Tetrahedron Vol. 45, No. 10, pp. 2905 to 2915, 1989 0040-4020/89 $3.00+.00 Printed in Great Britain. © 1989 Pergarnon Press plc 7-M!THYL- AND 7-PH!NTLCTCLOHIPTA-1,3,5-TRIIN!S FRON B!NZVAL!NI VIA 3,3a,,,5,5, &a­ 4 H!XAHYDRO·•,s,&-M!TH!NOCYCLOPBNTAPYRAZOLIS AND TBTRACYCLO[ •. 1. 0.01 ' • 0~' 1 lHIPTAHIS MANFRED CHRIStL••, ERICH BRUNN•, WOLFGANG R. ROTH~, AND HANS-WERHER LENNARTZ' Institut für Organische Chemie der Universität Würzburg•, Am Hubland, D-8700 Würzburg, Federal Republ ic of Germany Fakultät für Chemie der Universität Bochum~, Postfach 102148, D-4630 Bochum 1, Federal Republic of Germany (Received in Belgium 8 August 1988) Abstract: The addition of benzvalene < n to diazomethane, diazoethane, 2- diazopropane, phenyldiazomethane, and diphenyldiazomethane afforded the 1-pyrazolines 2a-; in good yields. By means of competition experiments, the relative reactivities of benzvalene 111 and norbornene with regard to diazomethane and 2-diazopropane have been determined. The fact that benz­ valene reacts about twice as fast as norbornene with both diazoalkanes cannot be rationalized on the basis of frontier orbital energies. On direct photolysis, the pyrazolines 2a-; were converted into the tetracy­ 2 4 3 clo[ 4. 1. 0. 0 • • 0 •., l heptanes 4a-; exclusi vely. These compounds gave the 1,3,5-cycloheptatrienes !5a,b,d,t,; in high yields on treatment with sil­ ver ions, thus providing better access to 7, 7-dimethyl-( Sdl and 7.7- diphenylcycloheptatriene C 5;1 than before. Su1•prisingly. the latter com­ pound is in equilibrium with a substantial Quantity of the norcaradiene form. - The heat of reaction for the rearrangement of •• to 5a has been determined, which allows to derive the heat of formation of tetracyclo­ l4.1.0.02'4.03''1heptane <4al. The most generally applicable methods for the synthesis of 1, 3,5-cyclohepta­ triene derivatives are reactions of the tropylium cation with nucleophiles and the addition of carbenes to benzene. 1 While the former can give unequivocally only 7- monosubstituted cycloheptatrienes, the latter is also suitable for the preparation of certain derivatives disubstituted in the 7-position. However, many carbenes do not react with benzene or qive products only in low yields. Obviously, 7, 7-di- methylcycloheptatriene < Sd) cannot be obtained via this route, since it has exclu­ sively been prepared by using other approaches 2 ' 3 Formed in low yield on ther­ molysis or photolysis of diphenyldiazomethane in benzene, 7,7-diphenylcyclohepta­ triene C5;) appears in the litersture for the firsttime in 1988. 4 We wish to report here a three-step reaction sequence rendering cycloheptatrienes with one or two methyl or phenyl substituents in the 7-position accessible in good yields. This method demonstrates a utilization of benzvalene as benzene equivalent. ,,3-Dipolar cycloadditiona of diazoalkanea with beniValent~ As early as 1973, we described the addition of diazomethane to benzvalene. • The yield of 1-pyrazoline 2a has now been increased considerably, and in addition diazoethane, 2-diazopropane, phenyldiazomethane, and diphenyldiazomethane have been found to give the corresponding pyrazolines 2b-; in good yields. In the cases of diazoethane and phenyldiazomethane, the ratios of the diastereemers 2b : 2c '"' 1. 7 : 1. 0 and 2• : 2f • 1. 5 : 1. 0, respectively, indicate only a minor stereoselectivity. The structure of the 1-pyrazolines 2 is established unambiguously by analytical and spectral data. The stereochemical assignment within the isomeric pairs 2b,c and 2e,r is based on the maqnitude of the coupling constants 3 ~3.Jo in the 'H-NHR 2905 2906 M. Cmusn et al. spectra (see Table 1) and on the y-gauche effect of the ~-3-substituent <R'> on the chemical shift of C-4 in the ' 3 C-NHR spectra <see Table 21. Although C-5 and C-7 match each other rather closely, their signals can be distinguiahed by means of long-range 13 C-H coupling constants as noted earlier for related tricyclo- 13. 1.0.02 •'Jhexane derivatives. 7 Similarly, the absorptions of C-4 and C-6 differ markedly in their fine structure with that of C-4 being much better resolved. diazoalkane R' R2 product yield CII + N2CR 1 R2 b NzCHz H H 2a 83 NzCHCH:~ H CH:r 2b 31 (58) l CH:~ H 2c NzCC CH:~ I z CH:r CH:r 2cl 93 Hz CHC, Hs H 2e 44 N c, "' ( 73) 5 ~ c, Hs H 2r ~H 2 N:z C< c, Hs > 2 c, Hs c, Hs 2g 72 Table 1. 'H-NHR chemical shifta < S values> and coupling conatants <absolute valuea, Hz) of ~-3,3a,4,5,6,6a-hexahydro-4, 5,6-methenocyclopentapyrazolea <2> in CDCl3. The multiplicities are given only for the parent compound <2a>: they are observed only in a high-field spectrum, aince at low field second order effecta interfere. The following coupling constanta are those of 2a with the deviations in the apectra or the derivatives beinc;r at moat ±0.5 Hz: ~3,3 • 18.0. ~JLLL.J• • 8.5, ~l.LLL••• .. 1.8, ~3LJI...LL,3• "'3.5, ~3.l...l...t..l..•'• = 2.5, ~:r •• • • 1.5, ~3•·•• = 7.0, 1.:ro.r • ~···" 1 . 3. ~· • ' • .l• . ., • .l• . ' • ~· . ., • 1 . 7. .l• . ' • 5. 0. ~· • 7 = 9. 2. 1.• • • • = 1 . 7. compd ~-3-H endo-3-H 3a-H 4-H 5-H 7-H 6-H 6a-H 2a 4.06 4. 15 2.23 2. 05 2. 12 1. 83 2.79 5. 15 ddd ddd dddt dq dt dqui dq ddq 2b. 4.23 1. 70-2.40 2.78 5. 20 2c~ 4. 06 1.70-2.40 2. 78 5. 12 2cl" 1. 70-2.30 2.73 5. 12 2•" 5. 18 2. 00-2. 30 1. 93 2.85 5. 33 zr• 2. 46 1. 30 1.93 1. 71 2. 85 2g• 2.93 1. 38 2.00 1. 70 2. 87 5.35 "1. 23 ( d, J = 7. 3, CH:r>. • 1. 52 ( d, J = 7. 5. CH:r>. c 1. 1 0 ( s. .!..!..Q.-CH:~>, 1. 43 ( s. endo-CH3 >. •7.00-7. 30 ( m, c, Hs). "6. 9-7:-s < m, c, Hs). f 4. 9-5. 4. 1 7. 30 (m, 2 c, Hs). Table 2. '.JC-NMR chemical shifts < S valuea> and 13 C-H couplinq constants <Hz> of ~-3.3a,4,5,6,6a-hexahydro-4,5,6-methenocyclopentapyrazoles <2>. The '.J..c.w values are given only for the parent compound <2a> <second line) with the deviationa in the apectra of the derivatives being at most ±3 Hz. Among the coupling constanta aerOB!! two or more bonds. the following are conaidered tobe unambiguous: .J~c-•·•-w 2 2 3 3 ~c-6,4-M • 13, ,lc-•,r-M • ,lc-7,'5-M • 3, ~c-7,3a-M = Ji!.c-?,6a-M • 8. Tbe specific aasignmenta are based on 1 ~c, w, substituent effects. and fine-structure patterns in the proton-coupled spectra. compd C-3 C-3a C-4 C-5 C-6 C-6a C-7 2a• 77. 5 37. 1 38. 4 7. 7 39. 2 98.7 0. 4 141 170 216 170 1 50 218 2.b··· 83. 0 44. 4 36 . ., 6. 6 37.9 97. 0 -0. 4 2o"' • 80. 2 39. 0 32. 8 5. 8 37. 9 97.8 0. 7 2cl c. f 84.8 46.8 34. 1 6. 7 38. 0 97. 3 1.1 ze··· 93. 3 47. 0 38.'2 8.0 39. 0 100.0 1.0 zt•·~ 89.0 41. 5 35. 0 6. 3 38. 8 98.9 2. 1 29°' I 97. 8 46.4 36.0 6. 3 38. 2 99. 3 2. 1 •solvent o,o,. •141 <.!.!l.SIR.-HL 139 <.!..1.2.-H>. •solvent CDCl:~. '18.1 <CH:~I. "12.9 <CH:~>. •20.9 <~-CH3), 27.6 (.!..!.Q.-CH:~>. •127.5-128.9 (.Q.-C. m-C . .R.-C>, 140.0 <!..1!.!..2.­ C) (C,Hs>. •121.1-128.8 <.Q.-C . .m-C, .R.-C), 138.6 <.ll!..!.2.-C> (C,H,). '126.4-128.4 (g_-C. m-c, ,2-C), 142. 6, 142. 9 ( ipso-C) ( 2 C., Hs >. Benzvalene additions 2907 Ethyl diazoacetate did not reoct with benzvalene <1>. However, methyl 2-diazo­ propionate and 1 afford both the stereoisomeric 1-pyrazolines. 1 The results of the reactions of 1 with tetrachlorodiazocyclopentadiene, diazofluorene, and 5-diazo- 10,11-dihydro-SH-dibenzo[a,dlcycloheptene will be described elsewhere.' With regard to the mechanism, the reaction of diazoalkanes with alkenes is one of the most thoroughly studied 1, 3-dipolar cycloadditions. This is true for experi- 10 mental as well as theoretical investigations. • Therefore, it was of interest to determine the rate of the reaction between diazomethane and benzvalene (1) and to integrate into the scale of dipolarophiles. 10 Because of the simPle experimental set-up, we have carried out competition experiments, in which 1 and norbornene, both in excess relative to the 1,3-dipole, competed for diazomethane and, in a second series, also for 2-diazopropane. The norbornene adduct 3a of diazomethane 10 ~ and the rate constant for its formation are known. 10 The norbornene adduct 3d of 2-diazopropane has now been obtained in 79% yield. In the experimental part, the data of the individual competition experiments are collected, from which the fol­ lowing ratios of the rate constants have been calculated according to ref. 11. 2a Rl = R2 = H 1 2 2cl R : R :CH3 k ... ft 1: II. 1 I ft I k. e o • v o I e n e di azomet hane: 1.