), 9.62 (t, J ϭ 2.6 Hz, 1 H, 1-

d) Pyrolysis of trans-6-(2-Methylcyclopropyl)hex-1-en-5-yne (6). ؊ H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 21.96 and 22.38 (2 ϫ

1-(1-Allylpropa-1,2-dienyl)-2-methylcyclopropane (77): ¹H NMR t, C-5, C-6), 50.20 (t, C-2), 125.51, 126.20, 127.96 (3 ϫ d, C-4, C-

Ϫ1

˜

7, C-8), 139.14 (s, C-3), 200.33 (d, C-1). Ϫ GC/IR: ν ϭ 3041 cm

(400.1 MHz, CDCl₃): δ ϭ 0.38, 0.60, 0.78, 0.91 (4 ϫ m, 4 H, 7-H

Ϫ 9-H), 1.07 (d, ³J ϭ 5.8 Hz, 3 H, 10-H), 2.79 (m, 2 H, 4-H), 4.79 (m), 2947 (s), 2889 (m), 2838 (m), 1742 (vs), 1042 (m), 1034 (m).

(dt, ⁵J ϭ 2.8, ⁵J ϭ 2.3 Hz, 2 H, 1-H), 5.03 (ddt, ²J ϭ 1.7, ³J ϭ Ϫ GC/MS (40 eV): m/z (%) ϭ 122 [M^ϩ] (55), 104 (27), 93 (47), 91

4

2

3

4

10.1, J ϭ 1.6 Hz, 1 H, 6-H), 5.09 (ddt, J ϭ 1.7, J ϭ 17.0, J ϭ (72), 79 (47), 78 (63), 77 (100), 65 (24), 53 (11), 51 (12). Ϫ The

1.6 Hz, 1 H, 6-H), 5.86 (ddt, J ϭ 10.1, J ϭ 17.0, J ϭ 6.8 Hz, 1 spectroscopic properties of 3-methylenecyclohexene (97)^[56]and 3-

3

H, 5-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 14.50 (t, C-9), methylenehexa-1,4-diene (95)^[57]were identical to those reported in

15.21 (d, C-8), 18.75 (q, C-10), 20.19 (d, C-7), 37.32 (t, C-4), 76.63

4028

the literature.

Eur. J. Org. Chem. 2001, 4009Ϫ4030

Thermal Pericyclic Tandem Reactions

FULL PAPER

h) Pyrolysis of 1,4-Bis(acetoxy)but-2-yne (12). ؊ 1-Acetylvinyl Acet-

ate (103):^{[58] 1}H NMR (400.1 MHz, CDCl₃): δ ϭ 2.21 (s, 3 H, 6-

[1]

[2]

W. v. d. Schulenburg, H. Hopf, R. Walsh, Chem. Eur. J. 2000,

6, 1963Ϫ1979.

B. M. Trost, Angew. Chem. 1995, 107, 285Ϫ307; Angew. Chem.

Int. Ed. Engl. 1995, 34, 259Ϫ280.

2

H), 2.38 (s, 3 H, 1-H), 5.14 and 5.94 (2 ϫ d, J ϭ 2.3 Hz, 2 H, 4-

H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 20.40 (q, C-6), 21.47

[3] [3a]

F. E. Ziegler, in Comprehensive Organic Synthesis (Eds.: B.

M. Trost, I. Fleming), Pergamon Press, Oxford, 1991, Vol. 5,

(q, C-1), 101.33 (t, C-4), 156.11 (s, C-3), 170.06 (s, C-5), 196.51 (s,

Ϫ1

˜

C-2). Ϫ GC/IR: ν ϭ 1725 cm (vs), 1620 (s), 1303 (s), 1260 (s),

[3b]

pp. 875Ϫ898. Ϫ

Wiley-Interscience, New York, N. Y. 1992. Ϫ

U. Beifuss, Angew. Chem. 1993, 105, 137Ϫ239; Angew. Chem.

T.-L. Ho, Tandem Organic Synthesis,

969 (m), 891 (m).

[3c]

L. F. Tietze,

i) Pyrolysis of trans-1-(3-Methoxyprop-1-ynyl)-2-methylcycloprop-

ane (18). ؊ 1-(Methoxymethyl)hexa-1,2,5-triene (108): ¹H NMR

(400.1 MHz, CDCl₃): δ ϭ 2.70 (m, 2 H, 4-H), 3.36 (s, 3 H, 8-H),

3.96 (dd, ³J ϭ 5.7, ⁵J ϭ 4.0 Hz, 2 H, 7-H), 5.04 (dd, ²J ϭ 1.7, ³J ϭ

[3d]

Int. Ed. Engl. 1993, 32, 131Ϫ230. Ϫ

Rev. 1996, 96, 115Ϫ136.

L. F. Tietze, Chem.

[4] [4a]

A. Loupy, A. Petit, J. Hamelin, F. Texier-Boullet, P. Jac-

quault, D. Mathe, Synthesis 1998, 1213Ϫ1234. Ϫ ^[4b]A. Loupy,

´

2

3

Top Curr. Chem. 1999, 206, 153Ϫ207. Ϫ ^[4c]R. S. Varma, Green

10.3 Hz, 1 H, 6-H), 5.10 (dd, J ϭ 1.7, J ϭ 17.4 Hz, 1 H, 6-H),

5.23 (m, 2 H, 1-H, 3-H), 5.87 (ddt, ³J ϭ 6.9, ³J ϭ 10.3, ³J ϭ

17.4 Hz, 5-H). Ϫ ¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 33.65 (t, C-

4), 57.41 (q, C-8), 71.87 (t, C-7), 88.23 and 90.03 (2 ϫ d, C-1, C-

3), 115.34 (t, C-6), 136.12 (d, C-5), 210.75 (s, C-2). Ϫ IR (film):

ν˜ ϭ 2983 cm^Ϫ1(m), 2925 (m), 2894 (m), 2856 (m), 2819 (m), 1965

(m), 1640 (w), 1193 (m), 1187 (m), 1101 (s), 992 (m), 913 (s). Ϫ

GC/MS (40 eV): m/z (%) ϭ 124 [M^ϩ] (1), 123 (10), 109 (11), 93

(14), 92 (18), 91 (33), 79 (23), 77 (19), 45 (100). Ϫ 4-(2-Methoxy-

ethylidene)cyclopentene (111): 3.05 and 3.12 (2 ϫ m, 4 H, 3-H, 5-

Chem. 1999, 1, 43 Ϫ55. Ϫ ^[4d]K. Tanaka, F. Toda, Chem. Rev.

[4e]

´

2000, 100, 1025Ϫ1074. Ϫ

A. de la Hoz, A. Dıaz-Ortis, A.

Moreno, F. Langa, Eur. J. Org. Chem. 2000, 3659Ϫ3673.

An introduction to the vast literature can be found in:

[5]

[5a]

P.

A. Wender, B. L. Miller, in Organic Synthesis Ϫ Theory and

Applications (Ed.: Th. Hudlicky), The JAI Press, Greenwich,

[5b]

´

R. E. Gawley, J. Aube,

CT, Vol. 2, 1993, pp. 27Ϫ66. Ϫ

Principles of Asymmetric Synthesis, Elsevier Science, Oxford,

1996. Ϫ ^[5c]T.-L. Ho, Stereoselectivity in Synthesis, Wiley-Inter-

science, New York, N. Y., 1999.

3

[6]

[7]

H), 3.35 (s, 3 H, 8-H), 3.92 (d, J ϭ 6.8 Hz, 2 H, 7-H), 5.54 (m, 1

J. D. Cox, G. Pilcher, Thermochemistry of Organic and Organo-

metallic Compounds, Academic Press, London, 1970, p. 142.

H, 6-H), 5.77 (m, 2 H, 1-H, 2-H). Ϫ ¹³C NMR (100.6 MHz,

CDCl₃): δ ϭ 35.48 and 38.96 (2 ϫ t, C-3, C-5), 57.76 (q, C-8),

70.34 (t, C-7), 118.38 (d, C-6), 128.97 and 129.52 (2 ϫ d, C-1, C-

2), 144.09 (s, C-4). Ϫ GC/IR: ν˜ ϭ 3070 cm^Ϫ1(s), 2986 (m), 2973

(m), 2902 (vs), 2829 (s), 1624 (w), 1199 (m), 971 (m), 920 (m). Ϫ

GC/MS (40 eV): m/z (%) ϭ 124 [M^ϩ] (1), 123 (1), 93 (11), 92 (100),

91 (63), 79 (27), 78 (10), 77 (30), 66 (28), 65 (11). Ϫ 3-(2-

Methoxyethylidene)cyclopentene (112, mixture of isomers): ¹H

NMR (400.1 MHz, CDCl₃): δ ϭ 2.52 (m, 4 H, 4-H, 5-H), 3.32 and

^[7a]Chemistry of Acetylenes (Ed.: H. G. Viehe), Marcel Dekker,

[7b]

New York, 1969. Ϫ

The Chemistry of the Carbon-Carbon

Triple Bond (Ed.: S. Patai), J. Wiley & Sons, Chichester, 1978,

Vol. 1 and 2.

[8]

H. Hopf, R. Kirsch, Tetrahedron Lett. 1985, 28, 3327Ϫ3330;

cf.: K. Banert, W. Fendel, J. Schlott, Angew. Chem. 1998, 110,

3488Ϫ3491; Angew. Chem. Int. Ed. 1998, 37, 3289Ϫ3292 and

refs. cited therein for heteroorganic variants of this process.

V. Dalacker, H. Hopf, Tetrahedron Lett. 1974, 15Ϫ18.

Carbocyclic Three- and Four-membered Rings Compounds (Ed.:

A. de Meijere), in Methods of Organic Chemistry (Houben-

Weyl), Thieme Verlag, Stuttgart, 1997, Vol. E 17aϪf.

C. A. Cornish, S. Warren, J. Chem. Soc., Perkin Trans. 1 1985,

2585Ϫ2598; cf.: K. Mori, M. Ikunaka, Tetrahedron 1984, 40,

3471Ϫ3478.

[9]

3

[10]

3.34 (2 ϫ s, 3 H, 8-H), 3.98 and 4.01 (2 ϫ d, 2 H, J ϭ 6.9 Hz, 7-

3

H), 5.33 and 5.47 (2 ϫ m, 1 H, 6-H), 6.13 and 6.16 (2 ϫ dd, J ϭ

4

6.2, J ϭ 1.2 Hz, 1 H, 2-H), 6.23 and 6.46 (2 ϫ m, 1 H, 1-H). Ϫ

[11]

¹³C NMR (100.6 MHz, CDCl₃): δ ϭ 25.83, 29.38, 31.19, 32.05 (t,

C-4, C-5), 57.54, 57.71 (q, C-8), 69.76, 70.35 (t, C-7), 113.20, 114.71

(d, C-6), 129.43, 134.23, 138.74, 140.57 (d, C-1, C-2), 150.65,

150.98 (s, C-3). Ϫ GC/IR: ν˜ ϭ 2989 cm^Ϫ1(m), 2931 (vs), 2893 (s),

2866 (s), 2824 (s), 1381 (m), 1198 (m), 1117 (vs), 915 (m), 830 (m).

Ϫ GC/MS (40 eV): m/z (%) ϭ 124 [M^ϩ] (70), 123 (23), 109 (19),

93 (59), 92 (43), 91 (100), 81 (20), 79 (29), 77 (56), 66 (13), 65 (19),

53 (12), 45 (25).

[12]

[13]

[14]

W. Schobert, M. Hanack, Synthesis 1972, 703.

W. Reppe, Liebigs Ann. Chemie 1956, 601, 81Ϫ138.

L. Brandsma, Preparative Acetylenic Chemistry, Elsevier Sci-

entific Publishing Company, Amsterdam, 1988, pp. 175Ϫ176.

The activation parameters for the propargyl Cope rearrange-

ment of hexa-1,2-dien-5-yne derivatives were determined first

by: H. Hopf, Tetrahedron Lett. 1972, 3571Ϫ3674.

[15]

[16] [16a]

j) Pyrolysis of 5-(2-methylcyclopropyl)pent-2-en-4-yne (mixture of

isomers, 20): 3-But-2-enylidenecyclopentene (119): ¹H NMR

(400.1 MHz, CDCl₃): δ ϭ 1.80 (d, ³J ϭ 6.3 Hz, 3 H, 9-H), 2.25 (m,

4 H, 4-H, 5-H), 5.60Ϫ6.20 (m, 5 H, 1-H, 2-H, 6-H Ϫ 8-H). Ϫ ¹³C

NMR (100.6 MHz, CDCl₃): δ ϭ 18.36 (q, C-9), 22.20 and 22.86 (2

Acetylenic bond participation in a classical Cope re-

arrangement was first reported in 1965 by Black and Landor:

D. K. Black, S. R. Landor, J. Chem. Soc. 1965, 6784Ϫ6788. Ϫ

[16b]

W. D. Hunstman, J. A. De Boer, M. H. Woosley, J. Am.

[16c]

Chem. Soc. 1966, 88, 5846Ϫ5850. Ϫ

acetylenic Cope rearrangements see: A. Viola, J. J. Collins, N.

Fillip, Tetrahedron 1981, 37, 3765Ϫ3811; cf.: F. Theron, M.

Verny, R. Vessiere, in The Chemistry of the Carbon-Carbon

For a review of these

ϫ t, C-4, C-5), 122.22, 123.72, 125.03, 125.96, 133.40 (5 ϫ d, C-1,

´

Ϫ1

˜

C-2, C-6 Ϫ C-8). Ϫ GC/IR: ν ϭ 3078 cm (m), 3044 (vs), 2981

`

(m), 2940 (vs), 2885 (s), 2836 (s), 1643 (w), 1442 (m), 1430 (m), 991

(m), 918 (m). Ϫ GC/MS (40 eV): m/z (%) ϭ 120 [M^ϩ] (30), 125

(25), 92 (21), 91 (47), 79 (100), 78 (29), 77 (49), 65 (10). Ϫ The

spectroscopic data of 2-allylcyclohexa-1,3-diene (75) are given un-

der c).

Triple Bond (Ed.: S. Patai), J. Wiley & Sons, Chichester, 1978,

part 1, pp. 421Ϫ430. Ϫ ^[16d]W. D. Huntsman, in The Chemistry

of Ketenes, Allenes, and Related Compounds (Ed.: S. Patai), J.

Wiley and Sons, Chichester, 1980, part 2, pp. 582Ϫ643.

Review: H. Hopf, Angew. Chem. 1984, 96, 947Ϫ958; Angew.

Chem. Int. Ed. Engl. 1984, 23, 947Ϫ959; cf. H. Hopf, Angew.

Chem. 2001, 113, 727Ϫ729; Angew. Chem. Int. Ed. 2001, 40,

705Ϫ707.

W. M. Schubert, R. R. Kitner, in The Chemistry of the Car-

bonyl Group (Ed.: S. Patai), Interscience Publishers, Chichester,

1966, 726Ϫ735.; cf.: F. E. Blacet, J. E. Lu Valle, J. Am. Chem.

Soc. 1939, 61, 273Ϫ276.

[17]

[18]

Acknowledgments

We thank the Fonds der Chemischen Industrie for the continuous

support of our studies, and Professors Dr. B. Ondruschka (Jena)

and Dr. R. Walsh (Reading, England) as well as Dr. Jörg Grunen-

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Received March 29, 2001

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4030

Eur. J. Org. Chem. 2001, 4009Ϫ4030

Article Doi

Thermal pericyclic tandem reactions

DOI: 10.1002/1099-0690(200111)2001:21<4009::AID-EJOC4009>3.0.CO;2-4

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