1607 Scheme
I11
:*
*
u *
*
1
6
4
(8) (a) W. von Philipsborn, J. Altman, E. Babad, J. J. Bloomfield. D. Ginsburg, and M. B. Rubin, Helv. Chim. Acta, 53, 725 (1970);(b) L. A. Paquette, R. H. Meisinger, and R. E. Wingard. Jr.. J. Am. Chem. SOC., 95, 2230 (1973);(c) M. J. Goldstein and S.A. Kline, Tetrahedron Lett., 1089 (1973),and references cited in these papers, (9)Thermochemical estimates5 place 6 about 21 (f6)kcal mol-' above 4. This means that 6 itself must be ver kinetically labile. The prototype, nonannulated molecule, tetracyclo~4,.~.0.02~9,05~8]dec-3-ene. shown below, and hereafter named felicene, may well be even less stable
W
2
7
1 * 3
tions implicated in the rearrangements of annulated bicyclo[4.2.0]octatrienes6 and the degenerate reactions of cyc l ~ o c t a t e t r a e n estudied ~ by Paquette and co-workers and also in the thermal behavior of several unsaturated bicyclo[4.2.2] and [4.2.1] species.* In order to add weight to these proposals, the specifically labeled 3,4,5,6,13,14-hexadeuterioanalogue of 1, prepared by photoaddition of 2 to hexadeuteriobenzene, was also pyrolyzed, and the products were analyzed for deuterium content. The mass spectra of 2 and of benzene were in accord with complete retention of all deuterium in the benzene, while those of 3 and butadiene showed that these molecules were dq and d2, respectively.12 Additionally samples of tetralin (d4) and butadiene ( d 2 ) were obtained by preparative G L C and their NMR spectra recorded. The absence of absorptions (
