PtCl2- and PtCl4-catalyzed cycloisomerization of polyunsaturated precursors

FULL PAPER

DOI: 10.1002/ejoc.200600521

PtCl₂- and PtCl₄-Catalyzed Cycloisomerization of Polyunsaturated Precursors

José Marco-Contelles,*^[a]Nieves Arroyo,^[a]Shazia Anjum,^[a]Emily Mainetti,^[b]

Nicolas Marion,^[b]Kevin Cariou,^[b]Gilles Lemière,^[b]Virginie Mouriès,^[b]

Louis Fensterbank,*^[b]and Max Malacria*^[b]

Keywords: PtCl₂-catalyzed cycloisomerization / Dienynes / Enynes / Cyclopropanes / 1,2-O-Acyl migration / Transition

metals

The PtCl₂- and PtCl₄-catalyzed cycloisomerization of polyun-

saturated precursors with different O-protecting groups at

the propargylic position is reported. The free hydroxy, O-

enyl derivatives were obtained in good yields. These prod-

ucts are formally the result of a 1,2-migration of an O-acyl

group, coupled to a cyclopropanation step. Related propar-

(bromomethyl)dimethylsilyl, O-methyl and O-propenyl de- gylic acetates with a pendant aromatic group (25) or substi-

rivatives 1a–f have afforded mixtures of skeletal rearrange-

ment products and/or polycyclic molecules incorporating a

cyclopropyl ring system in variable chemical yields. Other

parameters such as the variation of the alkenyl chains and

the triple-bond substitution have been examined and gave

new mechanistic elements. Very interestingly, for analogous

compounds containing an ester moiety, such as the O-4-nitro-

benzoyl or acetate group (1g–j, and 22) bicyclo[4.1.0]hept-2-

tuted at the terminal acetylenic carbon with a methoxycar-

bonyl group (24) did not afford this class of rearranged com-

pounds. This type of reaction seems restricted to propargylic

derivatives, because the suitably functionalized homopropar-

gylic acetate 24 only afforded 1,3-dienes.

Germany, 2006)

of 1,6-enynes^[3,4]constitutes one of the best-known exam-

ples of what have been called full atom economy reactions.^[5]

Since the pioneering work of Trost with electrophilic palla-

dium catalysts,^[6]some novel reactions featuring skeletal re-

arrangements,^[7]and cyclopropanation processes have been

Introduction

In the last few years, our groups have been actively work-

ing on the Pauson–Khand reaction^[1]and free radical chem-

istry^[2]of diversely functionalized 1,6-enynes, and in this

context, we have recently investigated the reactivity of sub-

strates of type 1 (Figure 1).

reported.^[8]With PtCl₂,^[9,10]or Au^Iand Au^IIIcatalysis,^[11–14]

[17]

and very recently Cu^I,^[15,16]FeCl₃

and In^{III [18,19]}

, a

number of reports from different laboratories have high-

lighted the scope and limitations of this new synthetic op-

portunity for the preparation of carbocycles and/or hetero-

cycles.

Very pleasantly, the PtCl₂-mediated cycloisomerization

of the substrates 1 (Figure 1) gave new and surprising re-

sults.^[20]Subsequent chemical developments of these re-

sults,^[21–23]as well as our theoretical contributions to this

area have also been recently reported.^[24–26]Now, in this pa-

per, we would like to describe in full some of the prelimi-

nary results^[20]of the PtCl₂-promoted cycloisomerization of

precursors 1, as well as new substrates for this reaction,

which illustrate the synthetic power of these transforma-

tions.

Figure 1. General 1,6-enyne framework.

Continuing with our interest in the straightforward as-

sembly of complex polycyclic structures from readily avail-

able precursors, we have concentrated on the PtCl₂-cata-

lyzed cycloisomerization of these polyunsaturated precur-

sors. In fact, transition-metal-catalyzed cycloisomerization

[a] Laboratorio de Radicales Libres,

C/ Juan de la Cierva 3, 28006 Madrid, Spain

Fax: +34-91-564-48-53

Results and Discussion

E-mail: iqoc21@iqog.csic.es

[b] Université Pierre et Marie Curie, Laboratoire de Chimie

Organique, UMR CNRS 7611,

1. Preliminary Results

Tour 44-54, case 229, place Jussieu 4, 75252 Paris cedex 05,

France

The choice of substrates 1 relied on several features: an

easily accessible branched structure, with two pendant ole-

Fax: +33-1-44-27-73-60

E-mail: max.malacria@upmc.fr

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PtCl₂- and PtCl₄-Catalyzed Cycloisomerization of Polyunsaturated Precursors

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fins connected by distinct tethers and a functionalized, eas- gio- and stereoselectivity, featuring a synthetically simple

ily modified and stereogenic propargylic position. When and efficient operation. Additionally, this reaction involves

submitted to typical reaction conditions (5 mol-% PtCl₂, the transformation of the alkyne moiety into a bis-carbene

toluene, 80 °C for 2.5 h), precursor 1a provided a mixture entity that accomplishes a bis-cyclopropanation, leading to

of the expected formal metathesis adduct 2a as a minor two fused bicyclo[3.0.1]hexane systems. Such bis-cyclopro-

fraction and a larger amount of a fairly complex structure, panation had been previously found by Chatani and Murai

compound 3a (48% yield, Scheme 1).

with a linear dienyne.^[27]Our branched system leads to a

Inspection of the NMR spectrum of 3a clearly showed particularly strained structure, which illustrates the syn-

us that no olefinic protons were present, but the high den- thetic power of these reactions. Recently, gold^[28]and ruthe-

sity of protons at high field suggested that these molecules nium^[29]catalyses have also given interesting entries into

were possibly polycyclic derivatives incorporating one or bis-cyclopropyl derivatives.

more cyclopropyl ring systems. Several structural hypothe-

The observed spectroscopic data of compounds 3b and

ses were raised, but a definitive structure was impossible to 3c, similar to that of the analogous derivative 3a, prompted

propose at this point. Finally, the solution to this problem us to assign the same structure to these molecules, as well

was obtained by X-ray diffraction analysis^[20]of the 4-nitro- as the same relative configuration at the newly formed ste-

benzoyl derivative of compound 3a (4), easily prepared by reocenters. As an additional proof of structure, the reaction

the standard method in an unoptimized reaction of silyl derivative 3b with tetrabutylammonium fluoride in

(Scheme 2).

THF at room temperature afforded a compound identical

The structure of compound 3a (Scheme 1) corresponds to polycycle 3a in quantitative yield (Scheme 1). Interest-

to the octahydro-2,2-dimethyl-1H-dicyclopropa[a,g]penta- ingly, methyl ether 1c gave diastereomerically pure 3c, in a

lene skeleton, which had not been described previously in very clean reaction (73% yield), with no detectable metathe-

the literature. Moreover, the formation of compound 3a sis adduct 2c. The use of PtCl₄also proved to be very re-

that involves the formation of four C–C and four new ste- warding for this reaction, since tetracycle 3c was isolated in

reocontrolled centers, is spectacular in terms of chemo-, re- 77% yield. In contrast, methallyl precursor 1d underwent

Scheme 1.

Scheme 2.

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in a clean reaction from which 3d was isolated as a single metathesis pathway or can be further trapped to give the

product in 34% yield with PtCl₂and in a slightly better tetracyclic structures 3a–e (Scheme 3).

yield (40%) with PtCl₄(Scheme 1, entries 5 and 6). We

Additional information was collected by examining the

could also show that the presence of a dimethyl group on behavior of O-allyl precursor 1f, which contains an ad-

the butenyl chain was not necessary, since we could isolate ditional unsaturation (Scheme 4) and is easily prepared

3e in 54% yield consistently as a single diastereomer from from precursor 1a.

precursor 1e. In that case, the use of PtCl₄did not result in

Despite all the possible interventions of the unsatura-

any improvement of the yield.

tions, a clean reaction (room temp. for 16 h) was observed,

These promising findings prompted us to expand and ex- since two major adducts (3f and 5) were isolated in good

plore this chemistry by preparing new precursors for the overall yield (44% and 36% yield, respectively, Scheme 4)

Pt^II-mediated cycloisomerization, as well as to define a and in both cases as single diastereoisomers. The structure

mechanistic rationale.^[20,24–26]Thus, all these results were of product 3f was proposed by analogy with spectroscopic

consistent with the intervention of a platinacyclo-propyl in- data of the products 3a–e. Structural assignment of product

termediate^{[7–9,29–31]}of type I that can evolve into a formal 5 was secured by derivatization and X-ray analysis of 6

(Scheme 5).^[32]These findings are supported by recent

mechanistic studies carried out by Soriano and Marco-

Contelles^[33]and represent an interesting possibility for

forming oxygenated heterocycles.

2. Variations on the O-Methyl Substrates

Scheme 3.

Starting from the general framework 1, we enlarged our

study, now considering 1,6-enynes 7, which feature the eas-

ily modifiable groups R, RЈ and R^ЈЈ(Figure 2).

Figure 2. 1,6-Enynes bearing a propargylic OMe group.

Alkenyl Chain (RЈ Group)

We first looked at the possibility of obtaining tetracycles

incorporating medium-sized rings that would result from

the trapping of carbene I with a long pendant alkene chain.

For this purpose, we prepared dienyne 7a, expecting that it

Scheme 4.

would lead to a bis-cyclopropyl-substituted 5,8-bicyclic

Scheme 5.

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PtCl₂- and PtCl₄-Catalyzed Cycloisomerization of Polyunsaturated Precursors

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Scheme 6.

system. When we submitted this compound to typical con-

ditions, we did not observe any polycyclic compound but a

mixture of two products. Metathesis adduct 8 was obtained

in 60% yield, along with diene 9 in 16% yield (Scheme 6).

To the best of our knowledge, although frequently occur-

ring when other metals are used,^[4]this is the first report of

the formation of a diene of type 9 in a Pt-catalyzed cyclo-

isomerization. Only the 1,6-enyne moiety was involved in

this reaction, most probably because the RЈ alkene is too

remote. Consequently, in contrast to the findings shown in

Scheme 1, the formal metathesis product was the major one.

We decided to test the reactivity of deuterated compound

7aD for evidence of atom scrambling, as previously de-

scribed by Murai^[34]and Oi and Inoue^[35]in this kind of

cycloisomerization.^[36]When this compound was submitted

Scheme 7.

to the same experimental conditions, it led to deuterated

Scheme 8.

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dienes 8D in a 7:3 ratio in favor of the abnormal metathesis was the dimethylenecyclopentane. No reaction was ob-

product. It should be noted that the stereochemistry of the served with the pendant allylic moiety (Scheme 9).

deuterium incorporation was fully consistent with literature

reports.^[3,35,37]The stereochemical assignment of exo diene our findings and those reported in the literature urged us

9D was based on nOe measurements (Scheme 6).

to consider cyclopropylplatinacarbene I as the key interme-

All this led us to refine our mechanistic proposal. All of

We then prepared a new precursor that possessed a gem- diate in these transformations. Trapping of this species by

dimethyl moiety on the RЈ chain. We hoped that a Thorpe– a pendant unsaturation would lead to polycycles 3.

Ingold effect would favor the formation of the cyclooctane

product.^[38]We were confident, from the results obtained

with 7a, that the first cyclopropanation would take place

easily, generating the platinacyclopropyl carbene species.

When we submitted 7b to cycloisomerization conditions, we

did not obtain the expected product but a mixture of two

compounds, cyclohexene 10 in 45% yield and cyclopentane

11 in 25% yield, analogous to 9. No trace of the metathesis

product was observed (Scheme 7).

Eventually, we supressed the pendant allylic chain to fo-

cus on the 1,6-enyne reactivity. Substrate 7c reacted slug-

gishly with PtCl₂and even worse with PtCl₄. Addition of

an olefin^[39,40]to the reaction medium allowed for the for-

mation of metathesis adduct 12 as the major compound,

along with diene 13 in a moderate overall yield.

Other evolutions are possible. Metallacarbene I can also

be viewed as a metallic zwitterion IЈ, which corresponds to

a metalated non-classical homoallylic cation.^[9,31]Zwitter-

ionic cyclohexyl intermediate II would contribute signifi-

cantly only when R = H, which alleviates severe 1,3-diaxial

interactions. Consecutive proton eliminations, possibly as-

sisted by platinum, affords methylenecyclohexene adducts

10 and 14. The formation of dienes 9, 11, 13, 15, and 17

(and notably 9D) is a signature of platinacyclopentene III.

This intermediate can originate from cyclopropylplatinacar-

bene I through a vinylcyclopropane to cyclopentene type of

mechanism or by direct oxidative cyclization after coordi-

nation of both unsaturations of the 1,6-enyne moiety. How-

ever, this possibility has not been supported by DFT calcu-

lations,^[30]and the observation of products deriving from

this intermediate is generally scarce. Therefore, we favor the

intervention of platinacyclopentene III as an evolution of

cyclopropylplatinacarbene I. β-hydride elimination gives

birth to intermediate IV, which leads to dimethylenecyclo-

pentane adducts after reductive elimination.

Substrate 7d, which does not bear the gem-dimethyl moi-

ety, gave a complex mixture from which no metathesis prod-

uct was observed and 14 and 15 could be isolated, albeit in

low yield (Scheme 8).

The formation of formal metathesis adducts 8, 12, and

16 from intermediate I has been fully studied recently. Cal-

culations by Soriano and Marco-Contelles on PtCl₂and by

Echavarren on gold complexes corroborate the initial

mechanism proposal by Murai, Inoue and Oi.^[25,34–36]Sin-

gle cleavage or double cleavage of the cyclopropyl moiety

explain the formation of both isomers.

Triple Bond Substitution (RЈЈ Group)

To gain more insight into this highly substrate-dependent

reaction, we also examined the substitution of the triple

bond. The easily synthesized compound 7e, which that fea-

tures a TMS group on the alkyne, showed no reaction

towards PtCl₂or PtCl₄catalysis. This lack of reactivity has

already been described with other silylated systems^[23,41]

If the triple bond is substituted by a TMS group or an

(Scheme 9). In the same vein, alkyl substitution gave a very alkyl chain, unproductive and unselective catalyses are ob-

low yield of cycloisomerization products (Ͻ15%). So, we served. In contrast, substitution by an electron-withdrawing

turned our attention to precursors bearing an electron- group (precursor 7f) restores a decent level of reactivity, as

withdrawing group. Methoxyester derivative 7f reacted evidenced by the formation of dienes 16 and 17, but does

readily with a good overall yield. Major product 16 came not allow the formation of tetracyclic adducts, probably due

from a formal metathesis reaction, and minor product 17 to unfavorable steric interactions.

Scheme 9.

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PtCl₂- and PtCl₄-Catalyzed Cycloisomerization of Polyunsaturated Precursors

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Scheme 10.

Finally, an interesting observation stems from the differ- responding free alcohols. In fact, for correlation purposes,

ence of reactivity between 7a and 7c and 7b and 7d, the we wanted to prepare product 4 (Scheme 2), which we had

latter giving more sluggish results. To account for this, we previously obtained by acylation of polycycle 3a, by direct

suspect that an additional coordination of the metal by the PtCl₂-cycloisomerization from the corresponding open pre-

remote unsaturation would somehow stabilize intermediate cursor 1g. In Scheme 11, we show the results we observed

I and favor its evolution through other pathways (e.g. diene in this PtCl₂-catalyzed cycloisomerization reaction. Con-

formation) when the second cyclization is too difficult to trary to our expectations, esters 1g, 1h and 1i gave the bicy-

take place. The same process would take place in the pres- clo[4.1.0]hept-2-en-2-yl 4-O-acyl derivatives 18a (76%), 18b

ence of an additional olefin.

(88%) and 18c (62%), respectively, in good yields and in

shorter reaction times than those of the O-alkyl derivatives.

All these considerations are summarized in Scheme 10.

In conclusion, we have carried out several experiments These compounds were accompanied by minor amounts of

on 1,6-enynes possessing a methoxy moiety on the propar- cyclopentene derivatives 19a, 19b and 19c, whose structure

1

gylic position, making subtle variations on the general assignment was based on H NMR spectra. No pure sam-

framework. The study of the influence of these parameters ple of 19 could be obtained, as it was always in a mixture

(gem-dimethyl on the enyne, additional unsaturation, triple with the corresponding product 18. Unmethylated precur-

bond substitution) allowed us to draw an overview of the sor 1j could also efficiently undergo the cycloisomerization

different mechanistic pathways involved from a single com- process to provide 18d with PtCl₂or PtCl₄. In that case,

mon carbene intermediate. DFT calculations to support no five-membered ring was detected. Additional proof of

these conclusions are ongoing and will be reported in due structure was obtained when compound 18b was trans-

course.

formed into trans ketone 20 after methanolysis

(Scheme 11). The stereochemical assignment of 20 was de-

duced from nOe studies.

3. Variations on the O-Acyl Substrates

Interestingly, a careful re-examination of the current lit-

Next, we considered precursors 1g–i, where a 4-nitroben- erature showed that this PtCl₂-mediated cycloisomerization

zoyloxy group or an acetate has been located at the propar- reaction of propargyl acetates was not entirely new, as some

gylic position. These compounds were easily synthesized by precedent was established by Ohloff in 1976 with Zn^II.^[42]

standard O-acylation (Et₃N, DMAP in CH₂Cl₂) of the cor- Some years later, Rautenstrauch also described the same

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Scheme 11.

reaction,^[43]and found that similar products were obtained their PtCl₂-catalyzed cycloisomerization reactions. It was

in moderate yields (10–40%) from related precursors, with noticed that on going from the free alcohol (or ethers) to

PdCl₂(CH₃CN)₂as a catalyst,. After this preliminary com- O-acyl derivatives, the major final resulting products were

munication, no further reports from this laboratory were completely different. For the O-acyl migration, the mecha-

available, and the potential interest of this new mode of nism may involve an initial cycloisomerization followed by

cycloisomerization reaction, as well as the potential syn- a migration, with the initial 1,2-migration being followed

thetic applications of the resulting building blocks, re- by intramolecular cyclopropanation or cyclization of a half-

mained unexplored. Recently, after we recently rediscovered rearranged intermediate.^[15,50–51]DFT calculations on our

this reactivity,^[20]Ohe and Uemura have reported the inter- substrates have not allowed us to discern an obvious path-

molecular version^[44,45]of this reaction. Further reports way so far.^[24]This result urged us to extend these observa-

from our laboratories,^[46,47]as well as the development of tions to other enynes, in order to explore the scope and

gold(I) or gold(III) catalyses,^[48,49]have established the ver- generality of the process. We could notably show that the

satility of this transformation and have enlarged its scope substitution on the alkyne favors the formation of allenyl

to even include asymmetric transformations.^[15,50–52]

Interestingly, a gem-dimethyl effect^[38]was observed in ment.^[23]

esters that can further undergo a thermal [3,3] rearrange-

the case of 21, which preferably gave 22 over 23

We have also prepared and submitted to cyclization pre-

(Scheme 12).

cursors 24, 25 and 26 (Figure 3). In compound 24, we have

incorporated a propargylic acetate and a methoxycarbonyl

group at the terminal position of the acetylenic moiety. Pro-

pargylic acetate 25 has been designed to determine if the

presumed Pt carbene intermediate could be trapped by the

pendant aromatic ring. Finally, we wanted to know if this

cycloisomerization, as shown in Scheme 8, is still possible

with the homopropargylic acetate 26 or is it limited to pro-

pargylic carboxylates.

Scheme 12.

Figure 3. Different enynes bearing an OAc group.

In summary, we have observed the important effect that

Precursor 24 was prepared from commercial 5-hexene-2-

the type of the substituents at propargylic centers in dif- one (27), via alcohol 28, as shown in Scheme 13. Under

ferently functionalized 1,6-enynes have on the course of the usual catalysis conditions, we only isolated the acyclic

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PtCl₂- and PtCl₄-Catalyzed Cycloisomerization of Polyunsaturated Precursors

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product 29 in low yield (11%). The structure of this com-

pound was firmly established based on its spectroscopic and

analytical data. The assigned configuration at the double

bonds rests on selective nOe Experiments. As observed be-

fore,^[23]the formation of compound 29 could simply be ex-

plained by hydrogen abstraction by Pt to form a dienylplati-

num hydride that undergoes reductive elimination. The

reasons why the expected product from a Rautenstrauch

isomerization^[20,43]have not been detected in this case are

still obscure and demand further investigation. In fact, the

reaction of terminal substituted alkynes seems to be very

substrate-dependent, as recent results have shown that con-

veniently functionalized 5-en-1-yn-3-ol derivatives substi-

tuted with methoxycarbonyl^[21]groups at the terminal al-

kyne moiety efficiently cyclize to give bicyclic adducts.

Scheme 14.

product detected and isolated, implying that the Rauten-

strauch isomerization^[43]seems restricted to propargylic car-

boxylates.

Scheme 13.

We have prepared precursor 25^[53]from commercially

available 4-phenyl-2-butanone (30), via propargylic alcohol

31 using standard protocols (Scheme 14). After PtCl₂-medi-

ated cycloisomerization, we were able to isolate and charac-

terize only the 1-acetoxyallene 32 that would originate from

a 1,3-acetate migration (Scheme 14). Formal C–H acti-

vation products consisting of an indene motif have been

obtained with ruthenium,^[44]platinum^[54]and gold cataly-

sis^[55]when the aromatic group is at the propargylic substi-

tution.

Similarly, we have synthesized compound 26 from 6-

methylhept-6-ene-2-one (33), via known alcohol 34.^[56]The

PtCl₂-promoted cycloisomerization of precursor 26 gave an

inseparable mixture of products 35 and 36 (Scheme 15) in

good yield. The structure of these molecules was clearly es-

tablished after careful spectroscopic analysis. Major isomer

35 is the skeletal rearrangement product,^[12]while com-

Scheme 15.

Conclusions

In conclusion, the PtCl₂- and PtCl₄-catalyzed cycloisom-

pound 36 is a typical 1,3-diene obtained in transition-metal erization of polyunsaturated precursors with different O-

promoted reactions.^[4]In no case was a cyclopropyl-derived protecting groups at the propargylic position has been re-

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J. Marco-Contelles, L. Fensterbank, M. Malacria et al.

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which was also applied to obtain precursors 7.^[1]Similarly, O-al-

lylation of 1a with NaH and allyl bromide gave 1f. O-Acyl precur-

sors 1g–j and 22 were prepared from the corresponding alcohol

with acetic anhydride, or p-nitrobenzoyl chloride in pyridine with

DMAP, or in CH₂Cl₂with Et₃N and DMAP.

ported. As a result, from free hydroxy, O-(bromomethyl)-

dimethylsilyl or O-alkyl derivatives, we have isolated mix-

tures of skeletal rearrangement products and/or polycyclic

molecules incorporating a cyclopropyl ring system in vari-

able yields. Although some of these reactions have no pre-

parative impact, they allowed for the isolation of new cylo-

isomerization products, which strongly support the interme-

diacy of cyclopropylplatinacarbene and platinacyclopen-

tene intermediates and give new mechanistic insight. Very

interestingly, for analogous compounds containing an ester

moiety, bicyclo[4.1.0]hept-2-en-yl 4-O-acyl compounds

were obtained in good yields. These products are formally

the result of a sequential process of cycloisomerization and

a 1,2-migration of the benzoyloxy group, the exact order of

the events being still under scrutiny. A related propargylic

acetate substituted at the terminal acetylenic carbon with a

methoxycarbonyl group or with a pendant aromatic group

did not afford this class of rearranged compounds. Simi-

larly, this type of reaction seems restricted to propargylic

derivatives, because a suitably functionalized homopropar-

gylic acetate only afforded 1,3-dienes.

4-Ethynyl-4-methoxy-6,6-dimethylocta-1,7-diene (1c): IR (neat): ν =

˜

3300, 3100, 2950, 2350, 1650, 1460, 1390 cm^–1. ¹H NMR

(200 MHz, CDCl₃): δ = 5.99 (dd, J = 17.7, 10.9 Hz, 1 H), 5.82 (m,

1 H), 5.12–4.80 (m, 4 H), 3.31 (s, 3 H, OMe), 2.53 (s, 1 H), 2.44

(d, J = 7.4 Hz, 2 H), 1.71 (s, 2 H), 1.18 (s, 3 H, CH₃), 1.12 (s, 3 H,

CH₃) ppm. ¹³C NMR (50 MHz, CDCl₃): δ = 149.3 (CH), 133.4

(CH), 118.3 (CH₂, CH=CH₂), 109.2 (CH₂, CH=CH₂), 84.1 (C),

76.7 (CH), 75.3 (C), 51.1 (CH₃, OMe), 49.6 (CH₂), 44.6 (CH₂),

36.7 (C), 28.5 (CH₃), 28.2 (CH₃) ppm. C₁₃H₂₀O (192.30): calcd. C

81.20, H 10.48; found C 80.91, H 10.72.

4-Ethynyl-4-methoxy-2,6,6-trimethylocta-1,7-diene (1d): IR (neat): ν

˜

= 3300, 3050, 2950, 2320, 1630, 1450, 1380 cm^–1. ¹H NMR

(200 MHz, CDCl₃): δ = 6.00 (dd, J = 17.7, 10.3 Hz, 1 H), 4.92–

4.77 (m, 4 H), 3.31 (s, 3 H, OMe), 2.53 (s, 1 H), 2.39 (s, 2 H), 1.79

(s, 3 H), 1.73 (s, 2 H), 1.17 (s, 3 H, CH₃), 1.12 (s, 3 H, CH₃) ppm.

¹³C NMR (50 MHz, CDCl₃): δ = 149.5 (CH), 141.6 (C), 115.3

(CH₂, CH=CH₂), 109.0 (CH₂, CH=CH₂), 84.4 (C), 76.9 (CH), 75.4

(C), 51.1 (CH₃, OMe), 49.7 (CH₂), 47.9 (CH₂), 36.6 (C), 28.2 (2

CH₃), 24.1 (CH₃) ppm.

4-Ethynyl-4-methoxy-3,3-octa-1,7-diene (1e): IR (neat): ν = 3309,

˜

Experimental Section

1

3078, 2922, 2853, 2109, 1642 cm^–1. H NMR (400 MHz, CDCl₃):

δ = 5.91–5.76 (m, 2 H), 5.12 (m, 2 H), 4.93 (m, 2 H), 3.35 (s, 3 H,

OMe), 2.50 (s, 1 H), 2.47 (d, J = 7.0 Hz, 2 H), 2.28–2.13 (m, 2 H),

1.75 (t, J = 8.1 Hz, 2 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ

= 138.5 (CH), 133.1 (CH), 118.6 (CH_2,CH=CH₂), 114.8 (CH₂,

CH=CH₂), 83.9 (C), 75.9 (C), 75.1 (C), 51.7 (CH₂), 42.5 (CH₂),

37.4 (CH₂), 28.3 (CH₂) ppm.

General: Reactions were carried out under an anhydrous atmo-

sphere of Ar. Glassware was flame-dried under an argon gas flow

prior to use. Anhydrous THF and Et₂O were obtained by distil-

lation over sodium/benzophenone under nitrogen and used imme-

diately. Triethylamine, pyridine and diisopropylamine were dried

and then distilled from KOH; toluene and CH₂Cl₂were dried and

then distilled from CaH₂. n-Butyllithium was purchased as 2.5 

solutions in hexanes and titrated before use. Other reagents were

commercially available and used without further purification, un-

less otherwise indicated. TLC was performed on Silica F254

(Merck) and detection by UV light at 254 nm or by charring with

phosphomolybdic-H₂SO₄reagent, and p-anisaldehyde. Column

chromatography was performed on Silica Gel 60 (Merck, 230

4-Ethynyl-6,6-dimethyl-4-O-propenyl-1,7-octadien-4-ol (1f): To

a

cold (0 °C) solution of 4-ethynyl-6,6-dimethyl-1,7-octadien-4-ol

(1a, 220 mg, 1.24 mmol) in dry THF (10 mL), NaH (99 mg,

2.48 mmol) was added, and the reaction mixture was stirred at the

same temperature for 10 min. Allyl bromide (0.15 mL, 2.48 mmol)

and a catalytic amount of tetrabutylammonium iodide were added.

The mixture was stirred for 18 h at room temp., until the reaction

was complete. The excess of NaH was destroyed by adding AcOH

(0.5 mL) and water (10 mL). The aqueous layer was extracted with

diethyl ether. The combined organic layers were washed with brine,

dried with Na₂SO₄and concentrated in vacuo. Purification by flash

column chromatography (CH₂Cl₂/hexane, 4:96) afforded 1f

1

mesh). H and ¹³C NMR spectra were recorded at room tempera-

ture, either at 200 MHz and 50 MHz with an AC200 Bruker spec-

trometer, at 250 MHz and 63 MHz with an AC250 Bruker spec-

trometer, at 300 MHz and 75 MHz with a Bruker Avance-300 spec-

trometer, or at 400 MHz and 100 MHz, respectively, with an

ARX400 AVANCE Bruker spectrometer. Chemical shifts are given

in ppm and referenced to the residual solvent signal (δ = 7.26 ppm

for CDCl₃) for ¹H NMR spectroscopy. For ¹³C NMR, shifts are

referenced to the central solvent peak (δ = 77.3 ppm for CDCl₃).

Coupling constants (J) are given in Hertz (Hz). The letters m, s, d,

t, q, and hept stand for multiplet, singlet, doublet, triplet, quadru-

plet, and heptuplet, respectively. IR spectra were recorded with a

Tensor 27 (ATR diamond) Bruker spectrometer. IR data is re-

ported as characteristic bands (cm^–1) in their maximal intensity.

The melting points were measured with an SMP3 Stuart Scientific

melting point apparatus or with a digital melting point apparatus

(Electrothermal) and are uncorrected. Elemental analysis was per-

formed by the Service Régional de Microanalyse de l’Université

Pierre et Marie Curie.

(202 mg, 81% yield) as a colorless oil. IR (neat): ν = 3304, 3081,

˜

2985, 1640, 1460, 1381, 1290, 1250 cm^–1. ¹H NMR (300 MHz,

CDCl₃): δ = 5.92 (dd, J = 17.5, 10.5 Hz, 1 H), 5.80 (m, 2 H), 5.27–

5.18 (m, 2 H), 5.18–4.91 (m, 2 H), 4.72–4.76 (m, 2 H), 4.11 (ddt, J

= 12.3, 4.9, 1.7 Hz, 1 H), 3.91 (ddt, J = 12.3, 4.9, 1.7 Hz, 1 H),

2.43 (s, 1 H), 2.38 (m, 2 H), 1.66 (m, 2 H), 1.06 (s, 3 H, CH₃), 1.05

(s, 3 H, CH₃) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 149.8 (CH),

135.6 (CH), 133.8 (CH), 118.6 (CH₂, CH=CH₂), 116.2 (CH₂,

CH=CH₂), 109.5 (CH₂, CH=CH₂), 84.8 (C), 76.9 (C), 75.4 (CH),

65.4 (CH₂), 50.5 (CH₂), 45.7 (CH₂), 37.1 (C), 28.9 (CH₃), 28.6

(CH₃) ppm. MS (70 eV): m/z (%) = 218 (1) [M]⁺, 177 (3), 135 (13),

107 (12), 91 (20), 79 (16), 69 (100), 55 (19), 41 (80). C₁₅H₂₂O

(218.33): calcd. C 82.52, H 10.16; found C 82.33, H 10.09.

5-Ethynyl-5-methoxy-3,3-dimethylundeca-1,10-diene (7a): IR (neat):

Synthesis of the Precursors: The synthesis of 1a and 1b and their

spectroscopic data have already been described.^[1]O-Methylation

of the tertiary alcohols with NaH and MeI provided 1c and 1d in

good yields (Ͼ80%). Precursor 1e was prepared by a similar route,

ν = 3305, 3080, 2940, 2105, 1640 cm^–1. ¹H NMR (400 MHz,

˜

CDCl₃): δ = 6.02 (dd, J = 17.3, 10.7 Hz, 1 H), 5.82 (ddt, J = 17.1,

10.5, 6.6 Hz, 1 H), 5.02 (dd, J = 17.3, 1.0 Hz, 1 H), 5.01 (dd, J =

17.1, 1.5 Hz, 1 H), 4.96 (dd, J = 10.7, 1.0 Hz, 1 H), 4.94 (dd, J =

4626

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Eur. J. Org. Chem. 2006, 4618–4633

PtCl₂- and PtCl₄-Catalyzed Cycloisomerization of Polyunsaturated Precursors

FULL PAPER

10.5, 1.5 Hz, 1 H), 3.32 (s, 3 H, OMe), 2.52 (s, 1 H), 2.07 (m, 2 H),

1.76 (m, 2 H), 1.69 (m, 2 H), 1.50–1.30 (m, 4 H), 1.18 (s, 3 H,

CH₃), 1.17 (s, 3 H, CH₃) ppm. ¹³C NMR (100 MHz, CDCl₃): δ

OMe), 2.47 (m, 2 H), 1.75 (s, 2 H), 1.12 (s, 3 H), 1.10 (s, 3 H) ppm.

¹³C NMR (100 MHz, CDCl₃): δ = 153.7 (C), 148.6 (CH), 132.2

(CH), 119.1 (CH₂, CH=CH₂), 109.8 (CH₂, CH=CH₂), 87.9 (C),

= 149.6 (CH), 139.3 (CH), 114.7 (CH_2,CH=CH₂), 109.6 (CH₂, 80.3 (C), 75.3 (C), 52.7 (CH₃), 51.5 (CH₃, OMe), 49.5 (CH₂), 43.8

CH=CH₂), 85.1 (C), 76.3 (C), 76.2 (CH), 51.2 (CH₃, OMe), 49.7

(CH₂), 40.1 (CH₂), 37.0 (C), 34.1 (CH₂), 29.4 (CH₂), 23.8 (CH₂),

28.8 (CH₃), 28.7 (CH₃) ppm; 7aD (C₁₆H₂₅DO): ¹H NMR

(400 MHz, CDCl₃): the same spectrum as that of 7a, except no

signal at δ = 2.52 ppm. ¹³C NMR (100 MHz, CDCl₃): the same

spectrum as that of 7a, except δ = 85.1 (t, J = 7 Hz) and 76.2 (t, J

= 39 Hz) ppm. CIMS: (NH₃) m/z (%) = 253 (15) [M + NH₄]⁺, 236

(21) [M + H]⁺, 221 [M – 15] ⁺, 204 [M – 31] ⁺.

(CH₂), 36.6 (C), 28.6 (CH₃), 27.9 (CH₃) ppm.

1-Allyl-1-ethynyl-3,3-dimethylpent-4-enyl 4Ј-Nitrobenzoate (1g): IR

(neat): ν = 3300, 3080, 2960, 2115, 1730, 1640, 1610, 1530, 1350

˜

1

cm^–1. H NMR (200 MHz, CDCl₃): δ = 8.29 (d, J = 9.0 Hz, 2 H,

Ar), 8.16 (d, J = 9.0 Hz, 2 H, Ar), 6.00 (dd, J = 17.4, 10.6 Hz, 1

H), 5.92 (m, 1 H), 5.18 (d, J = 16.2 Hz, 1 H trans), 5.16 (d, J =

11.2 Hz, 1 H cis), 4.95 (dd, J = 17.4, 1.0 Hz, 1 H trans), 4.84 (dd,

J = 10.6, 1.0 Hz, 1 H cis), 3.07 (dd, J = 14.0, 7.2 Hz, 1 H), 2.90

(dd, J = 14.0, 7.2 Hz, 1 H), 2.76 (s, 1 H), 2.40 (d, J = 15.0 Hz, 1

H), 2.11 (d, J = 15.0 Hz, 1 H), 1.23 (s, 3 H, CH₃), 1.20 (s, 3 H,

CH₃) ppm. ¹³C NMR (50 MHz, CDCl₃): δ = 163.0 (C, C=O), 148.4

5-Ethynyl-5-methoxy-7,7-dimethylundeca-1,10-diene (7b): IR (neat):

ν = 3300, 3070, 2940, 2100, 1640, 1460, 1075 cm^–1. ¹H NMR

˜

(400 MHz, CDCl₃): δ = 5.81 (m, 2 H), 5.02 (d, J = 17.3 Hz, 1 H),

4.98 (d, J = 17.7 Hz, 1 H), 4.95 (d, J = 11.5 Hz, 1 H), 4.89 (d, J = (CH), 136.5 (C, Ar), 132.0 (CH), 130.8 (2 CH, Ar), 128.5 (C, Ar),

10.2 Hz, 1 H), 3.29 (s, 3 H, OMe), 2.53 (s, 1 H), 2.15 (m, 2 H),

2.02 (m, 2 H), 1.76 (m, 2 H), 1.65 (d, J = 14.2 Hz, 1 H), 1.59 (d, J

= 14.2 Hz), 1.44 (m, 2 H), 1.04 (s, 3 H), 1.03 (s, 3 H) ppm. ¹³C

123.6 (2 CH, Ar), 119.7 (CH₂, CH=CH₂), 110.4 (CH₂, CH=CH₂),

82.8 (C), 79.1 (C), 77.0 (CH), 49.2 (CH₂), 44.8 (CH₂), 36.9 (C),

29.0 (CH₃), 28.0 (CH₃) ppm. GCMS (EI): m/z (%) = 286 (9) [M–

NMR (100 MHz, CDCl₃): δ = 139.8 (CH), 138.3 (CH), 114.5 (CH₂, C₃H₅], 150 (100). C₁₉H₂₁NO₄(327.38): calcd. C 69.71, H 6.47, N

CH=CH₂), 113.6 (CH₂, CH=CH₂), 84.4 (C), 76.2 (CH), 75.5 (C),

50.8 (CH₃, OMe), 48.1 (CH₂), 42.9 (2 CH₂), 39.7 (CH₂), 33.5 (C),

28.7 (CH₂), 28.5 (CH₃), 28.3 (CH₃) ppm. C₁₆H₂₆O (234.38): calcd.

C 81.99, H 11.18; found C 81.84, H 11.35.

4.28; found C 69.65; H, 6.60; N, 4.18.

1-Allyl-1-ethynyl-3,3-dimethylpent-4-enyl Acetate (1h): IR (neat): ν

˜

= 3300, 3100, 2950, 2350, 1750, 1640, 1440, 1370 cm^–1. H NMR

1

(200 MHz, CDCl₃): δ = 5.93 (dd, J = 17.2, 10.3 Hz, 1 H), 5.81 (m,

1 H), 5.13–5.04 (m, 2 H), 4.90 (dd, J = 17.7, 1.5 Hz, 1 H trans),

4.86 (dd, J = 10.3, 1.5 Hz, 1 H cis), 2.87 (dd, J = 14.3, 7.4 Hz, 1

H), 2.69 (dd, J = 14.3, 7.4 Hz, 1 H), 2.60 (s, 1 H), 2.15 (d, J =

15.3 Hz, 1 H), 1.95 (s, 3 H, OAc), 1.86 (d, J = 15.3 Hz, 1 H), 1.15 (s,

3 H, CH₃), 1.11 (s, 3 H, CH₃) ppm. ¹³C NMR (50 MHz, CDCl₃): δ

= 169.4 (C, C=O), 148.7 (CH), 132.3 (CH), 119.1 (CH₂, CH=CH₂),

5-Methoxy-3,3,5-trimethylhept-1-en-6-yne (7c): IR (neat): ν = 3309,

˜

1

3083, 2923, 2854, 2109, 1639 cm^–1. H NMR (400 MHz, CDCl₃):

δ = 6.01 (dd, J = 17.7, 10.8 Hz, 1 H), 4.92 (dd, J = 17.7, 1.3 Hz, 1

H), 4.87 (dd, J = 10.8, 1.3 Hz, 1 H), 3.33 (s, 3 H, OMe), 2.48 (s, 1

H), 1.83 (d, J = 14.6 Hz, 1 H), 1.76 (d, J = 14.6 Hz, 1 H), 1.42 (s,

3 H), 1.16 (s, 3 H), 1.14 (s, 3 H) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 149.6 (CH), 109.7 (CH₂, CH=CH₂), 85.8 (C), 74.9 109.7 (CH₂, CH=CH₂), 83.5 (C), 77.0 (C), 75.9 (CH), 49.1 (CH₂),

(CH), 73.4 (C), 52.7 (CH₂), 51.2 (CH₃, OMe), 37.0 (C), 28.9 (CH₃), 44.6 (CH₂), 36.8 (C), 28.9 (CH₃), 27.7 (CH₃), 22.2 (CH₃, OAc)

28.4 (CH₃), 28.0 (CH₃) ppm.

ppm.

5-Ethynyl-5-methoxy-non-1-ene (7d): IR (neat): ν = 3310, 3078,

1-Methallyl-1-ethynyl-3,3-dimethylpent-4-enyl 4Ј-Nitrobenzoate (1i):

˜

2926, 2856, 1642 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 5.84 (ddt,

J = 17.4, 10.4, 6.6 Hz, 1 H), 5.05 (dd, J = 17.4, 1.5 Hz, 1 H), 4.96

(dd, J = 10.4, 1.5 Hz, 1 H), 3.33 (s, 3 H, OMe), 2.46 (s, 1 H), 2.17

(m, 2 H), 1.75 (t, J = 8.4 Hz, 2 H), 1.67 (t, J = 7.8 Hz, 2 H), 1.43–

1.30 (m, 4 H), 0.92 (t, J = 7.1 Hz, 3 H) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 138.3 (CH), 114.5 (CH₂, CH=CH₂), 77.2 (CH), 76.1

IR (neat): ν = 3300, 3080, 2960, 2115, 1730, 1640, 1610, 1530, 1350

˜

1

cm^–1. H NMR (200 MHz, CDCl₃): δ = 8.29 (d, J = 9.2 Hz, 2 H,

Ar), 8.18 (d, J = 9.2 Hz, 2 H, Ar), 6.02 (dd, J = 17.4, 10.6 Hz, 1

H), 4.97 (dd, J = 10.6, 1.0 Hz, 1 H cis), 4.86 (d, J = 1.2 Hz, 2 H),

4.85 (dd, J = 17.4, 1.0 Hz, 1 H trans), 3.06 (d, J = 14.4 Hz, 1 H),

2.87 (d, J = 14.4 Hz, 1 H), 2.77 (s, 1 H), 2.42 (d, J = 15.0 Hz, 1

(C), 74.1 (C), 51.2 (CH₃, OMe), 37.5 (CH₂), 36.9 (CH₂), 28.1 H), 2.11 (d, J = 15.0 Hz, 1 H), 1.82 (s, 3 H, CH₃), 1.24 (s, 3 H,

(CH₂), 25.9 (CH₂), 22.9 (CH₂), 14.0 (CH₃) ppm.

CH₃), 1.20 (s, 3 H, CH₃) ppm. ¹³C NMR (50 MHz, CDCl3): δ =

163.1 (C, C=O), 148.5 (CH), 140.2 (C), 136.6 (C, Ar), 130.8 (2

CH+C, Ar), 126.6 (2 CH, Ar), 116.7 (CH₂, CH=CH₂), 110.3 (CH₂,

CH=CH₂), 83.1 (C), 79.0 (C), 77.5 (CH), 49.8 (CH₂), 48.2 (CH₂),

36.9 (C), 29.2 (CH₃), 27.9 (CH₃), 24.1 (CH₃) ppm. GCMS (EI):

m/z (%) = 286 (5) [M – C₄H₇], 150 (100).

(3-Allyl-3-methoxy-hept-6-en-1-ynyl)trimethylsilane (7e): IR (neat):

1

ν = 3078, 2956, 2928, 2856, 2165, 1642 cm^–1. H NMR (400 MHz,

˜

CDCl₃): δ = 5.83 (m, 2 H), 5.10 (m, 2 H), 5.05–4.93 (m, 2 H), 3.35

(s, 3 H), 2.45 (d, J = 7.4 Hz, 2 H), 2.18 (m, 2 H), 1.71 (t, J =

8.3 Hz, 2 H), 0.18 (s, 9 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ

= 138.8 (CH), 133.5 (CH), 118.4 (CH₂, CH=CH₂), 114.8 (CH₂,

CH=CH₂), 105.8 (C), 91.8 (C), 76.4 (C), 51.8 (CH₃, OMe), 42.6

(CH₂), 37.5 (CH₂), 28.6 (CH₂), 0.30 (3 CH₃, TMS) ppm.

1-Allyl-1-ethynylpent-4-enyl Acetate (1j): IR (neat): ν = 3295, 3079,

˜

2980, 2928, 2857, 2118, 1742, 1642 cm^–1. ¹H NMR (400 MHz,

CDCl₃): δ = 5.84–5.76 (m, 2 H), 5.15–4.94 (m, 4 H), 2.79–2.75 (m,

2 H), 2.59 (s, 1 H), 2.23–2.21 (m, 2 H), 2.06–2.04 (m, 1 H), 2.00 (s,

3 H, OAc), 1.91–1.82 (m, 1 H) ppm. ¹³C NMR (100 MHz, CDCl₃):

δ = 169.5 (C, C=O), 137.8 (CH), 132.1 (CH), 119.5 (CH₂,

CH=CH₂), 115.3 (CH₂, CH=CH₂), 82.8 (C), 78.2 (C), 75.0 (CH),

42.8 (CH₂), 37.7 (CH₂), 28.5 (CH₂), 22.1 (CH₃, OAc) ppm.

Methyl 4-Allyl-4-methoxy-6,6-dimethyloct-7-en-2-ynoate (7f): To a

solution of 1a (384 mg, 2 mmol, 1 equiv.) in dry THF (10 mL) was

added nBuLi (0.95 mL of a 2.2  solution, 2.1 mmol, 1.05 equiv.)

at –78 °C. Methyl chloroformate (0.46 mL, 6 mmol, 3 equiv.) was

added, and the mixture was allowed to warm to room temp. The

reaction was quenched with a saturated NH₄Cl solution and ex-

tracted with Et₂O. The combined organic layers were washed with

1-But-3-enyl-1-ethynyl-3,3-dimethylpent-4-enyl Acetate (21): IR

(neat): ν = 3306, 3081, 2965, 2931, 2873, 2117, 1743, 1642 cm^–1.

˜

brine, dried with MgSO₄and concentrated to give 7f (495 mg, 99%

¹H NMR (400 MHz, CDCl₃): δ = 5.94 (dd, J = 17.4, 10.6 Hz, 1

H), 5.78 (m, 1 H), 5.04–4.86 (m, 4 H), 2.61 (s, 1 H), 2.23–2.17 (m,

yield). IR (neat): ν = 3081, 2955, 2873, 2230, 1717, 1639 cm^–1. H

1

˜

NMR (400 MHz, CDCl₃): δ = 5.94 (dd, J = 17.4, 10.6 Hz, 1 H), 4 H), 2.03 (m, 1 H), 1.99 (s, 3 H, OAc), 1.93–1.90 (m, 1 H), 1.16

5.78 (m, 1 H), 5.11 (m, 2 H), 4.90 (dd, J = 17.4, 1.3 Hz, 1 H), 4.84

(dd, J = 10.6, 1.3 Hz, 1 H), 3.76 (s, 3 H, CO₂Me), 3.33 (s, 3 H,

(s, 3 H), 1.13 (s, 3 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ =

169.5 (C, C=O), 137.8 (CH), 132.1 (CH), 119.5 (CH₂, CH=CH₂),

Eur. J. Org. Chem. 2006, 4618–4633

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4627

J. Marco-Contelles, L. Fensterbank, M. Malacria et al.

115.3 (CH₂, CH=CH₂), 82.8 (C), 78.2 (C), 75.0 (CH), 42.8 (CH₂), 4,8-Dimethylnon-7-en-1-yn-4-yl Acetate (26): To a solution of 6-

FULL PAPER

37.7 (CH₂), 28.5 (CH₂), 22.1 (CH₃, OAc) ppm.

methyl-5-heptene-2-one (33, 2.0 g, 15.8 mmol) in a mixture of

THF/saturated aqueous solution of NH₄Cl (1:5, 70 mL), zinc dust

(6.18 g, 95.2 mmol) was added under argon. The mixture was

stirred in an ice bath (0 °C). Thereafter, propargyl bromide

(5.33 mL, 47.6 mmol) was added, and the reaction was stirred for

19 h at room temp. The mixture was concentrated, and the crude

material was extracted with ethyl acetate (3×10 mL). The organic

extract was washed with brine, dried with anhydrous Na₂SO₄and

concentrated under reduced pressure. Flash column chromatog-

raphy of the crude material, eluting with EtOAc/hexane (0.5:99.5),

gave unreacted 6-methyl-5-heptene-2-one (33, 883 mg) and known

compound 34^[56](211 mg, 12% yield) as a light yellow oil: [¹H

NMR (300 MHz, CDCl₃): δ = 5.09 (tm, J = 7.1 Hz, 1 H), 2.41 (d,

J = 2.7 Hz, 2 H), 2.16–2.04 (m, 3 H, 2 H, OH), 1.85 (s, 1 H), 1.71

(s, 3 H, CH₃), 1.65 (s, 3 H, CH₃), 1.69–1.58 (m, 2 H), 1.31 (s, 3 H,

CH₃) ppm].

Methyl 4-Acetyloxy-4-methyloct-7-en-2-ynoate (24): To a solution

of diisopropylamine (1.07 mL, 7.65 mmol) in THF (40 mL), cooled

to –78 °C, nBuLi (4.78 mL, 7.65 mmol, 1.6  in hexane) was added.

The solution was warmed to 0 °C for 15 min. Then, to this solu-

tion, cooled to –78 °C, methyl propiolate (0.82 mL, 9.18 mmol) was

slowly added. After stirring at –78 °C for 1 h, the reaction mixture

was treated with 5-hexene-2-one (27, 0.5 g, 5.1 mmol), stirred at

–78 °C for 30 min, and then warmed to room temp. The reaction

mixture was diluted with diethyl ether (40 mL), washed with an

aqueous solution of sodium bisulfate (1 , 2×40 mL), dried with

Na₂SO₄and concentrated in vacuo. Flash chromatography, eluting

with EtOAc/hexane (5:95), afforded 28 (660 mg, 71% yield) as a

yellow oil. IR (neat): ν = 3079, 2981, 2953, 2235, 1719, 1642, 1592,

˜

1436, 1372, 1256 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 5.73 (ddt,

J = 16.7, 10.1, 6.4 Hz, 1 H), 5.03 (dm, J = 16.7 Hz, 1 H), 4.85 (dm,

J = 10.1 Hz, 1 H), 3.67 (s, 3 H, CO₂CH₃), 2.25–2.07 (m, 2 H),

1.77–1.66 (m, 2 H), 1.43 (s, 3 H, CH₃) ppm. ¹³C NMR (75 MHz,

CDCl₃): δ = 154.3 (C=O), 138.1, 115.7, 90.9, 75.3, 68.0, 53.2

(CO₂CH₃), 42.2, 29.5, 29.2 ppm. To a solution of compound 28

(400 mg, 2.19 mmol) in dry pyridine (5 mL), DMAP (53.4 mg,

0.44 mmol) and acetic anhydride (336.3 mg, 3.30 mmol) were

added. The reaction mixture was stirred for 2.5 h at room temp.

The solvent was evaporated, and the crude material was purified

by flash chromatography (EtOAc/hexane, 4:96) to furnish 24

To a solution of compound 34 (290 mg, 1.75 mmol) in dry pyridine

(2 mL), DMAP (42.7 mg, 0.35 mmol) and acetic anhydride

(267.3 mg, 2 mL, 2.62 mmol) were added. The reaction mixture was

stirred at room temp. for 16 h. Purification by flash column

chromatography (EtOAc/hexane, 0.5:99.5) gave 26 (161.2 mg, 44%

yield) as a colorless oil. IR (neat): ν = 3310, 2966, 2925, 2857, 2121,

˜

1736, 1450, 1368, 1247 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ =

5.10 (tm, J = 7.1 Hz, 1 H), 2.75 (dd, J = 12.0, 2.0 Hz, 1 H), 2.55

(dd, J = 12.0, 2.0 Hz, 1 H), 1.97 (s, 4 H, OCOCH₃, H), 2.00–1.85

(m, 3 H), 1.80–1.65 (m, 1 H), 1.61 (s, 3 H, CH₃), 1.50 (s, 3 H, CH₃),

1.45 (s, 3 H, CH₃) ppm. ¹³C NMR (300 MHz, CDCl₃): δ = 170.7

(OCOCH₃), 132.3 (C), 123.9 (CH), 82.7 (C), 80.5 (C), 70.7 (CH),

38.1 (CH₂), 29.0 (CH₂), 26.0 (CH₃), 23.9 (CH₂), 22.6 (CH₃), 22.5

(OCOCH₃), 17.9 (CH₃) ppm. MS (70 eV): m/z (%) = 208 (9) [M]⁺,

191 (20), 175 (6), 147 (100), 131 (9), 73 (75), 55 (11), 41 (12).

C₁₃H₂₀O₂(298.30): calcd. C 74.96, H 9.68; found C 74.83, H 9.72.

(360 mg, 73% yield) as a colorless oil. IR (neat): ν = 3080, 2981,

˜

2239, 1747, 1720, 1642, 1435, 1370, 1313, 1262 cm^–1. ¹H NMR

(300 MHz, CDCl₃): δ = 5.68 (ddt, J = 16.7, 10.1, 6.4 Hz, 1 H), 4.99

(dm, J = 16.7 Hz, 1 H), 4.85 (dm, J = 10.1 Hz, 1 H), 3.65 (s, 3 H,

CO₂CH₃), 2.17–2.00 (m, 2 H), 1.93 (s, 3 H, OCOCH₃), 1.91–1.73

(m, 2 H), 1.59 (s, 3 H, CH₃) ppm. ¹³C NMR (75 MHz, CDCl₃): δ

= 169.4 (OCOCH₃), 154.1 (C=O), 137.4, 115.7, 87.2, 77.3, 73.9,

53.2 (CO₂CH₃), 40.3, 28.6, 26.1 (CH₃), 21.9 (OCOCH₃). MS

(70 eV) m/z 209 (1) [M – 15] ⁺, 182 (12), 169 (5), 150 (100), 149

(21), 133 (12), 122 (44), 111 (6), 105 (50), 77 (21), 43 (87) ppm.

C₁₂H₁₆O₄(224.25): calcd. C 64.27, H 7.19; found C 64.46 H, 7.28.

Cycloisomerization Products

General Procedure (GP) for the PtCl_n-Catalyzed Cycloisomerization

Reaction: To a degassed solution of the precursor in dry toluene

(0.025 ), PtCl_n(0.05 equiv.) was added at room temp. under ar-

gon. The reaction mixture was stirred at the stated temperature

until the reaction was complete. The reaction mixture was filtered,

and the solvent was evaporated under vacuum. Purification by

flash chromatography gave the corresponding products.

3-Methyl-5-phenylpent-1-yn-3-yl Acetate (25): A solution of 4-

phenyl-2-butanone (30, 0.5 g, 3.38 mmol) in a mixture of dry THF/

diethyl ether (1:1, 2 mL) was added dropwise, at room temp., to a

solution of ethynylmagnesium bromide (8.5 mL, 4.05 mmol, 0.5 

in THF) in anhydrous diethyl ether (8.5 mL), under argon. The

reaction mixture was stirred at room temp. for 12 h. Water (25 mL)

was added to quench the reaction, and the mixture was extracted

with diethyl ether (3×25 mL). The combined organic layers were

washed with brine and dried with anhydrous Na₂SO₄. The solvent

was evaporated under vacuum. Purification by flash chromatog-

raphy (EtOAc/hexane, 3:97) gave 31 (510 mg, 86% yield) which

showed spectroscopic data identical to those described in the litera-

ture^[39][¹H NMR (200 MHz, CDCl₃): δ = 7.25–7.10 (m, 5 H,

C₆H₅), 2.82–2.76 (m, 2 H), 2.73 (s, 1 H, OH), 2.43 (s, 1 H), 1.95–

1.84 (m, 2 H), 1.47 (s, 3 H, CH₃) ppm].

2-Ethenyl-4,4-dimethyl-1-(2-propenyl)-2-cyclopenten-1-ol (2a) and

(1aR*,3aS*,4aR*,5aR*,5bS*)-octahydro-2,2-dimethyl-3aH-dicy-

clopropa[a,g]pentalen-3a-ol (3a): Cyclization of precursor 1a

(178 mg, 1 mmol) with PtCl₂(10.4 mg, 0.04 mmol), following the

GP (80 °C, 2 h) gave, after purification by flash chromatography

(EtOAc/hexane, 5:95), triene 2a (35 mg, 20%) and compound 3a

1

(85 mg, 48%). 2a: IR (neat): ν = 3400, 2920, 1630, 1450 cm^–1. H

˜

NMR (200 MHz, CDCl₃): δ = 6.28 (dd, J = 18.0, 11.4 Hz, 1 H),

5.80 (m, 1 H), 5.69 (s, 1 H), 5.60 (dd, J = 18.0, 2.0 Hz, 1 H trans),

5.18–5.09 (m, 3 H, 2H+H cis), 2.63 (dd, J = 13.7, 8.0 Hz, 1 H),

2.41 (dd, J = 13.7, 8.0 Hz, 1 H), 2.17 (br. s, 1 H), 2.13 (d, J =

14.0 Hz, 1 H), 1.74 (d, J = 14.0 Hz, 1 H), 1.35 (s, 3 H, CH₃), 0.97

(s, 3 H, CH₃) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 142.4 (C),

To a solution of compound 31 (400 mg, 2.3 mmol) in dry pyridine

(5 mL), DMAP (56.1 mg, 0.46 mmol) and acetic anhydride

(351.9 mg, 0.5 mL, 3.45 mmol) were added. The reaction mixture 142.2 (CH), 134.2 (CH), 130.4 (CH), 118.6 (CH₂), 116.0 (CH₂),

was stirred overnight at room temp. The solvent was evaporated,

and the crude was purified by flash chromatography (EtOAc/hex-

ane, 1:99) to furnish 25 (333 mg, 70% yield) as a colorless oil, which

showed spectroscopic data identical to those described in the litera-

85.4 (C), 53.5 (CH₂), 44.7 (CH₂), 42.0 (C), 30.7 (CH₃), 28.8 (CH₃)

ppm. C₁₂H₁₈O (178.27): calcd. C 80.85, H 10.18; found C 80.62,

1

H 10.23. 3a: IR (neat): ν = 3370, 2950, 1460, 1360 cm^–1. H NMR

˜

(500 MHz, CDCl₃): δ = 2.21 (br. s, 1 H), 2.16 (dd, J = 14.1, 6.6 Hz,

ture^[51][¹H NMR (200 MHz, CDCl₃): δ = 7.25–7.10 (m, 5 H, 1 H), 1.71 (m, 1 H), 1.67 (dd, J = 14.1, 3.2 Hz, 1 H), 1.60 (d, J =

C₆H₅), 2.78–2.69 (m, 2 H), 2.53 (s, 1 H), 2.26–1.98 (m, 2 H), 1.93 14.2 Hz, 1 H), 1.36 (td, J = 7.9, 4.0 Hz, 1 H), 1.06 (s, 3 H, CH₃),

(s, 3 H, OCOCH₃), 1.65 (s, 3 H, CH₃) ppm].

1.03 (d, J = 14.2 Hz, 1 H), 0.92 (s, 3 H, CH₃), 0.89 (td, J = 7.9,

4628

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Eur. J. Org. Chem. 2006, 4618–4633

PtCl₂- and PtCl₄-Catalyzed Cycloisomerization of Polyunsaturated Precursors

FULL PAPER

4.7 Hz, 1 H), 0.85 (dd, J = 8.4, 4.9 Hz, 1 H), 0.78 (dd, J = 8.4,

PtCl₄(7 mg, 0.02 mmol), following the same procedure (80 °C, 2 h)

4.2 Hz, 1 H), 0.69 (dd, J = 4.9, 4.2 Hz, 1 H), 0.50 (dt, J = 4.7, and gave, after purification by flash chromatography (Et₂O/pen-

4.0 Hz, 1 H) ppm. ¹³C NMR (125 MHz, CDCl₃): δ = 99.2 (C), 47.2

tane, 2:98), compound 3d (32 mg, 40%). 3d: IR (neat): ν = 3040,

˜

(CH₂), 45.9 (C), 44.4 (CH₂), 39.3 (C), 35.4 (CH), 30.2 (CH₃), 28.1 2950, 1460 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 3.28 (s, 3 H,

(CH₃), 22.2 (CH₂), 20.5 (CH), 20.1 (CH), 11.5 (CH₂) ppm. GCMS OMe), 2.19 (d, J = 14.6 Hz, 1 H), 1.72 (d, J = 14.6 Hz, 1 H), 1.53

(EI): m/z (%) = 178 (6) [M], 145 (100). C₁₂H₁₈O (178.27): calcd. C

80.85, H 10.18; found C 80.65, H 9.98.

(d, J = 13.8 Hz, 1 H), 1.30 (s, 3 H, CH₃), 1.13 (d, J = 13.8 Hz, 1

H), 1.12 (m, 1 H), 1.09 (s, 3 H, CH₃), 0.94 (s, 3 H, CH₃), 0.91 (m,

1 H), 0.85–0.70 (m, 3 H), 0.64 (t, J = 3.7 Hz, 1 H) ppm. ¹³C NMR

(50 MHz, CDCl₃): δ = 103.2 (C), 52.3 (CH₃, OMe), 46.5 (CH₂),

45.3 (C), 45.2 (CH₂), 39.6 (C), 36.0 (CH), 31.0 (CH₃), 30.0 (C),

28.9 (CH, CH₂), 28.6 (CH₃), 23.8 (CH₃), 12.8 (CH₂) ppm.

(Bromomethyl){[2-ethenyl-4,4-dimethyl-1-(2-propenyl)-2-cyclo-

penten-1-yl]oxy}dimethylsilane (2b) and (Bromomethyl)dimethyl-

{[(1aR*,3aS*,4aR*,5aR*,5bS*)-octahydro-2,2-dimethyl-3aH-di-

cyclopropa[a,g]pentalen-3a-yl]oxy}silane (3b): Cyclization of precur-

sor 1b (308 mg, 0.94 mmol) with PtCl₂(12 mg, 0.047 mmol), fol-

lowing the GP (80 °C, 4 h) gave, after purification by flash

chromatography (hexane/CH₂Cl₂, 9:1), triene 2b (26 mg, 8%) and

(1aR*,3aS*,4aR*,5aR*,5bS*)-Octahydro-3aH-dicyclopropa[a,g]-

pentalen-3a-ol (3e): Cyclization of precursor 1e (83 mg, 0.5 mmol)

with PtCl₂(6.5 mg, 0.025 mmol), following the GP (80 °C, 2 h)

gave, after purification by flash chromatography (Et₂O/pentane,

compound 3b (188 mg, 61%). 2b: Oil. IR (neat): ν = 3080, 2940,

˜

1630, 1440, 1250 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 6.25 (dd, 2:98), compound 3e (45 mg, 53%). Alternatively, cyclization of pre-

J = 17.8, 11.2 Hz, 1 H), 5.77 (m, 1 H), 5.61 (s, 1 H), 5.59 (dd, J =

cursor 1e (102 mg, 0.62 mmol) was conducted with PtCl₄(10 mg,

18.0, 1.6 Hz, 1 H trans), 5.18–5.02 (m, 3 H, 2 H+H cis), 2.66 (dd, 0.03 mmol), following the same procedure (80 °C, 2 h) and gave,

J = 13.4, 7.0 Hz, 1 H), 2.49 (s, 2 H, CH₂–Br), 2.33 (dd, J = 13.4,

7.0 Hz, 1 H), 2.15 (d, J = 13.0 Hz, 1 H), 1.80 (d, J = 13.0 Hz, 1

after purification by flash chromatography (Et₂O/pentane, 5:95),

compound 3e (20 mg, 20%). IR (neat): ν = 3060, 2930, 1460 cm^–1.

˜

H), 1.17 (s, 3 H, CH₃), 1.06 (s, 3 H, CH₃), 0.28 [s, 6 H, Si(CH₃)₂] ¹H NMR (400 MHz, CDCl₃): δ = 3.33 (s, 3 H, OMe), 2.30 (dd, J

ppm. ¹³C NMR (50 MHz, CDCl₃): δ = 143.0 (C), 140.7 (CH), = 14.6, 7.5 Hz, 1 H), 1.80 (m, 1 H), 1.70–1.60 (m, 3 H), 1.38 (td,

134.8 (CH), 130.6 (CH), 117.5 (CH₂), 115.9 (CH₂), 88.5 (C), 52.5

(CH₂), 46.3 (CH₂), 41.7 (C), 30.4 (CH₃), 28.5 (CH₃), 17.6 (CH₂, H), 1.02 (m, 1 H), 0.93–0.83 (m, 3 H), 0.39 (m, 1 H) ppm. ¹³C

CH –Br), –0.9 [2 CH , Si(CH ) ] ppm. 3b: IR (neat): ν = 3060, NMR (100 MHz, CDCl₃): δ = 104.5 (C), 52.2 (CH₃, OMe), 41.3

J = 7.6, 3.3 Hz, 1 H), 1.29 (dd, J = 14.6, 3.0 Hz, 1 H), 1.21 (m, 1

˜

2

3

3 2

2990, 2960, 2870, 1740, 1450, 1350 cm^{–1 1}H NMR (200 MHz, (C), 37.7 (CH₂), 30.0 (CH₂), 26.2 (CH₂), 22.98 (CH₂), 22.97 (CH),

.

CDCl₃): δ = 2.54 (s, 2 H, CH₂–Br), 2.21 (dd, J = 15.0, 7.4 Hz, 1

H), 1.70 (m, 1 H), 1.69 (d, J = 9.4 Hz, 1 H), 1.63 (d, J = 14.0 Hz,

1 H), 1.37 (td, J = 7.4, 4.0 Hz, 1 H), 1.11 (d, J = 14.0 Hz, 1 H),

1.07 (s, 3 H, CH₃), 0.93 (s, 3 H, CH₃), 0.90 (m, 2 H), 0.76 (m, 2

H), 0.49 (q, J = 4.0 Hz, 1 H), 0.32 [s, 3 H, Si(CH₃)₂], 0.31 [s, 3 H,

Si(CH₃)₂] ppm. ¹³C NMR (50 MHz, CDCl₃): δ = 102.7 (C), 48.9

(CH₂), 45.9 (C), 45.5 (CH₂), 38.9 (C), 36.0 (CH), 30.3 (CH₃), 28.5

(CH₃), 22.5 (CH₂), 20.9 (2 CH), 18.3 (CH₂, CH₂–Br), 13.0 (CH₂),

–0.7 [2 CH₃, Si(CH₃)₂] ppm. GCMS (EI): m/z (%) = 330 (21)

[M(⁸¹Br)], 328 (21) [M(⁷⁹Br)], 145 (100). C₁₅H₂₅BrOSi (329.36):

calcd. C 54.70, H 7.65; found C 55.00 H, 7.87.

20.9 (CH), 20.3 (CH), 12.7 (CH₂) ppm.

p-Nitrobenzoate 4: To a solution of compound 3a (89 mg,

0.5 mmol, 1 equiv.) in CH₂Cl₂(2.5 mL) was added 4-nitrobenzoyl

chloride (371 mg, 2 mmol, 4 equiv.). The mixture was heated to

50 °C overnight and quenched with 10% aqueous HCl. The aque-

ous layer was extracted with Et₂O. The combined organic layers

were washed with brine and dried with MgSO₄. Purification by

flash chromatography on silica gel (pentane/CH₂Cl₂, 9:1) gave the

pure ester 4 (51 mg, 31 % yield). The solid product was recrys-

tallized from hexane/Et₂O. 4: Solid, m.p. 135 °C. IR (in CDCl₃

solution): ν = 3040, 2940, 1700, 1600, 1520, 1450 cm^–1. H NMR

1

˜

(1aR*,3aS*,4aR*,5aR*,5bS*)-Octahydro-3a-methoxy-2,2-dimethyl-

1H-dicyclopropa[a,g]pentalene (3c): Cyclization of precursor 1c

(97 mg, 0.5 mmol) with PtCl₂(6.5 mg, 0.025 mmol), following the

GP (80 °C, 3 h) gave, after purification by flash chromatography

(200 MHz, CDCl₃): δ = 8.23 (m, 4 H, Ar), 2.74 (dd, J = 15.7,

7.4 Hz, 1 H), 2.26 (d, J = 14.8 Hz, 1 H), 1.83 (dd, J = 15.7, 2.5 Hz,

1 H), 1.64 (m, 1 H), 1.49 (td, J = 7.4, 3.4 Hz, 1 H), 1.16 (d, J =

14.8 Hz, 1 H), 1.14 (s, 3 H, CH₃), 1.06 (m, 1 H), 0.93 (s, 3 H, CH₃),

(Et₂O/pentane: 2:98), compound 3c (71 mg, 73%). Alternatively, 0.96–0.84 (m, 3 H), 0.58 (q, J = 3.9 Hz, 1 H) ppm. ¹³C NMR

cyclization of precursor 1c (137 mg, 0.71 mmol) was conducted

with PtCl₄(12 mg, 0.036 mmol), following the same procedure

(80 °C, 1 h) and gave, after purification by flash chromatography

(50 MHz, CDCl₃): δ = 165.0 (C, C=O), 150.7 (C, Ar), 137.5 (C,

Ar), 131.0 (2 CH, Ar), 123.8 (2 CH, Ar), 109.9 (C), 46.3 (CH₂),

45.2 (C), 41.9 (CH₂), 40.2 (C), 35.2 (CH), 30.7 (CH₃), 28.9 (CH₃),

22.7 (CH₂), 21.0 (2 CH), 12.9 (CH₂) ppm.

(Et₂O/pentane, 2:98), compound 3c (105 mg, 77%). 3c: IR (neat):

1

ν = 2950, 1480, 1380 cm^–1. H NMR (200 MHz, CDCl ): δ = 3.28

˜

3

(1aR*,3aS*,4aR*,5aR*,5bR*)-Octahydro-3a-allyloxy-2,2,4a-tri-

methyl-1H-dicyclopropa[a,g]pentalene (3f) and Tetracycle 5: Cycliza-

tion of 1f with PtCl₂(85 mg, 0.39 mmol), following the GP (16 h

at room temp.) gave, after purification by flash chromatography

(CH₂Cl₂/hexane, 1:4), compounds 3f (38 mg, 44% yield) and 5

(s, 3 H, OMe), 2.36 (dd, J = 14.3, 7.0 Hz, 1 H), 1.61 (m, 1 H), 1.52

(dd, J = 14.3, 2.5 Hz, 1 H), 1.52 (d, J = 14.3 Hz, 1 H), 1.33 (td, J

= 7.4, 3.4 Hz, 1 H), 1.08 (d, J = 14.3 Hz, 1 H), 1.06 (s, 3 H, CH₃),

0.90 (s, 3 H, CH₃), 0.89 (td, J = 8.4, 4.4 Hz, 1 H), 0.82–0.70 (m, 3

H), 0.47 (q, J = 4.0 Hz, 1 H) ppm. ¹³C NMR (50 MHz, CDCl₃): δ

= 104.0 (C), 51.9 (CH₃, OMe), 46.2 (CH₂), 43.8 (C), 39.2 (C, CH₂),

35.8 (CH), 30.7 (CH₃), 28.3 (CH₃), 22.1 (CH₂), 21.7 (CH), 21.2

(CH), 12.2 (CH₂) ppm. C₁₃H₂₀O (192.30): C 81.20, H 10.48; found

C 81.07, H 10.59.

(31 mg, 36% yield). 3f: Oil. IR (neat): ν = 3060, 2950, 1650, 1450,

˜

1

1360, 1290 cm^–1. H NMR (300 MHz, CDCl₃): δ = 5.97 (dddd, J

= 17.3, 10.5, 5.6, 5.4 Hz, 1 H), 5.30 (dq, J = 17.3, 1.7 Hz, 1 H

trans), 5.12 (dq, J = 10.5, 1.3 Hz, 1 H cis), 4.05 (m, 2 H, 2H), 2.37

(dd, J = 15.1, 7.4 Hz, 1 H), 1.64 (m, 3 H), 1.38 (td, J = 7.5, 3.6 Hz,

(1aR*,3aS*,4aR*,5aR*,5bR*)-Octahydro-3a-methoxy-2,2,4a-tri- 1 H), 1.19 (d, J = 13.9 Hz, 1 H), 1.10 (s, 3 H, CH₃), 0.95 (m, 1 H),

methyl-1H-dicyclopropa[a,g]pentalene (3d): Cyclization of precursor

1d (86 mg, 0.4 mmol) with PtCl₂(5 mg, 0.02 mmol), following the

GP (80 °C, 3 h) gave, after purification by flash chromatography

0.94 (s, 3 H, CH₃), 0.86 (m, 2 H), 0.78 (m, 1 H), 0.50 (q, J = 3.8 Hz,

1 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 136.7 (CH), 116.0

(CH₂), 104.5 (C), 65.9 (CH₂), 47.6 (CH₂), 44.2 (C), 40.9 (CH₂),

(Et₂O/pentane, 2:98), compound 3d (29 mg, 34%). Alternatively, 39.5 (C), 36.5 (CH), 31.1 (CH₃), 28.6 (CH₃), 22.3 (CH, CH₂), 21.6

cyclization of precursor 1d (80 mg, 0.39 mmol) was conducted with

(CH), 12.8 (CH₂) ppm. MS (70 eV): m/z (%) = 218 (1) [M]⁺, 207

Eur. J. Org. Chem. 2006, 4618–4633

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4629

J. Marco-Contelles, L. Fensterbank, M. Malacria et al.

FULL PAPER

(6), 183 (16), 168 (51), 105 (21), 91 (100), 79 (12), 77 (29). C₁₅H₂₂O

1.10 (s, 3 H, CH₃) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 144.3

(218.33): calcd. C 82.52, H 10.16; found C 82.67, H 10.38. 5: IR

(CH), 139.9 (C), 139.4 (CH), 131.3 (CH), 115.7 (CH₂), 114.6

(neat): ν = 3060, 2950, 1650, 1450, 1360, 1290 cm^–1. ¹H NMR (CH₂), 92.7 (C), 50.6 (CH₃, O–Me), 46.6 (CH₂), 41.7 (C), 39.8

˜

(400 MHz, CDCl₃): δ = 5.95 (m, 1 H), 5.13 (d, J = 10.1 Hz, 1 H

(CH₂), 34.1 (CH₂), 30.1 (CH₃), 29.8 (CH₂), 29.7 (CH₃), 24.1 (CH₂)

cis), 5.12 (d, J = 17.2 Hz, 1 H trans), 4.26 (dd, J = 11.8, 7.3 Hz, 1 ppm. C₁₆H₂₆O (234.38): calcd. C 81.99, H 11.18; found C 81.85,

1

H), 3.55 (dd, J = 11.8, 7.0 Hz, 1 H), 3.13 (m, 1 H), 2.37 (dd, J = H 11.38. 8D, deuterated at C-2: H NMR (400 MHz, CDCl₃): the

14.4, 9.2 Hz, 1 H), 1.62 (d, J = 13.5 Hz, 1 H), 1.50 (dd, J = 8.0,

same spectrum as that of 8, except no signal at δ = 6.29 ppm and

3.2 Hz, 1 H), 1.45 (m, 1 H), 1.34 (m, 1 H), 1.19 (s, 3 H, CH₃), 0.98 δ = 5.59 (d, J = 1.8 Hz, 1 H), 5.09 (s, 1 H) ppm. ¹³C NMR

(s, 3 H, CH₃), 0.90 (d, J = 13.5 Hz, 1 H), 0.88 (m, 1 H), 0.49 (t, J (100 MHz, CDCl₃): same spectrum as that of 8, except δ = 131.3

= 4.1 Hz, 1 H), 0.39 (q, J = 4.6 Hz, 1 H), 0.21 (dd, J = 7.9, 4.5 Hz,

(t, J = 22 Hz) ppm; deuterated at C-1: ¹H NMR (400 MHz,

1 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 136.1 (CH), 117.0 CDCl₃): the same spectrum as that of 8, except no signal at δ =

(CH₂), 81.0 (C), 66.4 (CH₂), 43.4 (CH₂), 42.3 (CH₂), 38.5 (C), 35.5 5.59 ppm and δ = 6.29 (d, J = 11.4 Hz, 1 H), 5.09 (d, J = 11.4 Hz,

(CH), 34.7 (C), 29.0 (CH₃), 28.5 (CH₃), 16.4 (CH₂), 15.0 (CH₂), 1 H) ppm. ¹³C NMR (100 MHz, CDCl₃): the same spectrum as

13.5 (CH), 10.6 (CH) ppm. MS (70 eV): m/z (%) = 218 (1) [M]⁺, that of 8, except δ = 115.7 (t, J = 24 Hz) ppm. ESI-MS: m/z (%) =

183 (5), 161 (9), 135 (11), 105 (22), 97 (44), 69 (87), 43 (88).

C₁₅H₂₂O (218.33): calcd. C 82.52, H 10.16; found C 82.47, H 10.27.

274 (30) [M + K]⁺, 258 (100) [M + Na]⁺, 236 (10) [M + H]⁺. 9: IR

(neat): ν = 3080, 2930, 1640, 1460 cm^–^{1 1}H NMR (400 MHz,

.

˜

CDCl₃): δ = 5.82 (ddt, J = 17.1, 10.5, 6.6 Hz, 1 H), 5.58 (s, 1 H),

5.40 (s, 1 H), 5.01 (dd, J = 17.1, 1.5 Hz, 1 H), 4.94 (dd, J = 10.5,

1.5 Hz, 1 H), 4.93 (s, 1 H), 4.85 (s, 1 H), 3.07 (s, 3 H, O–CH₃),

2.09 (m, 2 H), 1.91 (d, J = 13.6 Hz, 1 H), 1.91 (m, 1 H), 1.59 (d, J

= 13.6 Hz, 1 H), 1.46–1.25 (m, 5 H), 1.23 (s, 3 H, CH₃), 1.13 (s, 3

H, CH₃) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 159.2 (C), 150.4

(C), 139.3 (CH), 114.7 (CH₂), 107.5 (CH₂), 104.3 (CH₂), 84.4 (C),

50.7 (CH₃), 49.7 (CH₂), 40.1 (C), 34.7 (CH₂), 34.2 (CH₂), 31.7

(CH₃), 31.1 (CH₃), 29.8 (CH₂), 23.7 (CH₂) ppm. 9D: ¹H NMR

(400 MHz, CDCl₃): the same spectrum as that of 9, except no sig-

nal at δ = 4.85 ppm. ¹³C NMR (100 MHz, CDCl₃): the same spec-

trum as that of 9, except δ = 104.3 (t, J = 23 Hz) ppm.

Ester 6: A solution of compound 5 (82 mg, 0.4 mmol, 1 equiv.) in

CH₂Cl₂/methanol (1:1, 8 mL) was cooled to –78 °C. Ozone was

bubbled into the solution until a persistent blue color was per-

ceived. The excess of ozone was then removed by bubbling argon

into the reaction vessel. Sodium borohydride (29 mg, 0.8 mmol,

2 equiv.) was added, and the mixture was slowly warmed to 0 °C.

After 1 h of stirring at 0 °C, the reaction was quenched with a satu-

rated ammonium chloride solution for 30 min. The aqueous layer

was extracted with Et₂O. The combined organic layers were washed

with brine, dried with MgSO₄, and the solvents were removed un-

der vacuum. To a cold (0 °C) solution of the resulting crude alcohol

(0.4 mmol, 1 equiv.) in CH₂Cl₂(3 mL) were added triethylamine

(110 µL, 0.8 mmol, 2 equiv.), DMAP (10 mg, 0.08 mmol,

0.2 equiv.) and 4-nitrobenzoyl chloride (82 mg, 0.44 mmol,

1.1 equiv.). After a 15 min of stirring at room temp., the reaction

was quenched with a saturated ammonium chloride solution. The

aqueous layer was extracted with Et₂O. The combined organic lay-

ers were washed with brine and dried with MgSO₄. Purification

by flash chromatography on silica gel (Et₂O/pentane, 2:8) gave the

desired ester 6 (87 mg, 65% yield over 2 steps). The solid product

was recrystallized from hexane/Et₂O. Solid, m.p. 94 °C. IR (film):

4-(2,2-Dimethylhex-5-enyl)-4-methoxy-3-methylenecyclohexene (10)

and 1-(2,2-Dimethylhex-5-enyl)-1-methoxy-2,3-dimethylenecyclo-

pentane (11): Cyclization of precursor 7b (80 mg, 0.34 mmol) with

PtCl₂(5 mg, 0.02 mmol), following the GP (50 °C, 6 h) gave, after

purification by flash chromatography on silica gel (pentane/Et₂O,

98:2), cyclohexene 10 (36 mg, 45%) and cyclopentane 11 (11 mg,

14%). 10: IR (neat): ν = 3080, 2940, 1640, 1460 cm^–1. ¹H NMR

˜

(400 MHz, CDCl₃): δ = 6.08 (d, J = 10.2 Hz, 1 H), 5.79 (ddt, J =

16.8, 10.2, 6.6 Hz, 1 H), 5.67 (m, 1 H), 5.13 (s, 1 H), 4.97 (d, J =

16.8 Hz, 1 H), 4.95 (s, 1 H), 4.88 (d, J = 10.2 Hz, 1 H), 3.15 (s, 3

H), 2.25 (m, 2 H), 2.03–1.90 (m, 3 H), 1.76 (dt, J = 12.2, 4.1 Hz,

1 H), 1.55 (m_AB, 2 H), 1.42 (m, 1 H), 1.35 (m, 1 H), 1.00 (s, 3 H,

CH₃), 0.97 (s, 3 H, CH₃) ppm. ¹³C NMR (100 MHz, CDCl₃): δ =

ν = 2960, 1720, 1600, 1520, 1280 cm^{–1 1}H NMR (400 MHz,

.

˜

CDCl₃): δ = 8.30 (d, J = 9.1 Hz, 2 H, Ar), 8.23 (d, J = 9.1 Hz, 2

H, Ar), 4.58 (m, 2 H), 4.25 (dd, J = 11.9, 7.3 Hz, 1 H), 3.51 (dd, J

= 11.9, 7.6 Hz, 1 H), 2.78 (m, 1 H), 2.17 (m, 1 H), 1.60 (d, J =

13.6 Hz, 1 H), 1.53 (dd, J = 8.1, 3.3 Hz, 1 H), 1.47 (m, 1 H), 1.37 146.1 (C), 140.5 (CH), 130.2 (CH), 128.2 (CH), 113.8 (CH₂), 112.1

(m, 1 H), 1.22 (s, 3 H, CH₃), 1.03 (d, J = 13.6 Hz, 1 H), 1.00 (s, 3 (CH₂), 79.2 (C), 49.4 (CH₃), 46.0 (CH₂), 44.0 (CH₂), 34.5 (C), 30.9

H, CH₃), 0.89 (td, J = 7.6, 5.1 Hz, 1 H), 0.50 (t, J = 4.0 Hz, 1 H),

(CH ), 29.2 (2 CH ), 29.0 (CH ), 25.3 (CH ) ppm. 11: IR (neat): ν

˜

2 3 2 2

1

0.40 (q, J = 4.6 Hz, 1 H), 0.23 (dd, J = 8.1, 4.8 Hz, 1 H) ppm. ¹³C

= 3080, 2930, 1640, 1450 cm^–1. H NMR (400 MHz, CDCl₃): δ =

NMR (100 MHz, CDCl₃): δ = 164.8 (C, C=O), 150.4 (C, Ar), 136.0 5.83 (ddt, J = 16.8, 10.2, 6.6 Hz, 1 H), 5.59 (s, 1 H), 5.41 (t, J =

(C, Ar), 130.7 (2 CH, Ar), 123.5 (2 CH, Ar), 79.7 (C), 66.7 (CH₂), 2.5 Hz, 1 H), 5.02 (d, J = 10.2 Hz, 1 H), 4.97 (d, J = 16.8 Hz, 1

63.7 (CH₂), 42.9 (CH₂), 38.5 (C), 37.3 (CH₂), 35.3 (CH), 34.5 (C), H), 4.95 (s, 1 H), 4.92 (t, J = 2.0 Hz, 1 H), 3.05 (s, 3 H), 2.55 (m,

29.0 (CH₃), 28.2 (CH₃), 16.5 (CH₂), 14.7 (CH₂), 13.4 (CH), 10.5 1 H), 2.36 (m, 1 H), 2.14 (ddd, J = 12.7, 8.1, 3.0 Hz, 1 H), 2.05

(CH) ppm.

(m, 2 H), 1.98 (d, J = 15.2 Hz, 1 H), 1.72 (m, 1 H), 1.43 (m, 2 H),

1.29 (d, J = 15.2 Hz, 1 H), 1.05 (s, 3 H, CH₃), 1.04 (s, 3 H, CH₃)

ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 150.7 (C), 147.5 (C), 139.8

(CH), 113.8 (CH₂), 106.6 (CH₂), 105.0 (CH₂), 86.0 (C), 50.0 (CH₃),

43.8 (CH₂), 42.8 (CH₂), 36.2 (CH₂), 34.0 (C), 29.8 (CH₂), 28.8

(CH₂), 28.6 (CH₃), 28.1 (CH₃) ppm.

5-(Hex-5-enyl)-5-methoxy-3,3-dimethyl-1-vinylcyclopentene (8) and

1-(Hex-5-enyl)-1-methoxy-4,4-dimethyl-2,3-dimethylenecyclo-

pentane (9): Cyclization of precursor 7a (92 mg, 0.4 mmol) with

PtCl₂(5 mg, 0.02 mmol), following the GP (50 °C, 6 h) gave, after

purification by flash chromatography on silica gel (pentane/

CH₂Cl₂, 9:1), cyclopentene 8 (55 mg, 60 %) and cyclopentane 9 5-Methoxy-3,3,5-trimethyl-1-vinylcyclopentene (12) and 1-Methoxy-

(15 mg, 16%). 8: IR (neat): ν = 3080, 2930, 1640, 1465 cm^–1. ¹H

1,4,4-trimethyl-2,3-dimethylenecyclopentane (13): Cyclization of

NMR (400 MHz, CDCl₃): δ = 6.29 (dd, J = 17.8, 11.2 Hz, 1 H), precursor 7c (166 mg, 1.0 mmol) with PtCl₂(14 mg, 0.05 mmol)

˜

5.82 (ddt, J = 17.1, 10.5, 6.6 Hz, 1 H), 5.70 (s, 1 H), 5.59 (dd, J =

17.8, 1.8 Hz, 1 H), 5.09 (dd, J = 11.2, 1.8 Hz, 1 H), 5.01 (dd, J =

17.1, 1.5 Hz, 1 H), 4.94 (dd, J = 10.5, 1.5 Hz, 1 H), 3.13 (s, 3 H,

and styrene (580 µL, 5 mmol), following the GP (80 °C, 1 h) gave,

after purification by flash chromatography on silica gel (pentane/

CH₂Cl₂, 9:1), a mixture of 12 and 13 (3:1, 82 mg, 49% yield). 12:

O–CH₃), 2.09 (m, 2 H, CH₂), 1.91 (d, J = 14.8 Hz, 1 H), 1.85 (d, ¹H NMR (400 MHz, CDCl₃): δ = 6.25 (dd, J = 18.2, 11.8 Hz, 1

J = 14.8 Hz, 1 H), 1.42–1.25 (m, 6 H, 3CH₂), 1.15 (s, 3 H, CH₃), H), 5.62 (s, 1 H), 5.60 (d, J = 18.2 Hz, 1 H), 5.09 (d, J = 11.8 Hz,

4630

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Eur. J. Org. Chem. 2006, 4618–4633

PtCl₂- and PtCl₄-Catalyzed Cycloisomerization of Polyunsaturated Precursors

1 H), 3.11 (s, 3 H, OMe), 2.06 (d, J = 14.1 Hz, 1 H), 1.67 (d, J = 2.72 (dd, J = 14.6, 6.0 Hz, 1 H), 2.60 (dd, J = 14.6, 6.0 Hz, 1 H),

FULL PAPER

14.1 Hz, 1 H), 1.47 (s, 3 H, CH₃), 1.12 (s, 3 H, CH₃), 1.08 (s, 3 H,

1.82 (d, J = 16.4 Hz, 1 H), 1.68 (d, J = 16.4 Hz, 1 H), 1.37 (td, J

CH₃) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 143.6 (CH), 141.1 = 8.4, 4.2 Hz, 1 H), 1.15 (s, 3 H, CH₃), 1.09 (s, 3 H, CH₃), 1.06–

(C), 131.1 (CH), 115.8 (CH₂, CH=CH₂), 89.3 (C), 50.7 (CH₃, 0.76 (m, 3 H) ppm. ¹³C NMR (50 MHz, CDCl₃): δ = 163.3 (C,

OMe), 49.7 (CH₂), 41.6 (C), 29.8 (CH₃), 29.7 (CH₃), 28.3 (CH₃) C=O), 150.8 (C, Ar), 143.6 (C), 135.4 (C, Ar), 135.0 (CH), 131.1

1

ppm. 13: H NMR (400 MHz, CDCl₃): δ = 5.54 (s, 1 H), 5.39 (s, (2 CH, Ar), 123.8 (2 CH, Ar), 116.2 (CH₂), 115.6 (C), 38.2 (CH₂),

1 H), 4.98 (s, 1 H), 4.84 (1s, 1 H), 3.11 (s, 3 H, OMe), 1.97 (d, J = 35.0 (CH₂), 29.6 (CH₃), 28.5 (CH₃), 28.1 (C), 26.9 (CH), 13.7 (CH),

13.6 Hz, 1 H), 1.58 (d, J = 13.6 Hz, 1 H), 1.47 (s, 3 H, CH₃), 1.33 10.2 (CH₂) ppm. GCMS (EI): m/z (%) = 327 (4) [M], 150 (100).

(s, 3 H, CH₃), 1.22 (s, 3 H, CH₃) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 158.7 (C), 107.2 (CH₂), 104.3 (CH₂), 82.2 (C), 51.9

C₁₉H₂₁NO₄(327.37): calcd. C 69.71, H 6.47, N 4.28; found C

70.02, H 6.65, N 4.48. 19a: characteristic signals: ¹H NMR

(CH₂), 50.9 (CH₃, OMe), 40.2 (C), 31.1 (CH₃), 31.0 (CH₃), 22.9 (200 MHz, CDCl₃): δ = 5.79 (dd, J = 17.4, 10.6 Hz, 1 H), 0.99 (s,

(CH₃) ppm.

6 H, 2 CH₃), 0.39 (m, 1 H) ppm.

4-Butyl-4-methoxy-3-methylenecyclohexene (14) and 1-Butyl-1-

methoxy-2,3-dimethylenecyclopentane (15): Cyclization of precursor

7d (180 mg, 1.0 mmol, 1 equiv.) following the GP (40 °C, 30 h) gave,

after purification by flash chromatography on silica gel (pentane/

CH₂Cl₂, 95:5), a mixture of 14 and 15 (14/15, 4:1, 38 mg, 21%

3-Allyl-5,5-dimethylbicyclo[4.1.0]hept-2-en-2-yl Acetate (18b): Cyc-

lization of 1h (230 mg, 1.04 mmol) with PtCl₂(14 mg, 0.05 mmol)

following the GP (2 h at 80 °C) gave, after purification by flash

chromatography (Et₂O/PE, 5:95) a mixture of 18b and 19b (18b/

19b, 97:3, 209 mg, 91% yield). 18b: IR (neat): ν = 3090, 2950, 1750,

˜

1

yield). 14: H NMR (400 MHz, CDCl₃): δ = 6.07 (d, J = 9.6 Hz, 1

1690, 1640, 1450, 1360 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ =

H), 5.71 (m, 1 H), 5.06 (s, 1 H), 4.98 (s, 1 H), 3.17 (s, 3 H, OMe), 5.56 (ddt, J = 17.0, 10.0, 7.0 Hz, 1 H), 4.95 (d, J = 17.0 Hz, 1 H

2.56–2.51 (m, 1 H), 2.35–2.23 (m, 1 H), 1.98–1.93 (m, 1 H), 1.62–

1.56 (m, 1 H), 1.38–1.24 (br. m, 6 H), 0.86–0.93 (m, 3 H, CH₃)

trans), 4.93 (d, J = 10.0 Hz, 1 H cis), 2.63 (dd, J = 14.8, 6.4 Hz, 1

H), 2.50 (dd, J = 14.8, 6.4 Hz, 1 H), 2.13 (s, 3 H, OAc), 1.61 (m_AB

,

ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 144.1 (C), 129.3 (CH), 2 H), 1.21 (m, 1 H), 1.05 (s, 3 H, CH₃), 0.97 (s, 3 H, CH₃), 0.96

128.4 (CH), 111.5 (CH₂), 77.2 (C), 49.4 (CH₃, OMe), 36.1 (CH₂), (m, 1 H), 0.77 (m, 1 H), 0.66 (m, 1 H) ppm. ¹³C NMR (50 MHz,

31.9 (CH₂), 29.7 (CH₂), 25.0 (CH₂), 24.1 (CH₂), 14.1 (CH₃) ppm. CDCl₃): δ = 169.4 (C, C=O), 143.4 (C), 135.4 (CH), 115.8 (CH₂),

1

15: H NMR (400 MHz, CDCl₃): 5.59 (s, 1 H), 5.41 (s, 1 H), 4.93

(s, 1 H), 4.91 (s, 1 H), 3.08 (s, 3 H, OMe), 2.56–2.51 (m, 1 H), 2.29

114.6 (C), 37.9 (CH₂), 34.9 (CH₂), 29.5 (CH₃), 28.5 (CH₃), 28.0 (C),

26.6 (CH), 20.8 (CH₃, OAc), 13.6 (CH), 9.8 (CH₂) ppm. C₁₄H₂₀O₂

(m, 1 H), 1.95 (m, 1 H), 1.59 (m, 1 H), 1.38–1.24 (m, 6 H), 0.89 (220.31): C 76.33, H 9.15; found C 76.29, H 9.28. 19b: characteristic

(m, 3 H, CH₃) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 148.8 (C), signals: ¹H NMR (200 MHz, CDCl₃): δ = 5.76 (dd, J = 17.2,

147.8 (C), 106.2 (CH₂), 105.0 (CH), 85.5 (C), 49.6 (CH₃, OMe),

30.3 (CH₂), 29.7 (CH₂), 29.4 (CH₂), 25.8 (CH₂), 23.2 (CH₂), 14.2

(CH₃) ppm.

10.5 Hz, 1 H), 2.12 (s, 3 H, OAc), 0.94 (s, 3 H, CH₃), 0.92 (s, 3 H,

CH₃), 0.21 (m, 1 H) ppm.

3-Methallyl-5,5-dimethylbicyclo[4.1.0]hept-2-en-2-yl 4Ј-Nitrobenzo-

Methyl 2-(5-Allyl-5-methoxy-3,3-dimethylcyclopent-1-enyl)acrylate ate (18c): Cyclization of 1i (243 mg, 0.7 mmol) with PtCl₂(9 mg,

(16) and Methyl (2-Allyl-2-methoxy-4,4-dimethyl-5-methylenecy-

clopentylidene)acetate (17): Cyclization of precursor 7f (125 mg,

0.5 mmol, 1 equiv.) following the GP (80 °C, 1 h) gave, after purifi-

cation by flash chromatography on silica gel (pentane/CH₂Cl₂, 9:1),

a mixture of 16 and 17 (16/17, 2.5:1, 80 mg, 64% yield). 16: IR

0.034 mmol) following the GP (2 h at 80 °C) gave, after purification

by flash chromatography (EtOAc/hexane, 1:99), a mixture of 18c

and 19c (18c/19c, 7:3, 213 mg, 88% yield). 18c: Solid, m.p. 57–

59 °C. IR (KBr): ν = 3110, 3070, 2960, 1730, 1610, 1525, 1350

˜

cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 8.31 (m, 4 H, Ar), 4.72,

(neat): ν = 3076, 2954, 2933, 2864, 1726, 1639 cm^–1. ¹H NMR (s, 1 H), 4.67 (s, 1 H), 2.63 (s, 2 H), 1.71 (m_AB, 2 H), 1.63 (s, 3 H,

˜

(400 MHz, CDCl₃): δ = 6.21 (s, 1 H), 6.20 (s, 1 H), 6.07 (s, 1 H),

5.67 (m, 1 H), 5.02 (m, 2 H), 3.77 (s, 3 H, CO₂Me), 3.12 (s, 3 H,

CH₃), 1.39 (td, J = 8.4, 4.4 Hz, 1 H), 1.13 (s, 3 H, CH₃), 1.09 (s, 3

H, CH₃), 1.12 (m, 1 H), 0.94–0.75 (m, 2 H) ppm. ¹³C NMR

OMe), 2.50 (m, 2 H), 1.88 (m, 2 H), 1.13 (s, 3 H, CH₃), 1.09 (s, 3 (50 MHz, CDCl₃): δ = 163.2 (C, C=O), 150.8 (C, Ar), 144.2 (C),

H, CH₃) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 167.7 (C=O), 142.5 (C), 135.4 (C, Ar), 131.1 (2 CH, Ar), 123.8 (2 CH, Ar), 115.3

148.4 (CH), 134.6 (C), 134.4 (CH), 133.0 (C), 124.2 (CH₂, (C), 112.3 (CH₂), 39.1 (CH₂), 38.0 (CH₂), 29.6 (CH₃), 28.7 (CH₃),

CH=CH₂), 117.8 (CH₂, CH=CH₂), 93.5 (C), 52.0 (CH₃), 50.3

28.0 (C), 27.0 (CH), 22.0 (CH₃), 13.6 (CH), 10.2 (CH₂) ppm.

(CH₃), 44.9 (CH₂), 43.8 (CH₂), 41.5 (C), 29.4 (CH₃), 28.9 (CH₃) GCMS (EI): m/z (%) = 341 (10) [M], 150 (100). C₂₀H₂₃NO₄

ppm. 17: IR (neat): ν = 3076, 2954, 2933, 2864, 1726, 1639 cm^–1.

(321.40): calcd. C 70.36, H 6.79, N 4.10; found C 70.65, H 7.00, N

4.40. 19c: characteristic signals: H NMR (200 MHz, CDCl₃): δ =

˜

1

¹H NMR (400 MHz, CDCl₃): δ = 6.56 (s, 1 H), 5.85 (m, 1 H), 5.72

(s, 1 H), 5.34 (s, 1 H), 5.12 (m, 2 H), 3.77 (s, 3 H, CO₂Me), 3.04 5.78 (dd, J = 17.4, 10.6 Hz, 1 H), 4.90 (d, J = 10.6 Hz, 1 H), 4.86

(s, 3 H, OMe), 2.74 (m, 1 H), 2.26 (m, 1 H), 1.88 (m, 2 H), 1.19 (s, (d, J = 17.4 Hz, 1 H), 1.30 (s, 3 H, CH₃), 0.98 (s, 3 H, CH₃), 0.96

3 H, CH₃), 1.05 (s, 3 H, CH₃) ppm. ¹³C NMR (100 MHz, CDCl₃): (s, 3 H, CH₃), 0.51 (t, J = 3.5 Hz, 1 H) ppm.

δ = 167.7 (C=O), 149.2 (CH), 139.1 (C), 134.0 (CH), 126.3 (C),

3-Allylbicyclo[4.1.0]hept-2-en-2-yl Acetate (18d): Cyclization of 1j

117.7 (CH₂, CH=CH₂), 115.1 (CH₂, CH=CH₂), 76.5 (C), 51.7

(192 mg, 1.0 mmol) with PtCl₂(14 mg, 0.05 mmol) following the

(CH₃), 49.7 (CH₃), 44.7 (CH₂), 38.3 (CH₂), 33.1 (C), 31.2 (CH₃),

GP (1 h at 80 °C) gave, after purification by simple filtration

through silica gel, compound 18d (178 mg, 93% yield). Alterna-

29.9 (CH₃) ppm.

5,5-Dimethyl-3-(2-propenyl)bicyclo[4.1.0]hept-2-en-2-yl 4-Nitroben-

zoate (18a): Cyclization of 1g (228 mg, 0.7 mmol) with PtCl₂(9 mg,

0.035 mmol) following the GP (2 h at 80 °C) gave, after purification

by flash chromatography (EtOAc/hexane, 2:98), a mixture of 18a

and 19a (95:5, 183 mg, 80% yield). 18a: solid, m.p. 73–75 °C. IR

tively, cyclization of precursor 1j (192 mg, 1.0 mmol) was con-

ducted with PtCl₄(17 mg, 0.05 mmol), following the same pro-

cedure (80 °C, 2 h) and gave compound 18d (190 mg, 98%) as an

oil. IR (neat): ν = 3076, 3006, 2977, 2922, 2859, 1754, 1638 cm^–1.

˜

¹H NMR (400 MHz, CDCl₃): δ = 5.62 (m, 1 H), 4.91 (m, 2 H),

2.62 (m, 2 H), 2.17 (s, 3 H), 1.96–1.67 (m, 4 H), 1.42 (m, 1 H), 1.20

(m, 1 H), 0.75 (m, 2 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ =

(KBr): ν = 3115, 3000, 2950, 2850, 1725, 1610, 1530 cm^–1. ¹H NMR

˜

(200 MHz, CDCl₃): δ = 8.33 (m, 4 H, Ar), 5.63 (m, 1 H), 4.99 (dd,

J = 17.2, 1.6 Hz, 1 H trans), 4.98 (dd, J = 11.0, 1.6 Hz, 1 H cis), 169.7 (C, C=O), 144.4 (C), 135.7 (CH), 116.8 (C), 115.9 (CH₂),

Eur. J. Org. Chem. 2006, 4618–4633

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4631

J. Marco-Contelles, L. Fensterbank, M. Malacria et al.

FULL PAPER

35.1 (CH₂), 23.8 (CH₂), 21.2 (CH₃, OAc), 19.7 (CH₂), 14.8 (CH),

12.5 (CH), 10.2 (CH₂) ppm.

(22 mg) and compound 32 [101.1 mg, 63% (74% taking into ac-

count the recovered starting material)]. Oil. IR (neat): ν = 3063,

˜

3027, 2985, 2922, 1976, 1747, 1603, 1497, 1453, 1368, 1215 cm^–1.

¹H NMR (300 MHz, CDCl₃): δ = 7.18–7.05 (m, 6 H), 2.67 (t, J =

8.0 Hz, 2 H), 2.38–2.20 (m, 2 H), 2.04 (s, 3 H), 1.77 (d, J = 2.0 Hz,

3 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 189.9, 169.1, 141.9,

128.8 (2 C), 128.7 (2 C), 126.3, 115.9, 110.6, 37.1, 33.9, 21.4, 21.3

ppm. MS (70 eV): m/z (%) = 216 (1) [M]⁺, 173 (42), 156 (84), 145

(48), 129 (46), 91 (100), 43 (81). C₁₄H₁₆O₂(216.28): calcd. C 77.75,

H 7.46; found C 77.65, H 7.24.

3-Allyl-5,5-dimethylbicyclo[4.1.0]heptan-2-one (20): To a solution of

acetate 18b (85 mg, 0.4 mmol, 1 equiv.) in methanol (3 mL) was

added potassium carbonate (113 mg, 0.8 mmol, 2 equiv.), and the

mixture was stirred for 10 min at room temp. The reaction was

quenched with a saturated ammonium chloride solution. The aque-

ous phase was extracted with Et₂O. The combined organic layers

were washed with brine and dried with MgSO₄. Purification by

flash chromatography on silica gel (Et₂O/pentane, 5:95) gave the

desired ketone 20 (64 mg, 93% yield) as a single diastereomer, the

relative stereochemistry of which was determined by NOESY ex-

1-Methyl-3-(2-methylpropenyl)cyclohex-3-en-1-yl Acetate (35) and

1-Methyl-3-methylene-4-[(methyl)ethylidene]cyclohex-1-yl Acetate

(36): Cyclization of precursor 26 (154.0 mg, 0.74 mmol) with PtCl₂

(9.84 mg, 0.037 mmol), following the GP (40 h at 40 °C) afforded,

after purification by flash chromatography (EtOAc/hexane, 4:96), a

mixture of compounds 35 and 36 (35/36, 4:1 (determined by GLC),

127.8 mg, 83% yield) that we were unable to separate by

periments. 20: Oil. IR (neat): ν = 3080, 2950, 1680, 1470, 1360

˜

1

cm^–1. H NMR (200 MHz, CDCl₃): δ = 5.60 (m, 1 H), 4.99–4.93

(m, 2 H), 2.35 (m, 1 H), 2.23–2.01 (m, 2 H), 1.72 (m, 1 H), 1.37–

1.14 (m, 3 H), 1.06 (s, 3 H, CH₃), 1.03 (s, 3 H, CH₃), 1.07–0.89 (m,

2 H) ppm. ¹³C NMR (50 MHz, CDCl₃): δ = 210.3 (C, C=O), 135.7

(CH), 117.1 (CH₂), 42.3 (CH), 36.0 (CH₂), 35.8 (CH₂), 30.2 (CH,

CH₃), 29.0 (C), 27.7 (CH₃), 26.5 (CH), 9.7 (CH₂) ppm. C₁₂H₁₈O

(178.27): calcd. C 80.84, H 10.18; found C 80.72, H 10.26.

chromatography. 35 + 36: IR (neat): ν = 2968, 2853, 1732, 1651,

˜

1

1436, 1367, 1236, 1209 cm^–1. H NMR (300 MHz, CDCl₃) (major

isomer 35): δ = 5.53 (br. s, H-4), 5.47 (br. s, H-7), 2.53 (d, J =

17.5 Hz, H-2), 2.28 (d, J = 17.5 Hz, H-2Ј), 2.20–2.05 (m, H-5, 2 H-

6), 1.97 (s, OCOCH₃), 1.76 (br. s, H-5Ј, H-9, H-10), 1.53 (s, H-11)

ppm; (minor isomer 36): δ = 4.96 (br. s, H-10), 4.61 (br. d, J =

2.1 Hz, H-10Ј), 3.12 (d, J = 13.5 Hz, H-2), 1.95 (s, OCOCH₃), 1.70

(s, H-5Ј, H-8, H-9), 1.52 (s, H-11) ppm. ¹³C NMR (75 MHz,

CDCl₃): δ = (major isomer 35) 169.6, 133.5, 132.1, 125.7, 122.5,

79.4, 39.9, 30.9, 25.6, 23.3, 22.2, 21.2, 18.5 ppm; (minor isomer 36)

169.5, 146.2, 128.6, 126.0, 109.7, 81.3, 39.6, 37.7, 28.6, 25.6, 23.3,

20.9, 18.9 ppm. GLC/MS: (70 eV, major isomer 35, retention time:

13.0 min) m/z (%) = 208 (5) [M]⁺, 148 (70), 133 (100), 119 (12), 105

(80), 91 (89), 43 (180); (minor isomer 36, retention time: 11.0 min)

148 (98), 133 (96), 119 (21), 105 (49), 91 (47), 43 (100). C₁₃H₂₀O₂

(208.30): calcd. C 74.96, H 9.68; found C 74.74, H 9.74.

3-But-3-enyl-5,5-dimethylbicyclo[4.1.0]hept-2-en-2-yl Acetate (22)

and 3-(2,2-Dimethylbut-3-enyl)bicyclo[4.1.0]hept-2-en-2-yl Acetate

(23): Cyclization of precursor 21 (40 mg, 0.17 mmol) with PtCl₂

(2.3 mg, 0.008 mmol), following the GP (80 °C, 1 h) gave, after pu-

rification by flash chromatography (Et₂OAc/pentane, 8:92), com-

pound 22 (24 mg, 60%) and compound 23 (12 mg, 30%). 22: IR

(neat): ν = 3076, 3002, 2953, 2865, 1753, 1694, 1640 cm^–1. ¹H NMR

˜

(400 MHz, CDCl₃): δ = 5.75 (m, 1 H), 4.96 (d, J = 18.8 Hz, 1 H),

4.93 (d, J = 9.1 Hz, 1 H), 2.16 (s, 3 H), 2.02 (m, 2 H), 1.93 (m, 2

H), 1.66 (d, J = 16.2 Hz, 1 H), 1.57 (d, J = 16.2 Hz, 1 H), 1.21 (m,

1 H), 1.09 (s, 3 H), 1.06 (m, 1 H), 1.02 (s, 3 H), 0.77 (m, 1 H), 0.66

(m, 1 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 169.8 (C=O),

143.4 (C), 138.8 (CH), 116.5 (C), 114.8 (CH₂, CH=CH₂), 38.5

(CH₂), 31.8 (CH₂), 30.0 (CH₂), 29.9 (CH₃), 28.8 (CH₃), 28.3 (C),

26.8 (CH), 21.2 (CH₃), 13.8 (CH), 10.0 (CH₂) ppm. C₁₅H₂₂O₂

(234.33): calcd. C 76.88, H 9.46; found C 76.85, H 9.54. 23: IR

Acknowledgments

(neat): ν = 3080, 3003, 2959, 2926, 2859, 1755, 1682, 1639 cm^–1.

˜

¹H NMR (400 MHz, CDCl₃): δ = 5.80 (dd, J = 17.7, 10.8 Hz, 1

H), 4.96 (m, 2 H), 2.15 (s, 3 H), 2.05–1.78 (m, 4 H), 1.65–1.58 (m,

1 H), 1.42–1.37 (m, 1 H), 1.28–1.24 (m, 2 H), 0.96 (s, 6 H), 0.73

(m, 2 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 169.3 (C=O),

148.8 (CH), 145.4 (C), 116.8 (C), 109.7 (CH₂, CH=CH₂), 43.7

(CH₂), 38.2 (C), 27.2 (CH₃), 27.0 (CH₃), 26.6 (CH₂), 21.1 (CH₃),

19.5 (CH₂), 14.4 (CH), 12.4 (CH), 9.2 (CH₂) ppm. C₁₅H₂₂O₂

(234.33): calcd. C 76.88, H 9.46; found C 76.97, H 9.69.

J. M.-C. thanks Johnson Matthey for the generous loan of platinum

and gold catalysts and MCYT (Spain) for financial support (Grant

no. BQU2003-00813). S. A. thanks MCYT (Spain) for a fellowship.

E. M. and G. L. thank the Ministère de la Recherche for a Ph.D.

grant. We thank Ministère de la Recherche, CNRS and Institut

Universitaire de France for financial support. Acknowledgment is

made of the EU for the COST D12 Action: “Cascade Free Radical

Reactions” and for a short-term scientific mission to Madrid

(E. M.). The authors thank J. Vaissermann and P. Herson (UPMC)

for the X-ray determinations.

Methyl (2Z,4Z)-3-Acetyloxy-4-methyl-2,4,7-octatrienoate (29):

Cyclization of precursor 24 (166 mg, 0.74 mmol) with PtCl₂

(9.7 mg, 0.036 mmol), following the GP (80 °C, 11 h) afforded, af-

ter purification by flash chromatography (EtOAc/hexane, 5:95),

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product 29 (17 mg, 11% yield). Oil. H NMR (300 MHz, CDCl₃):

δ = 6.03 (t, J = 7.5 Hz, 1 H), 5.80– 5.59 (m, 1 H), 5.71 (s, 1 H),

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Received: June 16, 2006

Published Online: August 10, 2006

Eur. J. Org. Chem. 2006, 4618–4633

www.eurjoc.org

4633

Article Doi

PtCl2- and PtCl4-catalyzed cycloisomerization of polyunsaturated precursors

DOI: 10.1002/ejoc.200600521

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