[6]Radialenes revisited

FULL PAPER

[6]Radialenes Revisited^[‡]

Thomas Höpfner,^[a]Peter G. Jones,^[b]Birte Ahrens,^[b]Ina Dix,^[a]Ludger Ernst,^[c]and

Henning Hopf*^[a]

Keywords: Carbenes / Conformation analysis / Epoxidations / Photochemistry / Isomerizations / Radialenes

[6]Radialene (2d) and its hexa- (2a) and dodecamethyl (2c)

derivatives were subjected to several novel chemical reac-

mixture from which the monoadduct 21 could be isolated.

The analogous product 24 and the bisadduct 25 were ob-

tions. Pyrolysis of 2a under flash vacuum conditions provided tained from 2c under the same conditions. Epoxidation of 2a

a mixture of 1,5-hydrogen shift products 9 and 10, and the

benzocyclobutenes 5 and 6, produced by electrocyclization

of an intermediate o-xylylene derivative 7. At the higher end

of the investigated temperature range (200−400 °C) the

with m-chloroperbenzoic acid gave the monoadduct 26, to-

gether with higher epoxidation products, which, however,

could not be separated. Depending on the reaction condi-

tions, 2c could be oxidized with m-chloroperbenzoic acid to

formation of cyclization products 11 was also observed. The give the epoxides 27, 28, and 29. Hydrochlorination of 2a

hydrocarbon 2c isomerized to the benzocyclobutene 12 un-

der these conditions. Photolysis at 254 nm converted 2c into

a novel isomer that, according to X-ray structural analysis,

gave a complex mixture of addition products, which was con-

verted into the olefins 9 and 10 by base treatment, showing

that the addition step takes place less regioselectively than

has the unusual twist configuration 14. Compound 2c was previously assumed. With Fe₂(CO)₉, 2a was converted into

photoisomerized through photoinduced hydrogen shift reac- the iron tricarbonyl complex 33 in poor yield. Repetition of

tions to 15, and the stable p-xylylenes 16 and 17. Dichloro- the literature procedure for the preparation of 2a allowed the

and dibromocarbene add to 2d with formation of the rotaradi- isolation of novel diastereomers of this oldest hexaradialene;

alene anti adducts 19a and 19b, respectively, the structures

of which were also established by X-ray structural analysis.

With dichlorocarbene, 2a provided the three dichlorocarbene

adducts 20, 22, and 23, whereas methylenation with diiodo-

methane/trimethylaluminium afforded a complex product

according to NMR experiments the methyl substituents of

this hydrocarbon are arranged as shown in the structure

cccaca-2a.

( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,

Germany, 2003)

Introduction

can convert radialenes into novel π-donors and π-acceptors,

of interest, inter alia, for the preparation of novel charge-

transfer complexes.^[4]In another recent application, radial-

enes have been employed in molecular scaffolding.^[5]The

first radialene to be prepared was 7,8,9,10,11,12-hexameth-

yl[6]radialene (2a), synthesized in 30% yield in 1961 by

Hopff and Wick, by treatment of the hexabromide 1a or

the corresponding chloride 1b with magnesium in meth-

anol/benzene.^[6]The analogous hexaethyl[6]radialene (2b)

was obtained by the same method from the corresponding

hexakis(1-bromopropyl)benzene (1c).^[7]In these elimination

reactions, the two radialenes, which according to X-ray

structural analysis possess the so-called bucket wheel con-

figuration (see Scheme 1),^[1b,3,8]were reported to be the only

products. The fully alkylated dodecamethyl[6]radialene (2c)

was obtained when tetramethylbutatriene (3), generated in

situ, was trimerized in the presence of a Ni⁰catalyst.^[9]The

unsubstituted parent system 2d was not synthesized until

more than 15 years after 2a.^[10Ϫ12]

Radialenes are cross-conjugated alicyclic hydrocarbons in

which all ring carbon atoms are sp²-hybridized and show

as many exocyclic double bonds as possible. Originally

more or less a laboratory curiosity, radialenes and their de-

rivatives have recently been receiving growing attention

from preparative chemists, spectroscopists, and materials

scientists.^[2,3]The introduction of polarizing substituents

[‡]

Alicyclic Chemistry, VIII. Part VII: Ref.^[1]

[a]

Institute of Organic Chemistry, Technical University of

Braunschweig,

Hagenring 30, 38106 Braunschweig, Germany

Fax: (internat.) ϩ49-(0)531-3915388

E-mail: H.Hopf@tu-bs.de

[b]

Institute of Inorganic and Analytical Chemistry, Technical

University of Braunschweig,

P. O. Box 3329, 38106 Braunschweig, Germany

Fax: (internat) ϩ49-(0)531-3915387

E-mail: p.jones@xray36.anchem.nat.tu-bs.de

[c]

NMR-Laboratory of the Chemical Institutes, Technical

University of Braunschweig,

Fax: (internat) ϩ49Ϫ(0)531/3918192

E-mail: L.Ernst@tu-bs.de

Although the chemical behavior of the [6]radialenes has

been studied to some extent (inter alia, addition of HCl,

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[6]Radialenes Revisited

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curs as 1,4-elimination process, this configuration of 1a rep-

resents the ideal stereochemical prerequisite and the re-

sulting hydrocarbon has the shown bucket-wheel structure

2a. If, on the other hand, the dehalogenation process takes

place stepwise Ϫ by a single-electron transfer process, for

example Ϫ the initially generated benzyl radical intermedi-

ates could undergo cis/trans-isomerization reactions and

cause the formation of isomers of 2a in the product mixture.

For the following reasons we believe that the second iso-

mer of 2a, which could be separated from the product mix-

ture by preparative thick layer chromatography (but with

substantial loss of material), has the structure cccaca-2a

1

(Scheme 2). The H NMR spectrum of this isomer shows

five different signals both for the CH and for the CH₃

groups, of which one signal in each set has a twofold inten-

sity (Table 1). This can only be explained in terms of an

unsymmetrical molecule displaying accidental chemical

equivalence of two CH and of two CH₃moieties. Similarly,

in the ¹³C NMR spectrum, there are five ϾCϭ signals (one

with twofold intensity), five CH₃signals (one with twofold

intensity) and six ϭCHϪ signals (see Exp. Sect.). Among

the nine possible diastereomers of 2a there are only three

unsymmetrical ones that would be compatible with the ob-

served NMR spectra. These are ccccca-2a, ccccaa-2a, and

cccaca-2a. NOE difference measurements with saturation of

the methyl signals were carried out in order to decide be-

tween these three possibilities. Because of the very close

chemical shifts, the spectra had to be recorded at an obser-

vation frequency of 600 MHz. Methine and methyl protons

belonging to the same ϭCHϪCH₃unit were identified by

H,H-COSY spectroscopy. The NOE results showed that the

two ϭCHϪCH₃pairs b/j, f/i, and one of the two acciden-

tally equivalent d,e/g,h pairs are arranged in a clockwise

fashion in the order described. As no interϪCH₃NOEs

were observed, it appears logical to orient the three remain-

ing ϭCHϪCH₃moieties such that the methyl groups with

identical shifts (g, h) and with very similar shifts (k, l) are

pointing toward each other. The resulting diastereomer is

cccaca-2a, and its methyl group orientation accounts for the

missing NOEs, since it is not possible to observe a signal

intensity increase at the point of irradiation or very close

Scheme 1. Preparation of [6]radialenes

HBr, Br₂, and H₂to 2a,^[6,7]various DielsϪAlder additions

to 2a^[13]and 2d^[11,14]), we thought it worthwhile to take an-

other look at these highly unsaturated compounds. In par-

ticular, we wanted to study the isomerization behavior of

[6]radialenes and also the addition of divalent species (carb-

enes, epoxidation) to them. In a comprehensive previous

study on the chemical behavior of [4]radialene we had

shown that this hydrocarbon could be cyclopropanated to

yield novel derivatives of [4]rotane.^[15]Before we performed

the corresponding experiments with various [6]radialenes

(see below), however, we were interested in the stereochem-

istry of the elimination reactions affording 2a Ϫ was this

really the only stereoisomer produced?

Results

The Stereochemistry of the Elimination of 1a to 2a

Elimination experiments under the classical conditions to it. If the isomer in question were ccccca-2a or ccccaa-2a,

(see above) indeed yielded 2a as the main product (isolated one would expect at least one NOE between proton a, b, or

yield 34%), but GC/MS analysis quickly showed that other c and one non-vicinal methyl group. Since this is not the

isomers Ϫ up to five were detected Ϫ were also produced. case, we favor structure cccaca-2a over the alternatives

Because of their low concentrations, however, it was im- ccccca-2a and ccccaa-2a. Scheme 3 shows the two possible

1

possible to separate any of these for spectral identification. assignments of the H NMR signals for cccaca-2a.

Only with methyl or n-butyllithium as dehalogenation re-

agent could a new isomer of 2a be generated in sufficient

amounts for structure assignment (see below). The reason

for this behavior is unclear; the difficulty in finding a

reasonable explanation begins with the unknown stereos-

tructure of 1a. According to B3LYP/6-31G(d) geometry op-

timization calculations,^[16]and through analogy with the

crystal structure of hexakis(bromomethyl)benzene,^[17]1a

should possess an all-anti configuration with the bromine

substituents oriented alternatively above and below the

carbocyclic plane. If it is assumed that debromination oc- methyl[6]radialene (2a)

Scheme 2. The three unsymmetrical diastereomers of hexa-

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1

which demand a conrotatory closure pathway of 7. How-

ever, as shown by Roth and co-workers in a comprehensive

study on the stereochemistry of the thermal ring-opening

of trans-7,8-dimethyl-benzocyclobutene,^[19]this hydro-

carbon Ϫ besides undergoing the allowed conrotatory iso-

merization Ϫ on heating also epimerizes to its cis isomer

via a ‘‘forbidden’’ disrotatory reaction. Not surprisingly,

this latter isomerization requires a higher activation energy.

Indeed in the case of 7, the disrotatory cyclization product

5 is generated as a minor product only, never being able to

surpass 6 in yield over the whole temperature range

studied (Scheme 4).

Table 1. H NMR chemical shifts, nuclear Overhauser effects, and

H,H-COSY cross-peaks for cccaca-2a

Signal

δ_H

Signal

δ_H

a

b

c

d,e

5.49 g,h

1.81

1.79

1.74

1.61

1.60

5.43

5.41

5.36

5.33

i

j

k

l

f

NOEs (irradiated signal Ǟ

enhanced signal)

g,h Ǟd,e

i Ǟ d,e and f

j Ǟ b and f

k Ǟ a

H,H-COSY crosspeaks

a o k

b o j

c o l

d,e o g,h

f o i

l Ǟ c

Scheme 3. Alternative signal assignments of cccaca-2a

The Thermal Isomerization of Hexamethyl- (2a) and

Dodecamethyl[6]radialene (2c)

In comparison with the highly reactive parent hydro-

carbon 2d, the polymethyl derivatives 2a and 2c are quite

stable. They can be handled readily in air and melt without

decomposition at 133 and 210 °C, respectively. To study

their behavior under harsher conditions we sealed small

samples of these hydrocarbons under vacuum in glass am-

poules and heated them for one hour at temperatures be-

tween 200 and 460 °C. While 2a had reacted completely

after 1 hour at 230 °C, 2c only began to isomerize around

330 °C. In both cases the formation of primary products

was accompanied by secondary reactions at longer pyrolysis

times or at higher temperatures, as shown by GC, GC/IR,

and GC/MS analyses of the pyrolysate.

With regard to the structure of 2a, which is formally

composed of three 2,4-hexadiene units, it comes as no sur-

prise that its thermal isomerization begins with a 1,5-hydro-

gen shift, producing hydrocarbon 4, in which one double

bond has moved into the ring, and another to the periphery.

Double repetition of this process provides the aromatic iso-

mer 9, a known compound,^[18]reaching its highest concen-

tration at 330 °C. The route to 9 passes through the

‘‘doubly-rearranged’’ hydrocarbon 7, a highly substituted o-

Scheme 4. Thermolysis of hexamethyl[6]radialene (2a)

Under pyrolysis conditions 6 can undergo conrotatory

xylylene that can undergo one of the reactions typical of ring-opening: presumably back to 7 but also ‘‘on’’ to the

this class of polyenes, electrocyclic ring-closure to produce isomeric o-xylylene 8. If this reacts by a 1,5-hydrogen shift,

benzocyclobutenes. That this cyclization actually occurs an isomer of 9, the trivinyl derivative 10, is produced. Al-

was verified by the isolation of isomer 6, which at inter- though this C₁₈H₂₄isomer could not be isolated from the

mediate temperatures (260 °C) is the main product of the pyrolysis mixture it was shown to be present by GC and

thermal isomerization of 2a. The formation of the cis iso- GC/MS comparison with an authentic sample available

mer 6 is in agreement with orbital-symmetry requirements, from another experiment (see below). With its two adjacent

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vinyl substituents, 10 can ring-close to afford the dihydro- pleased to find that irradiation with a 15 W low-pressure

naphthalene derivatives 11a and 11b, two isomers that mercury lamp at a wavelength of 254 nm in hexane solution

could not be separated by chromatography. Their structures for short reaction times (minutes, see below and Exp. Sect.)

were derived from their NMR spectroscopic data (see Exp. produced isomerization products of dodecamethyl[6]radia-

Sect.) as well as from several chemical transformations. lene (2c, Scheme 6).

Whereas dehydrogenation with DDQ transformed this mix-

ture into 2-vinyl-1,3,4-triethylnaphthalene, hydrogenation

over Pd/C yielded 1,2,3,4-tetraethyltetralin. It is not surpris-

ing that 11a/b, which according to the ¹³C NMR spectrum

of their mixture are produced in about equal amounts

(doubling of carbon signals), are formed only at higher tem-

peratures, since the cyclization step of 10 involves the tem-

porary loss of an aromatic ring system. Once the cyclization

has occurred, hydrogen shifts are necessary to arrive at

11a/b.

As already mentioned, dodecamethyl[6]radialene (2c) is

thermally much more stable than the hexamethyl derivative

2a. Up to 360 °C the pyrolysis mixture is dominated by the

benzocyclobutene 12, which was isolated from an experi-

ment at 350 °C in 17% yield by preparative thick layer chro-

matography and sublimation (Scheme 5). Its structure was

assigned from the usual spectroscopic and analytic data (see

Exp. Sect.), and for its formation we postulate a mechanism

analogous to the conversion of 2a into 6.

Scheme 6. Photolysis of dodecamethyl[6]radialene (2c) in confor-

mation 13

Scheme 5. Thermolysis of dodecamethyl[6]radialene (2c)

Although hydrocarbon 12 was shown to be homogeneous

by GC and HPLC analysis, its ¹H NMR spectrum indicated

the presence of at least two conformers. Line-broadening

was apparent for all signals at room temperature, and al-

though many signals became sharper on an increase in tem-

perature this process had not come to an end even at 100

°C. No attempt was made to quantify this phenomenon.

When the pyrolysis temperature was increased further,

the result was a most complex product mixture that we were

unable to separate.

The structure of 2c in the solid state has been determined

by Wilke and co-workers;^[21]as shown in the scheme, the

hydrocarbon prefers the chair-like structure 13. On ir-

radiation it isomerizes either to a new conformational iso-

mer 14 or to a polyene that has undergone a 1,5-hydrogen

shift: the hydrocarbon 15. For orbital symmetry reasons,

photochemically induced 1,5-hydrogen shifts must occur

antarafacially, and, indeed, with its twisted geometry, 2c

(see three-dimensional structure 13) fulfills this condition.

The structure of 15 was determined spectroscopically. When

the conformational isomer 14 was used as a substrate no

reaction back to 2c was observed, but a hydrogen shift pro-

cess took place, yielding 15. Finally, this polyene either pho-

The Photochemical Isomerization of

Dodecamethyl[6]radialene (2c)

When 2a is irradiated either in the absence or in the pres- toisomerizes back to 14 or undergoes a second 1,5-hydrogen

ence of a sensitizer it undergoes cycloaddition reactions to shift to yield the two p-xylylenes 16 and 17. The yields of

provide various oligomers and polymers.^[20]Since repetition the isomers strongly depend on the irradiation time. After

of these experiments in our hands in a 2-methylbutan/2- 4 minutes, 15 can be isolated in 22% yield (together with

methylpentane glass at Ϫ196 °C also did not provide mono- largely unchanged substrate), but after 18 minutes it cannot

meric isomerization products (formation of oligomers of be detected in the photolysate. After this relatively long

unknown structure), we decided to subject the sterically time, hydrocarbons 14, 16, and 17 were produced in 19, 16,

more shielded [6]radialene derivative 2c to photolysis. Al- and 4% yields, respectively. Whereas the structure of 17 was

though initial experiments were also disappointing (forma- also determined spectroscopically (largely by NMR spec-

tion of viscous oils of undetermined structure), we were troscopy, see Exp. Sect.), both 14 and 16 could be crys-

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tallized and subjected to X-ray structural analysis. Unfortu-

nately the structure of 16 proved to be severely disordered,

but that of 14 was of satisfactory quality and proved to be

a different modification from that previously determined,

which was reported briefly in a review article^[21]and is de-

posited in the Cambridge Database (refcode GAYTIJ).

The structure of the new polymorph of the radialene 14

is, to the best of our knowledge, only the fifth of a simple

radialene, the previously determined structures being the

first polymorph of 14^[19]and the hexamethyl,^[8]hexa-

ethyl,^[1b]and hexa-bromomethyl^[22]derivatives. All these

structures displayed crystallographic inversion symmetry

and almost ideal chair conformations, with absolute ring

torsion angles of ca. 46Ϫ48° in the hexasubstituted com-

pounds and 56° in the previous polymorph of the dodeca-

substituted 14. The new polymorph involves two indepen-

dent molecules, which are, however, closely similar (Fig-

ure 1); a least-squares fit of all atoms reveals an r.m.s. devi-

˚

ation of only 0.13 A, and this is reduced to 0.07 A if the

methyl groups are omitted. Ring bond lengths lie in the

2

˚

1.496Ϫ1.511 A range, and ring angles (at sp carbon atoms)

in the 109.1Ϫ110.8° range. The major and surprising differ-

ence from the earlier polymorph is that the ring confor-

mation is an almost ideal twist, with torsion angles (for

molecule 1) of 32, Ϫ70, 35, 31, Ϫ70, and 33° (starting with

the bond C1ϪC2, then C2ϪC3, etc.); the local twofold axis

passes through C1 and C4 and is valid for all atoms to a

reasonable approximation. This is the first observation of

the twist conformation in a radialene. Also in contrast to

the previous polymorph, and presumably as a consequence

of the twist conformation, there are substantial deviations

from planarity about the double bonds, especially C1ϪC7

and C4ϪC10, in which all torsion angles deviate by ca. 15°

from the ideal values of 0 and 180°. Associated with this

are short contacts that represent steric pressure between the

methyl carbon atoms of neighboring CϭCMe₂moieties

(C13···C24 3.07, C14···C15 3.05, C18···C19 3.09, C20···C21

Figure 1. The two independent molecules of compound 14 in the

crystal; ellipsoids represent 50% probability levels; hydrogen radii

are arbitrary

in the same flask under two-phase conditions. As illustrated

in Scheme 7, this experiment was successful, although the

two carbene adducts 19a and 19b were isolated only in

yields of 2 and 5%, respectively.

˚

3.06 A). The shortest such distance in the previous poly-

˚

morph was 3.29 A.

Carbene Additions to [6]Radialenes

As pointed out in the introduction, radialenes can be

converted into rotanes (or into ‘‘rotaradialenes’’ if not fully

cyclopropanated) by cyclopropanation. Having demon-

strated the usefulness of this concept for [4]radialene,^[15]we

were interested in extending it to the [6]radialenes. The sim-

plest model for such a reaction is, of course, [6]radialene

(2d) itself. Since we had no access to its various precursor

compounds, we decided to try to debrominate hexakis(bro-

momethyl)benzene (18), since the multiple elimination route

had already shown its practical usefulness in the cases of 2a

and 2b. Because of the known high reactivity of 2d^[10Ϫ12,14]

a trapping experiment was designed, in which [6]radialene

generated in situ could be intercepted by either dichloro- or

dibromocarbene produced from chloroform or bromoform Scheme 7. Dihalocarbene addition to [6]radialene (2d)

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Still, enough material was available to allow a structure

The crystal packings of both compounds each involve

determination by X-ray structural analysis for both ad- one independent halogen···halogen contact. In 19a the con-

ducts.

tact C1ϪCl1···Cl2ϪC1, via the c glide plane, displays a

˚

The halo derivatives 19a and 19b are not isostructural, distance of 3.548 A and angles of 84.1 and 173.5° at Cl1

but both molecules (Figures 2 and 3) display crystallo- and Cl2 respectively, making this a classical ‘‘type 2’’ con-

graphic inversion symmetry. The rings both display the tact,^[25]and resulting in the formation of layers of molecules

chair conformation, with absolute torsion angles in the parallel to (10Ϫ1) (Figure 4). In 19b the contact is

range of 49Ϫ54°. The bond lengths in the three-membered C1ϪBr1···Br2ϪC1, through an inversion center, with a dis-

˚

rings display the same pattern, with C1ϪC2 Ͻ C2ϪC3 Ͻ tance of 3.532 A and angles of 173.8 and 115.3° at Br1 and

C1ϪC3, although the differences are not large (see Br2 respectively; this is also a ‘‘type 2’’ contact, and results

refs.^[23,24]). Each C-halogen bond is synperiplanar to a ring in the formation of layers of molecules parallel to the yz

bond across C1ϪC3, and this may be the reason for the plane (Figure 5).

longer bonds. A similar effect is observed in the six-mem-

bered rings, in which the bond C4ϪC5 is not involved in

synperiplanar contacts and is the shortest, although the dif-

ferences are not great.

Figure 4. Packing diagram for compound 19a; the view direction

is perpendicular to (10Ϫ1); hydrogen atoms are omitted;

chlorineϪchlorine interactions are indicated by dashed bonds

Figure 2. The molecule of compound 19a in the crystal; ellipsoids

represent 50% probability levels; hydrogen radii are arbitrary; selec-

˚

ted molecular dimensions (A,°): C(1)ϪC(2) 1.491(2), C(1)ϪC(3)

1.527(2), C(2)ϪC(3) 1.518(2), C(3)ϪC(5)#1 1.502(2), C(3)ϪC(4)

1.502(2), C(4)ϪC(5) 1.487(2); Cl(1)ϪC(1)ϪC(3)ϪC(5)#1 2.89(14),

Cl(2)ϪC(1)ϪC(3)ϪC(4)Ϫ2.60(14)

Figure 5. Packing diagram for compound 19b; the view direction

is perpendicular to the yz plane; hydrogen atoms are omitted;

bromineϪbromine interactions are indicated by dashed bonds

No higher cyclopropanation products were obtained in

these two experiments, and the amounts of 19a/b available

did not suffice to subject them to further carbene addition.

Figure 3. The molecule of compound 19b in the crystal; ellipsoids

Unlike 2d, the hexamethyl derivative 2a does not react

with dibromocarbene. With dichlorocarbene Ϫ generated

from chloroform under phase-transfer conditions Ϫ how-

ever, three cyclopropanation products were obtained: the

represent 50% probability levels; hydrogen radii are arbitrary; selec-

˚

ted molecular dimensions (A,°): C(1)ϪC(2) 1.489(4), C(1)ϪC(3)

1.523(4), C(2)ϪC(3) 1.514(3), C(3)ϪC(4) 1.502(4), C(3)ϪC(5)#1

1.504(3), C(4)ϪC(5) 1.493(3); Br(1)ϪC(1)ϪC(3)ϪC(4) 2.6(3),

Br(2)ϪC(1)ϪC(3)ϪC(5)#1 Ϫ3.6(3)

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monoadduct 20 (8%), and the isomeric bisadducts 22 (17%)

and 23 (1%, Scheme 8).

Figure 6. The molecule of compound 22 in the crystal; ellipsoids

represent 30% probability levels; hydrogen radii are arbitrary; selec-

˚

ted molecular dimensions (A,°): C(1)ϪC(6) 1.521(6), C(1)ϪC(2)

1.524(6), C(1)ϪC(19) 1.527(6), C(1)ϪC(7) 1.538(6), C(2)ϪC(3)

1.501(7), C(3)ϪC(4) 1.503(7), C(3)ϪC(20) 1.534(6), C(3)ϪC(9)

1.550(6), C(4)ϪC(5) 1.475(6), C(5)ϪC(6) 1.480(7), C(7)ϪC(19)

1.495(7), C(9)ϪC(20) 1.489(7), C(2)ϪC(1)ϪC(7)ϪC(13) 7.8(8),

C(4)ϪC(3)ϪC(9)ϪC(15) Ϫ6.2(7), C(2)ϪC(1)ϪC(19)ϪCl(2) 8.6(6),

C(6)ϪC(1)ϪC(19)ϪCl(1) Ϫ0.6(6)

The ‘‘pseudo-para’’ compound 23 crystallizes with im-

posed inversion symmetry (Figure 7). The ring displays an

almost ideal chair conformation, with absolute torsion

angles of 53Ϫ54°. Bond lengths follow the pattern estab-

lished above, in that bonds without syn-periplanar interac-

tions are shorter [e.g. C4ϪC10 1.494(2), C3ϪC2Ј 1.497(2)

˚

A]. The crystal packing shows only one unusual contact,

the weak^[26]hydrogen bond C8ϪH8a···Cl2, with H···Cl 2.78

˚

A, angle 139°, via the n glide plane; this connects the mol-

ecules into layers parallel to (101) (Figure 8).

Scheme 8. Carbene addition to hexamethyl[6]radialene (2a) and do-

decamethyl[6]radialene (2c)

Whereas the structure of 20 follows from the spectroscopic

and analytical data (see Exp. Sect.), the structures of the bis-

adducts were determined by X-ray structural analysis.

The ‘‘pseudo-meta’’-substituted compound 22 (Figure 6)

crystallizes without imposed symmetry. Because of the

somewhat lower precision, comparison of the bond lengths

of the three-membered rings is less meaningful, but the

CH(Me)ϪCCl₂bonds are the shortest, corresponding to

the situation in 19a and 19b. The other bonds may be affec-

ted by the steric pressure of the chlorine substituents and

also the extra methyl group. The conformation of the six-

membered ring approximates well to a twist form with the

local twofold axis through C2 and C5, but the axis does not

hold for the methyl groups C14,16,17,18. The shortest

bonds in the ring, C4ϪC5 and C5ϪC6, are those not in-

volved in syn-periplanar contacts. There are no unusually

short intermolecular contacts.

Figure 7. The molecule of compound 23 in the crystal; ellipsoids

represent 50% probability levels; hydrogen radii are arbitrary; selec-

˚

ted molecular dimensions (A,°): C(1)ϪC(3) 1.505(2), C(1)ϪC(2)

1.506(2), C(1)ϪC(10) 1.535(2), C(1)ϪC(4) 1.541(2), C(2)ϪC(3)#1

1.497(2), C(4)ϪC(10) 1.494(2), C(3)ϪC(1)ϪC(4)ϪC(7) Ϫ9.3(2),

C(3)ϪC(1)ϪC(10)ϪCl(1) Ϫ7.4(2), C(2)ϪC(1)ϪC(10)ϪCl(2) 0.8(2)

2602

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[6]Radialenes Revisited

FULL PAPER

Figure 8. Packing diagram for compound 23 seen perpendicular to

(10Ϫ1); weak hydrogen bonds CH···Cl are shown as broken lines

Since, once more, no further cyclopropane derivatives

could be isolated from the product mixture, the reactivity

of the carbene was increased further by use of the diiodo-

methane/trimethylaluminium reagent.^[27]As hoped, mul-

tiple addition of methylene carbene occurred, as demon-

strated by GC/MS analysis, but only the monoadduct 21

could be isolated in poor yield (8%) by thick layer chroma-

tography on silica gel.

Scheme 9. Epoxidation of hexamethyl[6]radialene (2a) and dodeca-

methyl[6]radialene (2c)

The fully methylated [6]radialene 2c did not react with

dichloro- or dibromocarbene. Changing to the more reac-

tive methylene carbene, generated as above, provided two

products: the monoadduct 24 (47%) and a bisadduct 25

(Scheme 8). The X-ray structure analysis of 25 was unfortu-

nately again accompanied by severe disorder problems. We

propose the trans orientation of the cyclopropane rings, in

analogy with structure 23 of the dichlorocarbene adduct

of 2a.

29. The structure elucidation of the three epoxides 27؊29

rests largely on their H NMR spectra (see Exp. Sect.), the

1

number of methyl signals being of particular diagnostic

value (6 for 27, 3 for 28, and 12 for 29). The relative orien-

tation of the three-membered rings is unproven, since we

could not obtain suitable crystals for X-ray structural

analysis for either of these adducts.

Miscellaneous Additions to [6]Radialenes

Epoxidation of [6]Radialenes

The epoxidation of 2a with one equivalent of meta-

In their classical studies on [6]radialenes, Hopff and

chloroperbenzoic acid (MCPBA) at 0 °C furnished the Wick^[7]reported that 2a reacts with hydrochloric acid in

monoadduct 26 in 12% yield, together with several bis- acetic acid/diethyl ether to provide a single adduct, the tri-

epoxides and higher oxidation products as shown by GC/ chloride 30, in 66% yield. Since there is no a priori reason

MS analysis. Epoxide 26 was separated by medium pressure why only this regioisomer should be produced, we decided

chromatography on an octyl-derivatized silica gel phase, but to repeat the addition experiment under the original con-

the higher adducts turned out to be inseparable. Purifi- ditions. In fact, RP-HPLC analysis quickly showed that at

cation on neutral aluminium oxide had to be abandoned least five adducts were produced, all of which had practi-

because of poor separation efficiency, and on normal silica cally identical UV spectra, each with an absorption maxi-

gel the epoxides decomposed by ring-opening (Scheme 9).

mum at 220 nm. GC/MS analysis showed that three equiva-

Epoxidation of the less reactive permethyl derivative 2c lents of hydrochloric acid had been added to the radialene,

was more successful. With one equivalent of MCPBA at 0 but chromatographic separation on a preparative scale

°C a mixture consisting of the starting material 2c, the failed. We therefore subjected the product mixture to de-

mono-epoxide 27, and the bis-epoxide 28, produced in 1:2:1 hydrochlorination with potassium tert-butoxide in diethyl-

ratio, was obtained. Separation was again accomplished on eneglycol dimethyl ether. Triple elimination occurred readily

octyl-derivatized silica gel. Working with two equivalents and provided a 1:1-mixture of the 1,3,5- and the 1,2,4-trivi-

of the epoxidizing agent at 0 °C provided the bis-adduct nyl benzene derivatives 9 and 10, respectively (Scheme 10).

exclusively, and only at higher temperature (20 °C) and with

Clearly, an isomer of 30 must have been present in the

a large excess of MCPBA was the tris-adduct 29 produced. original mixture, in the form of the trichloride 31, both iso-

Clearly, the rate of oxidation is decreasing with increasing mers evidently being formed as mixtures of diastereomers.

degree of epoxidation; in fact, in no experiment were we

Very little is currently known about the potential for the

able to isolate a product possessing more oxirane rings than use of radialenes as ligands for metal organic compounds.

Eur. J. Org. Chem. 2003, 2596Ϫ2611

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2603

T. Höpfner, P. G. Jones, B. Ahrens, I. Dix, L. Ernst, H. Hopf

FULL PAPER

diode array detector with octadecyl-derivatized silica gel LiChros-

phere^100 RP-18 (5 µm). GC: DANI 86.10 HT with a capillary

column OV1-50 m with hydrogen as carrier gas; prep. GC: Shim-

adzu GC-8A and a packed SE-54 column. ¹H NMR: Bruker DMX

600, Bruker AM 400, and Bruker AC 200F at 600, 400, and

200 MHz, resp., in deuteriochloroform with TMS as int. standard.

¹³C NMR (¹H broad-band decoupled): Bruker AM 300 at

75.47 MHz, Bruker AM 400 and Bruker AC 200 F at 100.6 and

50.3 MHz, resp. in deuteriochloroform with δ(CDCl₃) ϭ 77.05 as

int. standard; the degree of substitution of the carbon atoms was

determined by employing the DEPT-135 technique; signal assign-

ment by H,H-COSY, H,H-NOE-difference, C,H-correlation, and

C,H-COLOC spectra. MS: Finnigan MAT 8340, EI (70 eV), FAB.

GC/MS: CarloϪErba HRGC 5160 with a DB1-30W capillary col-

umn and helium as carrier gas/Finnigan MAT 4515 (EI, 70 eV).

IR: Nicolet 320 FT-IR. UV: HP 8452 A Diode Array Spectropho-

tometer. GC/FT-IR: CarloϪErba HRGC 5160 with a DB1-30W

capillary column and helium as carrier gas/Nicolet 740 FT-IR spec-

trometer. Elemental analyses: Institute of Inorganic and Analytical

Chemistry, Technical University of Braunschweig. Literature pro-

cedures were used for the preparation of: hexakis(1-bromoethyl)-

benzene (1a),^[6,7]7,8,9,10,11,12-hexamethyl[6]radialene (2a),^[6,7]do-

decamethyl[6]radialene (2c),^[9]and hexakis(bromomethyl)benzene

(18).^[11]

1. A New Diastereomer of 7,8,9,10,11,12-Hexamethyl[6]radialene

(cccaca-2a): A nBuLi solution in hexane (1.6 , 44.9 mL, 72 mmol)

was added at 0 °C to a suspension of 1a (10.80 g, 15 mmol) in

anhydrous THF (300 mL). The mixture was warmed to room temp.

and stirred overnight, and the reaction was terminated by the ad-

dition of water (7.5 mL) and diethyl ether (300 mL). The reaction

mixture was washed carefully with water (4 ϫ 150 mL) and dried

with sodium sulfate, and the solvent was removed by distillation.

Silica gel (6 g) was added to the residue (4.98 g), and the resulting

mixture was prepurified by column chromatography (350 g SiO₂,

pentane). One of the fractions yielded product (650 mg), which was

subjected to multiple (fourfold) preparative thick layer chromatog-

raphy on silica gel with hexane, the central third of a product zone

always being used for the next chromatography step. Radialene 2a

was concentrated at the beginning of each zone, whereas further

isomers were concentrated at its end. Finally, cccaca-2a (22 mg,

0.7%) was obtained as a colorless oil. IR (film): ν˜ ϭ 3023 cm^Ϫ1

(m), 2972 (s), 2933 (s), 2912 (s), 2875 (m), 2856 (s), 1443 (s), 1375

Scheme 10. Miscellaneous reactions of hexamethyl[6]radialene (2a)

The first use of 2a for such a purpose was described by

Wilke and co-workers,^[18]who obtained the η⁶-stabilized o-

quinodimethane complex 32 in 83% yield on treatment of

this radialene with tris(acetonitrile)tricarbonylchromium in

dioxane at room temperature. On heating in dioxane under

carbon monoxide, metal complex 32 fragments and re-

arranges to the trivinylbenzene derivative 9, the yield again

being excellent (95%). When we heated 2a with [Fe(CO)₅]

in boiling dibutyl ether, only rearranged products (of unde-

(m), 1065 (m), 1035 (m), 984 (m), 877 (m), 862 (m), 848 (s), 831

1

termined structure) were obtained. Under milder conditions (s), 781 (w). H NMR (CDCl₃, 600 MHz): see Table 1; all CH

have q and all CH₃have d multiplicity, J ϭ 6.8Ϫ7.0 Hz. ¹³C NMR

(125 MHz, CDCl₃): δ ϭ 14.6 ppm (2 C), 14.7, 14.9, 15.5, 15.6

(CH₃), 116.2, 118.6, 120.3, 120.9, 121.1, 122.9 (ϭCHϪ), 135.9,

139.4 (2 C), 139.7, 141.4, 144.7 (ϭCϽ). UV (hexane): λ_max(lg ε) ϭ

206 nm (4.40). GC/MS (70 eV): m/z (%) ϭ 241 (19), 240 (100) [M^ϩ],

225 (37) [M^ϩϪ CH₃], 211 (41), 210 (11), 197 (40), 196 (64), 195

(21), 183 (39), 182 (50), 181 (60), 180 (13), 179 (24), 178 (18), 169

(45), 168 (32), 167 (59), 166 (27), 165 (57), 155 (37), 154 (17), 153

(31), 152 (22), 142 (12), 141 (27), 129 (16), 128 (22), 115 (19).

HRMS: C₁₈H₂₄: calcd. 240.18780, found 240.187Ϯ3 ppm.

{[Fe₂(CO)₉] in refluxing THF}, however, the η⁴complex 33

could be obtained, in which the radialene structure of the

ligand is maintained. At only 7%, the isolated yield of 33

was poor, one reason being extensive product loss during

the chromatographic purification of the metal complex. The

fully methylated hydrocarbon 2c did not react with

[Fe(CO)₅] in boiling dibutyl ether.

Experimental Section

2. Thermolysis of Hexamethyl[6]radialene (2a). a) On a Preparative

Scale at 300 °C: A sample of 2a (150 mg, 0.62 mmol) was placed

in a 200 mL glass ampoule, and this was sealed after evacuation

(0.1 Torr). After having been heated for 1 h at 300 °C, the pyrolys-

ate was separated by thick-layer chromatography (silica gel, hex-

ane) into two fractions: fraction 1 (26 mg, 17%) 1,3,5-triethenyl-

General: Melting points: Büchi melting point apparatus (Dr. Tot-

toli), uncorrected. Chromatography: TLC: MachereyϪNagel Poly-

gram Sil G/UV₂₅₄, Polygram Alox N/UV₂₅₄; SC: Merck Kieselgel

60 (230Ϫ400 mesh); octyl-derivatized silica gel: Knauer Europrep

˚

60Ϫ30 C8 (60 A, 20Ϫ45 µ); neutral aluminium oxide, activity I;

preparative thick layer chromatography: Merck Kieselgel PF 254/ 2,4,6-triethylbenzene (9), analytical and spectroscopic data ident-

366. HPLC: Merck L 6200 Intelligent Pump with a L 3000 photo ical with the authentic hydrocarbon obtained as described below

2604

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Eur. J. Org. Chem. 2003, 2596Ϫ2611

[6]Radialenes Revisited

FULL PAPER

by dehydrochlorination of 30/31; fraction 2 (35 mg, 23%): (E)- and

(Z)-4,6-diethenyl-5,7-diethyl-1,2-dihydro-1,2-dimethylbenzocyclo-

(s, C_ArϪCHϭCH₂), 137.49 (s, C_Ar), 136.60 (d, CHϭCH₂), 136.51

(s, C_Ar), 136.39 (d, CHϭCH₂), 135.12 (s, C_Ar), 135.03 (s, C_Ar),

butene in 1:1.3 ratio. Preparative gas chromatography (3m SE 54 133.20 (s, C_Ar), 131.62 (s, C_Ar), 131.01 (s, C_ArϪCHϭCH), 129.72

column, 200 °C, carrier gas H₂) furnished the analytically pure dia-

stereomers: a) Compound 5 (2.5 mg, 1.6%), colorless oil. GC/IR:

ν˜ ϭ 3088 cm^Ϫ1(w), 2969 (s), 2936 (m), 2903 (m), 2881 (m), 1316

(w), 1299 (w), 1069 (w), 993 (w), 922 (w). ¹H NMR (400 MHz):

(s, C_ArϪCHϭCH), 128.32 (d, CHϭCHϪCH₂), 127.79 (d, CHϭ

CHϪCH₂), 125.38 (d, CHϭCHϪCH₂), 125.34 (d, CHϭ

CHϪCH₂), 118.83 (t, CHϭCH₂), 118.69 (t, CHϭCH₂), 24.51 (t,

C

_ArϪCH₂ϪCH₂), 24.33 (t, C_ArϪCH₂ϪCH₂), 23.46 (t, CH₂ϪCH₃),

23.16 (t, 2 C, CH₂ϪCH₃), 23.00 (t, CHϭCH-CH₂), 22.94 (t, CHϭ

6.76 (dd, J_15,16Јϭ 17.9, J_15,16ϭ 11.3 Hz, 1 H, 15-H), 5.54 (dd, CHϪCH₂), 22.79 (t, CH₂ϪCH₃), 21.91 (t, CH₂ϪCH₃), 21.55 (t,

3

δ ϭ 6.83 ppm (dd, J_11,12Јϭ 17.6, J_11,12ϭ 11.2 Hz, 1 H, 11-H),

3

³J_12Ј,11ϭ 17.6, J_12Ј,12ϭ 2.0 Hz, 1 H, 12-HЈ), 5.47 (dd, J_16,15

ϭ

CH₂ϪCH₃), 15.63 (q, CH₃), 15.24 (q, 2 C, CH₃), 15.19 (q, CH₃),

14.94 (q, CH₃), 14.51 (q, CH₃), 2 quaternary carbon atoms could

not be identified. GC/MS (70 eV): m/z (%) ϭ 241 (18), 240 (100)

3

11.3, J_16,16Јϭ 2.3 Hz, 1 H, 16-H), 5.34 (dd, J_12,11ϭ 11.2,

³J_12,12Јϭ 2.0 Hz, 1 H, 12-H), 5.19 (dd, J_16Ј,15ϭ 17.9, J_16Ј,16

ϭ

3

2.3 Hz, 1 H, 16-HЈ), 3.16 (qd, J_2,10ϭ 7.0, J_2,1ϭ 2.0 Hz, 1 H, 2- [M^ϩ], 225 (49) [M^ϩϪ CH₃], 212 (16), 211 (97) [M^ϩϪ C₂H₅], 197

3

2

H), 3.01 (qd, ³J_1,9ϭ 7.0, ²J_1,2ϭ 2.0 Hz, 1 H, 1-H), 2.69 (q, ³J_13,14ϭ

(19), 196 (23), 195 (11), 183 (33), 182 (22), 181 (29), 179 (20), 178

3

7.5 Hz, 2 H, 13-H), 2.55 (q, J_17,18ϭ 7.6 Hz, 2 H, 17-H), 1.43 (d, (18), 169 (26), 168 (15), 167 (45), 166 (26), 165 (53), 155 (29), 154

³J_9,1ϭ 7.0 Hz, 3 H, 9-H), 1.39 (d, ³J_10,2ϭ 7.0 Hz, 3 H, 10-H), 1.10

(13), 153 (26), 152 (20), 141 (18), 128 (13), 115 (12).

3

(t, J_18,17ϭ 7.6 Hz, 3 H, 18-H), 1.07 (t, J_14,13ϭ 7.5 Hz, 3 H, 14-

H). ¹³C NMR (100.6 MHz): δ ϭ 144.05 ppm (s), 144.00 (s), 138.60

(s), 136.88 (s), 136.52 (s), 135.49 (d), 132.45 (d), 129.39 (s), 118.94

(t), 117.13 (t), 46.39 (d), 45.65 (d), 23.44 (t), 22.46 (t), 18.15 (q),

16.13 (q), 14.97 (q), 14.96 (q). GC/MS (70 eV): m/z (%) ϭ 241 (12),

240 (60) [M^ϩ], 226 (18), 225 (100) [M^ϩϪ CH₃], 212 (14), 211 (77)

[M^ϩϪ C₂H₅], 210 (12), 197 (49), 196 (61), 195 (16), 183 (40), 182

(41), 181 (48), 180 (13), 179 (23), 178 (21), 169 (37), 168 (29), 167

(58), 166 (33), 165 (69), 155 (34), 154 (18), 153 (38), 152 (29), 141

(26), 129 (14), 128 (22), 115 (19). b) Compound 6 (3.7 mg, 2.5%),

colorless oil. GC/IR: ν˜ ϭ 3086 cm^Ϫ1(w), 2973 (s), 2940 (m), 2907

(m), 2882 (m), 1030 (w), 993 (w), 922 (w). ¹H NMR (400 MHz):

Chemical Structure Confirmation for 11a/11b. 2-Ethenyl-1,3,4-trie-

thylnaphthalene: A sample of 2a (120 mg, 0.5 mmol) was thermo-

lyzed for 1 h at 360 °C as described above. The pyrolysate was dis-

solved in toluene (5 mL), DDQ (136 mg, 0.6 mmol) was added, and

the mixture was heated for 1 h at 100 °C. After solvent removal in

vacuo, column chromatography on silica gel with pentane yielded

the aromatic hydrocarbon (100 mg, 84%) as a colorless oil. IR

(film): ν˜ ϭ 3075 cm^Ϫ1(m), 2967 (s), 2932 (m), 2899 (m), 2873 (m),

1465 (m), 1452 (m), 1377 (m), 923 (m), 909 (m), 759 (s), 734 (m).

¹H NMR (400 MHz): δ ϭ 8.15Ϫ8.00 ppm (m, 2 H, 5-H, 8-H),

3

7.48Ϫ7.41 (m, 2 H, 6-H, 7-H), 6.97 (dd, J_13,14Јϭ 17.9, J_13,14

ϭ

δ ϭ 6.84 ppm (dd, J_11,12Јϭ 17.6, J_11,12ϭ 11.2 Hz, 1 H, 11-H),

3

2

3

11.4 Hz, 1 H, 13-H), 5.58 (dd, J_14,13ϭ 11.4, J_14,14Јϭ 2.1 Hz, 1

6.76 (dd, J_15,16Јϭ 17.9, J_15,16ϭ 11.3 Hz, 1 H, 15-H), 5.56 (dd,

3

2

³J_12Ј,11ϭ 17.6, J_12Ј,12ϭ 2.0 Hz, 1 H, 12-HЈ), 5.47 (dd, J_16,15

ϭ

2

3

H, 14-H), 5.27 (dd, J_14Ј,13ϭ 17.9, J_14Ј,14ϭ 2.1 Hz, 1 H, 14-HЈ),

3

2

3

3.12 (q, J_11,12ϭ 7.5 Hz, 2 H, 11-H), 3.11 (q, J_17,18ϭ 7.5 Hz, 2

H, 17-H), 2.84 (q, J_15,16ϭ 7.5 Hz, 2 H, 15-H), 1.31 (t, J_18,17

11.3, J_16,16ЈJ_16,16Јϭ 2.3 Hz, 1 H, 16-H), 5.35 (dd, J_12,11ϭ 11.2,

3

²J_12,12Јϭ 2.0 Hz, 1 H, 12-H), 5.19 (dd, J_16Ј,15ϭ 17.9, J_16Ј,16

ϭ

3

2

ϭ

3

2.3 Hz, 1 H, 16-HЈ), 3.75 (qd, ³J_2,10, ²J_2,1ϭ 6.9 Hz, 1 H, 2-H), 3.62

7.5 Hz, 3 H, 18-H), 1.25 (t, J_12,11ϭ 7.5 Hz, 3 H, 12-H), 1.15 (t,

³J_16,15ϭ 7.5 Hz, 3 H, 16-H). ¹³C NMR (100.6 MHz): δ ϭ 137.31

ppm (s, C-3), 136.65 (d, C-13), 136.47 (s, C-2), 135.59 (s, C-1),

134.82 (s, C-4), 131.58 (s, C-10), 130.67 (s, C9), 125.14 (d, C-6 or

C-7), 125.02 (d, C-5 or C-8), 124.67 (d, C-6 or C-7), 124.52 (d, C-

5 or C8), 119.18 (t, C-14), 23.71 (t, C-15), 22.94 (t, C-11), 21.54 (t,

C-17), 15.55 (q, 2C, C-12 and C-18), 14.92 (q, C-16). UV (hexane):

λ_max(lg ε) ϭ 238 nm (4.80), 294 (3.81). GC/MS (70 eV): m/z (%) ϭ

239 (14), 238 (79) [M^ϩ], 223 (33) [M^ϩϪ CH₃], 210 (17), 209 (100)

[M^ϩϪ C₂H₅], 195 (20), 194 (34), 193 (16), 181 (29), 180 (21), 179

(66), 178 (59), 167 (29), 166 (26), 165 (70), 153 (16), 152 (17), 115

(10). 1,2,3,4-Tetraethyl-5,6,7,8-tetrahydronaphthalene: A sample of

2a (120 mg, 0.5 mmol) was pyrolyzed for 1 h at 360 °C as described

above. The pyrolysate was dissolved in methanol (20 mL), Pd/C

(10%, 50 mg) was added, and the mixture was hydrogenated for 4 h

at room temp. under normal pressure. After filtration and solvent

removal, the tetralin (122 mg, 99%) was obtained as a colorless oil.

3

(qd, J_1,9

,

²J_2,1, 1 H, 1-H), 2.69 (q, J_13,14ϭ 7.5 Hz, 2 H, 13-H),

3

2.61Ϫ2.52 (m, 2 H, 17-H, 17-HЈ), 1.29 (d, J_9,1ϭ 7.5 Hz, 3 H, 9-

3

H), 1.27 (d, J_10,2ϭ 7.2 Hz, 3 H, 10-H), 1.10 (t, J_18,17ϭ 7.6 Hz,

3 H, 18-H), 1.06 (t, J_14,13ϭ 7.5 Hz, 3 H, 14-H). ¹³C NMR

3

(100.6 MHz): δ ϭ 145.33 ppm (s), 145.18 (s), 138.67 (s), 136.94 (s),

136.46 (s), 135.46 (d), 132.60 (d), 129.31 (s), 118.97 (t), 117.20 (t),

40.57 (d), 39.68 (d), 23.46 (t), 22.63 (t), 14.99 (q), 14.90 (q), 13.98

(q), 11.94 (q). GC/MS (70 eV): m/z (%) ϭ 241 (12), 240 (61) [M^ϩ],

226 (18), 225 (100) [M^ϩϪ CH₃], 212 (14), 211 (78) [M^ϩϪ C₂H₅],

210 (12), 197 (49), 196 (62), 195 (16), 183 (41), 182 (42), 181 (49),

180 (13), 179 (24), 178 (20), 169 (37), 168 (29), 167 (61), 166 (33),

165 (69), (34), 154 (18), 153 (38), 152 (30), 141 (26), 129 (14), 128

(23), 115 (20).

b) On a Preparative Scale at 360 °C: A sample of 2a (120 mg,

0.50 mmol) was placed in a 200 mL glass ampoule, and this was

sealed after evacuation (0.1 Torr) After having been heated for 1 h IR (film): ν˜ ϭ 2966 cm^Ϫ1(s), 2931 (s), 2904 (s), 2871 (s), 2835 (m),

at 360 °C the pyrolysate was separated by thick layer chromatogra-

phy (silica gel, hexane), to provide an inseparable mixture of 11a NMR (400 MHz): δ ϭ 2.78Ϫ2.71 ppm (m, 4 H, 5-H, 8-H), 2.66

1463 (m), 1451 (m), 1436 (m), 1376 (m), 1054 (m), 819 (w). ¹H

and 11b (76 mg, 63%) as a colorless oil. ¹H NMR (400 MHz): δ ϭ

(q, J ϭ 7.5 Hz, 4 H, 11-H, 17-H), 2.62 (q, J ϭ 7.5 Hz, 4 H, 13-

3

6.82 ppm (dd, J ϭ 17.8, J ϭ 11.5 Hz, 1 H, CHϭCH₂), 6.80 (dd, H, 15-H), 1.80Ϫ1.75 (m, 4 H, 6-H, 7-H), 1.18 (t, ³J ϭ 7.5 Hz, 4 H,

³J ϭ 17.7, ³J ϭ 11.6 Hz, 1 H, CHϭCH₂), 6.75 (dt, ³J could not

12-H, 18-H), 1.14 (t, ³J ϭ 7.5 Hz, 4 H, 14-H, 16-H). ¹³C NMR

(100.6 MHz): δ ϭ 138.08 ppm (s), 137.31 (s), 133.13 (s), 27.11 (t),

4

be determined because of signal overlap, J ϭ 1.8 Hz, 1 H, CHϭ

CHϪCH₂), 6.72 (dt, ³J undeterminable, ⁴J ϭ 1.8 Hz, 1 H, CHϭ 23.29 (t), 22.04 (t), 21.76 (t), 15.94 (q), 14.54 (q). UV (hexane):

3

CHϪCH₂), 6.10 (dt, J ϭ 9.9, J ϭ 4.9 Hz, 1 H, CHϭCHϪCH₂), λ_max(lg ε) ϭ 214 nm (4.61), 432 (sh, 4.07), 276 (2.57). GC/MS

6.08 (dt, ³J ϭ 9.8, ³J ϭ 4.9 Hz, 1 H, CHϭCHϪCH₂), 5.48 (dd, (70 eV): m/z (%) ϭ 245 (19), 244 (100) [M^ϩ], 230 (16), 229 (88)

³J ϭ 11.3, J ϭ 2.5 Hz, 1 H, H), 5.47 (dd, J ϭ 11.4, J ϭ 2.4 Hz, [M^ϩϪ CH₃], 216 (16), 215 (90) [M^ϩϪ C₂H₅], 201 (14), 200 (12),

1 H), 5.20 (dd, ³J ϭ 17.9, ²J ϭ 2.3 Hz, 2 H, HЈ), 2.80Ϫ2.60 (m, 16

187 (29), 185 (17), 173 (34), 171 (19), 159 (20), 157 (21), 156 (12),

H, CH₂), 2.27Ϫ2.20 (m, 4 H, CHϭCHϪCH₂), 1.21Ϫ1.03 (m, 18 155 (16), 145 (17), 143 (27), 142 (18), 141 (19), 131 (18), 129 (32),

2

3

2

H, CH₃). ¹³C NMR (100.6 MHz): δ ϭ 138.85 ppm (s, C_Ar), 137.61

128 (23), 117 (12), 115 (13), 105 (11).

Eur. J. Org. Chem. 2003, 2596Ϫ2611

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2605

T. Höpfner, P. G. Jones, B. Ahrens, I. Dix, L. Ernst, H. Hopf

FULL PAPER

3. Thermolysis of Dodecamethyl[6]radialene (2c): A sample of 2c

(108 mg, 0.3 mmol) was pyrolyzed for 1 h at 350 °C as described

above. The pyrolysate was separated by silica gel thick layer chro-

matography and the least polar fraction was sublimed under high

vacuum to afford 1,2-dihydro-1,1,2,2-tetramethy-4,6-bis(methyle-

NMR (100.6 MHz): δ ϭ 147.40 ppm (s, C-2), 145.30 (s, C-7),

140.03 (s, C-1), 137.55 (s, C-3), 134.04 (s, C-6), 131.23 (s, C-15),

124.90 (s, C-13), 115.43 (t, C-8), 30.95 (d, C-10), 24.83 (q, C-11),

24.02 (q, C-14), 23.96 (q, C-9), 23.03 (q, C-12), 22.64 (q, C-16).

UV (hexane): λ_max(lg ε) ϭ 192 nm (4.46), 224 (4.25), 290 (4.00).

thenyl)-5,7-bis(methylethyl)lbenzocyclobutene (12, 18 mg, 17%) as a MS (70 eV): m/z (%) ϭ 325 (11), 324 (41) [M^ϩ], 310 (25), 309 (100),

colorless solid, m.p. 192 °C. IR (KBr): ν˜ ϭ 3075 cm^Ϫ1(w), 2959

281 (36), 267 (16), 266 (11), 253 (17), 251 (22), 239 (16), 237 (11),

(s), 2923 (s), 2877 (m), 1636 (m), 1449 (m), 1371 (m), 897 (s), 790 225 (51), 223 (21), 211 (43), 197 (14), 183 (14). HRMS: C₂₄H₃₆,

1

(w). H NMR (400 MHz, C₂D₂Cl₄, 100 °C): δ ϭ 5.23Ϫ5.20 ppm calcd. 324.28170, found 324.281Ϯ2 ppm.

2

4

(m, 2 H, 14-H, 20-H), 4.87 (dq, J_14Ј,14ϭ 2.6, J_14Ј,15ϭ 0.9 Hz, 1

2

4

Fraction 3. Dodecamethyl[6]radialene (14): Twist boat conformation

(62 mg, 19%), colorless solid m.p. after recryst. from dichlorometh-

ane: 213Ϫ218 °C (decomp.). IR (KBr): ν˜ ϭ 2992 cm^Ϫ1(m), 2980

(m), 2918 (s), 2850 (s), 1452 (m), 1434 (m), 1367 (m), 1029 (w), 967

(w), 950 (w). ¹H NMR (400 MHz): δ ϭ 1.69 ppm (br. s, 12 H),

1.54 (br. s, 12 H), 1.48 (br. s, 12 H). ¹³C NMR (100.6 MHz): δ ϭ

137.44 ppm (s), 136.37 (s), 127.46 (s), 122.57 (s), 23.57 (q), 21.82

(q), 21.73 (q). UV (hexane): λ_max(lg ε) ϭ 224 nm (4.60). MS

(70 eV): m/z (%) ϭ 325 (28), 324 (100) [M^ϩ], 309 (63), 281 (25),

267 (11), 253 (11), 251 (12), 239 (11), 225 (25), 211 (20), 197 (11),

183 (11). HRMS: C₂₄H₃₆, calcd. 324.28170, found.

324.281Ϯ2 ppm. When the irradiation was terminated after 4 min,

isomer 15 could also be isolated from the pyrolysate by thick layer

chromatography. From 4 runs (65 mg 2c, 0.2 mmol) in 200 mL of

hexane a total amount of 50 mg (19%) 1-methylethenyl-2-methyl-

ethyl-3,4,5,6-tetrakis(methylethylidene)cyclohexene (15) was isolated

as a colorless oil. IR (film): ν˜ ϭ 3077 cm^Ϫ1(w), 2988 (m), 2962 (s),

2921 (s), 2907 (s), 2852 (s), 1454 (m), 1437 (m), 1368 (m), 889 (m),

H, 14-HЈ), 4.79 (dq, J_20Ј,20ϭ 2.6, J_20Ј,21ϭ 0.8 Hz, 1 H, 20-HЈ),

3.25 [br. s, 1 H, CH(CH₃)₂], 3.07 [sept, ³J ϭ 7.1 Hz, 1 H,

4

CH(CH₃)₂], 2.09 (dd, J_15,14ϭ 1.3, J_15,14Јϭ 0.9 Hz, 3 H, 15-H),

4

2.00 (dd, J_21,20ϭ 1.3, J_21,20Јϭ 0.9 Hz, 3 H, 21-H), 1.35 (s, 3 H,

cyclobutene-CH₃), 1.34 (s, 3 H, cyclobutene-CH₃), 1.31 (d, ³J ϭ

3

7.3 Hz, 3 H, CH₃-CH-CH₃), 1.28 (d, J ϭ 7.2 Hz, 3 H, CH₃-CH-

CH₃), 1.28 (s, 3 H, cyclobutene-CH₃), 1.25 (s, 3 H, cyclobutene-

CH₃), 1.25 (d, ³J ϭ 7.1 Hz, 3 H, CH₃-CH-CH₃), 1.16 (d, ³J ϭ

6.9 Hz, 3 H, CH₃-CH-CH₃). ¹³C NMR (100.6 MHz, C₂D₂Cl₄, 100

°C): δ ϭ 148.52 ppm, 146.74, 146.05, 144.57, 140.86, 139.98,

136.02, 116.41 (t, C-14 or C-20), 115.24 (t, C-14 or C-20), 49.83,

47.72, 31.88, 26.68, 26.46, 25.33, 25.07, 24.22, 23.71; six ¹³C signals

could not be identified. UV (hexane): λ_max(lg ε) ϭ 204 nm (4.65),

226 (sh, 4.13), 280 (3.00). MS (70 eV): m/z (%) ϭ 325 (10), 324 (34)

[M^ϩ], 310 (25), 309 (100) [M^ϩϪ CH₃], 281 (11), 267 (10), 253 (11),

225 (19), 211 (25). HRMS: C₂₄H₃₆, calcd. 324.28170, found

324.281Ϯ2 ppm.

4. Photolysis of Dodecamethyl[6]radialene (2c): A solution of 2c

(324 mg, 1 mmol) in freshly distilled hexane (340 mL) was ir-

radiated with a low-pressure mercury lamp (Heraeus TNN 15/32,

15W) for 20 min at room temp. in an immersion well photoreactor.

The solvent was removed in a rotary evaporator and the remaining

oil was separated by silica gel thick layer chromatography with hex-

ane. The obtained fractions were subjected to further thick layer

chromatographic purification (silica gel, pentane) to provide, be-

sides starting material (120 mg, 37%), three fractions.

2

816 (w). ¹H NMR (400 MHz): δ ϭ 4.97 ppm (dq, J_8,8Јϭ 2.9,

2

4

⁴J_8,9ϭ 1.4 Hz, 1 H, 8-H or 8-HЈ), 4.93 (dq, J_8,8Јϭ 2.9, J_8,9

ϭ

0.9 Hz, 1 H, 8-H or 8-HЈ), 3.07 (sept, ³J ϭ 6.9 Hz, 1 H, 10-H),

1.76 (s, 3 H, 9-H), 1.73 (s, 3 H, CH₃), 1.71 (s, 3 H, CH₃), 1.67 (s,

3 H, CH₃), 1.65 (s, 3 H, CH₃), 1.61 (s, 3 H, CH₃), 1.59 (s, 3 H,

3

CH₃), 1.52 (s, 3 H, CH₃), 1.50 (s, 3 H, CH₃), 1.10 (d, J ϭ 7.0 Hz,

3 H, 11-H or 12-H), 0.80 (d, J ϭ 6.8 Hz, 3 H, 11-H or 12-H). ¹³C

3

NMR (100.6 MHz): δ ϭ 145.64 ppm (s, C-2), 144.13 (s, C-1 or C-

7), 140.26 (s, C-1 or C-7), 137.13 (s), 136.59 (s), 136.57 (s), 136.47

(s), 125.77 (s), 124.33 (s), 114.06 (t, C-8), 31.83 (d, C-10), 24.69 (q),

24.62 (q), 24.29 (q), 23.99 (q), 23.78 (q), 23.54 (q, C-11 or C-12),

23.25 (q, C-9), 22.97 (q, C-11 or C-12), 22.35 (q), 22.16 (q), 20.05

(q); two olefinic C atoms could not be identified. UV (hexane):

λ_max(lg ε) ϭ 222 nm (4.47), 256 (4.20). MS (70 eV): m/z (%) ϭ 325

(24), 324 (91) [M^ϩ], 310 (26), 309 (100) [M^ϩϪ CH₃], 282 (13), 281

(56), 267 (24), 266 (12), 253 (19), 251 (21), 239 (21), 225 (48), 224

(15), 223 (20), 211 (34), 210 (11), 209 (15), 197 (16), 183 (17), 169

(10). HRMS: C₂₄H₃₆, calcd. 324.28170, found 324.281Ϯ2 ppm.

Fraction 1. 1,4-Bis(methylethenyl)-2,5-bis(methylethyl)-3,6-bis(me-

thylethylidene)cyclohexa-1,4-diene (17): 13 mg, 4%, colorless solid,

m.p. 100Ϫ105 °C (decomp.). IR (KBr): ν˜ ϭ 2987 cm^Ϫ1(s), 2963

(s), 2935 (s), 2923 (s), 2910 (s), 2870 (m), 1633 (m), 1448 (m), 1366

1

(m), 922 (w), 904 (s), 821 (w), 811 (w). H NMR (400 MHz): δ ϭ

3

5.09Ϫ5.03 ppm (m, 4 H, H-8, H-8Ј), 2.93 (dq, ³J₁ϭ 7.07, J₂

ϭ

6.99 Hz, 2 H, H-10), 1.85Ϫ1.83 (m, 6 H, H-9), 1.72 (s, 6 H, H-14),

1.69 (s, 6 H, H-15), 1.18 (d, ³J₂ϭ 6.99 Hz, 6 H, H-11 or H-12), 1.10

(d, ³J₁ϭ 7.07 Hz, 6 H, H-11 or H-12). ¹³C NMR (100.6 MHz): δ ϭ

145.60 ppm (s, C-2), 144.48 (s, C-1 or C-7), 142.03 (s, C-1 or C-7),

137.26 (s, C-3), 127.71 (s, C-13), 116.14 (t, C-8), 32.35 (d, C-10),

25.68 (q, C-11 or C-12), 25.15 (q, C-15), 24.06 (q, C-9), 23.05 (q,

C-11 or C-12), 21.42 (q, C-14). UV (hexane): λ_max(lg ε) ϭ 192 nm

(4.38), 224 (4.20), 294 (4.03). MS (70 eV): m/z (%) ϭ 325 (29), 324

(100) [M^ϩ], 323 (16), 310 (24), 309 (94), 281 (30), 267 (13), 266

(14), 251 (27), 239 (14), 237 (14), 225 (42), 223 (30), 211 (30), 209

(19). HRMS: C₂₄H₃₆, calcd. 324.28170, found 324.281Ϯ2 ppm.

5. Dichlorocarbene Addition to [6]Radialene (2d): A solution of

methyllithium in diethyl ether (1.6 , 30 mL, 48 mmol) was added

at Ϫ85 °C over 1 h to a suspension of hexakis(bromomethyl)ben-

zene (18, 7.63 g, 12.0 mmol) in anhydrous THF (130 mL). The re-

action mixture was allowed to warm to Ϫ45 °C over 2 h, stirred

for 30 min at this temperature, and again cooled to Ϫ85 °C. After

2-propanol (1.5 mL) and potassium tert-butoxide (20.2 g, 0.18 mol)

had been added, a solution of chloroform (21.5 g, 0.18 mol) in

anhydrous THF (70 mL) was slowly added. The mixture was al-

Fraction 2. 1,5-Bis(methylethenyl)-2,4-bis(methylethyl)-3,6-bis(me-

thylethylidene)cyclohexa-1,4-diene (16): 51 mg, 16%, colorless solid; lowed to warm to Ϫ40 °C within 2 h and left standing at Ϫ20 °C

m.p. after recryst. from dichloromethane/acetone: 130Ϫ135 °C (de-

overnight. For workup the reaction mixture was poured onto ice

(400 g), and after neutralization with acetic acid, sodium chloride

comp.). IR (KBr): ν˜ ϭ 3078 cm^Ϫ1(m), 2965 (s), 2925 (s), 2909 (s),

2869 (s), 2854 (s), 1626 (m), 1451 (m), 1438 (m), 1378 (m), 1367 (100 g) and diethyl ether (400 mL) were added. The phases were

(s), 904 (s). ¹H NMR (400 MHz): δ ϭ 5.05Ϫ5.01 ppm (m, 4 H, H-

separated, the aqueous phase was washed thoroughly with two

8, H-8Ј), 3.10 (dq, ³J₁ϭ 7.10, ³J₂ϭ 6.90 Hz, 2 H, H-10), 1.83Ϫ1.80 100 mL portions of ether, and the organic phases were united,

(m, 6 H, H-9), 1.72 (s, 6 H, H-16), 1.67 (s, 6 H, H-14), 1.16 (d,

washed with brine, and dried with sodium sulfate. After solvent

removal, the residue (7.63 g) was adsorbed on silica gel (14 g) and

³J₁ϭ 7.10 Hz, 6 H, H-12), 1.07 (d, ³J₂ϭ 6.90 Hz, 6 H, H-11). ¹³

C

2606

 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjoc.org

Eur. J. Org. Chem. 2003, 2596Ϫ2611

[6]Radialenes Revisited

FULL PAPER

prepurified by column chromatography (400 g of silica gel, pen-

tane/dichloromethane ϭ 4:1 (v/v)). One fraction yielded (E)-

1,1,7,7-tetrachloro-4,5,9,10-tetramethylidenedispiro[2.2.2.2]decane

(19a, 69 mg, 2%, after recrystallization from hexane/dichlorometh-

(KBr): ν˜ ϭ 3057 cm^Ϫ1(w), 3024 (m), 2999 (m), 2977 (s), 2954 (s),

2936 (s), 2913 (s), 2874 (m), 2855 (s), 1452 (s), 1438 (s), 1372 (m),

1337 (m), 1034 (m), 985 (s), 974 (m), 851 (s), 844 (s), 827 (s), 822

(s), 798 (s), 757 (m). ¹H NMR (400 MHz): δ ϭ 5.48 ppm (q,

3

ane) as a colorless solid, m.p. 160 °C (decomp.). IR (KBr): ν˜ ϭ ³J_16,17ϭ 7.0 Hz, 1 H, 16-H), 5.45 (q, J_14,15ϭ 7.0 Hz, 1 H, 14-H),

3097 cm^Ϫ1(w), 1637 (m), 1416 (s), 1300 (m), 1062 (s), 1035 (s),

5.37 (q, J_18,19ϭ 7.2 Hz, 1 H, 18-H), 5.36 (q, J_10,11ϭ 6.9 Hz, 1

3

1

3

1012 (m), 941 (m), 910 (s), 757 (s), 742 (s). H NMR (400 MHz): H, 10-H), 5.30 (q, J_12,13ϭ 7.1 Hz, 1 H, 12-H), 2.09 (q, J_2,9

ϭ

δ ϭ 5.35 ppm (d, ²J_11Ј,11ϭ 0.68 Hz, 4 H, 11-HЈ), 4.97 (d, ²J_11Ј,11ϭ

6.8 Hz, 1 H, 2-H), 1.86 (d, J_13,12ϭ 7.1 Hz, 3 H, 13-H), 1.83 (d,

3

0.65 Hz, 4 H, 11-H), 2.03 (s, 4 H, 2-H). ¹³C NMR (100.6 MHz): ³J_15,14ϭ 7.0 Hz, 3 H, 15-H), 1.77 (d, J_17,16ϭ 7.0 Hz, 3 H, 17-H),

3

δ ϭ 144.70 ppm (s, C-4), 113.66 (t, C-11), 64.79 (s, C-1), 43.41 (s,

1.76 (d, J_19,18ϭ 7.1 Hz, 3 H, 19-H), 1.65 (d, J_11,10ϭ 6.8 Hz, 3

C-3), 25.44 (t, C-2). UV (acetonitrile): λ_max(lg ε) ϭ 198 nm (4.36), H, 11-H), 1.49 (d, J_9,2ϭ 6.8 Hz, 3 H, 9-H). ¹³C NMR

3

240 nm (3.86). MS (70 eV): m/z (%) ϭ 326 (0.9), 325 (0.9), 324

(100.6 MHz): δ ϭ 139.91 ppm (s, C-6), 139.80 (s, C-4), 138.99 (s,

(3.8), 323 (1.7), 322 (7.5), 321 (2.1), 320 (5.8) [M^ϩ], 289 (10), 288 C-8), 138.55 (s, C-5), 138.50 (s, C-7), 123.35 (d, C-18), 122.76 (d,

(20), 287 (30), 286 (51), 285 (33), 284 (49) [M^ϩϪ HCl], 253 (11), C-12), 122.36 (d, C-16), 121.82 (d, C-14), 119.67 (d, C-10), 69.68

252 (27), 251 (53), 250 (58), 249 (78), 248 (36) [M^ϩϪ 2 HCl], 216 (s, C-1), 43.42 (s, C-3), 34.94 (d, C-2), 15.15 (q, C-15), 15.12 (q, C-

(31), 215 (55), 214 (91), 213 (100), 212 (7) [M^ϩϪ 3 HCl], 200 (11),

17), 14.96 (q, C-13), 14.41 (q, C-11), 13.95 (q, C-19), 12.02 (q, C-

199 (12), 180 (25), 179 (91), 178 (92), 177 (19), 176 (16), 165 (31), 9). UV (acetonitrile): λ_max(lg ε) ϭ 194 nm (4.33). MS (70 eV): m/

153 (19), 152 (42), 151 (17), 139 (12). HRMS: C₁₄H₁₂Cl₄: calcd.

321.966452; found 321.966Ϯ3 ppm.

z (%) ϭ 322 (10) [M^ϩ], 309 (16), 307 (25) [M^ϩϪ CH₃], 293 (13),

289 (30), 288 (21), 287 (94) [M^ϩϪ Cl], 272 (15), 271 (22) [M^ϩ

Ϫ

HCl Ϫ CH₃], 260 (11), 259 (29), 258 (22), 257 (30), 252 (19), 251

(47) [M^ϩϪ Cl Ϫ HCl], 245 (15), 244 (12), 243 (34), 242 (13), 237

(40), 236 (32), 235 (28), 231 (22), 229 (17), 224 (29), 223 (100), 222

(63), 221 (53), 215 (11), 209 (32), 208 (38), 207 (70), 206 (25), 205

(20), 203 (15), 196 (13), 195 (43), 194 (38), 193 (62), 192 (37), 191

(39), 190 (15), 189 (19), 181 (29), 180 (25), 179 (53), 178 (43), 167

(27), 166 (26), 165 (64), 155 (12), 153 (28), 152 (28). HRMS:

C₁₉H₂₄Cl₂, calcd. 322.125508, found. 322.125Ϯ2 ppm.

6. Dibromocarbene Addition to [6]Radialene (2d): This preparation

was as described above for the dichlorocarbene reaction, but by use

of 18 (6.36 g, 10.0 mmol) and a solution of methyllithium in diethyl

ether (1.6 , 25 mL, 40.0 mmol) diluted with anhydrous THF

(100 mL), potassium tert-butoxide (16.83 g, 0.15 mol), and bromo-

form (37.91 g, 0.15 mol) in anhydrous THF (70 mL), yielding (E)-

1,1,7,7-tetrabromo-4,5,9,10-tetramethylidenedispiro[2.2.2.2]decane

(19b, 243 mg, 5%) as colorless needles after chromatography and

recrystallization from dichloromethane, m.p. 184 °C (decomp.). IR

(KBr): ν˜ ϭ 3095 cm^Ϫ1(w), 1635 (m), 1420 (s), 1408 (m), 1066 (s),

1024 (s), 999 (m), 939 (m), 914 (s), 751 (s), 702 (s), 616 (s). ¹H

Fraction 2. (E)-1,1,6,6-Tetrachloro-4,8,9,10-tetraethylidene-2,7-di-

methylbispiro[2.1.2.3]decane (22): 68 mg, 17%, colorless solid, m.p.

141.5 °C. IR (KBr): ν˜ ϭ 3096 cm^Ϫ1(w), 2999 (m), 2962 (m), 2934

(s), 2913 (s), 2875 (m), 2855 (m), 1453 (s), 1373 (m), 835 (s), 817

(s), 778 (s), 737 (s). ¹H NMR (400 MHz): δ ϭ 5.83 ppm (q,

2

NMR (400 MHz): δ ϭ 5.43 ppm (d, J_11Ј,11ϭ 0.67 Hz, 4 H, 11-

2

HЈ), 5.01 (d, J_11Ј,11ϭ 0.63 Hz, 4 H, 11-H), 2.23 (s, 4 H, 2-H). ¹³C

NMR (100.6 MHz): δ ϭ 145.45 ppm (s, C-4), 114.73 (t, C-11),

42.42 (s, C-1), 35.62 (s, C-3), 27.63 (t, C-2). UV (acetonitrile): λ_max

(lg ε) ϭ 192 nm (4.36). MS (70 eV): m/z (%) ϭ 422 (1), 420 (5), 418

(5), 416 (1) [M^ϩϪ HBr], 342 (20), 341 (17), 340 (43), 339 (27), 338

(24), 337 (12) [M^ϩϪ HBr Ϫ Br], 260 (23), 259 (16), 258 (24), 257

(9) [M^ϩϪ2 HBr Ϫ Br], 180 (47), 179 (100), 178 (67). MS (CI,

NH₃, pos.): m/z (%) ϭ 520 (4), 518 (5), 516 (4) [M ϩ NH₄^ϩ], 505

(10), 503 (41), 502 (11), 501 (62), 499 (42), 497 (11) [M ϩ H^ϩ], 424

(15), 423 (23), 422 (46), 421 (41), 420 (56), 419 (33), 418 (30), 417

(10), 416 (5) [M Ϫ Br^Ϫ], 358 (29), 356 (35), 354 (15) [M Ϫ HBr Ϫ

Br^Ϫϩ NH₃], 343 (38), 342 (56), 341 (88), 340 (100), 339 (72), 338

(52), 337 (19) [M Ϫ HBr Ϫ Br^Ϫ], 261 (22), 260 (35), 259 (32), 258

(30), 257 (12) [M Ϫ 2 HBr Ϫ Br^Ϫ], 181 (11), 180 (53), 179 (84), 178

(46). C₁₄H₁₂Br₄(499.86): calcd. C 33.64, H 2.42; found C 33.39, H

2.31.

3

³J_19,20ϭ 7.2 Hz, 1 H, 19-H), 5.54 (q, J_17,18ϭ 7.1 Hz, 1 H, 17-H),

3

5.49 (q, J_15,16ϭ 7.0 Hz, 1 H, 15-H), 5.19 (q, J_12,13ϭ 7.4 Hz, 1

3

H, 12-H), 2.39 (q, J_7,14ϭ 6.7 Hz, 1 H, 7-H), 2.24 (q, J_2,11

6.9 Hz, 1 H, 2-H), 1.90 (d, J_16,15ϭ 7.0 Hz, 3 H, 16-H), 1.88 (d,

ϭ

3

J_18,17ϭ 7.1 Hz, 3 H, 18-H), 1.83 (d, J_20,19ϭ 7.2 Hz, 3 H, 20-H),

3

1.73 (d, J_13,12ϭ 7.4 Hz, 3 H, 3-H), 1.51 (d, J_11,2ϭ 6.9 Hz, 3 H,

11-H), 1.34 (d, ³J_14,7ϭ 6.7 Hz, 3 H, 14-H). ¹³C NMR 100.6 MHz):

δ ϭ 139.28 ppm (s, C-9), 139.11 (s, C-10), 136.60 (s, C-4), 136.00

(s, C-8), 128.80 (d, C-19), 126.15 (d, C-15), 122.97 (d, C-17), 122.05

(d, C-12), 73.54 (s, C-1), 71.73 (s, C-6), 45.97 (s, C-5), 42.26 (s, C-

3), 36.26 (d, C-2), 33.29 (d, C-7), 15.58 (q, C-16), 15.35 (q, C-18),

15.21 (q, C-20), 14.53 (q, C-13), 12.74 (q, C-14), 9.43 (q, C-11).

UV (acetonitrile): λ_max(lg ε) ϭ 212 nm (4.31). MS (CI, NH₃, pos.):

m/z (%) ϭ 411 (10), 410 (11), 409 (48), 408 (22), 407 (100), 406

(11), 405 (78) [M ϩ H]^ϩ, 373 (21), 372 (11), 371 (48), 370 (11), 369

(42) [M Ϫ Cl]^ϩ, 337 (32), 336 (12), 335 (50), 333 (14) [M Ϫ Cl

Ϫ HCl]^ϩ.

7. Dichlorocarbene Addition to Hexamethyl[6]radialene (2a): Aque-

ous sodium hydroxide solution (10%, 7 mL) was added at Ϫ10 °C

to a solution of 2a (240 mg, 1 mmol) and benzyltriethylammonium

chloride (46 mg, 0.2 mmol) in pentane (20 mL) and chloroform

(10 mL). After stirring for 2 h at Ϫ10 °C, the mixture was poured

onto water (50 mL) and ice (100 g), the phases were separated, and

the aqueous layer was extracted with diethyl ether (3 ϫ 40 mL).

The combined organic phases were neutralized and dried with so-

dium sulfate, and the solvent was removed in vacuo. Preparative

thick layer chromatography with hexane yielded 2a (40 mg, 17%)

and crude addition mixture, which was resubmitted to chromatog-

raphy (aluminium oxide, activity 1; pentane), providing two frac-

tions.

Fraction 3. 1,1,7,7-Tetrachloro-4,5,9,10-tetraethylidene-2,8-dimeth-

ylbispiro[2.2.2.2]decane (23): 4 mg, 1%, colorless, poorly soluble

solid, m.p. 220 °C (decomp.). IR (KBr): ν˜ ϭ 3067 cm^Ϫ1(w), 2984

(m), 2954 (s), 2928 (m), 2914 (m), 1454 (s), 1438 (s), 987 (m), 966

1

(m), 853 (m), 830 (s), 810 (s), 774 (m), 671 (m), 641 (s). H NMR

(400 MHz): δ ϭ 5.52 ppm (q, ³J_12,13ϭ 7.0 Hz, 2 H, 12-H), 5.45 (q,

3

³J_14,15ϭ 7.3 Hz, 2 H, 14-H), 2.16 (q, J_2,11ϭ 6.9 Hz, 2 H, 2-H),

3

1.81 (d, J_15,14ϭ 7.3 Hz, 6 H, 15-H), 1.63 (d, J_13,12ϭ 7.0 Hz, 6

H, 13-H), 1.57 (d, J_11,2ϭ 6.9 Hz, 6 H, 11-H). A ¹³C NMR spec-

3

trum could not be registered because of the poor solubility of 23

in CDCl₃. UV (acetonitrile): λ_max(lg ε) ϭ 192 nm (4.23), 196

(4.22), 204 (4.15). MS (70 eV): m/z (%) ϭ 404 (1) [M^ϩ], 371 (34),

Fraction 1. 1,1-Dichloro-4,5,6,7,8-pentaethylidene-2-methylspi-

ro[2.5]octane (20): 25 mg, 8%, colorless solid, m.p. 114 °C. IR 369 (35) [M^ϩϪ Cl], 335 (24), 334 (16), 333 (34) [M^ϩϪ Cl Ϫ HCl],

Eur. J. Org. Chem. 2003, 2596Ϫ2611

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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

2607

T. Höpfner, P. G. Jones, B. Ahrens, I. Dix, L. Ernst, H. Hopf

FULL PAPER

321 (11), 319 (19), 307 (26), 306 (14), 305 (39), 300 (11), 299 (29), C-10), 121.52 (s, C-13), 41.66 (s, C-3 or C-1), 30.83 (s, C-1 or C-

298 (31), 297 (54) [M^ϩϪ Cl Ϫ 2 HCl], 285 (11), 284 (13), 283 (26), 3), 25.26 (q, C-9), 24.01 (t, C-2), 22.92 (q, C-11), 22.12 (q, C-12),

282 (11), 272 (16), 271 (47), 270 (47), 269 (100), 268 (20), 267 (11),

21.70 (q, C-15 or C-17), 21.00 (q, C-14 and C-15 or C-17). UV

263 (37), 262 (34), 261 (34), 257 (11), 256 (14), 255 (26), 254 (15), (hexane): λ_max(lg ε) ϭ 196 nm (4.44), 234 (4.22). MS (70 eV): m/z

253 (14), 249 (11), 248 (16), 247 (31), 246 (14), 243 (17), 242 (14), (%) ϭ 339 (22), 338 (79) [M^ϩ], 324 (27), 323 (100), 296 (11), 295

241 (33), 240 (11), 235 (33), 234 (37), 233 (54), 232 (24), 231 (20). (41), 281 (21), 280 (12), 265 (15), 253 (16), 239 (35), 238 (11), 237

C₂₀H₂₄Cl₄, calcd. 404.0632, found 404.063Ϯ2 ppm.

(19), 225 (22), 224 (11), 223 (12), 211 (24), 209 (15), 197 (20).

C₂₅H₃₈(338.58): calcd. C 88.69, H 11.31; found C 88.33, H 11.67.

8. Cyclopropanation of Hexamethyl[6]radialene (2a): A solution of

trimethylaluminium (2 , 3.6 mL, 7.2 mmol) in toluene was added Fraction 3: 1,1,7,7-Tetramethyl-4,5,9,10-tetrakis(methylethylidene)-

at Ϫ10 °C to a solution of 2a (240 mg, 1 mmol) and diiodomethane dispiro[2.2.2.2]decane (25): 48 mg, 27%, as a colorless solid, m.p.

(2.68 g, 10 mmol) in pentane (75 mL). After stirring for 3 h, the

250 °C (decomp.). IR (KBr): ν˜ ϭ 3063 cm^Ϫ1(w), 3013 (m), 2980

mixture was allowed to warm to 0 °C and the reaction was termin-

ated by the addition of aqueous sodium hydroxide (10%, 20 mL). (m), 1368 (s), 1125 (m), 1088 (s), 1032 (m), 988 (m), 734 (m). H

(s), 2951 (s), 2921 (s), 2907 (s), 2867 (s), 2852 (s), 1452 (m), 1441

1

The phases were separated, the aqueous phase was extracted with

NMR (400 MHz): δ ϭ 1.80 ppm (s, 12 H, 13-H), 1.44 (s, 12 H, 14-

pentane (3 ϫ 10 mL), and the combined organic phases were neu- H), 1.25 (s, 12 H, 11-H), Ϫ0.10 (s, 4 H, 2-H). ¹³C NMR

tralized and dried with sodium sulfate. The solvent and excess di-

iodomethane were removed in vacuo (0.1 Torr), and the remaining

oil was fractionated by preparative thick layer chromatography (sil-

ica gel) with hexane to yield 4,5,6,7,8-pentaethylidene-1-methylspi-

(100.6 MHz): δ ϭ 139.09 ppm (s, C-4), 121.25 (s, C-12), 43.09 (s,

C-3 or C-1), 31.49 (s, C-1 or C-3), 25.25 (q, C-11), 23.09 (t, C-2),

22.45 (q, C-13), 22.20 (q, C-14). UV (hexane): λ_max(lg ε) ϭ 194 nm

(4.44). MS (70 eV): m/z (%) ϭ 352 (23), 338 (28) [M^ϩ], 337 (100),

ro[2.5]octane (21, 20 mg, 8%) as a colorless oil. IR (KBr): ν˜ ϭ 3073 310 (14), 309 (48), 295 (23), 294 (12), 281 (20), 279 (25), 267 (15),

cm^Ϫ1(w), 2995 (s), 2974 (s), 2932 (s), 2914 (s), 2858 (s), 1444 (s), 253 (39), 252 (11), 251 (20), 239 (22), 238 (11), 237 (13), 225 (29),

1390 (m), 1375 (m), 1095 (m), 1035 (m), 991 (m), 864 (m), 848 (s), 224 (11), 223 (19), 211 (36), 210 (11), 209 (16), 197 (22), 195 (15),

832 (m), 817 (m). ¹H NMR (400 MHz): δ ϭ 5.37 ppm (q, ³J ϭ

193 (12), 183 (22), 181 (11), 179 (12). C₂₅H₃₈(338.58): calcd. C

3

7.0 Hz, 1 H), 5.30 (q, ³J ϭ 6.8 Hz, 1 H), 5.24 (q, J ϭ 6.9 Hz, 1 88.57, H 11.43; found C 88.31, H: 11.69.

3

H), 5.19 (q, J ϭ 7.0 Hz, 1 H), 5.12 (q, J ϭ 7.1 Hz, 1 H), 1.81 (d,

10. Epoxidation of Hexamethyl[6]radialene (2a): A solution of 2a

(240 mg, 1 mmol) and 3-chloroperbenzoic acid (69%, 250 mg,

1 mmol) in chloroform (25 mL) was stirred for 90 min at Ϫ10 °C.

Ether was added (50 mL) and the reaction mixture washed thor-

oughly with sodium carbonate solution (10%, 3 ϫ 20 mL). The

organic phase was neutralized and dried with sodium sulfate, the

solvent was removed in vacuo, and the remaining oil was chromato-

graphed on octyl-derivatized silica gel with methanol/water (85:15,

v/v): besides starting material (9 mg), 4,5,6,7,8-pentaethylidene-9-

methyl-1-oxaspiro[2.5]octane (26, 30 mg, 12%) was isolated as a col-

orless solid m.p. 102 °C. IR (KBr): ν˜ ϭ 3024 cm^Ϫ1(w), 2988 (m),

2968 (s), 2928 (s), 2914 (s), 2871 (m), 2855 (s), 1441 (m), 1376 (m),

1368 (m), 995 (m), 986 (m), 911 (m), 870 (m), 862 (m), 848 (s), 832

(s), 827 (m), 783 (m). ¹H NMR (400 MHz): δ ϭ 5.50 ppm (q,

³J ϭ 7.0 Hz, 3 H), 1.80 (d, ³J ϭ 6.9 Hz, 3 H), 1.71 (d, ³J ϭ 7.0 Hz,

3 H), 1.71 (d, J ϭ 6.9 Hz, 3 H), 1.70 (d, J ϭ 6.7 Hz, 3 H), 1.28

(br. s, 1 H, 2-H), 0.87 (d, J_9,1ϭ 6.1 Hz, 3 H, 9-H), 0.77 (br. s, 1

3

H, 2-H), 0.56 (br. s, 1 H, 1-H). ¹³C NMR (100.6 MHz): δ ϭ 141.95

ppm (s), 141.58 (s), 140.80 (s), 140.47 (s), 140.36 (s), 120.82 (d),

120.53 (d), 119.44 (d), 118.76 (d), 116.50 (d), 34.27 (s, C-3), 18.37

(d, C-1), 17.28 (t, C-2), 14.69 (q), 14.66 (q), 14.54 (q), 14.42 (q),

14.10 (q), 13.82 (q). UV (hexane): λ_max(lg ε) ϭ 198 nm (4.32). GC/

MS (70 eV): m/z (%) ϭ 254 (8) [M^ϩ], 240 (19), 239 (100) [M^ϩ

Ϫ

CH₃], 226 (12), 225 (66), 211 (51), 210 (76), 209 (23), 197 (38), 196

(48), 195 (74), 193 (13), 184 (11), 183 (65), 182 (47), 181 (85), 180

(25), 179 (43), 178 (24), 170 (14), 169 (78), 168 (31), 167 (54), 166

(35), 165 (75), 156 (14), 155 (54), 154 (25), 153 (43), 152 (26), 143

(13), 142 (16), 141 (39), 129 (24), 128 (29), 115 (23), 105 (11), 91

(27), 79 (11), 77 (23). HRMS: C₁₉H₂₆, calcd. 254.2035, found

254.203Ϯ3 ppm.

3

³J_10,11ϭ 7.0 Hz, 1 H, 10-H), 5.40 (q, J ϭ 6.9 Hz, 1 H), 5.39 (q,

³J ϭ 7.0 Hz, 1 H), 5.29 (q, ³J ϭ 7.0 Hz, 1 H), 5.27 (q, ³J ϭ 7.1 Hz,

3

1 H), 2.90 (q, J_2,9ϭ 5.3 Hz, 1 H, 2-H), 1.88 (d, ³J ϭ 7.1 Hz, 3

3

9. Cyclopropanation of Dodecamethyl[6]radialene (2c): A solution

of 2c (162 mg, 0.5 mmol) and diiodomethane (1.34 g, 5 mmol) in

pentane (40 mL) was treated with a solution of trimethylaluminium

H), 1.81 (d, J ϭ 6.7 Hz, 3 H), 1.79 (d, J ϭ 6.5 Hz, 3 H), 1.75 (d,

³J ϭ 6.9 Hz, 3 H), 1.75 (d, J_11,10ϭ 7.0 Hz, 3 H, 11-H), 1.12 (d,

3

³J_9,2ϭ 5.3 Hz, 3 H, 9-H). ¹³C NMR (100.6 MHz): δ ϭ 139.24 ppm

(2 , 2 mL, 4 mmol) in toluene, and the reaction mixture was (s), 138.90 (s, C-4), 138.43 (s), 137.47 (s), 135.43 (s), 122.53 (d),

stirred for 4 h at room temp. The methylenation was terminated by

the addition of aqueous sodium hydroxide solution (20%, 20 mL),

the phases were separated, and the aqueous phase was extracted

with ether (2 ϫ 20 mL). After the combined organic layers had

been neutralized and dried (sodium sulfate), the solvent was re-

moved under vacuum and the product mixture was fractionated by

thick layer chromatography (silica gel, pentane): Fraction 1: sub-

strate (18 mg, 11%).

122.00 (d), 121.72 (d), 121.29 (d), 117.75 (d, C-10), 67.95 (s, C-3),

60.59 (d, C-2), 14.84 (q), 14.61 (q), 14.47 (q), 13.84 (q, C-11), 13.09

(q, C-9), 13.02 (q). UV (hexane): λ_max(lg ε) ϭ 194 nm (4.39). MS

(70 eV): m/z (%) ϭ 257 (16), 256 (71) [M^ϩ], 242 (19), 241 (100)

[M^ϩϪ CH₃], 228 (12), 227 (60), 226 (11), 213 (40), 212 (55), 211

(16), 199 (30), 198 (27), 197 (37), 185 (24), 184 (16), 183 (26), 182

(15), 181 (11), 171 (17), 169 (22), 168 (19), 167 (27), 166 (12), 165

(24), 157 (16), 156 (11), 155 (26), 154 (14), 153 (26), 152 (17), 143

(14), 142 (12), 141 (20), 129 (15), 128 (17), 115 (16).

Fraction 2. 1,1-Dimethyl-4,5,6,7,8-pentakis(methylethylidene)spi-

ro[2.5]octane (24): 79 mg, 47%, as a colorless solid, m.p. 240 °C 11. Mono- and Bis-Epoxidation of Dodecamethyl[6]radialene (2c): A

(decomp.). IR (KBr): ν˜ ϭ 3057 cm^Ϫ1(w), 3011 (m), 2986 (s), 2977 solution of 3-chloroperbenzoic acid (64 mg, 0.25 mmol) in CH₂Cl₂

(s), 2956 (m), 2923 (s), 2908 (s), 2853 (s), 1456 (m), 1439 (m), 1367 (2 mL) was slowly added at Ϫ22 °C to a solution of 2c (81 mg,

(m), 1142 (m), 1125 (m), 1096 (m), 1072 (m), 981 (m). ¹H NMR 0.25 mmol) in CH₂Cl₂(5 mL). After the reaction mixture had been

(400 MHz): δ ϭ 1.78 ppm (s, 3 H, 11-H), 1.63 (s, 6 H, H-15, H-

stirred for 1 h at Ϫ22 °C, sodium carbonate solution (10%, 5 mL)

17), 1.55 (s, 3 H, 12-H), 1.50 (s, 3 H, 14-H), 1.26 (s, 3 H, 9-H), was added and the mixture was diluted with CH₂Cl₂(40 mL) and

Ϫ0.05 (s, 2 H, 2-H). ¹³C NMR (100.6 MHz): δ ϭ 138.69 ppm (s, water (40 mL). The aqueous phase was extracted with CH₂Cl₂(2

C-5), 137. 82 (s, C-6), 137.53 (s, C-4), 122.71 (s, C-16), 122.46 (s, ϫ 20 mL), and the combined organic phases were neutralized and

2608

 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjoc.org

Eur. J. Org. Chem. 2003, 2596Ϫ2611

[6]Radialenes Revisited

FULL PAPER

dried with sodium sulfate. After solvent removal the residue was

separated on RP-8-silica gel with methanol/water (9:1, v/v), yield-

ing two fractions.

GC/MS (70 eV): m/z (%) ϭ 372 (0.5) [M^ϩ], 299 (39), 271 (27), 243

(20), 241 (19), 229 (23), 215 (16), 213 (18), 201 (15), 199 (14), 198

(14), 187 (18), 185 (16), 173 (16), 171 (18), 159 (16), 157 (14), 135

(11), 133 (14), 121 (11), 119 (15), 107 (16), 105 (17), 93 (11), 91

(17), 43 (100). No HRMS could be obtained because of the very

low intensity of the molecular ion signal.

Fraction 1. 2,2-Dimethyl-4,5,6,7,8-pentakis(methylethylidene)-1-ox-

aspiro[2.5]octane (27): 40 mg, 47%, colorless solid, m.p. 248 °C (de-

comp.). IR (KBr): ν˜ ϭ 2985 cm^Ϫ1(s), 2966 (m), 2958 (m), 2927 (s),

2910 (s), 2852 (s), 1453 (s), 1442 (s), 1375 (s), 1367 (s), 1245 (m), 13. 1,3,5-Triethenyl-2,4,6-triethylbenzene (9) and 1,2,4-Triethenyl-

1137 (m), 1117 (m), 1100 (s), 875 (s), 801 (m). ¹H NMR (400 MHz):

3,5,6-triethylbenzene (10): A stream of hydrogen chloride was

δ ϭ 1.77 ppm (s, 6 H, 11-H), 1.67 (s, 6 H, 15-H), 1.65 (s, 6 H, 17- passed through a solution of 2a (120 mg, 0.5 mmol) in diethyl ether

H), 1.59 (s, 6 H, 12-H), 1.54 (s, 6 H, 14-H), 1.41 (s, 6 H, 9-H). ¹³C

(15 mL) and acetic acid (2 mL) at Ϫ22 °C for 30 min. The reaction

NMR (100.6 MHz): δ ϭ 136.71 ppm (s, C-6), 135.14 (s, C-5), mixture was diluted cautiously with ice water (40 mL) and ex-

134.75 (C-4), 125.79 (C-13), 123.39 (s, C-16), 122.92 (s, C-10), 73.20 tracted several times with ether. The combined organic phases were

(s, C-3), 69.72 (s, C-2), 23.23 (q, C-9), 22.39 (q, C-11), 21.65 (q, C-

17), 21.52 (q, C-12), 21.17 (q, C-15), 20.88 (q, C-14). UV (hexane):

neutralized with sodium carbonate solution and dried with sodium

sulfate. After solvent removal the residual oil was taken up in dieth-

λ_max(lg ε) ϭ 194 nm (4.46), 236 (4.22). MS (70 eV): m/z (%) ϭ 341 yleneglycol dimethyl ether (5 mL), potassium tert-butoxide

(17), 340 (60) [M^ϩ], 326 (16), 325 (58) [M^ϩϪ CH₃], 323 (23), 322 (336 mg, 3 mmol) was added, and the mixture was heated for 2 h

(90) [M^ϩϪ H₂O], 308 (11), 307 (42), 297 (25), 283 (16), 282 (11),

at 100 °C. After the mixture had cooled to room temp., water was

269 (20), 268 (22), 267 (100), 255 (12), 241 (16), 239 (39), 237 (17), added (30 mL), the mixture was extracted thoroughly with diethyl

225 (42), 224 (24), 223 (17), 213 (11), 210 (16), 209 (30), 207 (12), ether, and the combined organic phases, after neutralization, were

199 (12), 197 (17), 196 (11), 195 (15), 194 (11), 193 (14), 185 (14), dried with sodium sulfate. After solvent removal under vacuum,

181 (11), 179 (14), 171 (14), 169 (11), 167 (11), 165 (14), 157 (13), preparative thick layer chromatography (silica gel, hexane) fur-

105 (13). HRMS: C₂₄H₃₆O: calcd. 340.2766, found

nished two fractions.

340.276Ϯ2 ppm.

Fraction 1: 1,3,5-Triethenyl-2,4,6-triethylbenzene (9): 22 mg, 18%),

colorless solid, m.p. 56.5 °C (ref.^[18]55Ϫ56 °C). IR (KBr): ν˜ ϭ 3087

Fraction 2. 2,2,8,8-Tetramethyl-4,5,9,10-tetrakis(methylethylidene)-

1,7-dioxadispiro[2.2.2.2]decane (28): 25 mg, 28%, colorless solid,

m.p. 245 °C (decomp.). IR (KBr): ν˜ ϭ 3005 cm^Ϫ1(m), 2982 (m),

2970 (m), 2956 (m), 2927 (s), 2912 (s), 2855 (m), 1454 (m), 1442

(m), 1381 (m), 1369 (m), 1116 (m), 1100 (m), 972 (m). ¹H NMR

(400 MHz): δ ϭ 1.72 ppm (s, 12 H), 1.49 (s, 12 H, 13-H), 1.26 (s, HЈ), 2.67 (q, J_9,10ϭ 7.4 Hz, 6 H, 9-H), 1.01 (t, J_10,9ϭ 7.4 Hz, 9

12 H). ¹³C NMR (100.6 MHz): δ ϭ 133.96 ppm (s), 126.61 (s), H, 10-H). ¹³C NMR (100.6 MHz): δ ϭ 138.79 ppm (s, C-1), 135.76

74.14 (s, C-3 or C-2), 67.10 (s, C-2 or C-3), 25.94 (q), 23.07 (q), (s, C-2), 135.76 (d, ¹J_C,Hϭ 154 Hz, C-7), 119.04 (t, ¹J_C,Hϭ 156 Hz,

21.91 (q). UV (hexane): λ_max(lg ε) ϭ 192 nm (4.23), 216 (4.29).

MS (70 eV): m/z (%) ϭ 356 (22) [M^ϩ], 342 (21), 341 (74) [M^ϩ

CH₃], 338 (14) [M^ϩϪ H₂O], 324 (12), 323 (42), 313 (29), 299 (12), (4.47). MS (70 eV): m/z (%) ϭ 241 (12), 240 (64) [M^ϩ], 226 (18),

298 (22), 297 (22), 295 (19), 285 (14), 284 (22), 283 (100), 271 (14),

225 (100) [M^ϩϪ CH₃], 212 (13), 211 (70) [M^ϩϪ C₂H₅], 210 (11),

cm^Ϫ1(m), 3001 (m), 2976 (s), 2942 (m), 2882 (m), 995 (m), 924

3

(m), 840 (w). ¹H NMR (400 MHz): δ ϭ 6.79 ppm (dd, J_7,8Ј

ϭ

3

2

17.9, J_7,8ϭ 11.3 Hz, 3 H, 7-H), 5.48 (dd, J_8,7ϭ 17.9, J_8,8Ј

ϭ

3

2

2.3 Hz, 3 H, 8-H), 5.23 (dd, J_8Ј,7ϭ 11.3, J_8Ј,8ϭ 2.3 Hz, 3 H, 8-

3

1

2

1

C-8), 24.03 (t, J_C,Hϭ 127, J_C,Hϭ 4 Hz, C-9), 14.51 (q, J_C,Hϭ

2

Ϫ

127, J_C,Hϭ 5 Hz, C-10). UV (hexane): λ_max(lg ε) ϭ 220 nm

257 (12), 256 (12), 255 (50), 253 (14), 241 (26), 240 (11), 239 (11), 197 (50), 196 (46), 183 (37), 182 (27), 181 (34), 179 (11), 178 (12),

227 (24), 225 (25), 213 (26), 211 (12), 210 (12), 199 (23), 197 (12), 169 (28), 168 (19), 167 (37), 166 (20), 165 (39), 155 (23), 154 (11),

195 (11), 185 (14), 171 (15). C₂₄H₃₆O₂: calcd. 356.27153, found 153 (22), 141 (14).

356.271Ϯ2 ppm.

Fraction 2. 1,2,4-Triethenyl-3,5,6-triethylbenzene (10): 26 mg, 22%,

12. Threefold Epoxidation of Dodecamethyl[6]radialene (2c): A solu-

tion of 3-chloroperbenzoic acid (256 mg, 1 mmol) in CH₂Cl₂

(4 mL) was slowly added to a solution of 2c (81 mg, 0.25 mmol) in

CH₂Cl₂(5 mL), and the mixture was stirred for 1 h at 20 °C. The

oxidation was terminated by addition of sodium carbonate solu-

tion (10%, 5 mL), and a mixture of CH₂Cl₂(40 mL) and water

colorless solid, m.p. 58 °C. IR (KBr): ν˜ ϭ 3078 cm^Ϫ1(m), 2965 (s),

2931 (s), 2895 (m), 2871 (s), 1629 (m), 1464 (m), 1452 (m), 1436

(m), 1368 (m), 1289 (m), 991 (s), 916 (s), 837 (m). ¹H NMR

3

(400 MHz): δ ϭ 6.82 ppm (dd, J_13,14Јϭ 17.9, J_13,14ϭ 11.3 Hz, 1

3

H, 13-H), 6.71 (dd, J_7,8Јϭ 18.0, J_7,8ϭ 11.4 Hz, 1 H, 7-H), 6.69

(dd, J_9,10Јϭ 17.9, J_9,10ϭ 11.4 Hz, 1 H, 9-H), 5.49 (dd, J_14,13

3

ϭ

2

3

2

(40 mL) was added. The aqueous phase was extracted with CH₂Cl₂11.4, J_14,14Јϭ 2.2 Hz, 1 H, 14-H), 5.44 (dd, J_8,7ϭ 11.4, J_8,8Ј

ϭ

3

2

(2 ϫ 20 mL), and the combined organic phases were neutralized

and dried with sodium sulfate. After solvent removal the residue

was purified by column chromatography (Alox, CH₂Cl₂) to yield

13,14,15,16,17,18-hexamethyl-7,11,13-tris(methylethylidene)-1,5,9-

trioxatrispiro[2.0.2.1.2.2]dodecane (29, 56 mg, 60%) as colorless

solid, m.p. Ͼ 250 °C. IR (KBr): ν˜ ϭ 3000 cm^Ϫ1(m), 2965 (m),

2929 (s), 2911 (s), 2877 (m), 2855 (m), 1459 (m), 1455 (m), 1386

2.2 Hz, 1 H, 8-H), 5.41 (dd, J_10,9ϭ 11.4, J_10,10Јϭ 2.2 Hz, 1 H,

10-H), 5.23 (dd, ³J_14Ј,13ϭ 17.9, ²J_14Ј,14ϭ 2.2 Hz, 1 H, 14-HЈ), 5.18

(dd, ³J_10Ј,9ϭ 17.9, ²J_10Ј,10ϭ 2.3 Hz, 1 H, 10-HЈ), 5.18 (dd, ³J_8Ј,7ϭ

2

18.0, J_8Ј,8ϭ 2.3 Hz, 1 H, 8-HЈ), 2.73Ϫ2.64 (m, 6 H, 11-H, 15-H,

17-H), 1.11 (t, ³J ϭ 7.5 Hz, 3 H, 16-H or 18-H), 1.10 (t, ³J ϭ

7.4 Hz, 3 H, 16-H or 18-H), 1.02 (t, J_12,11ϭ 7.4, 3 H, 12-H). ¹³C

3

NMR (100.6 MHz): δ ϭ 138.90 ppm (s, C-5 or C-6), 137.74 (s, C-

(m), 1371 (s), 1099 (m), 890 (m), 884 (m), 824 (m), 781 (m). ¹H 4), 137.42 (s, C-3), 137.25 (s, C-5 or C-6), 136.74 (d, C-7), 136.61

NMR (400 MHz): δ ϭ 1.86 ppm (s, 3 H), 1.84 (s, 3 H), 1.69 (s, 3 (s, C-1), 136.59 (d, C-9), 136.06 (d, C-13), 134.95 (s, C-2), 119.44

H), 1.63 (s, 3 H), 1.60 (s, 3 H), 1.53 (s, 3 H), 1.49 (s, 3 H), 1.46 (s,

(t, C-8), 119.27 (t, C-10), 118.94 (t, C-14), 23.78 (t, C-11), 23.11 (t,

3 H), 1.45 (s, 3 H), 1.38 (s, 3 H), 1.34 (s, 3 H), 1.25 (s, 3 H). ¹³C C-15 or C-17), 22.79 (t, C-15 or C-17), 15.26 (q, C-16 or C-18),

NMR (100.6 MHz): δ ϭ 132.83 ppm (s), 130.74 (s), 129.95 (s), 15.12 (q, C-16 or C-18), 14.65 (q, C-12). UV (hexane): λ_max(lg ε) ϭ

129.50 (s), 128.57 (s), 126.41 (s), 74.32 (s), 73.23 (s), 72.57 (s), 71.89

(s), 67.15 (s), 65.48 (s), 25.58 (q), 25.27 (q), 23.51 (q), 23.49 (q),

194 nm (4.28), 226 (4.46). MS (70 eV): m/z (%) ϭ 241 (16), 240 (82)

[M^ϩ], 226 (18), 225 (100) [M^ϩϪ CH₃], 212 (16), 211 (96) [M^ϩ

Ϫ

22.97 (q), 22.65 (q), 22.56 (q), 22.25 (q), 22.15 (q), 21.62 (q), 21.37 C₂H₅], 197 (42), 196 (42), 195 (11), 163 (44), 162 (31), 161 (37), 159

(q), 20.94 (q). UV (hexane): λ_max(lg ε) ϭ 192 nm (4.25), 224 (4.12). (14), 158 (12), 169 (31), 168 (22), 167 (42), 166 (22), 165 (42), 155

Eur. J. Org. Chem. 2003, 2596Ϫ2611

www.eurjoc.org

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2609

T. Höpfner, P. G. Jones, B. Ahrens, I. Dix, L. Ernst, H. Hopf

FULL PAPER

Table 2. Crystallographic data for compounds 19a, 19b, 14, 22, and 23

Compound

19a

19b

14

22

23

Empirical formula

M_r

Habit

C₁₄H₁₂Cl₄

322.04

colorless prism

0.62ϫ0.40ϫ0.28

monoclinic

P2₁/c

C₁₄H₁₂Br₄

499.88

colorless prism

0.52ϫ0.36ϫ0.24

monoclinic

P2₁/n

C₂₄H₃₆

324.53

colorless tablet

0.7ϫ0.4ϫ0.2

triclinic

C₂₀H₂₄Cl₄

406.19

colorless tablet

0.7ϫ0.4ϫ0.15

monoclinic

P2₁/n

C₂₀H₂₄Cl₄

406.19

colorless tablet

0.54ϫ0.54ϫ0.35

monoclinic

P2₁/n

Cryst. size [mm]

Crystal system

Space group

Cell constants

P(Ϫ1)

˚

a [A]

5.9349(12)

15.115(2)

8.3711(12)

90

107.798(12)

90

715.0(2)

2

1.496

0.81

6.1303(8)

8.4097(10)

15.2847(16)

90

101.378(8)

90

772.50(16)

2

2.149

10.4

9.1841(10)

14.0705(16)

17.656(2)

71.027(8)

88.748(6)

81.716(6)

2134.4(4)

4

1.010

0.06

720

Ϫ100

9.652(2)

13.253(3)

15.574(3)

90

90.29(3)

90

1992.2(7)

4

1.354

0.59

10.542(2)

8.079(2)

11.373(2)

90

101.92(2)

90

947.8(3)

2

1.423

0.62

˚

b [A]

˚

c [A]

α [°]

β [°]

γ [°]

3

˚

V [A ]

Z

D_x[Mg·m^Ϫ3

]

µ [mm^Ϫ1

F(000)

T [°C]

2θ_max

]

328

Ϫ130

55

472

Ϫ100

50

848

Ϫ130

50

424

Ϫ130

55

50

Refl. measured

Refl. indep.

R_int

3242

1639

0.012

83

0.062

0.023

1.08

2846

1353

0.037

83

0.040

0.019

0.95

10949

7355

0.024

457

0.108

0.045

0.85

0.15

5666

3467

0.056

223

0.188

0.070

1.04

2455

2182

0.012

112

0.078

0.029

1.08

Parameters

wR(F², all refl.)

R [F, Ͼ4σ(F)]

S

Ϫ3

˚

max. ∆ρ [e·A

]

0.36

0.39

1.2

0.4

(28), 154 (13), 153 (28), 152 (20), 141 (16), 128 (11). C₁₈H₂₄: calcd. ation of a CH₂Cl₂solution at Ϫ18 °C; 22 from ethanol; 23 from

240.18780, found 240.187Ϯ2 ppm.

ethanol. Numerical details are presented in Table 2. Data collection

and reduction: Crystals were mounted in inert oil on glass fibers

and transferred to the cold gas stream of the diffractometer (19a,

22, 23: Stoe STADI-4; 19b, 14: Siemens P4, with appropriate low

temperature attachments). Measurements were performed by use

of monochromated Mo-K_αradiation. An absorption correction for

compound 19b was performed on the basis of ψ-scans. Structure

solution and refinement: The structures were solved with direct

methods and refined anisotropically against F²(program

SHELXL-97, G.M. Sheldrick, University of Göttingen). H atoms

were included with a riding model or rigid methyl groups.

14. Tricarbonyliron Complex 33 of Hexamethyl[6]radialene (2a): A

suspension of 2a (0.240 g, 1.0 mmol) and Fe₂(CO)₉(2.18 g,

6.0 mmol) in THF (60 mL) was heated at 50 °C for 2 h. After cool-

ing to room temp. the reaction mixture was filtered, the solvent

was removed in vacuo, and the remainder was purified twice by

preparative silica gel thick layer chromatography with hexane. Be-

sides unchanged 2a, 33 (28 mg, 7%) was isolated as a colorless

solid, m.p. 98 °C, still containing traces of 2a. IR (KBr): ν˜ ϭ 3067

cm^Ϫ1(w), 2970 (m), 2937 (m), 2915 (m), 2874 (m), 2857 (m), 2029

(s), 1969 (s), 1962 (s), 1955 (s), 1948 (s), 1925 (m), 1915 (m), 1442

(m), 664 (m), 618 (m), 607 (s). ¹H NMR (400 MHz): δ ϭ 5.98 ppm

CCDC-202808 (19a), -202809 (19b), -202810 (14), -202811 (22),

and -202812 (23) contain the supplementary crystallographic data

for this paper. These data can be obtained free of charge at

www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge

Crystallographic Data Centre, 12, Union Road, Cambridge

CB2 1EZ, UK; Fax: (internat.) ϩ44-1223/336-033; E-mail:

deposit@ccdc.cam.ac.uk].

3

(q, J_11,17ϭ 7.2 Hz, 1 H, 11-H), 5.76 (q, J_9,15ϭ 7.1 Hz, 1 H, 9-

3

H), 5.70 (q, J_12,18ϭ 7.1 Hz, 1 H, 12-H), 5.67 (q, J_10,16ϭ 7.5 Hz,

3

1 H, 10-H), 2.74 (q, J_7,13ϭ 7.1 Hz, 1 H, 7-H), 2.24 (q, J_8,14

ϭ

3

6.3 Hz, 1 H, 8-H), 2.01 (d, J_16,10ϭ 7.5 Hz, 3 H, 16-H), 1.93 (d,

³J_18,12ϭ 7.1 Hz, 1 H, 18-H), 1.91 (d, J_15,9ϭ 7.1 Hz, 3 H, 15-H),

3

1.85 (d, ³J_17,11ϭ 7.2 Hz, 3 H, 17-H), 1.55 (d, ³J_14,8ϭ 6.3 Hz, 3 H,

14-H), 1.28 (d, ³J_13,7ϭ 7.1 Hz, 3 H, 13-H). ¹³C NMR (100.6 MHz):

δ ϭ 138.88 ppm (s, C-5), 137.18 (s, C-3), 136.49 (s, C-6), 134.72 (s,

C-4), 128.84 (d, C-12), 125.98 (d, C-9), 124.21 (d, C-10), 123.66 (d,

C-11), 112.06 (s, C-2), 99.06 (s, C-1), 51.88 (d, C-8), 50.08 (s, C-7),

18.61 (q, C-14), 16.93 (C-16), 16.66 (q, C-17), 16.30 (q, C-15), 15.12

(q, C-18), 14.66 (q, C-13). The carbonyl signals could not be ident-

ified. UV (hexane): λ_max(lg ε) ϭ 198 nm (4.64), 228 nm (4.53). MS

(70 eV): m/z (%) ϭ 378 (0.7) [M^ϩ], 352 (25), 325 (16), 324 (68), 297

(22), 296 (100), 295 (15), 294 (61), 292 (11) [M^ϩϪ 3 CO].

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2610

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www.eurjoc.org Eur. J. Org. Chem. 2003, 2596Ϫ2611

[6]Radialenes Revisited

FULL PAPER

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Received February 12, 2003

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[6]Radialenes revisited

DOI: 10.1002/ejoc.200300075

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