2883
tained by catalytic hydrogenation of 2a to the known5 dibenzobicyclo[3.3.0]octadiene (3). 2a was also obtained, albeit at a very slow rate, by the unsensitized photolysis of l a in benzene solution, again using a R'
R1.
& + & ? y JI , \
1
6.92 (2 H); A": 281 my (E 1400), 273 (1900), and 219 (26,000), and 5b, mp 129-130'; nmr multiplets at 'T 2.1-2.3 (1 H) and 2.6-3.2 (7 H), doublet (J = 5 cps) centered at 'T 5.50 (1 H), multiplet at 'T 5.9-6.1 280 my (E (2 H),and singlet at 'T 6.23 (3 H); A":: 1400), 272 (2100), and 223 (27,000). 'T
R2
2
1
R1, R* = H b, R', R2= COOMe c, R',R2 =CN d , R', R2 = CF3 e , R1=H; R2=COOMe a,
4
= COOMe; R2= H b, R1= H; R2 = COOMe
5a, R'
It thus appears that the formation of the dibenzotricyclo[3.3.0.02~8]octadienering system by photolysis of suitable dibenzobicyclo[2.2.2]octatrienes is quite general. The scope of this reaction is under investigation. Engelbert Ciganek
3
Pyrex filter. Rearrangement of the derivatives Ib-d to 2b-d, on the other hand, proceeded fairly rapidly in benzene or cyclohexane solution, using Pyrex vessels and ordinary sunlamps, although for preparative purposes acetone sensitization proved more connmr multiplet at venient. Thus, 2b, mp 98-99'; T 2.6-3.1 (8 H), singlets at T 4.97 (1 H), 5.51 (1 H), 6.17 (3 H), and 6.32 (3 H); A':t 279 my ( E 1200), 271, (1500), 265 (1400), and 217 (sh, 25,000), was obtained in 96% yield by photolysis of l b . 6 Irradiation of l c 7 gave 2c, rnp 179-180'; nmr multiplet at 'T 2.8-3.3 (8 H) and singlets at T 4.86 (1 H) and 5.44 (1 H); Xs:" 279 mp ( E 650), 271 ( E 890), and 221 (28,000), in 80% yield. 2d, mp 81.5-82.5'; proton nmr multiplet at T 2.5-3.2 (8 H)and singlets at T 5.10 (1 H)and 278 rnp ( E 800), 270 (960), 264 5.86 (1 H); "::A: (780), and 215 (28,000), was isolated in 7 4 7 yield from the photolysis of l d . 8 In all three cases, inspection of the nmr spectra of the crude rearrangement products indicated the presence only of the 1,2 isomers 2b-d . Irradiation of l e 9 gave 2e, rnp 169.5-170.5"; nmr multiplet at T 2.6-3.1 (8 H)and singlets at 'T 5.03 (1 H), 6.23 (2 H),and 6.32 (3 H); ",:A: 280 mp ( E 1600), 272 (1900), 266 (1500), and 220 (27,000), in 75 yield. The nmr spectrum of the crude product indicated the presence of less than 5 % of other isomer(s) of 2e. On the other hand, irradiation of 1-methoxycarbonyldibenzobicyclo[2.2.2]octatriene (4)'O gave a mixture of the isomers 5a and 5b (ratio 67 :33) in 91 % yield. Chromatographic separation on Florisil gave 5a, mp 101-102"; nmr multiplet at 7 2.4-3.1 (8 H), triplet (J = 6.5 cps) centered at T 5.96 (1 H), singlet at T 6.20 (3 H), and doublet (J = 6.5 cps) centered at 131 (1965); 2a and some of its derivatives have also been prepared recently by s. J. Cristol and B. B. Jarvis, starting from the dibenzobicyclo[3.2. lloctadiene system: S. J. Cristol, private communication. ( 5 ) W. Baker, J. F. W. McOmie, S.D. Parfitt, and D. A. M. Watkins, J . Chem. Soc., 4026 (1957). (6) 0. Diels and I
