The cycloaddition-cycloelimination pathway to homotropilidenes - Synthesis and properties of homotropilidenes

FULL PAPER

The Cycloaddition-Cycloelimination Pathway to Homotropilidenes ؊ Synthesis

and Properties of Homotropilidenes

Jürgen Sauer,*^[a]Peter Bäuerlein,^[a]Wolfgang Ebenbeck,^[a]Rainer Dyllick-Brenzinger,^[a]

Charalampos Gousetis,^[a]Heinz Sichert,^[a]Theodor Troll,^[a]and Uwe Wallfahrer^[a]

Dedicated to Prof. Siegfried Hünig on the occasion of his 80th birthday

Keywords: Azo compounds / Cycloadditions / Kinetics / Photolysis / Rearrangements / Substituent effects

The cycloaddition-cycloelimination reaction sequence be- homotropilidenes (bicyclo[5.1.0]octa-2,5-dienes) 13−26. Sub-

tween 3,6-disubstituted 1,2,4,5-tetrazines

cyclopropenes 10 provides 3,4-diazanorcaradienes 11, which have been observed to exert significant influences on the

undergo [4+2] cycloadditions with additional cyclopropenes Cope rearrangement rate and, in cases of unsymmetrically

9

and various

stituents at various positions of the homotropilidene skeleton

10 to form tetracyclic azo compounds 12. Photolysis of these substituted homotropilidenes, on the equilibrium positions.

compounds, with accompanying loss of nitrogen, affords

Introduction

In 1940 Cope reported the first examples of thermally

induced rearrangements of 1,5-hexadienes.^[1]This [3,3]-

sigmatropic rearrangement, by WoodwardϪHoffmann no-

menclature,^[2,3]not only turned out to be of tremendous

synthetic value,^[4Ϫ6]but its mechanism has been the topic

of heated discussion for nearly 50 years. In two remarkable

contributions, Doering quite recently offered a critical dis-

cussion of all mechanistic aspects.^[7,8]Houk summarized all

relevant articles to show how quantum mechanical calcula-

tions have been used to analyse and predict the rates and

mechanisms of this and other pericyclic reactions.^[9,10]

Historically, as illustrated in Scheme 1, three models have

been the focus of mechanistic attention, as demonstrated

for the degenerate Cope rearrangement of the parent system

Ǟ

ǟ

1

1Ј. One possible pathway is a single-step, concerted

mechanism, involving an aromatic-type transition state 2.

Two alternatives are represented by intermediates 3 and 4:

Either a bond fission of 1,5-hexadiene 1 between C-3 and

C-4 may produce two allyl radicals, shown as 3, or bond

formation between C-1 and C-6 may produce a cyclohexa-

1,4-diyl diradical 4.

A logical but nevertheless ingenious extension of the

Cope rearrangement of 1 was the synthesis of homotropili-

dene (5), bullvalene (6), barbaralane (7) and semibullvalene

(8), all of which display the phenomenon of the degenerate

[3,3]-sigmatropic rearrangement. The same mechanistic di-

chotomy also exists in principle for these compounds, as

described for 1 ^Ǟ_ǟ1Ј, with either a concerted reaction (trans-

ition state analogous to 2) or two-step rearrangements in-

volving biradical intermediates analogous to 3 or 4.

Scheme 1. The Cope rearrangement of 1,5-hexadienes

In this contribution, we give a full report on our investi-

gations of the synthesis of symmetrically and unsymmet-

rically substituted homotropilidenes by means of a cycload-

dition-cycloelimination sequence utilizing 1,2,4,5-tetrazines

and cyclopropenes as starting materials.^[11Ϫ16]

Results and Discussion

[a]

Institut für Organische Chemie der Universität Regensburg,

Universitätsstrasse 31, 93040 Regensburg, Germany

Fax: (internat.) ϩ 49-(0)941/943Ϫ4946

Homotropilidene (5) itself was first synthesized in Doer-

E-mail: rudolf.vasold@chemie.uni-regensburg.de

ing’s group,^[17,18]by cyclopropanation of 1,3,5-cyclohepta-

Eur. J. Org. Chem. 2001, 2639Ϫ2657

WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001

1434Ϫ193X/01/0714Ϫ2639 $ 17.50ϩ.50/0

2639

J. Sauer et al.

FULL PAPER

triene at the 3- and 4-positions and subsequent separation

from other isomers by GC (Scheme 2, path A). However,

this pathway is limited as cyclopropanation preferentially

takes place at the 1- and 2-positions, affording isomeric

mixtures. Similarly, the cyclocondensation, as outlined in

pathway B, can only be performed in few cases.^[19,20]Reac-

tion sequences C, D, E and F all include a 1,4-elimination

step (CO, Cl₂, N₂) from a suitable precursor with concomit-

ant ring opening of one cyclopropane unit. Pathway F of-

fers the greatest potential for variation, because substituents

on the 1,2,4,5-tetrazine and the cyclopropene can be varied

for the initial [4ϩ2] cycloaddition step. As 3,4-diazanorcar-

adienes can, in principle, be isolated, a variety of different

cyclopropenes can also be employed in the cycloaddition

steps F₁and F₂, thus producing unsymmetrically substi-

tuted azo compounds, which represent precursors for un-

symmetrical homotropilidenes.^{[11Ϫ16,21,22]}The value of this

synthetic approach is illustrated in the following sections.

Scheme 3. Synthesis of 3,4-diazanorcaradienes 11 (Ph ϭ phenyl, 2-

Py ϭ 2-pyridyl, 2-Thia ϭ 1,3-thiazol-2-yl, 5-Oxa ϭ 2-methyl-1,3,4-

oxadiazol-5-yl)

The dienophilic activity of cyclopropene is influenced re-

markably by methyl substitution on 10. While the introduc-

tion of one methyl group at position 3 of compound 10

slightly increases the rate, the introduction of a second

methyl group sharply reduces the reactivity: 3,3-Dimethyl-

cyclopropene (10e) is less reactive (in terms of rate con-

stants) than 10a by a factor of approximately 5000Ϫ6000

(reaction with 9a, 20 °C, 1,4-dioxane).^[24]Interestingly

enough, the diphenyl derivative 10f was quite sluggish in re-

activity.

Scheme 2. Synthetic pathways leading to homotropilidenes

Synthesis of 3,4-Diazanorcaradienes 11 and Azo

Compounds 12

By virtue of their high angle strain, cyclopropenes 10 in

3,4-Diazanorcaradienes 11 are still quite reactive dienes

general act as very reactive 2π components in [4ϩ2] cyclo- in DielsϪAlder reactions with inverse electron demand. The

additions with the extremely electron poor 1,2,4,5-tetrazines diene activity drops considerably in the 1,2,4,5-tetrazine Ǟ

9, to form 3,4-diazanorcaradienes 11 in good to excellent 1,2,4-triazine Ǟ 3,4-diazanorcaradiene series;^[23]the rate

yields (Scheme 3 and Exp. Sect.).^[22,23]Depending on the constants for the same dienophile are reduced by a factor

reactivities of the two components, the cycloaddition step of more than 1000 for each nitrogen atom fewer in this six-

can be performed by introducing gaseous cyclopropenes at membered heterocycle series. When cyclopropenes are used

Ϫ78 °C or at ambient temperature. The reaction can be as dienophiles, the tetracyclic azo compounds 12 are

monitored conveniently by the disappearance of the tetra- formed in good to very good yields from 3,4-diazanorcara-

zine colour, with the reaction mixture turning, for example, dienes 11. More active dienes 11 readily add to cyclopro-

from purple (tetrazine) to yellow or orange-yellow (diaz- penes 10 at room temperature or slightly elevated temper-

anorcaradiene).

ature; sluggish systems, however, can be accelerated by

2640

Eur. J. Org. Chem. 2001, 2639Ϫ2657

Synthesis and Properties of Homotropilidenes

FULL PAPER

working at higher temperatures and/or using high pressure

(up to 8 kbar). For the synthesis of symmetrical azo com-

pounds 12, the intermediate 3,4-diazanorcaradienes 11 do

not need to be isolated and azo compounds 12 can be ob-

tained in a one-pot synthesis. Table 1 offers a collection of

azo compounds 12, representing precursors for homotropil-

idenes 13؊26. For the synthesis of the dicyano derivative

12iϪ12o we applied traditional transformation sequences

R¹ϭ CO₂CH₃Ǟ CO₂H Ǟ COCl Ǟ CONH₂Ǟ CN.

Photolysis of Azo Compounds 12 to Homotropilidenes

13؊26

Aliphatic azo compounds are valuable precursors for the

synthesis of energy-rich intermediates, such as alkyl rad-

icals, as well as a variety of aliphatic compounds with inter-

esting and unusual structures. The reactions are usually ini-

tiated by thermolysis or photolysis of the corresponding

azo compounds.^[29Ϫ32]

Tetracyclic azo compounds 12 offer a rather simple route

to homotropilidenes, and in most cases studied the

photolytic pathway was a successful one. Photolysis of azo

compounds 12 was carried out either in an immersion well

photoreactor or on an optical bench (for details, see Exp.

Sect.). Inert solvents such as benzene, acetonitrile or dichlo-

romethane were used. Depending on the structure of 12,

its concentration, the solvent used and the photochemical

conditions, the nitrogen extrusion was usually completed

within a few hours and the reactions could easily be mon-

itored by thin layer chromatography. Only in a few cases

was the yield of homotropilidene lower than 50%.

Table 1. Substituted tetracyclic azo compounds 12

Homotropilidenes ؊ Structure and Equilibrium Position

In this study homotropilidene substitution was varied in

two ways, as depicted in Schemes 4 to 8:

i. Variation at positions 2 and 6: CO₂CH₃, CN, Ph, 2-Py

(2-pyridyl), 2-Thia (1,3-thiazol-2-yl), 5-Oxa [2-methyl-

(1,3,4-oxadiazol-5-yl)].

ii. Hydrogen was exchanged for methyl, phenyl and tert-

butyl to yield symmetrical and unsymmetrical monoalkyl-,

dialkyl-, and trialkyl-substituted homotropilidenes. Sub-

stituents at positions 2 and 6 were also in part varied.

The structural confirmation of the homotropilidenes

13؊26 shown in Scheme 4 to 8 relies on the ¹H NMR spec-

tra obtained at low temperature when the Cope rearrange-

ment is slow. Table 2 summarizes typical values for chemical

shifts of protons at the cyclopropane moiety, the seven-

membered ring and the methyl groups at different positions,

together with the J and J coupling constants for geminal

protons and those in adjacent positions. Chemical shift data

and coupling constants convincingly establish both the

structure and the existence of the trans conformation of

homotropilidenes 13؊26.

The obvious alternative synthetic approach, starting from

3,6-dicyano-1,2,4,5-tetrazine (9b), is impracticable because

the very sensitive dicyanotetrazine 9b can only be obtained

in small amounts and stored for a limited time at low tem-

perature in the solid state.^[25,26]Compound 9b surpasses the

diester tetrazine 9a in reactivity: The rate constants for the

[4ϩ2] cycloaddition with 1-methoxycyclohexene, for in-

stance, have been determined as 9b:9a ϭ 970:1 (20 °C, diox-

ane)^[27]and parallel the half-wave reduction potentials of

the tetrazines.^[28]

2

3

¹H and ¹³C NMR spectra unequivocally corroborate the

correct structures for 11 and 12 (see Exp. Sect.). In particu-

lar, the chemical shifts of the protons and carbon atoms

of the cyclopropane units, in combination with the proton-

proton coupling constants (ABX₂spin systems), are

conclusive^[21Ϫ23]and need no further detailed discussion.

The characteristic azo chromophore in 12 (λ ഠ 350 nm)

shows low extinction coefficients for the forbidden n-π*

transition (see Exp. Sect.).

Scheme 4. 2,6-Disubstituted homotropilidenes 13/13Ј

Eur. J. Org. Chem. 2001, 2639Ϫ2657

2641

J. Sauer et al.

FULL PAPER

Scheme 5. Monomethyl derivatives of 2,6-disubstituted homotropi-

[a]

lidenes 14؊17:

(Ͼ 95%)

16a was observed as the major Cope isomer

Ǟ

ǟ

Ǟ

ǟ

Symmetrical Homotropilidenes 13 13Ј, 20 20Ј

and 21 21Ј

Ǟ

ǟ

On photolysis, symmetrically substituted azo compounds

12 yield symmetrical homotropilidenes, which can undergo

degenerate Cope rearrangement at elevated temperature.

2,6-Disubstituted homotropilidenes 13/13Јa؊f, together

with the 4,8-dialkyl derivatives 20/20Јa؊f and the 1,5-di-

methyl homotropilidenes 21/21Јa؊c are easily obtained in

good yields (Schemes 4 and 6). At temperatures below Ϫ30

°C, the [3,3]-sigmatropic rearrangement is slow on the

1

Scheme 6. Dialkyl derivatives of 2,6-disubstituted homotropili-

denes 18؊23

NMR timescale in all cases. A typical H NMR spectrum

shows the signals of protons for the cyclopropane unit and

the protons of the seven-membered ring, with the anticip-

ated values for chemical shifts, multiplicity and coupling

constants confirming the homotropilidene structure and

trans conformation (Table 2).

1

At elevated temperatures, the H NMR spectra became

temperature-dependant, and on passing a coalescence point

a fast equilibrium is reached (vide infra) during which pro-

tons and/or substituents at position 4/8, and also 1/3 or 5/

7, become equivalent.

Unsymmetrical Alkyl-Substituted Homotropilidenes 14, 16/

17, 18, 22/23 and 26

Scheme 7. Diphenyl derivatives of 2,6-disubstituted homotropili-

denes 24/25

Unsymmetrical substitution on the homotropilidene skel-

eton gives rise to two nonequivalent Cope tautomers. The

analysis of the ¹H NMR spectra for monomethyl homotro-

pilidenes (Table 2) convincingly confirms the existence of voured for 16a and 16b, while the 3-isomer 17a is preferred

the 8-methyl isomer for 14aϪ14d (Scheme 5). In the case of for the dicyano derivative (Scheme 5). As is to be expected,

a single methyl group at position 1/3, the 1-isomer is fa- the two geminal methyl groups prefer position 8 (18a and

2642

Eur. J. Org. Chem. 2001, 2639Ϫ2657

Synthesis and Properties of Homotropilidenes

FULL PAPER

18b in Scheme 6), whereas in the competition between two more stable isomer. Finally, for a trisubstitution pattern, the

methyl groups in positions 3/8 versus 1/4, the isomer 22 3,8,8-combination 26 is preferred over the alternative 4,4,8-

(22a and 22b in Scheme 6), with the substituents in posi- arrangement 27 (Scheme 8).

tions 3/8 of the homotropilidene skeleton, seems to be the

Unsymmetrical Diphenyl-Substituted Homotropilidenes 24a

and 25a

Only one case of unsymmetrical disubstitution with two

phenyl groups can be presented. While we find the two

phenyl substituents at position 1/7 for the diester derivative

24a, the dicyano derivative 25a prefers the phenyl rings in

position 3/5, in conjugation with the cyano groups

(Scheme 7). A detailed discussion of all equilibrium phe-

nomena is given, together with the kinetic data (vide infra).

Scheme 8. Trimethyl derivatives of 2,6-disubstituted homotropili-

denes 26/27

Table 2. ¹H NMR chemical shifts (δ values, CDCl₃/TMS, 60, 90, 250 or 400 MHz) and coupling constants ⁿJ(¹H,¹H) [Hz] of 3,4-

homotropilidenes 13aϪ26a

[d]

^[a]Solvent [D₈]toluene at 214 K. Ϫ ^[b]Solvent [D₈]toluene at 226 K. Ϫ ^[c]Solvent CD₂Cl₂at 223 K. Ϫ Observed ⁿJ (¹H,¹H) long-range

[e]

[f]

[g]

[k]

[h]

couplings (see Exp. Sect.). Ϫ Solvent [D₈]toluene. Ϫ At 235 K. Ϫ

Solvent CD₂Cl₂/CS_2[l](2:1) at 188 K. Ϫ

Solvent CD₂Cl₂at

[i]

[j]

227 K. Ϫ Solvent CD₂Cl₂at 216 K. Ϫ Solvent CD₂Cl₂at 233 K. Ϫ Solvent CD₂Cl₂. Ϫ Solvent CD₂Cl₂at 220 K.

Eur. J. Org. Chem. 2001, 2639Ϫ2657

2643

J. Sauer et al.

FULL PAPER

¹H NMR Spectroscopic Temperature Dependence in

fers the energetically favoured trans conformation 5_trans

with the minimum conformational strain, due to an ob-

served dihedral angle of 80° between the substituents in po-

sition 1/2 and 6/7.^[37]In contrast, the corresponding cis con-

formation 5_cisexists in an almost eclipsed conformation

with a reduced dihedral angle of 5Ϫ10°, and is therefore

less favoured,^[37]with a difference in free energy of ∆G.

The mechanism for the degenerate Cope rearrangement

given in Figure 1 proceeds through the cis conformation 5_cis

by a concerted pathway involving an aromatic transition

state 2. The sigmatropic rearrangement is then followed by

a conformational change to form the more stable trans con-

former 5Ј_trans. Hence, the experimental free activation en-

ergy ∆G^϶_expfor the total sequence is determined as the sum

of the difference in free energies ∆G between the two con-

formers (5_transand 5_cis) and the activation energy ∆G_C^϶_ope

required for the Cope rearrangement [Equation (1)].

Ǟ

ǟ

Ǟ

ǟ

Symmetrical Homotropilidenes 13 13Ј, 20 20Ј

Ǟ

ǟ

and 21 21Ј

As already mentioned, symmetrical homotropilidenes

have temperature-dependant ¹H NMR spectra. At lower

temperature (Ϫ76 °C to ϩ110 °C), depending on the struc-

ture of the homotropilidenes, the Cope rearrangement is

1

‘‘frozen’’ and the H NMR spectra can easily be analysed

(Table 2). At elevated temperatures, the signals belonging to

exchangeable positions (4/8, 1/3, 5/7) broaden and, finally,

at still higher temperatures (ϩ40 °C to ϩ200 °C) the area

of fast exchange is reached.

We measured the ¹H NMR spectra in such inert solvents

as CD₂Cl₂, CDCl₃, C₂D₂Cl₄, CS₂, [D₈]toluene or mixtures

(Table 5, Exp. Sect.), depending on the homotropilidene

structure and the rate of the degenerate Cope rearrange-

ment (which varied considerably). In a number of cases, it

was possible to measure ¹H NMR spectra over a large tem-

perature range (∆T ഠ 80Ϫ120 °C) and spectra were usually

taken at more than 10Ϫ15 different temperatures. Rate con-

stants at different temperatures were obtained by complete

line-shape analysis using the RSHKUBO program.^[33Ϫ35]

Calculations for ∆G^϶, ∆H^϶and ∆S^϶values are based on

the Eyring equation (see Table 4 and 5 and Figure 2).^[36]

In addition, ∆G^϶values for the degenerate Cope re-

arrangement were available for a number of homotropilid-

enes, from the coalescence temperatures of signals for the

appropriate substituents (Table 5). These data obtained for

activation parameters are given in Table 4, together with

corresponding data from the literature.

∆G^϶_expϭ ∆G ϩ ∆G_C^϶_ope

(1)

Steric and electronic effects of substituents in different

positions of the homotropilidene system have a consider-

able influence both on the conformational equilibrium

Ǟ

5_{trans ǟ}5_cisand on the rate of the sigmatropic rearrange-

Ǟ

ment 5_{cis ǟ}5Ј_cis, making accurate mechanistic predictions

difficult. Unsymmetrically substituted homotropilidenes,

represented by the two trans Cope isomers 5_transand 5Ј_trans

,

differ in their energies, and so their ratios are different from

1:1. Again, these substituents are expected to influence the

equilibrium by means of steric and electronic factors. A col-

lection of unsymmetrical homotropilidenes synthesized in

our group is given in Table 3, and also includes the known

3-methylhomotropilidene (28)^[40]for comparative discus-

sion. It is important to note that the exclusively formed or

dominant Cope isomer is shown in Table 3.

A number of symmetrical homotropilidenes, including

both those synthesized by us and those obtained according

to the literature, gave ∆G^϶_expvalues obtained from coales-

cence measurements or NMR line-shape analysis; these are

displayed in Table 4. Apart from a very few exceptions, the

corresponding ∆G^϶_expvalues relate to 298 K. Some of the

activation parameters from coalescence measurements were

obtained at slightly different temperatures; however, this

still allows for direct comparison.

Substituents Effects on Equilibria and Rates of Cope

Rearrangement of Homotropilidenes

Figure 1 illustrates the current stage of mechanistic dis-

cussion of degenerate Cope rearrangements of homotropil-

idenes, together with the corresponding energy profile for

this sequence. Results obtained from NMR studies,^[37]pho-

toelectron spectroscopy^[38]and force field calculations^[39]

suggest that the parent structure of homotropilidene 5 pre-

The question that now arises is, how do substituents in

unsymmetrical homotropilidenes influence the equilibrium

of Cope isomers? Table 3 gives a selection of compounds

with symmetrical substitution patterns in positions 2/6

(R¹ϭ CO₂CH₃, CN, 2-Py, 2-Oxa, Ph or H) and bearing

methyl or phenyl groups in various positions around the

homotropilidene skeleton. Predictions about the preferred

positions of alkyl groups are based on the Schleyer rule,^[41]

EHT calculations by Hoffmann and Stohrer^[42]and

MNDO/2-calculations by Dewar and Lo.^[43]As outlined in

the following sequence, a methyl group prefers an olefinic

position over a cyclopropane position over an sp³-carbon

Figure 1. Valence isomerization energy profile of homotropilidene 5 atom.

2644

Eur. J. Org. Chem. 2001, 2639Ϫ2657

Synthesis and Properties of Homotropilidenes

FULL PAPER

Table 3. Preferred structural isomer of unsymmetrically substituted homotropilidenes (percentage of isomer)

Table 4. ∆G^϶₂₉₈values (kcal/mol; 298 K) for the Cope rearrangement of homotropilidenes

[a]

[b]

∆G^϶₂₇₄at 274 K. Ϫ ∆G₃^϶₂₀at 320 K.

The homotropilidenes 14, 18, 22 and 26 exactly follow

the Schleyer rule, as shown by comparison of these com-

pounds with their alternative structural isomers in previous

schemes. These results are consistent with those obtained

Eur. J. Org. Chem. 2001, 2639Ϫ2657

2645

J. Sauer et al.

FULL PAPER

by Maas^[44,45]using simple 4,8-dialkyl-substituted homotro- influence of substituents on the conformational equilibrium

pilidenes unsubstituted at position 2/6. In all these com- has to be taken into account as well. As shown for barbara-

pounds, alkyl and phenyl substituents prefer the cyclopro- lanes and semibullvalenes, methyl and phenyl groups in

pane position at C-8 rather than the sp³-carbon atom at these positions significantly reduced the rate of the degener-

C-4.

An interesting substituent effect was observed with

ate Cope rearrangement.^[50]

The disubstituted homotropilidenes 13a and 13b exhibit

homotropilidenes 16 and 17. In contrast to 17a and 3- only slightly different ∆G^϶_expvalues compared to the parent

methylhomotropilidene (28),^[40]the elucidated structures of system 5. Within this pair of compounds, however, the dicy-

16a and 16b are in disagreement with the Schleyer rule. We ano derivative 13b is slower in rate than the corresponding

assume that this outcome is the result mainly of steric ef- diester derivative 13a. This trend has also been found to be

fects. Possibly because of a large dihedral angle between the operative for both the homotropilidene analogues 20a/20c

methyl group and the substituent R¹(R¹ϭ CO₂CH₃or 2- and 20b/20d. These observed relatively insignificant sub-

Py), the steric interaction in the unexpected Cope isomer stituent effects, which are based on experimental ∆G_e^϶_xp

16a and 16b is minimal,^[37]whereas in their alternative values involving two processes, are not regarded as having

structural isomer 17 (R¹ϭ CO₂CH₃/2-Py) a substantial further relevance.

steric strain would be invoked.

A simpler explanation can be given for the increase in

The dicyano derivative 17a displays no steric interaction rate of the degenerate Cope rearrangement induced by alkyl

between the substituents in position 2 and 3, because of disubstitution in positions 4/8. Calculations on the effect of

the small steric demand of the nonbulky cyano group. The substituents on the stability of cyclopropane bonds^[42]and

equilibrium of compound 17a is thus not dictated by steric analogous kinetic studies on semibullvalenes^[51]confirmed

effects and this is therefore consistent with the Schleyer rule. this result. According to this, the electron-donating alkyl

Similar steric effects have been found to be responsible groups in position 4/8, residing on the opposite side of the

for the opposite equilibria observed for compounds 24a and cyclopropane bond, weaken this bond and facilitate an en-

25a. Introduction of bulky phenyl groups adjacent to the hanced sigmatropic rearrangement rate. Furthermore, a

ester substituents in position 2/6 raises the steric congestion change in the conformational equilibrium, as initially as-

dramatically and the sterically less hindered isomer 24a, sumed, favouring the cis conformer over the trans con-

with phenyl groups attached to the cyclopropane ring in former because of steric interaction between the pseudoax-

positions 1 and 7, is subsequently formed. In the corres- ial substituents in position 4 and the hydrogen atoms on the

ponding dicyano derivative 25a, the steric interactions are cyclopropane unit (position 1 and 7), is not believed to oc-

reduced for reasons already mentioned above. Furthermore, cur. It has been shown that the rate of rearrangement for

additional conjugative factors (Ph in position 3/5 adjacent the tert-butyl-substituted homotropilidenes 20b and 20d is

to CN in position 2/6) favour the formation of isomer 25a, slower than for the corresponding methyl derivatives 20a

and this is found to be consistent with the Schleyer rule.

Earlier kinetic studies investigating the Cope rearrange-

and 20c.

The opposite trend in reactivity has been observed for

ment of homotropilidenes have been carried out by compounds 21a/21b, an effect which is generated by steric

Kessler,^[39,46,47]Guenther,^[37,48]Winstein^[49]and Maas.^[44,45]interactions. The enhanced steric interaction between the

These results are given in Table 4 and are compared with methyl substituents in position 1 and 5 and the ester groups

kinetic data obtained from our compounds. As already in- in position 2 and 6 shifts the conformational equilibrium

dicated, mechanistic interpretation of the ∆G^϶_expvalues is towards the trans conformer, thus reducing the rate of re-

complicated by the fact that both the conformational equi- arrangement. As expected, steric interactions are lessened

Ǟ

librium 5_{trans ǟ}5

_cisand the Cope rearrangement 5_cis^Ǟ_ǟ5Ј_cisin homotropilidene 21b, due to small steric demand from

are influenced by substituents attached to the parent homo- the corresponding cyano groups in position 2 and 6, and so

tropilidene skeleton, through steric and electronic effects. an enhanced rate of rearrangement was observed for the

Even in bridged homotropilidene derivatives, the effects of dicyano derivative 21b as compared to diester derivative

substituents on the rate of rearrangement are not fully un- 21a.

derstood, as shown by an excellent kinetic study on barbar-

Unfortunately, our kinetic data do not allow us to con-

alanes and semibullvalenes by Jackman and Quast.^[50]Op- clude whether the individual Cope rearrangement occurs

posing substituent effects, for instance, have been observed through a concerted mechanism or a nonconcerted one. Ac-

within different classes of bridged homotropilidenes. Con- cording to an article by Doering et al.^[7,8]and calculations

sequently, discussion of our results is limited to expressing (Becke3LYP/6Ϫ31G* level) by Borden and Houk^[52,53]on

trends rather than drawing absolute conclusions.

1,5-hexadienes bearing cyano and vinyl groups in different

Substituents such as methyl, attached to the parent positions, these systems are specified as the so-called ‘‘cha-

homotropilidene 5 in position 1/3/5 or 7 (see 28, 29, 31 in meleonic’’ transition states for the Cope rearrangement.

Table 4), have a minor effect on the free activation energy The relative importance of the cyclohexane-1,4-diyl (4) and

∆G^϶_exp, while introduction of phenyl groups and Ϫ in par- bis(allyl) radical (3) resonance contributors can be altered

ticular Ϫ methyl groups at position 2/6, increase the energy by substituents, depending on the carbon atoms to which

barrier for the degenerate Cope rearrangement (see com- the substituents are attached. There is no doubt that similar

pounds 13c and 30 in Table 4). Electronic effects aside, the effects have to be considered in our systems.

2646

Eur. J. Org. Chem. 2001, 2639Ϫ2657

Synthesis and Properties of Homotropilidenes

FULL PAPER

under nitrogen. Solvents for reactions were dried according to

standard procedures. Ϫ The synthesis of dienophiles 10a,^[22]10b,^[54]

10c,^[54]10d,^[55,56,57]10e,^[22]10f^[58]and tetrazines 9a Ϫ 9f^[22]were

performed according to published procedures. Ϫ The petroleum

ether (PE) used had a boiling range of 40Ϫ60 °C. Ϫ Activation

parameters and experimental kinetic parameters are listed in

Table 5 and 6, Arrhenius plots are shown in Figure 2.

Conclusion

Symmetrical and unsymmetrical homotropilidenes were

prepared by photolysis of substituted tetracyclic azo com-

pounds 12. Substituents attached to different positions of

the homotropilidene skeleton show strong effects on the

equilibria of unsymmetrical homotropilidenes, as well as on

the rate of the degenerate Cope rearrangement for symmet-

rical homotropilidenes. Electronic substituent effects aside,

steric interactions have been shown to influence both equi-

librium position and reaction rates. Steric substituent effects

are mainly responsible for the change of the conformational

equilibrium 5_trans^Ǟ_ǟ5_cisinitiating the sigmatropic rearrange-

ment.

Synthesis of 3,4-Diazanorcaradienes. ؊ General Procedure (1) for

the Synthesis of 3,4-Diazanorcaradienes 11h, 11j and 11k: A stirred

suspension of tetrazine 9 in an inert solvent (vide infra) was cooled

to Ϫ78 °C under Ar. The corresponding cyclopropene 10aϪ10c

was generated in situ according to the literature procedure and

passed through the cooled suspension. The reaction mixture was

allowed to warm to room temp. and stirring was continued until

the red colour of the tetrazine had disappeared. After completion

of the reaction, the solvent was evaporated and the crude product

was purified as described below.

Experimental Section

Synthesis of Tetracyclic Azo Compounds. ؊ General Procedure (2)

for the Synthesis of Tetracyclic Azo Compounds 12d؊12f: Tetrazine

9 was dissolved at room temp. in an inert solvent (vide infra) and

a large excess of the corresponding cyclopropene 10cϪ10f was ad-

ded to the solution. The reaction mixture was stirred until the char-

acteristic red colour of the tetrazine had disappeared (reaction

times: see below). After completion of the reaction, as indicated by

TLC analysis, the solvent was evaporated and the crude product

was purified as described below.

General Remarks: IR spectra were recorded with a Beckman Accu-

lab 1, and UV/Vis spectra with a Beckman Model 24 and a Carl

Zeiss Specord M500 UV spectrophotometer. Ϫ NMR spectra were

obtained with a Varian T 60 and Bruker WH 90, AC 250 and ARX

400 machines (60, 90, 250 and 400 MHz for ¹H, 22.63, 63 and

100 MHz for ¹³C); δ values are reported in ppm downfield from

tetramethylsilane; s, d, dd, dt and m indicate singlet, doublet, doub-

let of doublets, doublet of triplets and multiplet. The degree of

substitution of the C atoms was determined by DEPT-135 and

DEPT-90 methods and is indicated as quat. C, ϭCH, ϪCH₂Ϫ,

ϪCH₃. Ϫ Mass spectra were measured by electron impact at an

ionizing voltage of 70 eV, with Varian MAT 90 and MAT311A in-

struments. Ϫ Melting points were determined either with a Büchi

melting point apparatus (Ͻ 280 °C) or with a copper block (Ͼ 280

°C) and are uncorrected. Ϫ Elemental analyses were performed in

the microanalytical laboratory of the University of Regensburg,

with Heraeus Mikro U/E and CHN-Rapid instruments. In some

cases, for oily compounds in particular, no correct elemental ana-

lysis could be obtained, such as for 12q, 16b, 21c, 22a and 22b. Ϫ

For analytical thin layer chromatography, precoated plastic sheets

(POLYGRAM SIL G/UV254, Macherey & Nagel) were used. Ϫ

Silica gel 60 (particle size 0.040Ϫ0.063 nm, Merck) was used for

flash column chromatography (FC). Ϫ Reactions were carried out

General Procedure (3) for the Synthesis of Tetracyclic Azo Com-

pounds 12b, 12c, 12g, 12p؊12r, 12t, 12u and 12w؊12y: A stirred

suspension of 3,4-diazanorcaradiene 11 in an inert solvent (vide

infra) was cooled to Ϫ78 °C under Ar. The corresponding cyclo-

propene 10aϪ10c was generated in situ and transferred in a weak

nitrogen stream into the reaction flask, maintained at dry ice tem-

perature. The reaction mixture was allowed to warm to room temp.

and stirring was continued until the reaction was complete (reac-

tion times: see below). After evaporation of the solvent, the crude

material was purified as described below.

General Procedure (4) for the Synthesis of Tetracyclic Azo Com-

pound 12h: 3,4-Diazanorcaradiene 11 was dissolved at room tem-

perature in an inert solvent (vide infra) and a large excess of the

corresponding cyclopropene 10dϪ10f was added to the solution.

Stirring of the reaction mixture was continued until the reaction

Table 5. Activation parameters ∆H^϶, ∆S^϶and ∆G^϶for the Cope rearrangement of homotropilidenes

[a]

[b]

[c]

At 353 K. Ϫ Determined at the coalescence temperature. Ϫ The methyl group prefers the 3-position by 1.1 kcal/mol.

Eur. J. Org. Chem. 2001, 2639Ϫ2657

2647

J. Sauer et al.

FULL PAPER

Table 6. Experimental kinetic parameter for the degenerate Cope rearrangement of homotropilidenes 13a, 13b, 16a, 17b, 20a, 21a and 21b

Synthesis of 3,4-Diazanorcaradienes

Dimethyl

1,6-Diphenyl-3,4-diazanorcaradiene-2,5-dicarboxylate

(11f): Compound 10f (1.00 g, 5.20 mmol) was added in portions at

room temp. to a stirred solution of 9a (800 mg, 4.00 mmol) in

CH₂Cl₂(20 mL), and stirring was continued until the red colour of

the tetrazine had disappeared. Purification by recrystallization

(CCl₄) afforded 11f (1.05 g, 2.90 mmol, 72%) as yellow crystals;

1

m.p. 172Ϫ174 °C. Ϫ IR (KBr): ν˜ ϭ 3080Ϫ2960, 1720 cm^Ϫ1. Ϫ H

2

NMR (250 MHz, CDCl₃, θ ϭ 248 K): δ ϭ 0.96 (d, J ϭ 5.0 Hz, 1

H, 7-H_syn), 3.60 (d, ²J ϭ 5.0 Hz, 1 H, 7-H_anti), 3.63 (s, 6 H, OCH₃),

7.03 (s, broad, 10 H, Ar-H). Ϫ UV/Vis (CH₂Cl₂): λ (ε) ϭ 252

(6300). Ϫ C₂₁H₁₈N₂O₄(362.4): calcd. C 69.60, H 5.00, N 7.73;

found C 69.28, H 5.21, N 7.77.

Figure 2. Arrhenius plots for the Cope rearrangements of homotro-

7-Methyl-2,5-diphenyl-3,4-diazanorcaradiene (11h): Compounds 9c

(1.30 g, 5.55 mmol) and 10c were stirred in CH₂Cl₂(80 mL) at

room temp. overnight according to General Procedure (1). Purifica-

tion by recrystallization (CH₂Cl₂/EtOAc) afforded 11h (1.40 g,

pilidenes 13a, 13b, 16a, 17b, 20a, 21a, 21b

was complete (reaction times: see below). After evaporation of the

solvent, the crude material was purified as described below.

˜

5.40 mmol, 98%) as yellow crystals; m.p. 135 °C. Ϫ IR (KBr): ν ϭ

3040, 2925, 1530, 1495, 1450, 1440, 1390, 755, 680 cm^Ϫ1. Ϫ ¹H

NMR (250 MHz, CDCl₃): δ ϭ 0.73 (m, 1 H, 7-H_syn), 1.60 (d, ³J ϭ

6.1 Hz, 3 H, 7-CH₃-anti), 2.47 (d, ³J ϭ 4.4 Hz, 2 H, 1-H, 6-H),

7.41Ϫ8.34 (m, 10 H, Ar-H). Ϫ UV/Vis (CH₃CN): λ (ε) ϭ 315

(17780). Ϫ C₁₈H₁₆N₂(260.3): calcd. C 83.04, H 6.20, N 10.76;

found C 83.33, H 6.38, N 10.57.

General Procedure (5) for the High-Pressure Synthesis of Tetracyclic

Azo Compounds 12v, 12z and 12b₁: The 3,4-diazanorcaradiene 11

was dissolved in CH₂Cl₂(3Ϫ4 mL) and transferred into a high-

pressure vessel. After addition of the cyclopropene 10e, the reaction

vessel was pressurized to max. 8.0 kbar at a temperature of 52Ϫ60

°C until completion of the reaction was indicated by TLC analysis

(reaction times: see below). After evaporation of the solvent, the

crude material was purified as described below.

1-Methyl-2,5-bis(2-pyridyl)-3,4-diazanorcaradiene

(11j):

Com-

pounds 9d (2.30 g, 9.73 mmol) and 10b were stirred at room temp.

overnight in CH₂Cl₂(60 mL) and toluene (40 mL) according to

General Procedure (1). Purification by FC (CH₂Cl₂/ethanol ϭ 10:1)

and recrystallization (CH₂Cl₂/n-hexane) afforded 11j (1.60 g,

6.10 mmol, 63%) as yellow crystals; m.p. 139Ϫ142 °C. Ϫ IR (KBr):

Synthesis of 3,4-Homotropilidenes. ؊ General Procedure (6) for the

Photolysis of Tetracyclic Azo Compounds 13a, 14a؊14b, 16a, 17a,

20a؊20c, 21a؊21b and 25a: The photolysis was carried out in a

water-cooled immersion well photoreactor constructed from

quartz. The photoreactor was provided with a medium-pressure

mercury lamp (HPK 125 W, Philips) and a Pyrex filter. The photo-

active compound was dissolved in an inert solvent (vide infra) and

photolyzed with magnetic stirring (reaction times: see below).

˜

ν ϭ 3090, 3060, 3000, 2940, 1585, 1565, 1550, 1460, 1430, 1390,

1

1380, 1350, 1040, 1020, 995, 970, 790, 740, 705 cm^Ϫ1. Ϫ H NMR

2

3

(250 MHz, CDCl₃): δ ϭ 0.60 (dd, J ϭ 3.8, J ϭ 5.2 Hz, 1 H, 7-

2

3

H_syn), 1.56 (s, 3 H, CH₃), 2.23 (dd, J ϭ 3.8, J ϭ 9.7 Hz, 1 H, 7-

H_anti), 3.13 (dd, ³J ϭ 5.2, J ϭ 9.7 Hz, 1 H, 6-H), 7.36Ϫ7.43 (m, 2

3

General Procedure (7) for the Photolysis of Tetracyclic Azo Com-

pounds 13b؊13f, 14c؊14d, 16b, 18a؊18b, 20d؊20f, 21c, 22a؊22b

and 26a: The photochemical reaction was carried out on an optical

bench arrangement, utilizing a focused high-pressure lamp (type

HBO-500 W; Osram) and a glass filter (λ_maxϭ 280 nm; Schott).

The reactant was dissolved in an inert solvent (vide infra) and irra-

H, Ar-H), 7.79Ϫ7.86 (m, 2 H, Ar-H), 8.05Ϫ8.09 (m, 1 H, Ar-H),

8.50Ϫ8.54 (m, 1 H, Ar-H), 8.73Ϫ8.76 (m, 2 H, Ar-H). Ϫ C₁₆H₁₄N₄

(262.3): calcd. C 73.26, H 5.38, N 21.26; found C 72.83, H 5.16,

N 21.24.

7-Methyl-2,5-bis(2-pyridyl)-3,4-diazanorcaradiene (11k): Com-

diated with stirring in a water-cooled quartz cell (reaction times: pounds 9d (2.30 g, 9.73 mmol) and 10c were stirred in CH₂Cl₂

see below).

2648

(70 mL) and toluene (40 mL) at room temp. overnight according

Eur. J. Org. Chem. 2001, 2639Ϫ2657

Synthesis and Properties of Homotropilidenes

FULL PAPER

to General Procedure (1). Purification by FC (DMF/CH₂Cl₂/tolu-

ene ϭ 1:2:3) and recrystallization (CH₂Cl₂/n-hexane) afforded 11k

H, 6-H, 8-H), 3.97 (s, 6 H, OCH₃). Ϫ ¹³C NMR (22.63 MHz,

CDCl₃): δ ϭ 18.7 (ϭCH, 4 C, 2-C, 4-C, 6-C, 8-C), 28.2 (ϪCH₃, 6

(1.95 g, 7.43 mmol, 76%) as yellow crystals; m.p. 165Ϫ166 °C. Ϫ C, CH₃), 29.1 (ϭCH, 2 C, 3-C, 7-C), 29.1 (quat. C, 2 C, tBu-C),

IR (KBr): ν˜ ϭ 3060, 3020, 2960, 2920, 2875, 1580, 1560, 1530, 52.8 (ϪCH₃, 2 C, OCH₃), 74.6 (quat. C, 2 C, 1-C, 5-C), 172.1 (quat.

1490, 1470, 1385, 1260, 1150, 1120, 1100, 990, 785, 745 cm^Ϫ1. Ϫ

C, 2 C, CϭO). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 275 (356), 283

3

¹H NMR (250 MHz, CDCl₃): δ ϭ 0.65 (dd, ³J ϭ 5.9, J ϭ 4.2 Hz, (294), 295 (322), 332 (36), 372 (50). Ϫ C₂₀H₃₀N₂O₄(362.5): calcd.

3

1 H, 7-H_syn), 1.58 (d, J ϭ 5.9 Hz, 3 H, 7-CH₃-anti), 3.31 (d, J ϭ C 66.27, H 8.34, N 7.73; found C 66.26, H 8.26, N 7.51.

4.2 Hz, 2 H, 1-H, 6-H), 7.35Ϫ7.42 (m, 2 H, Ar-H), 7.76Ϫ7.84 (m,

Dimethyl exo,exo-2,6-Dimethyl-19,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

2 H, Ar-H), 8.47Ϫ8.57 (m, 2 H, Ar-H), 8.71Ϫ8.74 (m, 2 H, Ar-H).

dec-9-ene-1,5-dicarboxylate (12f): This compound was synthesized

Ϫ UV/Vis (CH₃CN): λ (ε) ϭ 248 (12200), 323 (15800). Ϫ C₁₆H₁₄N₄

according to General Procedure (2); 9a (7.10 g, 35.9 mmol) and 10b

in CH₂Cl₂(20 mL), after purification by recrystallization (meth-

(262.3): calcd. N 21.26; found N 21.27.

anol), gave 12f (7.50 g, 26.9 mmol, 75%) as colourless crystals; m.p.

Synthesis of Tetracyclic Azo Compounds

1

158Ϫ159 °C. Ϫ IR (KBr): ν ϭ 1730 cm^Ϫ1. Ϫ H NMR (90 MHz,

˜

Dimethyl exo,exo-3-Methyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]dec-

9-ene-1,5-dicarboxylate (12b): This compound was synthesized ac-

cording to General Procedure (3); 11a (2.50 g, 11.9 mmol) and 10c,

after stirring in benzene (30 mL) at room temp. for 15 min and

purification by recrystallization (methanol), yielded 12b (2.18 g,

2

3

CDCl₃): δ ϭ 0.12Ϫ0.63 (m, J ϭ 7.5, J ϭ 4.5, J ϭ 8.0 Hz, 4 H,

3,7-H_syn, 3,7-H_anti), 1.23 (s, 6 H, 2,6-CH₃), 1.81 (dd, ³J ϭ 8.0, ³J ϭ

4.5 Hz, 2 H, 4-H, 8-H), 4.00 (s, 6 H, OCH₃). Ϫ ¹³C NMR

(22.63 MHz, CDCl₃): δ ϭ 13.4 (ϪCH₂Ϫ, 2 C, 3-C, 7-C), 16.9

(ϪCH₃, 2 C, 2,6-CH₃), 18.5 (ϭCH, 2 C, 4-C, 8-C), 20.8 (quat. C,

2 C, 4-C, 8-C), 52.8 (ϪCH₃, 2 C, OCH₃), 78.5 (quat. C, 2 C, 1-C,

5-C), 171.1 (quat. C, 2 C, CϭO). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ

368 (68). Ϫ C₁₄H₁₈N₂O₄(278.3): calcd. C 60.42, H 6.52, N 10.07;

found C 60.45, H 6.65, N 10.03.

8.25 mmol, 69%) as colourless crystals, m.p. 70Ϫ71 °C. Ϫ IR

1

(KBr): ν ϭ 1735 cm^Ϫ1. Ϫ H NMR (90 MHz, CDCl₃): δ ϭ 0.10

˜

(dt, ²J ϭ 7.6, ³J ϭ 3.8 Hz, 1 H, 7-H_syn), 0.5 (m, ³J ϭ 5.9, ³J ϭ

3.1 Hz, 1 H, 3-H_syn), 0.5 (m, J ϭ 7.6, J ϭ 7.6 Hz, 1 H, 7-H_anti),

2

3

0.96 (d, J ϭ 5.9 Hz, 3 H, 3-CH₃-anti), 1.67 (d, J ϭ 3.1 Hz, 2 H,

Dimethyl exo,exo-3,6-Dimethyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

dec-9-ene-1,5-dicarboxylate (12g): This compound was synthesized

according to General Procedure (3); 11b (2.40 g, 10.7 mmol) and

10c in benzene (30 mL), after recrystallization (methanol), yielded

2-H, 4-H), 1.89 (dd, ³J ϭ 3.8, J ϭ 7.6 Hz, 2 H, 6-H, 8-H). Ϫ UV/

3

Vis (1,4-dioxane): λ (ε) ϭ 372 (68). Ϫ C₁₃H₁₆N₂O₄(264.3): calcd.

C 59.08, H 6.10, N 10.60; found C 59.01, H 6.03, N 10.74.

Dimethyl exo,exo-2-Methyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]dec-

9-ene-1,5-dicarboxylate (12c): This compound was synthesized ac-

cording to General Procedure (3); 11b (5.00 g, 23.8 mmol) and 10a,

after stirring in CH₂Cl₂(30 mL) at room temp. for 15 min and

purification by recrystallization (methanol), yielded 12c (4.50 g,

12g (2.26 g, 8.13 mmol, 76%) as colourless crystals; m.p. 107Ϫ108

1

°C. Ϫ IR (KBr): ν ϭ 1720 cm^Ϫ1. Ϫ H NMR (60 MHz, CDCl₃):

˜

3

δ ϭ 0.20Ϫ0.54 (m, 3 H, 3/7-H_syn, 3-H_anti), 0.96 (d, J ϭ 6.6 Hz, 3

H, 3-CH₃-anti), 1.20 (s, 3 H, 6-CH₃), 1.72 (dd, ³J ϭ 3.6, ³J ϭ

3

7.4 Hz, 1 H, 8-H), 1.38Ϫ1.95 (m, J ϭ 2.6, J ϭ 8.0 Hz, 2 H, 2-H,

4-H), 4.00 (s, 6 H, OCH₃). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 370

(71). Ϫ C₁₄H₁₈N₂O₄(278.3): calcd. C 60.42, H 6.52, N 10.07; found

C 60.47, H 6.43, N 10.14.

17.0 mmol, 71%) as colourless crystals, m.p. 98Ϫ99 °C. Ϫ IR

1

(KBr): ν ϭ 1740 cm^Ϫ1. Ϫ H NMR (90 MHz, CDCl₃): δ ϭ 0.08

˜

2

3

2

(ddd, J ϭ 7.8, J ϭ 3.6, J ϭ 3.6 Hz, 1 H, 7-H_syn), 0.32 (dd, J ϭ

3

2

3

6.7, J ϭ 4.8 Hz, 1 H, 3-H_syn), 0.40 (dd, J ϭ 6.7, J ϭ 6.8 Hz, 1

Dimethyl exo,exo-2,4-Diphenyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

dec-9-ene-1,5-dicarboxylate (12h): This compound was synthesized

according to General Procedure (4); 11a (4.00 g, 19 mmol) and 10f

(3.60 g, 18.7 mmol) were stirred in CH₂Cl₂(70 mL) at reflux for

40 h. Purification of the crude product by recrystallization (meth-

anol) gave 12h (4.80 g, 11.9 mmol, 63%) as colourless crystals; m.p.

181Ϫ182 °C. Ϫ IR (KBr): ν˜ ϭ 1774, 1745 cm^Ϫ1. Ϫ ¹H NMR

(60 MHz, CDCl₃): δ ϭ 0.15 (dt, ²J ϭ 7.0, ³J ϭ 3.5 Hz, 1 H, 7-

H, 3-H_anti), 0.58 (ddd, ²J ϭ 7.8, ³J ϭ 7.8, ³J ϭ 7.8 Hz, 1 H, 7-

3

H_anti), 1.19 (s, 3 H, CH₃), 1.60 (dd, J ϭ 6.8, J ϭ 4.8 Hz, 1 H, 4-

3

H), 1.88 (dd, J ϭ 7.8, J ϭ 3.6 Hz, 1 H, 6-H), 2.08 (dd, J ϭ 7.8,

³J ϭ 3.6 Hz, 1 H, 8-H), 3.96 (s, 6 H, OCH₃). Ϫ UV/Vis (1,4-diox-

ane): λ (ε) ϭ 371 (72). Ϫ C₁₃H₁₆N₂O₄(264.3): calcd. C 59.08, H

6.10, N 10.60; found C 59.38, H 6.21, N 10.69.

Dimethyl exo,exo-3,7-Dimethyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

dec-9-ene-1,5-dicarboxylate (12d): This compound was synthesized

according to General Procedure (2); 9a (7.20 g, 36.4 mmol) and

10c, after stirring in CH₂Cl₂(30 mL) at room temp. for 15 min and

purification by recrystallization (methanol), yielded 12d (6.70 g,

2

3

H_syn), 0.73 (dt, J ϭ 7.0, J ϭ 7.0 Hz, 1 H, 7-H_anti), 1.33 (s, 2 H,

3

3-H_syn, 3-H_anti), 2.59 (dd, J ϭ 7.0, J ϭ 3.5 Hz, 2 H, 6-H, 8-H),

3.59 (s, 6 H, OCH₃), 7.02Ϫ7.53 (m, 10 H, Ar-H). Ϫ UV/Vis (1,4-

dioxane): λ (ε) ϭ 370 (117). Ϫ C₂₄H₂₂N₂O₄(402.4): calcd. C 71.62,

H 5.51, N 6.96; found C 71.43, H 5.52, N 6.85.

24.1 mmol, 66%) as colourless crystals; m.p. 110Ϫ111 °C. Ϫ IR

1

(KBr): ν ϭ 1730 cm^Ϫ1. Ϫ H NMR (90 MHz, CDCl₃): δ ϭ 0.37

˜

exo,exo-3-Methyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]dec-

9-ene-1,5-dicarbonitrile (12j): Hydrolysis of the carboxylic ester 12b

(13.0 g, 49.2 mmol) with KOH (7.80 g, 140 mmol) in aqueous

methanol (120 mL, H₂O/methanol ϭ 1:2) and acidification with

conc. HCl yielded, after recrystallization (H₂O), the dicarboxylic

acid (10.0 g, 42.2 mmol, 86%). This (9.50 g, 40.2 mmol) was stirred

with SOCl₂(94.8 g, 58.0 mL, 797 mmol) at room temperature for

3.5 h; addition of conc. ammonia (300 mL) in acetone (100 mL)

then produced the amide (7.00 g, 29.9 mmol, 74%) as colourless

crystals after recrystallization (H₂O/ethanol ϭ 1:10). A suspension

of the amide (6.60 g, 28.2 mmol) and freshly distilled POCl₃

3

(tq, J ϭ 6.0, J ϭ 3.0 Hz, 2 H, 3,7-H_syn), 0.93 (d, J ϭ 6.0 Hz, 6

3

H, 3,7-CH₃-anti), 1.63 (d, J ϭ 3.0 Hz, 4 H, 2-H, 4-H, 6-H, 8-H),

3.97 (s, 6 H, OCH₃). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 371 (79). Ϫ

C₁₄H₁₈N₂O₄(278.3): calcd. C 60.42, H 6.52, N 10.07; found C

60.65, H 6.57, N 10.25.

Dimethyl

exo,exo-3,7-Di-tert-butyl-9,10-diazatetracyclo-

[3.3.2.0²·⁴.0⁶·⁸]dec-9-ene-1,5-dicarboxylate (12e): This compound

was synthesized according to General Procedure (2); 9a (1.00 g,

5.05 mmol) and 10d (1.25 g, 13.0 mmol) were stirred in CH₂Cl₂

(10 mL) at room temp. overnight. Purification of the crude product

by FC (Et₂O) gave 12e (213 mg, 0.59 mmol, 12%) as colourless (6.61 g, 4.02 mL, 43.1 mmol) in 1,2-dichloroethylene (150 mL) was

crystals, m.p. 124Ϫ125 °C. Ϫ IR (KBr): ν ϭ 2960, 1740 cm^Ϫ1. Ϫ

heated at reflux for 18 h. After evaporation of the solvent, the crude

material was purified by recrystallization (CH₃CN), affording 12j

(2.40 g, 12.1 mmol, 43%) as colourless crystals, m.p. 175Ϫ176 °C.

˜

¹H NMR (90 MHz, CDCl₃): δ ϭ 0.33 (t, ³J ϭ 4.0 Hz, 2 H, 3-H_syn

,

3

7-H_syn), 0.80 (s, 18 H, tBu-H), 1.73 (d, J ϭ 4.0 Hz, 4 H, 2-H, 4-

Eur. J. Org. Chem. 2001, 2639Ϫ2657

2649

J. Sauer et al.

FULL PAPER

1

Ϫ IR (KBr): ν˜ ϭ 2250 cm^Ϫ1. Ϫ H NMR (90 MHz, [D₆]DMSO,

(2.10 g, 6.29 mmol, 91%). This (1.80 g, 5.39 mmol) was stirred with

θ ϭ 323 K): δ ϭ 0.04 (dt, ²J ϭ 7.6, J ϭ 3.6 Hz, 1 H, 7-H_syn), 0.45 SOCl₂(16.3 g, 10.0 mL, 137 mmol) at room temp. for 3.5 h; after

(tq, J ϭ 6.2, J ϭ 3.1 Hz, 1 H, 3-H_syn), 0.74 (dt, J ϭ 7.6, J ϭ removal of excess SOCl₂, addition of conc. ammonia (50 mL) in

7.6 Hz, 1 H, 7-H_anti), 0.95 (d, J ϭ 6.2 Hz, 3 H, 3-CH₃-anti), 2.13 acetone (30 mL) then gave the amide (1.03 g, 3.10 mmol, 58%) as

(d, J ϭ 3.1 Hz, 2 H, 2-H, 4-H), 2.29 (dd, J ϭ 3.6, J ϭ 7.6 Hz,

3

2

3

colourless crystals after recrystallization (CH₃CN). A suspension of

2 H, 6-H, 8-H). Ϫ UV/Vis (methanol): λ (ε) ϭ 368 (78). Ϫ the amide (1.60 g, 4.82 mmol) and freshly distilled POCl₃(1.25 g,

C₁₁H₁₀N₄(198.2): calcd. C 66.65, H 5.09, N 28.27; found C 66.82, 0.76 mL, 8.15 mmol) in 1,2-dichloroethylene (20 mL) was heated at

H 5.15, N 28.35.

reflux for 20 h. After evaporation of the solvent, the crude material

was purified by FC (CH₂Cl₂) and recrystallization (CH₂Cl₂/n-hex-

ane), affording 12m (0.77 g, 2.60 mmol, 54%) as colourless crystals,

exo,exo-2-Methyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]dec-

9-ene-1,5-dicarbonitrile (12k): Hydrolysis of the carboxylic ester 12c

(10.0 g, 37.8 mmol) with KOH (6.00 g, 108 mmol) in aqueous

methanol (90 mL, H₂O/methanol ϭ 1:2) and acidification with

conc. HCl yielded, after recrystallization (H₂O), the dicarboxylic

acid (7.30 g, 30.9 mmol, 82%). This (7.10 g, 30.1 mmol) was stirred

with SOCl₂(70.9 g, 43.5 mL, 596 mmol) at room temp. for 2.5 h,

and after removal of excess SOCl₂, addition of conc. ammonia

(230 mL) in acetone (60 mL) then gave the amide (3.60 g,

15.5 mmol, 51%) as colourless crystals, after recrystallization (H₂O/

ethanol ϭ 3:10). A suspension of the amide (3.40 g, 14.5 mmol)

˜

m.p. 165Ϫ167 °C. Ϫ IR (KBr): ν ϭ 3070, 2965, 2910, 2875, 2245

1

3

cm^Ϫ1. Ϫ H NMR (90 MHz, CDCl₃): δ ϭ 0.40 (t, J ϭ 4.0 Hz, 2

3

H, 3,7-H_syn), 0.87 (s, 18 H, tBu-H), 1.85 (d, J ϭ 4.0 Hz, 4 H, 2-H,

4-H, 6-H, 8-H). Ϫ ¹³C NMR (22.63 MHz, CDCl₃): δ ϭ 19.4 (ϭCH,

4 C, 2-C, 4-C, 6-C, 8-C), 28.0 (ϪCH₃, 6 C, CH₃), 29.0 (quat. C, 2

C, tBu-C), 29.3 (ϭCH, 2 C, 3-C, 7-C), 64.4 (quat. C, 2 C, 1-C, 5-

C), 118.2 (quat. C, 2 C, CN). Ϫ UV/Vis (methanol): λ (ε) ϭ 369

(39), 350 (22), 333 (22). Ϫ C₁₈H₂₄N₄(296.4): calcd. C 72.94, H 8.16,

N 18.90; found C 72.61, H 8.00, N 18.99.

and freshly distilled POCl₃(3.41 g, 2.07 mL, 22.2 mmol) in 1,2- exo,exo-2,6-Dimethyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

dichloroethylene (70 mL) was heated at reflux for 1 d. After evap- dec-9-ene-1,5-dicarbonitrile (12n): Hydrolysis of the carboxylic ester

oration of the solvent, the crude material was purified by recrystal-

12f (7.50 g, 27.0 mmol) with KOH (5.30 g, 94.6 mmol) in aqueous

lization (methanol), affording 12k (1.50 g, 7.57 mmol, 52%) as col- methanol (90 mL, H₂O/methanol ϭ 1:2) and acidification with

ourless crystals, m.p. 128Ϫ130 °C. Ϫ IR (KBr): ν ϭ 2250 cm^Ϫ1. Ϫ

¹H NMR (60 MHz, CDCl₃): δ ϭ 0.32 (ddd, ²J ϭ 5.9, ³J ϭ 3.7, acid (6.00 g, 24.0 mmol, 89%). This (2.50 g, 10.0 mmol) was stirred

conc. HCl yielded, after recrystallization (H₂O), the dicarboxylic

˜

³J ϭ 3.7 Hz, 1 H, 7-H_syn), 0.48 (dd, J ϭ 6.1, J ϭ 3.8 Hz, 1 H, 3-

with SOCl₂(32.6 g, 20.0 mL, 274 mmol) at room temp. for 3 h;

2

3

H_syn), 0.63 (dd, ³J ϭ 7.3, ²J ϭ 6.1 Hz, 1 H, 3-H_anti), 0.83 (ddd, after removal of excess SOCl₂, addition of conc. ammonia (75 mL)

3

2

³J ϭ 7.8, J ϭ 7.8, J ϭ 5.9 Hz, 1 H, 7-H_anti), 1.43 (s, 3 H, CH₃), in acetone (18 mL) then gave the amide (1.30 g, 5.20 mmol, 52%)

1.77 (dd, ³J ϭ 7.3, ³J ϭ 3.8 Hz, 1 H, 4-H), 2.00 (ddd, ³J ϭ 7.8,

as colourless crystals after recrystallization (ethanol). A suspension

3

³J ϭ 7.8, J ϭ 3.7 Hz, 1 H, 6-H or 8-H), 2.15 (ddd, ³J ϭ 7.8, J ϭ of the amide (2.80 g, 11.3 mmol) and freshly distilled POCl₃

7.8, ³J ϭ 3.7 Hz, 1 H, 8-H or 6-H). Ϫ UV/Vis (methanol): λ (ε) ϭ (2.50 g, 1.52 mL, 16.3 mmol) in 1,2-dichloroethylene (70 mL) was

367 (77). Ϫ C₁₁H₁₀N₄(198.2): calcd. C 66.65, H 5.09, N 28.27;

found C 67.14, H 5.26, N 28.00.

heated at reflux for 1 d. Purification of the crude product by recrys-

tallization (methanol) afforded 12n (1.37 g, 6.46 mmol, 57%) as col-

ourless crystals, m.p. 159Ϫ160 °C. Ϫ IR (KBr): ν˜ ϭ 2250 cm^Ϫ1. Ϫ

exo,exo-3,7-Dimethyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

dec-9-ene-1,5-dicarbonitrile (12l): Hydrolysis of the carboxylic ester

12d (6.50 g, 23.4 mmol) with KOH (3.80 g, 68.1 mmol) in aqueous

methanol (60 mL, H₂O/methanol ϭ 1:2) and acidification with

conc. HCl yielded, after recrystallization (H₂O), the dicarboxylic

acid (5.80 g, 23.2 mmol, 99%). This (5.50 g, 22.0 mmol) was stirred

with SOCl₂(65.2 g, 40.0 mL, 548 mmol) at room temp. for 3 h;

after removal of excess SOCl₂, addition of conc. ammonia

2

3

¹H NMR (60 MHz, CDCl₃): δ ϭ 0.40 (dd, J ϭ 7.3, J ϭ 4.0 Hz,

2 H, 3,7-H_syn), 0.65 (dd, ²J ϭ 7.3, ³J ϭ 7.2 Hz, 2 H, 3,7-H_anti), 1.44

3

(s, 6 H, 2,6-CH₃), 1.81 (dd, ³J ϭ 7.2, J ϭ 4.0 Hz, 2 H, 4-H, 8-H).

Ϫ UV/Vis (methanol): λ (ε) ϭ 366 (71). Ϫ C₁₂H₁₂N₄(212.2): calcd.

C 67.90, H 5.70, N 26.40; found C 67.89, H 5.66, N 26.14.

exo,exo-2,4-Diphenyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

dec-9-ene-1,5-dicarbonitrile (12o): Hydrolysis of the carboxylic ester

(150 mL) in acetone (50 mL) then gave the amide (5.00 g, 12h (2.30 g, 5.70 mmol) with KOH (1.20 g, 21.5 mmol) in aqueous

20.2 mmol, 92%) as colourless crystals, after recrystallization (H₂O/ methanol (60 mL, H₂O/methanol ϭ 1:2) and acidification with

ethanol ϭ 1:1). A suspension of the amide (4.60 g, 18.5 mmol) and conc. HCl yielded, after recrystallization (H₂O), the dicarboxylic

freshly distilled POCl₃(4.38 g, 2.66 mL, 28.6 mmol) in 1,2-dichlor- acid (2.10 g, 5.60 mmol, 98%). This (2.10 g, 5.60 mmol) was stirred

oethylene (120 mL) was heated at reflux for 2 d. After evaporation with SOCl₂(16.3 g, 10.0 mL, 137 mmol) at room temp. for 2 h.

of the solvent, the crude material was purified by recrystallization After removal of excess SOCl₂, addition of conc. ammonia (75 mL)

(methanol), affording 12l (2.50 g, 11.8 mmol, 64%) as colourless in acetone (18 mL) then gave the amide (1.60 g, 4.30 mmol, 77%)

crystals, m.p. 170Ϫ173 °C. Ϫ IR (KBr): ν˜ ϭ 2260 cm^Ϫ1. Ϫ ¹H as colourless crystals after recrystallization (ethanol). A suspension

3

NMR (60 MHz, CD₂Cl₂): δ ϭ 0.53 (tq, J ϭ 5.9, J ϭ 3.2 Hz, 2 of the amide (1.50 g, 4.00 mmol) and freshly distilled POCl₃(1.50 g,

H, 3,7-H_syn), 1.00 (d, ³J ϭ 5.9 Hz, 6 H, 3,7-CH₃-anti), 1.72 (d, ³J ϭ 4.00 mmol) in 1,2-dichloroethylene (70 mL) was heated at reflux

3.2 Hz, 4 H, 2-H, 4-H, 6-H, 8-H). Ϫ ¹³C NMR (22.63 MHz,

for 2 d. Purification of the crude product by recrystallization (meth-

CDCl₃): δ ϭ 13.5 (ϭCH, 2 C, 3-C, 7-C), 15.4 (ϪCH₃, 2 C, 3,7- anol) afforded 12o (120 mg, 0.36 mmol, 9%) as colourless crystals,

CH₃-anti), 23.5 (ϭCH, 4 C, 2-C, 4-C, 6-C, 8-C), 64.0 (quat. C, 2 m.p. 192Ϫ194 °C. Ϫ IR (KBr): ν ϭ 2250 cm^Ϫ1. Ϫ ¹H NMR

˜

C, 1-C, 5-C), 118.4 (quat. C, 2 C, CN). Ϫ UV/Vis (1,4-dioxane): λ (60 MHz, CD₂Cl₂): δ ϭ 0.43 (dt, ²J ϭ 7.6, ³J ϭ 3.6 Hz, 1 H, 7-

2

3

2

(ε) ϭ 367 (81). Ϫ C₁₂H₁₂N₄(212.2): calcd. C 67.90, H 5.70, N H_syn), 0.93 (dt, J ϭ 7.6, J ϭ 7.6 Hz, 1 H, 7-H_anti), 1.26 (d, J ϭ

26.40; found C 67.82, H 5.66, N 26.36.

2

7.5 Hz, 1 H, 3-H_syn), 1.52 (d, J ϭ 7.5 Hz, 1 H, 3-H_anti), 2.62 (dd,

³J ϭ 7.6, ³J ϭ 3.6 Hz, 2 H, 6-H, 8-H), 7.22Ϫ7.61 (m, 10 H, Ar-

H). Ϫ C₂₂H₁₆N₄(336.4): calcd. C 78.54, H 4.80, N 16.66; found C

78.49, H 4.99, N 16.69.

exo,exo-3,7-Di-tert-butyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

dec-9-ene-1,5-dicarbonitrile (12m): Hydrolysis of the carboxylic ester

12e (2.50 g, 6.91 mmol) with KOH (2.00 g, 35.8 mmol) in aqueous

methanol (40 mL, H₂O/methanol ϭ 1:2) and acidification with conc. exo,exo-1,5-Diphenyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

HCl yielded, after recrystallization (H₂O), the dicarboxylic acid dec-9-ene (12p): Compounds 11g (1.66 g, 5.79 mmol) and 10a were

2650

Eur. J. Org. Chem. 2001, 2639Ϫ2657

Synthesis and Properties of Homotropilidenes

FULL PAPER

stirred in CH₂Cl₂(50 mL) at 35 °C overnight, according to General

Procedure (3). After purification by FC (EtOAc/n-hexane ϭ 2:1)

and recrystallization (Et₂O), a mixture of two azo compounds was

obtained as colourless crystals containing 12p (479 mg, 1.67 mmol,

29%) in a 3:2 ratio (determined by analytical HPLC: LiChrosorb

RP 18, methanol/H₂O ϭ 90:10). Subjection of this mixture to

photolysis according to General Procedure (7) gave a mixture of the

corresponding homotropilidenes, which could then be separated by

preparative HPLC (LiChroprep. RP 8, methanol/H₂O ϭ 93:7).

C), 149.2 (ϭCH, 2 C, Ar-C), 161.8 (quat. C, 2 C, Ar-C). Ϫ UV/

Vis (CH₃CN): λ (ε) ϭ 259 (7310), 379 (111). Ϫ C₁₉H₁₈N₄(302.4):

calcd. C 75.47, H 6.00, N 18.53; found C 75.66, H 6.14, N 18.45.

exo,exo-2-Methyl-1,5-bis(2-pyridyl)-9,10-diazatetracyclo-

[3.3.2.0²·⁴.0⁶·⁸]dec-9-ene (12u): Compounds 11i (1.00 g, 4.03 mmol)

and 10b were stirred in CH₂Cl₂(55 mL) and toluene (70 mL) at

room temp. for 4 h according to General Procedure (3). Purifica-

tion of the crude product by FC (CH₂Cl₂/ethanol ϭ 15:1) and

recrystallization (CH₂Cl₂/n-hexane) afforded 12u (780 mg,

2.58 mmol, 63%) as colourless crystals, m.p. 134Ϫ135 °C. Ϫ IR

1

Analytical data for 12p obtained from the inseparable mixture: H

NMR (250 MHz, CDCl₃): δ ϭ 0.16Ϫ0.81 (m, 4 H, 3,7-H_syn, 3,7-

˜

(KBr): ν ϭ 3060, 3010, 2970, 2930, 2870, 1585, 1565, 1465, 1430,

3

H_anti), 1.83 (dd, J ϭ 7.7, J ϭ 3.7 Hz, 4 H, 2-H, 4-H, 6-H, 8-H),

7.24Ϫ7.56 (m, 6 H, Ar-H), 7.77Ϫ7.86 (m, 4 H, Ar-H).

1070, 1035, 990, 880, 870, 855 cm^Ϫ1. Ϫ ¹H NMR (250 MHz,

2

3

CDCl₃): δ ϭ 0.12Ϫ0.15 (m, 1 H, 7-H_syn), 0.38 (dd, J ϭ 6.2, J ϭ

exo,exo-3-Methyl-1,5-diphenyl-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]-

7.8 Hz, 1 H, 3-H_anti), 0.48 (dd, ²J ϭ 6.2, J ϭ 3.6 Hz, 1 H, 3-H_syn),

dec-9-ene (12q): Compounds 11g (2.50 g, 10.1 mmol) and 10c were 0.61Ϫ0.66 (m, 1 H, 7-H_anti), 0.98 (s, 3 H, 2-CH₃), 1.88 (dd, J ϭ

stirred in CH₂Cl₂(50 mL) at 35 °C for 15 h according to General 3.6, J ϭ 7.8 Hz, 1 H, 4-H), 2.13Ϫ2.18 (m, 1 H, 6-H), 2.52Ϫ2.57

3

Procedure (3). Purification by FC (EtOAc/n-hexane ϭ 2:1) and

(m, 1 H, 8-H), 7.25Ϫ7.30 (m, 2 H, Ar-H), 7.76Ϫ7.85 (m, 3 H, Ar-

recrystallization (Et₂O) afforded 12q (1.43 g, 4.77 mmol, 51%) as H), 8.10Ϫ8.12 (m, 1 H, Ar-H), 8.69Ϫ8.72 (m, 2 H, Ar-H). Ϫ ¹³C

colourless crystals, m.p. 106Ϫ108 °C. Ϫ IR (KBr): ν˜ ϭ 3060, 3030, NMR (100 MHz, CDCl₃): δ ϭ 6.1 (ϪCH₂Ϫ, 1 C, 7-C), 12.1 (ϭ

2950, 2920, 1600, 1490, 1440, 1315, 1050, 1020, 750, 680 cm^Ϫ1. Ϫ

CH, 1 C, 8-C), 13.4 (ϪCH₂Ϫ, 1 C, 3-C), 17.1 (ϭCH, 1 C, 6-C),17.5

2

3

¹H NMR (250 MHz, CDCl₃): δ ϭ 0.35 (dt, J ϭ 6.2, J ϭ 3.4 Hz, (ϪCH₃, 1-C, 2-CH₃), 23.1 (quat. C, 1 C, 2-C), 24.9 (ϭCH, 1 C, 4-

1 H, 3-H_syn), 0.66Ϫ0.77 (m, 2 H, 7-H_syn, 7-H_anti), 1.11 (d, ³J ϭ C), 75.5 (quat. C, 1 C, 5-C), 78.6 (quat. C, 1 C, 1-C), 122.1 (ϭCH,

6.1 Hz, 3 H, 3-CH₃-anti), 1.57 (d, ³J ϭ 3.4 Hz, 2 H, 2-H, 4-H), 1 C, Ar-C), 122.4 (ϭCH, 1 C, Ar-C), 122.6 (ϭCH, 1 C, Ar-C),

3

1.77 (dd, ³J ϭ 7.7 Hz; J ϭ 3.6 Hz, 2 H, 6-H, 8-H), 7.23Ϫ7.52 (m,

123.2 (ϭCH, 1 C, Ar-C), 136.4 (ϭCH, 1 C, Ar-C), 136.5 (ϭCH, 1

6 H, Ar-H), 7.78Ϫ7.81 (m, 4 H, Ar-H). Ϫ UV/Vis (CH₃CN): λ C, Ar-C), 148.7 (ϭCH, 1 C, Ar-C), 149.1 (ϭCH, 1 C, Ar-C), 160.4

(ε) ϭ 224 (6890), 386 (66).

(quat. C, 1 C, Ar-C), 161.4 (quat. C, 1 C, Ar-C). Ϫ UV/Vis

(CH₃CN): λ (ε) ϭ 255 (7210), 260 (7450), 348 (16.6), 362 (29.4),

380 (59.3). Ϫ C₁₉H₁₈N₄(302.4): calcd. C 75.47, H 6.00, N 18.53;

found C 75.34, H 6.00, N 18.54.

exo,exo-3,7-Dimethyl-1,5-diphenyl-9,10-diazatetracyclo]-

[3.3.2.0²·⁴.0⁶·⁸dec-9-ene (12r): Compounds 11h (2.85 g, 10.9 mmol)

and 10c were stirred in CH₂Cl₂(50 mL) at 35 °C for 15 h according

to General Procedure (3). Purification by FC (EtOAc/n-hexane ϭ exo,exo-3,3-Dimethyl-1,5-bis(2-pyridyl)-9,10-diazatetracyclo-

2:1) and recrystallization (Et₂O) afforded 12r (1.44 g, 4.80 mmol,

[3.3.2.0²·⁴.0⁶·⁸]dec-9-ene (12v): Compounds 11i (638 mg,

44%) as colourless crystals, m.p. 141Ϫ143 °C. Ϫ IR (KBr): ν ϭ 2.56 mmol) and 10e (940 mg, 13.8 mmol) in CH₂Cl₂(3 mL) were

3070, 3040, 3010, 2950, 1600, 1490, 1445, 1210, 1070, 1025, 755, pressurized in a reaction vessel to 8.0 kbar at 60 °C for 3 d accord-

700 cm^Ϫ1. Ϫ H NMR (60 MHz, CDCl₃): δ ϭ 0.65 (m, 2 H, 2-H, ing to General Procedure (5). Purification by FC (CH₂Cl₂/eth-

˜

1

3

3,7-H_syn), 1.11 (d, J ϭ 6.1 Hz, 6 H, 3,7-CH₃-anti), 1.52 (d, J ϭ anol ϭ 15:1) and recrystallization (EtOAc) afforded 12v (549 mg,

3.2 Hz, 4 H, 2-H, 4-H, 6-H, 8-H), 7.23Ϫ7.53 (m, 6 H, Ar-H), 1.74 mmol, 68%) as pink crystals, m.p. 159Ϫ160 °C. Ϫ IR (KBr):

7.63Ϫ7.82 (m, 4 H, Ar-H). Ϫ ¹³C NMR (22.63 MHz, CDCl₃): δ ϭ ν˜ ϭ 3060, 3010, 2970, 2930, 2880, 1585, 1570, 1470, 1430, 1320,

1

13.7 (ϭCH, 2 C, 3-C, 7-C), 16.3 (ϪCH₃, 2 C, 3,7-CH₃-anti), 25.8 1120, 1100, 1065, 1040, 1005, 820, 780, 735, 700, 620 cm^Ϫ1. Ϫ H

2

3

(ϭCH, 4 C, 2-C, 4-C, 6-C, 8-C), 74.1 (quat. C, 2 C, 1-C, 5-C), 127.3 NMR (250 MHz, CDCl₃): δ ϭ 0.14 (dt, J ϭ 6.5, J ϭ 3.6 Hz, 1

2

3

(ϭCH, 2 C, Ar-C), 127.8 (ϭCH, 2 C, Ar-C), 128.5 (ϭCH, 2 C, Ar- H, 7-H_syn), 0.53 (dt, J ϭ 6.5, J ϭ 7.7 Hz, 1 H, 7-H_anti), 0.93 (s, 3

C), 142.9 (quat. C, 2 C, Ar-C). Ϫ UV/Vis (CH₃CN): λ (ε) ϭ 29 H, 3-CH₃-syn), 1.13 (s, 3 H, 3-CH₃-anti), 2.10 (s, 2 H, 2-H, 4-H),

3

(8895), 385 (62). Ϫ C₂₂H₂₂N₂(300.3): calcd. N 8.97; found N 8.60. 2.25 (dd, J ϭ 3.6, J ϭ 7.7 Hz, 2 H, 6-H, 8-H), 7.29Ϫ7.35 (m, 2

H, Ar-H), 7.81Ϫ7.88 (m, 2 H, Ar-H), 8.15Ϫ8.19 (m, 2 H, Ar-H),

exo,exo-3-Methyl-1,5-bis(2-pyridyl)-9,10-diazatetracyclo-

8.74Ϫ8.77 (m, 2 H, Ar-H). Ϫ ¹³C NMR (63 MHz, CDCl₃): δ ϭ

[3.3.2.0²·⁴.0⁶·⁸]dec-9-ene (12t): Compounds 11i (1.50 g, 6.04 mmol)

5.9 (ϪCH₂Ϫ, 1 C, 7-C), 18.0 (ϭCH, 2 C, 6-C, 8-C), 19.2 (ϪCH₃,

and 10c were stirred in CH₂Cl₂(50 mL) and toluene (35 mL) at

room temp. for 2 d according to General Procedure (3). Purifica-

tion of the crude product by FC (CH₂Cl₂/ethanol ϭ 15:1) and

1 C, 3-CH₃-syn), 23.6 (quat. C, 1 C, 3-C), 30.6 (ϪCH₃, 1 C, 3-CH₃-

anti), 37.8 (ϭCH, 2 C, 2-C, 4-C), 76.6 (quat. C, 2 C, 1-C, 5-C),

122.2 (ϭCH, 2 C, Ar-C), 122.8 (ϭCH, 2 C, Ar-C), 139.4 (ϭCH, 2

recrystallization (CH₂Cl₂/n-hexane) afforded 12t (576 mg,

C, Ar-C), 149.3 (ϭCH, 2 C, Ar-C), 162.0 (quat. C, 2 C, Ar-C). Ϫ

1.90 mmol, 47%) as colourless crystals, m.p. 147Ϫ149 °C. Ϫ IR

UV/Vis (CH₃CN): λ (ε) ϭ 213 (6270), 382 (92). Ϫ C₂₀H₂₀N₄

˜

(KBr): ν ϭ 3060, 3010, 2970, 2940, 2890, 1580, 1565, 1530, 1465,

(316.4): calcd. C 75.92, H 6.37, N 17.71; found C 76.23, H 6.34,

N 17.68.

1430, 1315, 1150, 1095, 1070, 1050, 1035, 1000, 990, 820, 780, 755,

710, 700, 650, 620 cm^Ϫ1. Ϫ ¹H NMR (250 MHz, CDCl₃): δ ϭ 0.11

2

3

(dt, J ϭ 6.4, J ϭ 3.6 Hz, 1 H, 7-H_syn), 0.41Ϫ0.54 (m, J ϭ 3.0,

exo,exo-3,7-Dimethyl-1,5-bis(2-pyridyl)-9,10-diazatetracyclo-

³J ϭ 6.1 Hz, 1 H, 3-H_syn), 0.41Ϫ0.54 (m, J ϭ 6.4, J ϭ 7.8 Hz, 1 [3.3.2.0²·⁴.0⁶·⁸]dec-9-ene (12w): Compounds 11k (600 mg,

H, 7-H_anti), 0.91 (d, J ϭ 6.1 Hz, 3 H, 3-CH₃-anti), 1.94 (d, J ϭ 2.29 mmol) and 10c were stirred in CH₂Cl₂(50 mL) at room temp.

3.0 Hz, 2 H, 2-H, 4-H), 2.18 (dd, J ϭ 3.6, J ϭ 7.8 Hz, 2 H, 6-H, overnight according to General Procedure (3). Purification by FC

8-H), 7.28Ϫ7.33 (m, 2 H, Ar-H), 7.79Ϫ7.86 (m, 2 H, Ar-H), (EtOAc/n-hexane ϭ 3:1) and recrystallization (CH₂Cl₂/n-hexane)

8.12Ϫ8.16 (m, 2 H, Ar-H), 8.72Ϫ8.75 (m, 2 H, Ar-H). Ϫ ¹³C NMR afforded 12w (489 mg, 1.54 mmol, 67%) as colourless crystals, m.p.

2

3

˜

(63 MHz, CDCl₃): δ ϭ 5.2 (ϪCH₂Ϫ, 1 C, 7-C), 13.2 (ϪCH₃, 1 C, 167Ϫ168 °C. Ϫ IR (KBr): ν ϭ 3070, 3030, 2980, 2940, 2880, 1585,

3-CH₃-anti), 16.4 (ϭCH, 1 C, 3-C), 17.6 (ϭCH, 2 C, 6-C, 8-C), 1570, 1530, 1455, 1430, 1310, 1145, 1095, 1060, 1045, 995, 770,

26.4 (ϭCH, 2 C, 2-C, 4-C), 75.1 (ϭCH, 2 C, 1-C, 5-C), 122.1 (ϭ

750, 700 cm^Ϫ1. Ϫ ¹H NMR (250 MHz, CDCl₃): δ ϭ 0.40 (tq, ³J ϭ

CH, 2 C, Ar-C), 122.4 (ϭCH, 2 C, Ar-C), 136.4 (ϭCH, 2 C, Ar- 6.2, ³J ϭ 3.0 Hz, 2 H, 3,7-H_syn), 0.88 (d, ³J ϭ 6.2 Hz, 6 H, 3,7-CH₃-

Eur. J. Org. Chem. 2001, 2639Ϫ2657

2651

J. Sauer et al.

FULL PAPER

anti), 1.93 (d, ³J ϭ 3.0 Hz, 4 H, 2-H, 4-H, 6-H, 8-H), 7.27Ϫ7.33 (m, exo,exo-3,3-Dimethyl-1,5-bis(2-methyl-1,3,4-oxadiazol-5-

2 H, Ar-H), 7.79Ϫ7.86 (m, 2 H, Ar-H), 8.15Ϫ8.19 (m, 2 H, Ar-H), yl)-9,10-diazatetracyclo[3.3.2.0²·⁴.0⁶·⁸]dec-9-ene (12b₁): Compounds

8.72Ϫ8.75 (m, 2 H, Ar-H). Ϫ UV/Vis (CH₃CN): λ (ε) ϭ 258 11m (99.4 mg, 0.385 mmol) and 10e (272 mg, 4.40 mmol) in

(8000), 380 (54). Ϫ C₂₀H₂₀N₄(316.4): calcd. C 75.92, H 6.37, N CH₂Cl₂(4 mL) were pressurized in a reaction vessel to 7.2 kbar at

17.71; found C 76.08, H 6.28, N 17.67.

52 °C for 3 d, according to General Procedure (5). Purification by

recrystallization (CH₂Cl₂/n-hexane) afforded 12b₁(71.8 mg,

0.220 mmol, 57%) as colourless crystals, m.p. 163Ϫ164 °C. Ϫ IR

exo,exo-2,6-Dimethyl-1,5-bis(2-pyridyl)-9,10-diazatetracyclo-

[3.3.2.0²·⁴.0⁶·⁸]dec-9-ene (12x): Compounds 11j (890 mg,

3.39 mmol) and 10b were stirred in CH₂Cl₂(60 mL) and toluene

(40 mL) at room temp. overnight according to General Procedure

(3). Purification of the crude product by FC (CH₂Cl₂/n-hexane/

ethanol ϭ 10:1:2) and recrystallization (CH₂Cl₂/n-hexane) afforded

12x (460 mg, 1.45 mmol, 43%) as colourless crystals, m.p. 154Ϫ155

˜

(KBr): ν ϭ 3050, 3010, 2960, 2930, 2870, 1585, 1560, 1445, 1385,

1345, 1240, 1080, 1030, 965, 940, 820 cm^Ϫ1. Ϫ ¹H NMR (250 MHz,

CDCl₃): δ ϭ 0.36 (dt, ²J ϭ 7.5, ³J ϭ 3.7 Hz, 1 H, 7-H_syn), 0.80 (dt,

3

²J ϭ 7.5, J ϭ 7.7 Hz, 1 H, 7-H_anti), 1.06 (s, 3 H, 3-CH₃-syn), 1.17

(s, 3 H, 3-CH₃-anti), 2.00 (s, 2 H, 2-H, 4-H), 2.13 (dd, ³J ϭ 7.7,

³J ϭ 3.7 Hz, 6-H, 8-H), 2.68 (s, 6 H, Ar-CH₃). Ϫ ¹³C NMR

(63 MHz, CDCl₃): δ ϭ 6.6 (ϪCH₂, 1 C, 7-C), 11.2 (ϪCH₃, 2 C,

Ar-CH₃), 16.0 (ϪCH₂, 2 C, 6-C, 8-C), 19.1 (ϪCH₃, 1 C, 3-CH₃-

syn), 24.4 (quat.C, 1 C, 3-C), 30.3 (ϪCH₃, 1 C, 3-CH₃-anti), 35.3

(ϪCH, 2 C, 2-C, 4-C), 70.1 (quat. C, 2 C, 1-C, 5-C), 165.3 (quat.

C, 2 C, Ar-C), 166.7 (quat. C, 2 C, Ar-C). Ϫ UV/Vis (CH₃CN): λ

(ε) ϭ 385 (140). Ϫ MS (EI, 70 eV): m/z (%) ϭ 298 (23), 297 (83),

283 (11), 201 (100), 187 (30). Ϫ C₁₆H₁₈N₆O₂(326.4): calcd. C

58.88, H 5.56, N 25.75; found C 58.93, H 5.83, N 25.31.

˜

°C. Ϫ IR (KBr): ν ϭ 3050, 3010, 2950, 2930, 2870, 1585, 1560,

1465, 1425, 1300, 1145, 1080, 1035, 985, 795, 785, 765 cm^Ϫ1. Ϫ ¹H

2

3

NMR (400 MHz, CDCl₃): δ ϭ 0.45 (dd, J ϭ 6.2, J ϭ 3.8 Hz, 2

2

3

H, 3,7-H_syn), 0.54 (dd, J ϭ 6.2, J ϭ 7.9 Hz, 2 H, 3,7-H_anti), 1.01

(s, 6 H, 2,6-CH₃), 2.29 (dd, ³J ϭ 3.8, J ϭ 7.9 Hz, 2 H, 4-H, 8-H),

3

7.29Ϫ7.33 (m, 2 H, Ar-H), 7.80Ϫ7.88 (m, 4 H, Ar-H), 8.71Ϫ8.73

(m, 2 H, Ar-H). Ϫ ¹³C NMR (100 MHz, CDCl₃): δ ϭ 13.5

(ϪCH₂Ϫ, 2 C, 3-C, 7-C), 17.6 (ϪCH₃, 2 C, CH₃), 19.5 (ϭCH, 2

C, 4-C, 8-C), 22.7 (quat. C, 2 C, 2-C, 6-C), 79.5 (quat. C, 2 C, 1-

C, 5-C), 122.7 (ϭCH, 2 C, Ar-C), 123.4 (ϭCH, 2 C, Ar-C), 136.6

(ϭCH, 2 C, Ar-C), 148.7 (ϭCH, 2 C, Ar-C), 160.6 (quat. C, 2 C,

Ar-C). Ϫ UV/Vis (CH₃CN): λ (ε) ϭ 260 (6910), 342 (13), 361 (28),

390 (55). Ϫ C₂₀H₂₀N₄(316.4): calcd. C 75.92, H 6.37, N 17.71;

found C 75.67, H 6.42, N 17.55.

Synthesis of 3,4-Homotropilidenes

Dimethyl 3,4-Homotropilidene-2,6-dicarboxylate (13a): Compound

12a (500 mg, 2.00 mmol), after photolysis in benzene (200 mL) at

room temp. for 15 min according to General Procedure (6) and

purification by distillation at 0.001 Torr, yielded 13a (351 mg,

1.58 mmol, 79%) as an colourless oil. Ϫ IR (film): ν˜ ϭ 1715 cm^Ϫ1

.

exo,exo-3,6-Dimethyl-1,5-bis(2-pyridyl)-9,10-diazatetracyclo-

[3.3.2.0²·⁴.0⁶·⁸]dec-9-ene (12y): Compounds 11k (910 mg,

3.47 mmol) and 10b were stirred in CH₂Cl₂(60 mL) at room temp.

overnight according to General Procedure (3). Purification by FC

(CH₂Cl₂/n-hexane/ethanol ϭ 15:2:1) and recrystallization (CH₂Cl₂/

n-hexane) afforded 12y (531 mg, 1.68 mmol, 48%) as colourless

Ϫ ¹H NMR (100 MHz, [D₈]toluene, θ ϭ 214 K): δ ϭ 0.13 (dt, ²J ϭ

3

2

3

3.5, J ϭ 6.0 Hz, 1-H, 8-H_syn), 1.34 (dt, J ϭ 3.5, J ϭ 9.0 Hz, 1

3

H, 8-H_anti), 1.78 (dd, J ϭ 6.0, J ϭ 9.0 Hz, 2 H, 1-H, 7-H), 1.92

2

3

2

3

(dt, J ϭ 16.0, J ϭ 8.5 Hz, 1 H, 4-H_eq), 2.62 (dt, J ϭ 16.0, J ϭ

3

4.0 Hz, 1 H, 4-H_ax), 3.76 (s, 6 H, OCH₃), 6.91 (dd, J ϭ 8.5, J ϭ

4.0 Hz, 2 H, 3-H, 5-H). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 286

(1150). Ϫ C₁₂H₁₄O₂(222.2): calcd. C 64.85, H 6.35; found C 65.01,

H 6.47.

˜

crystals, m.p. 159Ϫ161 °C. Ϫ IR (KBr): ν ϭ 3060, 3010, 2980,

2940, 2880, 1585, 1565, 1465, 1430, 1310, 1080, 1045, 1035, 995,

775, 760, 750 cm^Ϫ1. Ϫ ¹H NMR (400 MHz, CDCl₃): δ ϭ 0.33 (dd,

3

2

3

²J ϭ 6.2, J ϭ 7.7 Hz, 2 H, 7-H_anti), 0.41Ϫ0.43 (m, J ϭ 6.1, J ϭ

3,4-Homotropilidene-2,6-dicarbonitrile (13b): Compound 12i

(400 mg, 2.20 mmol), after photolysis in benzene (50 mL) at room

temp. for 7 h according to General Procedure (7) and purification

by filtration and evaporation of the solvent, yielded 13b (344 mg,

3

2

3

2.9, J ϭ 3.1 Hz, 1 H, 3-H_syn), 0.46 (dd, J ϭ 6.2, J ϭ 3.7 Hz, 1

H, 7-H_syn), 0.99 (s, 3 H, 6-CH₃), 1.02 (d, ³J ϭ 6.1 Hz, 3 H, 3-CH₃-

anti), 1.86 (dd, ³J ϭ 3.7, ³J ϭ 7.7 Hz, 1 H, 8-H), 1.90 (dd, ³J ϭ

2.9, ³J ϭ 8.0 Hz, 1 H, 2-H or 4-H), 2.29 (dd, ³J ϭ 3.1, ³J ϭ 8.0 Hz,

1 H, 4-H or 2-H), 7.27Ϫ7.34 (m, 2 H, Ar-H), 7.78Ϫ7.87 (m, 3 H,

Ar-H), 8.13Ϫ8.17 (m, 1 H, Ar-H), 8.71Ϫ8.76 (m, 2 H, Ar-H). Ϫ

UV/Vis (CH₃CN): λ (ε) ϭ 260 (7450), 342 (17), 364 (31), 380 (58).

Ϫ C₂₀H₂₀N₄(316.4): calcd. C 75.92, H 6.37, N 17.71; found C

75.43, H 6.78, N 17.45.

˜

2.20 mmol, quant.) as a colourless oil. Ϫ IR (KBr): ν ϭ 3090, 2990,

2220, 1630 cm^Ϫ1. Ϫ ¹H NMR (100 MHz, [D₈]toluene, θ ϭ 226 K):

δ Ϫ0.19 (dt, ²J ϭ 3.5, ³J ϭ 6.0 Hz, 1-H, 8-H_syn), 0.49 (dt, ²J ϭ 3.5,

3

³J ϭ 9.0 Hz, 1 H, 8-H_anti), 0.81 (dd, J ϭ 6.0, J ϭ 9.0 Hz, 2 H, 1-

H, 7-H), 1.28 (dt, ²J ϭ 18.0, ³J ϭ 8.0 Hz, 1 H, 4-H_eq), 2.00 (dt,

²J ϭ 18.0, ³J ϭ 4.0 Hz, 1 H, 4-H_ax), 5.42 (dd, ³J ϭ 8.0, ³J ϭ 4.0 Hz,

2 H, 3-H, 5-H). Ϫ UV/Vis (methanol): λ (ε) ϭ 270 (1745). Ϫ MS

(EI, 70 eV): m/z (%) ϭ 156 (61) [M^ϩ], 128 (100). Ϫ C₁₀H₈N₂

(156.2): calcd. C 76.90, H 5.16, N 17.94; found C 76.98, H 5.18,

N 18.11.

exo,exo-3,3,7-Trimethyl-1,5-bis(2-pyridyl)-9,10-diazatetracyclo-

[3.3.2.0²·⁴.0⁶·⁸]dec-9-ene (12z): Compounds 11k (684 mg,

2.61 mmol) and 10e (1.00 g, 14.7 mmol) in CH₂Cl₂(3 mL) were

pressurized in a reaction vessel to 8.0 kbar at 60 °C for 3 d accord-

ing to General Procedure (5). Purification by FC (CH₂Cl₂/EtOAc/

n-hexane ϭ 3:1:1) and recrystallization (EtOAc) afforded 12z

(641 mg, 1.94 mmol, 74%) as colourless crystals, m.p. 201Ϫ203 °C.

2,6-Diphenyl-3,4-homotropilidene (13c): An inseparable mixture of

two azo compounds containing 60% of 12p (287 mg, 1.00 mmol)

was photolyzed in CH₃CN (15 mL) at room temp. for 15 min ac-

cording to General Procedure (7). Separation by preparative HPLC

(LiChroprep. RP 8, methanol/H₂O ϭ 93:7) afforded the desired

homotropilidene 13c (245 mg, 0.95 mmol, 95%) as colourless crys-

˜

Ϫ IR (KBr): ν ϭ 3060, 3020, 2960, 2930, 2870, 1585, 1565, 1535,

1465, 1430, 1315, 1150, 1095, 1065, 1040, 1000, 780, 755, 705, 600

cm^Ϫ1. Ϫ ¹H NMR (250 MHz, CDCl₃): δ ϭ 0.41 (tq, ³J ϭ 6.1, ³J ϭ

3.0 Hz, 1 H, 7-H_syn), 0.88 (s, 3 H, 3-CH₃-syn), 0.89 (d, ³J ϭ 6.1 Hz,

tals; m.p. 100Ϫ101 °C, ref. m.p. 101 °C.^[39][59]Ϫ IR (KBr): ν ϭ

˜

3

3050, 3010, 1590, 1485, 1440, 825, 750, 685 cm^Ϫ1. Ϫ ¹H NMR

(250 MHz, CDCl₃): δ ϭ 0.25Ϫ0.30 (m, broad, 1 H, 8-H_syn),

3 H, 7-CH₃-anti), 1.07 (s, 3 H, 3-CH₃-anti), 2.00 (d, J ϭ 3.0 Hz,

2 H, 6-H, 8-H), 2.08 (s, 2 H, 2-H, 4-H), 7.28Ϫ7.34 (m, 2 H, Ar-

H), 7.80Ϫ7.87 (m, 2 H, Ar-H), 8.19Ϫ8.23 (m, 2 H, Ar-H),

8.73Ϫ8.76 (m, 2 H, Ar-H). Ϫ UV/Vis (CH₃CN): λ (ε) ϭ 261 (91),

381 (8830). Ϫ C₂₁H₂₂N₄(330.4): calcd. C 76.33, H 6.71, N 16.96;

found C 76.33, H 6.47, N 16.86.

3

1.46Ϫ1.55 (m, broad, 1 H, 8-H_anti), 2.14 (m, broad, J ϭ 7.2 Hz, 2

3

H, 1-H, 7-H), 2.67 (dt, broad, ²J ϭ 15.2, J ϭ 8.0 Hz, 1 H, 4-H_eq),

3.51 (m, broad, ²J ϭ 15.2 Hz, 1 H, 4-H_ax), 6.44Ϫ6.48 (m, broad, 2

H, 3-H, 5-H), 7.18Ϫ7.34 (m, 6 H, Ar-H), 7.55Ϫ7.60 (m, 4 H, Ar-

2652

Eur. J. Org. Chem. 2001, 2639Ϫ2657

Synthesis and Properties of Homotropilidenes

H). Ϫ MS (EI, 70 eV): m/z (%) ϭ 259 (19) [M^ϩ], 238 (100). Ϫ UV/ (23), 123 (11), 59 (27), 58 (49). Ϫ C₁₄H₁₂N₂S₂(272.4): calcd. C

FULL PAPER

Vis (CH₃CN): λ (ε) ϭ 267 (11750), 246 (13580), 220 (15260).

61.73, H 4.44, N 10.28; found C 61.46, H 4.74, N 10.14.

Dimethyl 8-Methyl-3,4-homotropilidene-2,6-dicarboxylate (14a):

Compound 12b (792 mg, 3.00 mmol), after photolysis in benzene

(300 mL) at room temp. for 10 min according to General Procedure

(6) and purification by distillation at 0.001 Torr, yielded 14a

2,6-Bis(2-pyridyl)-3,4-homotropilidene (13d): Compound 12s

(302 mg, 1.05 mmol) was photolyzed in CH₃CN (45 mL) at room

temp. for 5 h, according to General Procedure (7). Purification by

FC (CH₂Cl₂/ethanol ϭ 15:1) and recrystallization (methanol/H₂O)

afforded 13d (83.3 mg, 0.320 mmol, 30%) as brown crystals, m.p.

70Ϫ72 °C. Ϫ IR (KBr): ν˜ ϭ 3060, 3010, 2980, 2860, 1660, 1585,

1565, 1470, 1430, 1155, 995, 790, 780, 750 cm^Ϫ1. Ϫ ¹H NMR

(250 MHz, CDCl₃): δ ϭ 0.21Ϫ0.22 (m, 1 H, 8-H_syn), 1.49Ϫ1.57 (m,

1 H, 8-H_anti), 2.24Ϫ2.30 (m, 2 H, 1-H, 7-H), 2.79Ϫ2.92 (m, 1 H,

4-H_eq), 3.54Ϫ3.61 (m, 1 H, 4-H_ax), 7.08Ϫ7.31 (m, 4 H, 3-H, 5-H,

Ar-H), 7.44Ϫ7.82 (m, 4 H, Ar-H), 8.53Ϫ8.61 (m, 2 H, Ar-H). Ϫ

C₁₈H₁₆N₂(260.3). calcd. C 83.06, H 6.20, N 10.76; found C 83.08,

H 6.62, N 10.66.

˜

(560 mg, 2.37 mmol, 79%) as a colourless oil. Ϫ IR (film): ν ϭ

1710 cm^Ϫ1. Ϫ ¹H NMR (100 MHz, CDCl₃): δ ϭ 0.59 (tq, ³J ϭ

3

5.5, J ϭ 5.5 Hz, 1 H, 8-H_syn), 1.30 (d, J ϭ 5.5 Hz, 3 H, 8-CH₃-

anti), 1.73 (d, ³J ϭ 5.5 Hz, 2 H, 1-H, 7-H), 2.74 (td, ²J ϭ 18.0,

³J ϭ 8.0 Hz, 1 H, 4-H_eq), 3.0Ϫ3.5 (m, ²J ϭ 18.0, ³J ϭ 4.0 Hz, 1

3

H, 4-H_ax), 3.85 (s, 6 H, OCH₃), 6.93 (dd, J ϭ 8.0, J ϭ 4.0 Hz, 2

H, 3-H, 5-H). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 290 (1500). Ϫ

C₁₃H₁₆O₄(236.2): calcd. C 66.08, H 6.83; found C 66.02, H 6.72.

8-Methyl-3,4-homotropilidene-2,6-dicarbonitrile (14b): Compound

12j (800 mg, 4.04 mmol) was photolyzed in benzene (300 mL) at

room temp. for 3.5 h according to General Procedure (6). Purifica-

tion by recrystallization (benzene/PE) afforded 14b (650 mg,

3.80 mmol, 96%) as yellow crystals, m.p. 64Ϫ70 °C. Ϫ IR (KBr):

2, 6-Bis(2-methyl-1, 3, 4-oxadiazol-5-yl)-3, 4-homotro-

pilidene (13e): Compound 12a₁(98 mg, 0.328 mmol) was

photolyzed in CH₂Cl₂(20 mL) at room temp. for 3.5 h according

to General Procedure (7). Purification by FC (CHCl₃/ethanol ϭ

15:1) and recrystallization (CH₂Cl₂/n-pentane) afforded 13e

(69.0 mg, 0.255 mmol, 78%) as colourless crystals, m.p. 160Ϫ161

°C. Ϫ IR (KBr): ν˜ ϭ 3080, 3010, 2960, 2895, 1650, 1575, 1520,

ν ϭ 2215 cm^Ϫ1. Ϫ ¹H NMR (90 MHz, CDCl₃, θ ϭ 235 K): δ ϭ

˜

3

1.02 (tq, J ϭ 5.9, J ϭ 5.4 Hz, 1 H, 8-H_syn), 1.33 (d, J ϭ 5.9 Hz,

3 H, 8-CH₃-anti), 1.73 (dd, J ϭ 5.4, J ϭ 1.8 Hz, 2 H, 1-H, 7-H),

3

5

2

3

2

2.87 (dt, J ϭ 18.1, J ϭ 8.1 Hz, 1 H, 4-H_eq), 3.42 (dtt, J ϭ 18.1,

³J ϭ 3.7, ⁵J ϭ 1.8 Hz, 1 H, 4-H_ax), 6.65 (dd, ³J ϭ 8.1, ³J ϭ 3.7 Hz,

2 H, 3-H, 5-H). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 257 (980). Ϫ MS

(EI, 70 eV): m/z (%) ϭ 170 (18) [M^ϩ], 142 (100). Ϫ C₁₁H₁₀N₂

(170.2): calcd. C 77.62, H 5.92, N 16.46; found C 77.73, H 5.76,

16.48.

1

1220, 1050, 1030, 1010, 970, 905, 810, 720, 670 cm^Ϫ1. Ϫ H NMR

(400 MHz, CD₂Cl₂, θ ϭ 223 K): δ ϭ 0.41 (dt, ²J ϭ 4.1, ³J ϭ

2

3

6.2 Hz, 1-H, 8-H_syn), 1.63 (dt, J ϭ 4.1, J ϭ 9.3 Hz, 1 H, 8-H_anti),

3

5

2.28 (ddd, ³J ϭ 9.3, J ϭ 6.2, J ϭ 1.9 Hz, 2 H, 1-H, 7-H), 2.54 (s,

2

3

6 H, Ar-CH₃), 2.94 (dt, J ϭ 16.4, J ϭ 8.6 Hz, 1 H, 4-H_eq), 3.58

2

3

5

3

(dtt, J ϭ 16.4, J ϭ 4.1, J ϭ 1.9 Hz, 1 H, 4-H_ax), 6.94 (dd, J ϭ

8.6, ³J ϭ 4.1 Hz, 2 H, 3-H, 5-H). Ϫ ¹³C NMR: (63 MHz, CD₂Cl₂,

θ ϭ 223 K): δ ϭ 11.1 (ϪCH₃, 2 C, Ar-CH₃), 14.2 (ϪCH₂Ϫ, 1 C,

8-C), 16.6 (ϭCH, 2 C, 1-C, 7-C), 25.5 (ϪCH₂Ϫ, 1 C, 4-C), 126.1

(quat. C, 2 C, 2-C, 6-C), 135.0 (ϭCH, 2 C, 3-C, 5-C), 163.2 (quat.

C, 2 C, Ar-C), 165.3 (quat. C, 2 C, Ar-C). Ϫ UV/Vis (1,4-dioxane):

λ (ε) ϭ 233 (15400). Ϫ MS (EI, 70 eV): m/z (%) ϭ 271 (10) [M^ϩ],

270 (62), 269 (86), 243 (17), 229 (23), 228 (55), 212 (27), 187 (41),

186 (28), 185 (19), 173 (20), 161 (29), 160 (20), 145 (19), 135 (100),

131 (20), 117 (14), 116 (13), 115 (24), 105 (13), 104 (14), 103 (25),

91 (12), 90 (14), 83 (18), 77 (28),43 (81), 39 (12). Ϫ C₁₄H₁₄N₄O₂

(270.4): calcd. C 62.19, H 5.22, N 20.72; found C 61.88, H 5.10,

N 20.52.

8-Methyl-2,6-diphenyl-3,4-homotropilidene (14c): Compound 12q

(450 mg, 1.50 mmol), after photolysis in acetonitrile (15 mL) at

room temp. for 15 min according to General Procedure (7) and

purification by recrystallization (methanol), yielded 14c (346 mg,

1.27 mmol, 85%) as colourless needles, m.p. 89Ϫ90 °C. Ϫ IR

Ϫ1

˜

(KBr): ν ϭ 3050, 2960, 1630, 1590, 1445, 830, 760, 750, 690 cm

.

1

Ϫ H NMR (250 MHz, CDCl₃): δ ϭ 0.54Ϫ0.63 (m, 1 H, 8-H_syn),

1.44 (d, ³J ϭ 5.9 Hz, 3 H, 8-CH₃-anti), 1.82 (d, broad, ³J ϭ 4.5 Hz,

2 H, 1-H, 7-H), 2.59Ϫ2.78 (m, broad, 1 H, 4-H_eq), 3.46 (d, broad,

²J ϭ 16.5 Hz, 1 H, 4-H_ax), 6.43 (dd, broad, J ϭ 7.8, J ϭ 3.9 Hz,

2 H, 3-H, 5-H), 7.18Ϫ7.34 (m, 6 H, Ar-H), 7.50Ϫ7.58 (m, 4 H, Ar-

H). Ϫ ¹³C NMR (22.63 MHz, CDCl₃): δ ϭ 19.4 (ϪCH₃, 1 C, 8-

CH₃), 21.5 (ϭCH, 1 C, 8-C), 26.3 (ϪCH₂Ϫ, 1 C, 4-C), 27.7 (ϭCH,

2 C, 1-C, 7-C), 124.3 (ϭCH, 2 C), 126.7 (ϭCH, 2 C), 127.8 (ϭCH,

2 C), 128.1 (ϭCH, 2 C), 139.0 (quat. C, 2 C), 142.0 (quat. C, 2 C).

Ϫ MS (EI, 70 eV): m/z (%) ϭ 273 (25) [M^ϩ], 272 (100). Ϫ UV/Vis

(CH₃CN): λ (ε) ϭ 268 (11840), 244 (14350), 225 (13470). Ϫ C₂₁H₂₀

(272.2): calcd. C 92.66, H 7.40; found C 92.74, H 7.40.

3

2,6-Bis(2-thiazolyl)-3,4-homotropilidene (13f): Compound 12c₁

(104 mg, 0.345 mmol) was photolyzed in CH₂Cl₂(30 mL) at room

temp. for 9 h according to General Procedure (7). Purification by

FC (CH₂Cl₂/EtOAc ϭ 1:1) and recrystallization (CH₂Cl₂/n-pent-

ane) afforded 13f (60.9 mg, 0.224 mmol, 65%) as colourless crys-

˜

tals, m.p. 79Ϫ80 °C. Ϫ IR (KBr): ν ϭ 3100, 3080, 3060, 3030, 2970, 8-Methyl-2,6-bis(2-pyridyl)-3,4-homotropilidene (14d): Compound

1620, 1475, 1305, 1220, 1130, 1050, 950, 910, 850, 825, 730, 650, 12t (316 mg, 1.05 mmol), after photolysis in CH₃CN (45 mL) at

1

620 cm^Ϫ1. Ϫ H NMR (400 MHz, CD₂Cl₂, θ ϭ 223 K): δ ϭ 0.47 room temp. for 4.5 h according to General Procedure (7) and puri-

2

3

2

3

(dt, J ϭ 3.7, J ϭ 6.1 Hz, 1 H, 8-H_syn), 1.63 (dt, J ϭ 3.7, J ϭ fication by recrystallization (methanol), yielded 14d (208 mg,

3

5

9.1 Hz, 1 H, 8-H_anti), 2.30 (ddd, J ϭ 9.1, J ϭ 6.1, J ϭ 2.0 Hz, 2 0.756 mmol, 72%) as colourless crystals, m.p. 122Ϫ124 °C. Ϫ IR

2

3

H, 1-H, 7-H), 2.84 (dt, J ϭ 15.4, J ϭ 8.8 Hz, 1 H, 4-H_eq), 3.55 (KBr): ν˜ ϭ 3090, 3050, 3000, 2950, 2920, 2860, 1635, 1585, 1565,

2

3

5

3

(dtt, J ϭ 15.4, J ϭ 4.4, J ϭ 2.0 Hz, 1 H, 4-H_ax), 7.12 (dd, J ϭ

1470, 1440, 1155, 990, 790, 775, 745 cm^Ϫ1. Ϫ ¹H NMR (250 MHz,

3

8.8, J ϭ 4.4 Hz, 2 H, 3-H, 5-H), 7.33 (d, ³J ϭ 3.2 Hz, 2 H, Ar- CDCl₃): δ ϭ 0.49Ϫ0.55 (m, ³J ϭ 5.9, ³J ϭ 4.7 Hz, 1 H, 8-H_syn),

H), 7.78 (d, ³J ϭ 3.2 Hz, 2 H, Ar-H). Ϫ ¹³C NMR: (63 MHz, 1.51 (d, ³J ϭ 5.9 Hz, 3 H, 8-CH₃-anti), 1.92 (d, broad, ³J ϭ 4.7 Hz,

CD₂Cl₂, θ ϭ 223 K): δ ϭ 13.9 (ϪCH₂Ϫ, 1 C, 8-C), 19.0 (ϭCH, 2 2 H, 1-H, 7-H), 2.87 (dt, broad, ²J ϭ 15.5, ³J ϭ 8.4 Hz, 1 H, 4-H_eq),

C, 1-C, 7-C), 25.1 (ϪCH₂Ϫ, 1 C, 4-C), 118.1 (ϭCH, 2 C, Ar-C), 3.52 (dt, broad, ²J ϭ 15.5, ³J ϭ 4.2 Hz, 1 H, 4-H_ax), 7.11Ϫ7.14 (m,

3

131.3 (ϭCH, 2 C, 3-C, 5-C), 133.1 (quat. C, 2 C, 2-C, 6-C), 142.8 2 H, Ar-H), 7.18 (dd, broad, J ϭ 8.4, J ϭ 4.2 Hz, 2 H, 3-H, 5-

(ϭCH, 2 C, Ar-C), 169.9 (quat. C, 2 C, Ar-C). Ϫ UV/Vis (1,4-

dioxane): λ (ε) ϭ 270 (13800), 282 (15800), 295 (16300). Ϫ MS (EI,

H), 7.47Ϫ7.50 (m, 2 H, Ar-H), 7.62Ϫ7.69 (m, 2 H, Ar-H),

8.53Ϫ8.56 (m, 2 H, Ar-H). Ϫ ¹³C NMR (63 MHz, CDCl₃): δ ϭ

70 eV): m/z (%) ϭ 273 (21) [M^ϩ], 272 (74), 271 (100), 257 (27), 245 19.3 (ϪCH₃, 1 C, 8-CH₃), 21.2 (ϭCH, 1 C, 8-C), 26.1 (ϪCH₂Ϫ, 1

(36), 188 (21), 187 (17), 186 (20), 174 (16), 173 (14), 162 (16), 136

C, 4-C), 26.5 (ϭCH, 2 C, 1-C, 7-C), 119.5 (ϭCH, 2C, Ar-C), 121.5

Eur. J. Org. Chem. 2001, 2639Ϫ2657

2653

J. Sauer et al.

FULL PAPER

(ϭCH, 2 C, Ar-C), 131.5 (ϭCH, 2 C, 3-C, 5-C), 136.3 (ϭCH, 2 C, 2960, 2880, 1635, 1585, 1520, 1270, 1160, 1060, 995, 880, 795, 780,

Ar-C), 138.3 (quat. C, 2 C, 2-C, 6-C), 148.9 (ϭCH, 2 C, Ar-C),

750 cm^Ϫ1. Ϫ ¹H NMR (250 MHz, CDCl₃): δ ϭ 0.59 (s, 3H, 8-

158.5 (quat. C, 2 C, Ar-C). Ϫ C₁₉H₁₈N₂(274.4): calcd. C 83.17, H CH₃-syn), 1.53 (s, 3 H, 8-CH₃-anti), 2.05 (s, 2 H, 1-H, 7-H), 2.95

2

3

2

3

6.61, N 10.21; found C 83.04, H 6.54, N 10.22.

(dt, J ϭ 16.5, J ϭ 8.6 Hz, 1 H, 4-H_eq), 3.52 (dt, J ϭ 16.5, J ϭ

4.0 Hz, 1 H, 4-H_ax), 7.09Ϫ7.14 (m, 2 H, Ar-H), 7.18 (dd, ³J ϭ 8.6,

³J ϭ 4.0 Hz, 2 H, 3-H, 5-H), 7.37Ϫ7.42 (m, 2 H, Ar-H), 7.60Ϫ7.71

(m, 2 H, Ar-H), 8.53Ϫ8.56 (m, 2 H, Ar-H). Ϫ C₂₀H₂₀N₂(288.4):

calcd. C 83.29, H 6.99, N 9.71; found C 83.49, H 6.76, N 9.63.

Dimethyl 1-Methyl-3,4-homotropilidene-2,6-dicarboxylate (16a):

Compound 12c (450 mg, 1.70 mmol), after photolysis in benzene

(200 mL) at room temp. for 15 min according to General Procedure

(6) and purification by distillation at 0.001 Torr, yielded 16a

˜

(333 mg, 1.41 mmol, 83%) as a colourless oil. Ϫ IR (film): ν ϭ

8,8-Dimethyl-2,6-bis(2-methyl-1,3,4-oxadiazol-5-yl)-3,4-homo-

tropilidene (18b): Compound 12b₁(68.0 mg, 0.208 mmol) was

photolyzed in CH₃CN (30 mL) at room temp. for 5 h according to

General Procedure (7). Purification by FC (CH₂Cl₂/EtOAc ϭ 1:1)

and recrystallization (CH₂Cl₂/n-hexane) afforded 18b (56.0 mg,

0.188 mmol, 90%) as colourless crystals, m.p. 96Ϫ97 °C. Ϫ IR

1715 cm^Ϫ1. Ϫ ¹H NMR (100 MHz, CDCl₃): δ ϭ 0.37 (dd, ²J ϭ

3

2

3

4.5, J ϭ 6.0 Hz, 1-H, 8-H_syn), 1.17 (dd, J ϭ 4.5, J ϭ 10.0 Hz, 1

H, 8-H_anti), 1.21 (s, 3 H, 1-CH₃), 1.45 (dd, J ϭ 6.0, J ϭ 10.0 Hz,

3

2

3

2 H, 7-H), 2.08 (dt, J ϭ 14.2, J ϭ 8.5 Hz, 1 H, 4-H_eq), 2.82 (dt,

²J ϭ 14.2, J ϭ 5.0 Hz, 1 H, 4-H_ax), 3.82 (s, 6 H, OCH₃), 7.02 (dd,

3

³J ϭ 8.5, J ϭ 5.0 Hz, 2 H, 3-H, 5-H). Ϫ ¹³C NMR (22.63 MHz,

3

˜

(film): ν ϭ 3010, 2960, 2940, 2910, 1630, 1570, 1520, 1440, 1430,

CDCl₃): δ ϭ 19.3 (ϪCH₃, 1 C, 1-CH₃), 21.1 (quat. C, 1 C, 1-C),

23.9 (ϭCH, 1 C, 7-C), 25.3 (ϪCH₂Ϫ, 1 C, 8-C or 4-C), 25.6

(ϪCH₂Ϫ, 1 C, 4-C or 8-C), 51.5 (ϪCH₃, 1 C, OCH₃), 51.6 (ϪCH₃,

1 C, OCH₃), 134.4 (quat. C, 1 C, 2-C or 6-C), 136.8 (quat. C, 1 C,

6-C or 2-C), 141.8 (ϭCH, 1 C, 3-C or 5-C), 142.2 (ϭCH, 1 C, 3-

C or 5-C), 167.1 (quat. C, 1 C, CϭO), 167.7 (quat. C, 1 C, CϭO).

Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 250 (3400). Ϫ C₁₃H₁₆O₄(236.2):

calcd. C 66.08, H 6.83; found C 66.00, H 7.01.

1420, 1345, 1220, 1115, 1040, 1010, 990, 905, 875, 830, 735, 705

cm^Ϫ1. Ϫ ¹H NMR (250 MHz, CDCl₃): δ ϭ 0.77 (s, 3 H, 8-CH₃-

5

4

syn), 1.47 (s, 3 H, 8-CH₃-anti), 2.05 (dt, J ϭ 2.0, J ϭ 0.5 Hz, 2

H, 1-H, 7-H), 2.54 (s, 6 H, Ar-CH₃), 2.96 (dt, ²J ϭ 17.7, ³J ϭ

2

3

5

8.5 Hz, 1 H, 4-H_eq), 3.51 (dtt, J ϭ 17.7, J ϭ 3.7, J ϭ 2.0 Hz, 1

3

4

H, 4-H_ax), 6.86 (ddt, J ϭ 3.7, J ϭ 8.5, J ϭ 0.5 Hz, 2 H, 3-H, 5-

H). Ϫ ¹³C NMR: (63 MHz, CDCl₃): δ ϭ 11.0 (ϪCH₃, 2 C, Ar-

CH₃), 15.6 (ϪCH₃, 1 C, 8-CH₃), 23.7 (quat. C, 1 C, 8-C), 26.6

(ϪCH₂Ϫ, 1 C, 4-C), 27.1 (ϪCH₃, 1 C, 8-CH₃), 28.5 (ϭCH, 2 C,

1-C, 7-C), 125.3 (quat. C, 2 C, 2-C, 6-C), 132.8 (ϭCH, 2 C, 3-C,

5-C), 162.9 (quat. C, 2 C, Ar-C), 165.8 (quat. C, 2 C, Ar-C). Ϫ

UV/Vis (1,4-dioxane): λ (ε) ϭ 235 (20600). Ϫ MS (EI, 70 eV): m/z

(%) ϭ 298 (49) [M^ϩ], 297 (92), 202 (13), 201 (100), 187 (22), 173

(56), 172 (18), 132 (14), 130 (14), 129 (12), 128 (14), 116 (15), 115

(22), 104 (22), 103 (22), 91 (18), 89 (12), 77 (33), 56 (11), 43 (49),

41 (12). Ϫ C₁₆H₁₈N₄O₂(298.4): calcd. C 64.40, H 6.08, N 18.78;

found C 64.10, H 6.18, N 18.45.

1-Methyl-2,6-bis(2-pyridyl)-3,4-homotropilidene (16b): Compound

12u (511 mg, 1.69 mmol) was photolyzed in acetonitrile (30 mL) at

room temp. for 4.5 h according to General Procedure (7). Purifica-

tion by FC (CH₂Cl₂/n-hexane/ethanol ϭ 15:2:1) afforded 16b

(434 mg, 1.58 mmol, 93%) as a yellow oil. Ϫ IR (film): 3070, 3020,

2970, 2910, 2860, 1635, 1580, 1565, 1470, 1430, 1270, 1155, 1095,

1000, 910, 700 cm^Ϫ1. Ϫ ¹H NMR (250 MHz, CDCl₃): δ ϭ 0.54

2

3

(dd, J ϭ 6.5, J ϭ 3.8 Hz, 1 H, 8-H_syn), 1.39 (dd, J ϭ 3.8, J ϭ

9.3 Hz, 1 H, 7-H), 1.43 (s, 3 H, 1-CH₃), 1.92Ϫ1.99 (m, ²J ϭ 6.5,

³J ϭ 9.3 Hz, 1 H, 8-H_anti), 2.82 (dt, J ϭ 14.0, J ϭ 8.6 Hz, 1 H,

2

3

Dimethyl 4,8-Dimethyl-3,4-homotropilidene-2,6-dicarboxylate (20a):

Compound 12d (834 mg, 3.00 mmol), after photolysis in benzene

(300 mL) at room temp. for 15 min according to General Procedure

(6) and purification by distillation at 0.001 Torr, yielded 20a

(548 mg, 2.19 mmol, 73%) as a colourless oil. Ϫ IR (film): ν˜ ϭ

1720, 1705 cm^Ϫ1. Ϫ ¹H NMR [90 MHz, CD₂Cl₂/CS₂(2:1), θ ϭ

2

4-H_eq), 3.41Ϫ3.51 (m, J ϭ 14.0 Hz, 1 H, 4-H_ax), 7.07Ϫ7.12 (m, 2

H, Ar-H), 7.23Ϫ7.33 (m, 3 H, 5-H, Ar-H), 7.55Ϫ7.66 (m, 3 H, 3-

H, Ar-H), 8.53Ϫ8.55 (m, 2 H, Ar-H). Ϫ The isolated compound

1

contained about 10% of an inseparable impurity (according to H

NMR).

3

188 K]: δ ϭ 0.67 (tq, J ϭ 6.0, J ϭ 5.5 Hz, 1-H, 8-H_syn), 1.24 (d,

3-Methyl-3,4-homotropilidene-2,6-dicarbonitrile (17a): Compound

12k (1.30 g, 6.56 mmol), after photolysis in benzene (250 mL) at

room temp. for 24 h according to General Procedure (6) and puri-

³J ϭ 6.0 Hz, 3 H, 8-CH₃-anti), 1.36 (d, J ϭ 7.0 Hz, 3 H, 4-CH₃-

3

anti), 1.67 (d, ³J ϭ 5.5 Hz, 2 H, 1-H, 7-H), 3.12 (tq, ³J ϭ 7.0, ³J ϭ

3

8.0 Hz, 1 H, 4-H_eq), 3.78 (s, 6 H, OCH₃), 7.06 (d, J ϭ 8.0 Hz, 2

fication by distillation at 0.001 Torr, yielded 17a (1.10 g, 6.46 mmol,

H, 3-H, 5-H). Ϫ ¹³C NMR (22.63 MHz, CD₂Cl₂, θ ϭ 200 K): δ ϭ

19.0 (ϪCH₃, 1 C, 8-CH₃or 4-CH₃), 21.0 (ϪCH₃, 1 C, 4-CH₃or 8-

CH₃), 24.8 (ϭCH, 2 C), 31.7 (ϭCH, 2 C), 52.6 (ϪCH₃, 2 C,

OCH₃), 131.7 (quat. C, 2 C, 2-C, 6-C), 144.5 (ϭCH, 2 C, 3-C, 5-

C, 168.8 (quat. C, 2 C, CϭO). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ

297 (2500). Ϫ C₁₄H₁₈O₄(250.3): calcd. C 67.18, H 7.25; found C

66.85, H 7.23.

1

98%) as a colourless oil. Ϫ IR (film): ν ϭ 2220 cm^Ϫ1. Ϫ H NMR

˜

(90 MHz, CDCl₃): δ ϭ 0.57 (dt, ²J ϭ 4.7, ³J ϭ 5.8 Hz, 1 H, 8-

H_syn), 1.27 (dt, ²J ϭ 4.7, J ϭ 9.0 Hz, 1 H, 8-H_anti), 1.83Ϫ2.17 (m,

3

³J ϭ 5.8, ³J ϭ 9.0 Hz, 2 H, 1-H, 7-H) and 2.10 (s, 3 H, 3-CH₃),

2

3

2

2.48 (dd, J ϭ 14.7, J ϭ 8.6 Hz, 1 H, 4-H_eq), 3.57Ϫ3.87 (m, J ϭ

3

14.7, J ϭ 5.4 Hz, 1 H, 4-H_ax), 6.79 (dd, J ϭ 8.6, J ϭ 5.4 Hz, 1

H, 5-H). Ϫ ¹³C NMR (22.63 MHz, CDCl₃): δ ϭ 10.7 (ϪCH₂Ϫ, 1

C, 8-C), 18.6 (ϭCH, 1 C, 1-C or 7-C), 18.7 (ϭCH, 1 C, 7-C or 1-

C), 24.9 (ϪCH₃, 1 C, 3-CH₃), 32.5 (ϪCH₂Ϫ, 1 C, 4-C), 108.9 (quat.

C, 1 C, 2-C or 6-C), 115.8 (quat. C, 1 C, 6-C or 2-C), 118.3 (quat.

C, 1 C, CN), 118.6 (quat. C, 1 C, CN), 146.0 (ϭCH, 1 C, 5-C),

157.9 (quat. C, 1 C, 3-C). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 243

(2270). Ϫ MS (EI, 70 eV): m/z (%) ϭ 170 (63) [M^ϩ], 155 (100). Ϫ

C₁₁H₁₀N₂(170.2): calcd. C 77.62, H 5.92, N 16.46; found C 77.53,

H 5.65, 16.59.

Dimethyl

4,8-Di-tert-butyl-3,4-homotropilidene-2,6-dicarboxylate

(20b): Compound 12e (145 mg, 0.400 mmol), after photolysis in

methanol (100 mL) at room temp. for 110 min according to Gen-

eral Procedure (6) and purification by recrystallization (CH₂Cl₂),

yielded 20b (77.6 mg, 0.232 mmol, 58%) as colourless crystals; m.p.

91Ϫ94 °C. Ϫ IR (KBr): ν˜ ϭ 2970, 2950, 2870, 1715, 1655 cm^Ϫ1

Ϫ

.

¹H NMR (60 MHz, CD₂Cl₂, θ ϭ 227 K): δ ϭ 0.49 (t, ³J ϭ

6.0 Hz, 1 H, 8-H_syn), 0.93 (s, 9 H, tBu-H), 1.00 (s, 9 H, tBu-H),

3

8,8-Dimethyl-2,6-bis(2-pyridyl)-3,4-homotropilidene (18a): Com-

pound 12v (255 mg, 0.807 mmol), after photolysis in CH₃CN

1.92 (d, J ϭ 6.0 Hz, 2 H, 1-H, 7-H), 3.00 (t, J ϭ 8.0 Hz, 1 H, 4-

H_eq), 3.73 (s, 6 H, OCH₃), 6.95 (d, ³J ϭ 8.0 Hz, 2 H, 3-H, 5-H). Ϫ

(45 mL) at room temp. for 4.5 h according to General Procedure ¹³C NMR (22.63 MHz, C₂D₂Cl₄, θ ϭ 413 K): δ ϭ 27.7 (ϪCH₃, 6

(7) and purification by FC (CH₂Cl₂/ethanol ϭ 15:1), yielded 18a

C, tBu-CH₃), 34.2 (quat. C, 2 C, tBu-C), 47.4 (ϭCH, 2 C, 4-C, 8-

˜

(204 mg, 0.707 mmol, 88%) as a red oil. Ϫ IR (oil): ν ϭ 3060, 3010, C), 50.7 (ϪCH₃, 2 C, OCH₃), 80.1 (broad, 1-C, 7-C, 3-C, 5-C),

2654

Eur. J. Org. Chem. 2001, 2639Ϫ2657

Synthesis and Properties of Homotropilidenes

132.9 (quat. C, 2 C, 2-C, 6-C), 167.7 (quat. C, 2 C, CϭO). Ϫ UV/ 2 H, Ar-H), 7.42 (d, ³J ϭ 9.3 Hz, 2 H, 3-H, 5-H), 7.54Ϫ7.93 (m, 4

FULL PAPER

Vis (1,4-dioxane): λ (ε) ϭ 217 (17060). Ϫ C₂₀H₃₀O₄(334.4): calcd.

H, Ar-H), 8.43Ϫ8.64 (m, 2 H, Ar-H). Ϫ C₂₀H₂₀N₂(288.4): calcd.

C 71.82, H 9.04; found C 71.73, H 8.80.

N 9.71; found N 9.57.

4,8-Dimethyl-3,4-homotropilidene-2,6-dicarbonitrile (20c): Com-

Dimethyl 1,5-Dimethyl-3,4-homotropilidene-2,6-dicarboxylate (21a):

pound 12l (1.00 g, 4.72 mmol) was photolyzed in benzene (250 mL) Compound 12f (556 mg, 2.00 mmol) was photolyzed in benzene

at room temp. for 4 h according to General Procedure (6). Purifica- (200 mL) at room temp. for 15 min according to General Procedure

tion by recrystallization (methanol), cooling to Ϫ78 °C, afforded (6). Evaporation of the solvent afforded 21a (135 mg, 0.540 mmol,

20c (440 mg, 2.39 mmol, 51%) as colourless crystals, m.p. 77Ϫ79 27%) as a colourless oil. Ϫ IR (film): 1710 cm^Ϫ1. Ϫ ¹H NMR

1

3

2

°C. Ϫ IR (film): 2220 cm^Ϫ1. Ϫ H NMR (90 MHz, CD₂Cl₂, θ ϭ (90 MHz, [D₈]toluene): δ ϭ 0.40 (dd, J ϭ 6.0, J ϭ 4.5 Hz, 1 H,

3

216 K): δ ϭ 1.16 (tq, J ϭ 6.0, J ϭ 5.1 Hz, 1 H, 8-H_syn), 1.29 (d, 8-H_syn), 0.97 (dd, ³J ϭ 9.2, ²J ϭ 4.5 Hz, 1 H, 8-H_anti), 1.22 (s, 3 H,

³J ϭ 6.0 Hz, 3 H, 8-CH₃-anti), 1.36 (d, J ϭ 7.4 Hz, 3 H, 4-CH₃-

1-CH₃), 1.55 (qdd, ³J ϭ 6.0, ³J ϭ 9.2, ⁵J ϭ 2.2 Hz, 1 H, 7-H), 1.91

3

anti), 1.73 (d, ³J ϭ 5.1 Hz, 2 H, 1-H, 7-H), 3.08 (tq, ³J ϭ 7.4, ³J ϭ (dd, J ϭ 13.0, J ϭ 8.5 Hz, 1 H, 4-H_eq), 2.01 (d, J ϭ 2.2 Hz, 3

2

3

5

8.1 Hz, 1 H, 4-H_eq), 6.67 (d, J ϭ 8.1 Hz, 2 H, 3-H, 5-H). Ϫ ¹³C H, 5-CH₃), 3.25 (dd, J ϭ 13.0, J ϭ 6.0 Hz, 1 H, 4-H_ax), 3.81 (s,

NMR (22.63 MHz, CDCl₃, θ ϭ 233 K): δ ϭ 18.3 (ϪCH₃, 1 C, 8- 6 H, OCH₃), 7.17 (dd, ³J ϭ 8.5, ³J ϭ 6.0 Hz, 1 H, 3-H). Ϫ ¹³C

CH₃or 4-CH₃), 20.7 (ϪCH₃, 1 C, 4-CH₃or 8-CH₃), 25.6 (ϭCH, NMR (22.63 MHz, CDCl₃): δ ϭ 17.6 (ϪCH₂Ϫ, 1 C, 8-C or 4-C),

2 C, 1-C, 7-C), 27.0 (ϭCH, 1 C, 4-C or 8-C), 33.6 (ϭCH, 8-C or 21.8 (quat. C, 1 C, 1-C), 23.1 (ϭCH, 1 C, 7-C), 25.5 (ϪCH₃, 2 C,

4-C), 113.9 (quat. C, 2 C, 2-C, 6-C), 119.4 (quat. C, 2 C, CN), 1-CH₃, 5-CH₃), 34.5 (ϪCH₂Ϫ, 1 C, 4-C or 8-C), 51.2 (ϪCH₃, 1 C,

149.2 (ϭCH, 2 C, 3-C, 5-C). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 280 OCH₃), 51.4 (ϪCH₃, 1 C, OCH₃), 127.4 (quat. C, 1 C, 2-C or 6-

(2860). Ϫ MS (EI, 70 eV): m/z (%) ϭ 183 (39) [M^ϩ], 169 (100). Ϫ C), 136.1 (quat. C, 1 C, 6-C or 2-C), 142.7 (ϭCH, 1 C, 3-C), 151.7

3

2

3

C₁₂H₁₂N₂(182.4): calcd. N 15.21; found N 15.16.

(quat. C, 1 C, 5-C), 166.8 (quat. C, 1 C, CϭO), 168.9 (quat. C, 1

C, CϭO). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 257 (2320). Ϫ C₁₄H₁₈O₄

(250.3): calcd. C 67.18, H 7.25; found C 66.77, H 7.10.

4,8-Di-tert-butyl-3,4-homotropilidene-2,6-dicarbonitrile

(20d): Compound 12m (208 mg, 0.70 mmol), after photolysis in

methanol (30 mL) at room temp. for 100 min according to General 1,5-Dimethyl-3,4-homotropilidene-2,6-dicarbonitrile (21b): Com-

Procedure (7) and purification by recrystallization (methanol),

pound 12n (1.00 g, 4.72 mmol) was photolyzed in benzene

yielded 20d (114 mg, 0.43 mmol, 61%) as colourless crystals; m.p.

(250 mL) at room temp. for 8 h according to General Procedure

1

120Ϫ122 °C. Ϫ IR (KBr): ν ϭ 2970, 2870, 2220, 1640 cm^Ϫ1. Ϫ H (6). Purification by recrystallization (methanol), cooling to Ϫ78 °C,

˜

3

NMR (60 MHz, CD₂Cl₂, θ ϭ 233 K): δ ϭ 0.96 (t, J ϭ 6.0 Hz, 1 afforded 21b (400 mg, 2.17 mmol, 46%) as colourless crystals, m.p.

H, 8-H_syn), 0.97 (s, 9 H, tBu-H), 1.03 (s, 9 H, tBu-H), 1.85 (d, ³J ϭ

75Ϫ76 °C. Ϫ IR (KBr): ν ϭ 2210 cm^Ϫ1. Ϫ ¹H NMR (60 MHz,

˜

6.0 Hz, 2 H, 1-H, 7-H), 2.98 (t, J ϭ 8.0 Hz, 1 H, 4-H_eq), 6.50 (d, CDCl₃): δ ϭ 0.67 (dd, ³J ϭ 5.8, ²J ϭ 4.6 Hz, 1 H, 8-H_syn), 1.03

³J ϭ 8.0 Hz, 2 H, 3-H, 5-H). Ϫ ¹³C NMR (22.63 MHz, CDCl₃, (dd, ³J ϭ 8.8, ²J ϭ 4.6 Hz, 1 H, 8-H_anti), 1.36 (s, 3 H, 1-CH₃), 1.72

θ ϭ 233 K): δ ϭ 23.7 (ϭCH, 2 C, 1-C, 7-C), 27.7 (ϪCH₃, 3 C, (qdd, ³J ϭ 5.8, ³J ϭ 8.8, ⁵J ϭ 1.8 Hz, 1 H, 7-H), 2.10 (d, ⁵J ϭ

3

CH₃), 28.2 (ϪCH₃, 3 C, CH₃), 30.0 (quat. C, 1 C, tBu-C), 40.5

1.8 Hz, 3 H, 5-CH₃), 2.45 (dd, ²J ϭ 14.2, ³J ϭ 8.6 Hz, 1 H, 4-H_eq),

2

3

(quat. C, 1 C, tBu-C), 45.7 (ϭCH, 1 C, 8-C), 50.8 (ϭCH, 1 C, 4- 3.53 (dd, J ϭ 14.2, J ϭ 5.4 Hz, 1 H, 4-H_ax), 6.69 (dd, J ϭ 8.6,

C), 115.0 (quat. C, 2 C, C-2, C-6), 119.5 (quat. C, 2 C, CN), 145.9 ³J ϭ 5.4 Hz, 1 H, 3-H). Ϫ ¹³C NMR (22.63 MHz, CDCl₃): δ ϭ

(ϭCH, 2 C 3-C, 5-C). Ϫ C₁₈H₂₄N₂(268.4): calcd. C 80.55, H 9.01, 17.5 (ϪCH₂Ϫ, 1 C, 8-C), 24.5 (quat. C, 1 C, 1-C), 24.7 (ϭCH, 1

N 10.44; found C 80.31, H 9.07, N 10.39.

C, 7-C), 26.2 (ϪCH₃, 2 C, 1-CH₃, 5-CH₃), 32.2 (ϪCH₂Ϫ, 1 C, 4-

C), 110.0 (quat. C, 2 C, 2-C, 6-C), 118.5 (quat. C, 1 C, CN), 120.5

(quat. C, 1 C, CN), 145.5 (ϭCH, 1 C, 3-C), 159.0 (quat. C, 1 C, 5-

C). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 248 (2290). Ϫ MS (EI, 70 eV):

m/z (%) ϭ 184 (40) [M^ϩ], 169 (100). Ϫ C₁₂H₁₂N₂(184.2): calcd. C

78.23, H 6.57, N 15.21; found C 78.01, H 6.93, N 14.96.

4,8-Dimethyl-2,6-diphenyl-3,4-homotropilidene (20e): Compound

12r (455 mg, 1.45 mmol), after photolysis in CH₃CN (15 mL) at

room temp. for 15 min according to General Procedure (7) and

purification by recrystallization (methanol), yielded 20e (320 mg,

1.12 mmol, 77%) as colourless needles, m.p. 91Ϫ92 °C. Ϫ IR

˜

(KBr): ν ϭ 3060, 2960, 2900, 1635, 1595, 1495, 1450, 860, 840, 760, 1,5-Dimethyl-2,6-bis(2-pyridyl)-3,4-homotropilidene (21c): Com-

690 cm^Ϫ1. Ϫ ¹H NMR (250 MHz, CD₂Cl₂): δ ϭ 0.65 (tq, ³J ϭ 5.9, pound 12x (369 mg, 1.17 mmol), after photolysis in CH₃CN

3

³J ϭ 5.6 Hz, 1 H, 8-H_syn), 1.46 (d, J ϭ 5.9 Hz, 3 H, 8-CH₃-anti), (30 mL) at room temp. for 5.5 h according to General Procedure

3

1.50 (d, J ϭ 5.5 Hz, 3 H, 4-CH₃-anti), 1.84 (d, J ϭ 5.6 Hz, 2 H,

(7) and purification by FC [CH₂Cl₂/PE/ethanol ϭ 10:2:1], yielded

1-H, 7-H), 3.06 (tq, ³J ϭ 5.5, ³J ϭ 8.5 Hz, 1 H, 4-H_eq), 6.53 (d, 21c (343 mg, 1.15 mmol, 98%) as a colourless oil. Ϫ IR (KBr): ν ϭ

˜

³J ϭ 8.5 Hz, 2 H, 3-H, 5-H), 7.20Ϫ7.35 (m, 6 H, Ar-H), 7.51Ϫ7.59 3050, 2990, 2940, 2920, 2850, 1575, 1550, 1460, 1420, 1370, 1265,

(m, 4 H, Ar-H). Ϫ MS (EI, 70 eV): m/z (%) ϭ 287 (20) [M^ϩ], 244

1140, 1080, 1040, 1020, 1005, 985, 960, 900, 770, 720 cm^Ϫ1. Ϫ H

1

3

2

(100). Ϫ UV/Vis (CH₃CN): λ (ε) ϭ 264 (12110), 247 (14930), 225 NMR (250 MHz, CDCl₃): δ ϭ 0.41 (dd, J ϭ 6.3, J ϭ 3.9 Hz, 1

(16480). Ϫ C₂₂H₂₂(286.3): calcd. C 92.21, H 7.75; found C 91.93,

2

3

H, 8-H_syn), 1.00 (dd, J ϭ 3.9, J ϭ 9.3 Hz, 1 H, 8-H_anti), 1.34 (s,

3 H, 1-CH₃), 1.78 (d, ⁵J ϭ 0.5 Hz, 3 H, 5-CH₃), 2.05Ϫ2.13 (m,

³J ϭ 6.3, ³J ϭ 9.3 Hz, 1 H, 7-H), 2.43 (dd, ²J ϭ 13.2, ³J ϭ 8.6 Hz,

1 H, 4-H_eq), 3.69 (dd, ²J ϭ 13.2, ³J ϭ 6.1 Hz, 1 H, 4-H_ax),

H 7.93.

4,8-Dimethyl-2,6-bis(2-pyridyl)-3,4-homotropilidene (20f): Com-

pound 12w (180 mg, 0.568 mmol), after photolysis in CH₃CN

(45 mL) at room temp. for 4.5 h according to General Procedure

(7) and purification by recrystallization (CH₂Cl₂/n-hexane), yielded

3

7.05Ϫ7.12 (m, 3 H, Ar-H), 7.46 (dd, J ϭ 8.6, J ϭ 6.1 Hz, 1 H,

3-H), 7.58Ϫ7.63 (m, 3 H, Ar-H), 8.54Ϫ8.61 (m, 2 H, Ar-H).

20f (133 mg, 0.462 mmol, 81%) as colourless crystals, m.p. 88Ϫ91 Dimethyl 3,8-Dimethyl-3,4-homotropilidene-2,6-dicarboxylate (22a):

˜

°C. Ϫ IR (KBr): ν ϭ 3050, 3000, 2920, 2900, 2860, 1640, 1580,

Compound 12g (975 mg, 3.50 mmol), after photolysis in benzene

1560, 1470, 1425, 1260, 1165, 1090, 880, 780, 745, 700 cm^Ϫ1. Ϫ ¹H (150 mL) at room temp. for 20 min according to General Procedure

NMR (250 MHz, CD₂Cl₂, θ ϭ 220 K): δ ϭ 0.70 (tq, ³J ϭ 5.6, ³J ϭ (6) and purification by distillation at 0.001 Torr, yielded 22a

5.6 Hz, 1 H, 8-H_syn), 1.56 (d, J ϭ 5.6 Hz, 3 H, 8-CH₃-anti), 1.56

3

˜

(680 mg, 2.72 mmol, 78%) as a colourless oil. Ϫ IR (film): ν ϭ

3

1

3

(d, J ϭ 5.6 Hz, 3 H, 4-CH₃-anti), 1.96 (d, J ϭ 5.6 Hz, 2 H, 1-H,

1715 cm^Ϫ1. Ϫ H NMR (60 MHz, CDCl₃): δ ϭ 0.40 (dt, J ϭ 6.0,

7-H), 3.18 (tq, J ϭ 5.6, J ϭ 9.3 Hz, 1 H, 4-H_eq), 7.09Ϫ7.29 (m, ³J ϭ 6.0 Hz, 1 H, 8-H_syn), 1.25 (d, J ϭ 6.0 Hz, 3 H, 8-CH₃-anti),

3

Eur. J. Org. Chem. 2001, 2639Ϫ2657

2655

J. Sauer et al.

3 H, 8-CH₃-syn), 1.51 (d, J ϭ 7.2 Hz, 3 H, 4-CH₃-anti), 1.54 (s, 3

FULL PAPER

1.58 (d, ³J ϭ 6.0 Hz, 2 H, 1-H, 7-H), 2.07 (s, 3 H, 3-CH₃), 2.30

3

2

3

(dd, J ϭ 8.0, J ϭ 13.5 Hz, 1 H, 4-H_eq), 3.47Ϫ3.80 (m, J ϭ 6.0, H, 8-CH₃-anti), 2.04 (s, 2 H, 1-H, 7-H), 3.18Ϫ3.34 (m, ³J ϭ 7.2,

²J ϭ 13.5 Hz, 1 H, 4-H_ax), 3.73 (s, 6 H, OCH₃), 7.18 (dd, ³J ϭ 8.0,

³J ϭ 8.5 Hz, 1 H, 4-H_eq), 7.09Ϫ7.14 (m, 2 H, Ar-H), 7.32 (d, ³J ϭ

³J ϭ 6.0 Hz, 1 H, 5-H). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 274 8.5 Hz, 2 H, 3-H, 5-H), 7.37Ϫ7.42 (m, 2 H, Ar-H), 7.62Ϫ7.69 (m,

(1150).

2 H, Ar-H), 8.54Ϫ8.57 (m, 2 H, Ar-H). Ϫ C₂₁H₂₂N₂(302.4): calcd.

C 83.41, H 7.33, N 9.26; found C 83.47, H 7.12, N 9.26.

3,8-Dimethyl-2,6-bis(2-pyridyl)-homotropilidene (22b): Compound

12y (430 mg, 1.36 mmol), after photolysis in CH₃CN (35 mL) at

room temp. for 5 h according to General Procedure (7) and puri-

fication by FC (CH₂Cl₂/PE/ethanol ϭ 15:2:1), yielded 22b (237 mg,

Acknowledgments

We are grateful to the Deutsche Forschungsgemeinschaft, the

Fonds der Chemischen Industrie and BASF AG for financial sup-

port of this research.

˜

0.822 mmol, 60%) as a yellow oil. Ϫ IR (KBr): ν ϭ 3060, 3010,

2960, 2940, 2910, 2870, 2585, 2560, 1470, 1430, 1375, 1150, 1000,

910, 775, 730 cm^Ϫ1. Ϫ ¹H NMR (400 MHz, CDCl₃): δ ϭ

3

0.44Ϫ0.49 (m, J ϭ 5.9 Hz, 1 H, 8-H_syn), 1.18 (d, J ϭ 5.9 Hz, 3

3

H, 8-CH₃-anti), 1.73 (d, J ϭ 1.7 Hz, 3 H, 3-CH₃), 1.79Ϫ2.05 (m,

2 H, 1-H, 7-H), 2.41 (dd, J ϭ 13.9, J ϭ 8.7 Hz, 4-H_eq), 3.83 (dd,

2

3

[1]

A. C. Cope, E. M. Hardy, J. Am. Chem. Soc. 1940, 62,

²J ϭ 13.9, J ϭ 5.2 Hz, 1 H, 4-H_ax), 7.11 (dd, 1 H, J ϭ 5.2, J ϭ

8.7 Hz, 1 H, 5-H), 7.09Ϫ7.15 (m, 2 H, Ar-H) 7.36Ϫ7.40 (m, 1 H,

Ar-H), 7.46Ϫ7.48 (m, 1 H, Ar-H), 7.57Ϫ7.68 (m, 2 H, Ar-H),

8.53Ϫ8.60 (m, 2 H, Ar-H).

3

441Ϫ444.

[2]

R. B. Woodward, R. Hoffmann, Angew. Chem. 1969, 81,

797Ϫ869; Angew. Chem. Int. Ed. Engl. 1969, 8, 781Ϫ853.

[3]

R. B. Woodward, R. Hoffmann, The Conservation of Orbital

Symmetry, Academic Press, New York, 1970.

Dimethyl 1,7-Diphenyl-3,4-homotropilidene-2,6-dicarboxylate (24a):

A suspension of 12h (240 mg, 0.64 mmol) in tetrachloroethylene

(2.5 mL) was heated at 120 °C for 41 h. Purification by recrystal-

lization (methanol) afforded 24a (170 mg, 0.45 mmol, 71%) as col-

ourless crystals; m.p. 163Ϫ165 °C. Ϫ IR (KBr): ν˜ ϭ 1700 cm^Ϫ1. Ϫ

¹H NMR (90 MHz, CDCl₃): δ ϭ 1.31 (d, ²J ϭ 6.5 Hz, 1 H, 8-

[4]

S. J. Rhoads in Molecular Rearrangements, vol. 1 (Ed.: P. de

Mayo), John Wiley & Sons, New York, 1963, pp. 684Ϫ696.

[5]

S. J. Rhoads, N. R. Raulius, Org. React. 1975, 22, 1Ϫ252.

[6]

J. J. Gajewski in Hydrocarbon Thermal Rearrangements, Aca-

demic Press, New York, 1981, pp. 166Ϫ176.

[7]

W. v. E. Doering, Y. Wang, J. Am. Chem. Soc. 1999, 121,

2

3

H_syn), 2.82 (d, J ϭ 6.5 Hz, 1 H, 8-H_anti), 2.97 (dt, ²J ϭ 14.0, J ϭ

10112Ϫ10118.

[8]

3

8.8 Hz, 1 H, 4-H_eq), 3.61 (s, 6 H, OCH₃), 3.96 (dt, ²J ϭ 14.0, J ϭ

W. v. E. Doering, Y. Wang, J. Am. Chem. Soc. 1999, 121,

10967Ϫ10975.

O. Wiest, D. Montiel, K. N. Houk, J. Phys. Chem. A 1997,

101, 8378Ϫ8388.

5.0 Hz, 1 H, 4-H_ax), 6.89Ϫ7.30 (m, 10 H, Ar-H), 7.45 (dd, ³J ϭ

8.8, ³J ϭ 5.0 Hz, 2 H, 3-H, 5-H). Ϫ ¹³C NMR (22.63 MHz,

CDCl₃): δ ϭ 20.5 (ϪCH₂Ϫ, 1 C, 8-C or 4-C), 25.7 (ϪCH₂Ϫ, 1 C,

4-C or 8-C), 36.5 (quat. C, 2 C, 1-C, 7-C), 51.5 (ϪCH₃, 2 C,

OCH₃), 126.2 (ϭCH, 4 C, Ar-C), 128.1 (ϭCH, 2 C, Ar-C), 128.9

(ϭCH, 4 C, Ar-C), 137.8 (quat. C, 2 C, Ar-C or 2-C, 6-C), 139.1

(quat. C, 2 C, 2-C, 6-C or Ar-C), 141.5 (ϭCH, 2 C, 3-C, 5-C),

166.6 (quat. C, 2 C, CϭO). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 257

(5550). Ϫ MS (EI, 70 eV): m/z (%) ϭ 374 (89) [M^ϩ], 255 (100). Ϫ

C₂₂H₂₂O₄(374.5): calcd. C 76.97, H 5.93; found C 76.94, H 6.02.

[9]

[10]

K. N. Houk, Y. Li, J. D. Evanseck, Angew. Chem. 1992, 104,

711Ϫ739; Angew. Chem. Int. Ed. Engl. 1992, 31, 682Ϫ708.

[11]

W. Dittmar, G. Heinrichs, A. Steigel, T. Troll, J. Sauer, Tetra-

hedron Lett. 1970, 1623Ϫ1627.

H. D. Fühlhuber, C. Gousetis, T. Troll, J. Sauer, Tetrahedron

Lett. 1978, 3903Ϫ3906.

R. D. Dyllick-Brenzinger, J. F. M. Oth, H. D. Fühlhuber, C.

[12]

[13]

Gousetis, T. Troll, J. Sauer, Tetrahedron Lett. 1978, 3907Ϫ3911.

[14]

C. Gousetis, J. Sauer, Tetrahedron Lett. 1979, 1295Ϫ1298.

[15]

3,5-Diphenyl-3,4-homotropilidene-2,6-dicarbonitrile (25a): Com-

pound 12o (400 mg, 1.19 mmol), after photolysis in acetone

(400 mL) at room temp. for 8 h according to General Procedure (6)

and purification by recrystallization (methanol), yielded 25a

H. D. Fühlhuber, C. Gousetis, J. Sauer, H. J. Lindner, Tetrahed-

ron Lett. 1979, 1299Ϫ1302.

[16]

N. Biedermann, J. Sauer, Tetrahedron Lett. 1994, 7935Ϫ7938.

[17]

W. v. E. Doering, W. R. Roth, Tetrahedron 1963, 19, 27Ϫ35.

[18]

W. v. E. Doering, W. R. Roth, Angew. Chem. 1963, 75, 27Ϫ35.

(230 mg, 0.75 mmol, 63%) as colourless crystals, m.p. 189Ϫ191 °C.

[19]

O. L. Chapman, R. A. Fugiel, J. Am. Chem. Soc. 1969, 91,

1

Ϫ IR (KBr): ν ϭ 2205 cm^Ϫ1. Ϫ H NMR (90 MHz, CDCl₃): δ ϭ

˜

215Ϫ216.

2

3

0.82 (dt, J ϭ 5.2, J ϭ 6.0 Hz, 1 H, 8-H_syn), 1.2Ϫ1.7 (m, 1 H, 8-

[20]

E. Vedejs, M. F. Salomon, P. O. Wecks, J. Am. Chem. Soc. 1973,

95, 6770Ϫ6778.

A. Steigel, J. Sauer, D. A. Kleier, G. Binsch, J. Am. Chem. Soc.

1972, 94, 2770Ϫ2779.

P. Bäuerlein, W. Ebenbeck, C. Gousetis, H. Sichert, T. Troll, F.

Utz, J. Sauer, Eur. J. Org. Chem. 2001, 2629Ϫ2638, preceding

paper.

J. Sauer, ‘‘1,2,4,5-Tetrazines’’ in Comprehensive Heterocyclic

Chemistry II (Eds.: A. R. Katritzky, C. W. Rees, E. F. V.

Scriven), Pergamon Press, Oxford, 1996, vol. 6, pp. 901Ϫ957.

F. Thalhammer, U. Wallfahrer, J. Sauer, Tetrahedron Lett. 1990,

31, 6851Ϫ6854.

T. Curtius, A. Darapsky, E. Muller, Ber. Dtsch. Chem. Ges.

3

5

H_anti), 2.28 (ddd, J ϭ 9.1, J ϭ 6.0, J ϭ 1.3 Hz, 2 H, 1-H, 7-H),

3.21 (d, ²J ϭ 13.3 Hz, 1 H, 4-H_eq), 4.63 (dt, ²J ϭ 13.3, ⁵J ϭ 1.3 Hz,

1 H, 4-H_ax), 7.2Ϫ7.5 (m, 10 H, Ar-H). Ϫ ¹³C NMR (22.63 MHz,

CDCl₃): δ ϭ 9.9 (ϪCH₂Ϫ, 1 C, 8-C), 20.4 (ϭCH, 2 C, 1-C, 7-C),

40.2 (ϪCH₂Ϫ, 1 C, 4-C), 109.7 (quat. C, 2 C, 2-C, 6-C), 118.7

(quat. C, 2 C, CN), 127.3 (ϭCH, 4 C, Ar-C), 128.8 (ϭCH, 2 C,

Ar-C), 129.7 (ϭCH, 4 C, Ar-C), 138.2 (quat. C, 2 C, Ar-C), 159.8

(quat. C, 2 C, 3-C, 5-C). Ϫ UV/Vis (1,4-dioxane): λ (ε) ϭ 258

(18350). Ϫ MS (EI, 70 eV): m/z (%) ϭ 308 (100) [M^ϩ]. Ϫ C₂₂H₁₆N₂

(308.4): calcd. C 85.67, H 5.24, N 9.09; found C 85.76, H 5.23,

N 8.99.

[21]

[22]

[23]

[24]

[25]

1906, 39, 3410Ϫ3437.

4,8,8-Trimethyl-2,6-bis(2-pyridyl)-3,4-homotropilidene

(26a): Compound 12z (176 mg, 0.531 mmol) was photolyzed in

CH₃CN (45 mL) at room temp. for 4.5 h according to General Pro-

cedure (7). Purification by FC (CH₂Cl₂/n-hexane/ethanol ϭ 10:2:1)

afforded 26a (170 mg, 0.531 mmol, quant.) as a yellow oil. Ϫ IR

(film): ν˜ ϭ 3070, 3040, 2950, 2910, 2850, 1630, 1570, 1555, 1455,

[26]

E. Gryszkiewicz-Trochimowski, M. Bousquet, C. R. Acad. Sci.

1961, 253, 292Ϫ294.

[27]

K. Elender, Diplomarbeit, Universität Regensburg, 1996.

[28]

R. Gleiter, V. Schehlmann, J. Spanget-Larsen, H. Fischer, F. A.

Neugebauer, J. Org. Chem. 1988, 53, 5756Ϫ5762.

N. J. Turro, Modern Molecular Photochemistry, University Sci-

ence Books, Mill Valley, California, 1991.

[29]

1

1415, 770, 730 cm^Ϫ1. Ϫ H NMR (250 MHz, CDCl₃): δ ϭ 0.63 (s,

2656

Eur. J. Org. Chem. 2001, 2639Ϫ2657

Synthesis and Properties of Homotropilidenes

FULL PAPER

R. Bicker, H. Kessler, A. Steigel, W.-D. Stohrer, Chem. Ber.

1975, 108, 2708Ϫ2721.

H. Guenther, J. B. Pawliczek, J. Ulmen, W. Grimme, Angew.

Chem. 1972, 84, 539Ϫ540.

L. Birladeanu, D. L. Harris, S. Winstein, J. Am. Chem. Soc.

1970, 92, 6387.

L. M. Jackman, E. Fernandes, M. Heubes, H. Quast, Eur. J.

Org. Chem. 1998, 2209Ϫ2227.

D. Moskau, R. Aydin, W. Leber, H. Guenther, H. Quast, H.-

D. Martin, K. Hassenrueck, L. S. Miller, K. Grohmann, Chem.

Ber. 1989, 122, 925Ϫ931.

D. A. Hrovat, B. R. Beno, H. Lange, H.-Y. Yoo, K. N. Houk,

W. T. Borden, J. Am. Chem. Soc. 1999, 121, 10529Ϫ10537.

D. A. Hrovat, J. C. Chen, K. N. Houk, W. T. Borden, J. Am.

Chem. Soc. 2000, 122, 7456Ϫ7460.

G. L. Closs, K. D. Krantz, J. Org. Chem. 1966, 31, 638.

D. Seyferth, R. L. Lambert, Jr., J. Organomet. Chem. 1969,

16, 21Ϫ26.

[30]

[47]

[48]

[49]

[50]

[51]

W. Adam, T. Oppenländer, Angew. Chem. 1986, 98, 659Ϫ670;

Angew. Chem. Int. Ed. Engl. 1986, 25, 661Ϫ672.

[31]

W. Adam, O. De Lucchi, Angew. Chem. 1980, 92, 815Ϫ832;

Angew. Chem. Int. Ed. Engl. 1980, 19, 762Ϫ779.

[32]

P. S. Engel, Chem. Rev. 1980, 80, 99Ϫ150.

[33]

P. W. Anderson, J. Phys. Soc. Jpn. 1954, 9, 316Ϫ325.

[34]

R. Kubo, K. Tomita, J. Phys. Soc. Jpn. 1954, 9, 888Ϫ919.

[35]

R. A. Sack, Mol. Phys. 1958, 1, 163Ϫ167.

[36]

For further detailed information see: R. Dyllick-Brenzinger,

Dissertation, ETH Zürich, 1977.

[37]

H. Guenther, J. Ulmen, Chem. Ber. 1975, 108, 3132Ϫ3140.

[38]

[52]

[53]

P. Bischof, R. Gleiter, E. Heilbronner, V. Hornung, G. Schro-

eder, Helv. Chim. Acta 1970, 53, 1645Ϫ1657.

H. Kessler, W. Ott, H. J. Lindner, H. G. von Schnering, E.-M.

[39]

Peters, K. Peters, Chem. Ber. 1980, 113, 90Ϫ103.

[40]

[54]

[55]

R. Bicker, H. Kessler, W. Ott, Chem. Ber. 1975, 108,

3151Ϫ3158.

[41]

J. C. Barborak, S. Chari, P. v. R. Schleyer, J. Am. Chem. Soc.

[56]

1971, 93, 5275Ϫ5277.

K. C. Lilje, R. S. Macomber, J. Org. Chem. 1974, 39,

[42]

R. Hoffmann, W.-D. Stohrer, J. Am. Chem. Soc. 1971, 93,

3600Ϫ3602.

[57]

[58]

6941Ϫ6948.

H. Sichert, Dissertation, Universität Regensburg, 1980.

W. C. Perkin, D. H. Wadsworth, J. Org. Chem. 1972, 37,

800Ϫ801.

[43]

M. J. S. Dewar, D. H. Lo, J. Am. Chem. Soc. 1971, 93,

7201Ϫ7207.

[44]

[59]

G. Maas, J. K. Kettenring, Chem. Ber. 1982, 115, 627Ϫ644.

W. Ott, Dissertation, Universität Frankfurt, 1975.

[45]

G. Maas, J. K. Kettenring, Chem. Ber. 1984, 117, 575Ϫ584.

Received December 18, 2000

[46]

H. Kessler, W. Ott, J. Am. Chem. Soc. 1976, 98, 5014Ϫ5016.

[O00643]

Eur. J. Org. Chem. 2001, 2639Ϫ2657

2657

Article Doi

The cycloaddition-cycloelimination pathway to homotropilidenes - Synthesis and properties of homotropilidenes

DOI: 10.1002/1099-0690(200107)2001:14<2639::aid-ejoc2639>3.0.co;2-0

Source and publish data:

Authors:

Article abstract of DOI:10.1002/1099-0690(200107)2001:14<2639::aid-ejoc2639>3.0.co;2-0

Full text of DOI:10.1002/1099-0690(200107)2001:14<2639::aid-ejoc2639>3.0.co;2-0

Products guided by the article

R&D Labs maybe for 53922-23-9

Relevant to this article

Hot Product