Thermal stereomutation of cyclopropanes
The syntheses of optically active trans-1-phenylcyclopropane-2-d, (-)-13 and (+)-13, are achieved by Haller-Bauer cleavages of the corresponding ketones (+)-10 and (-)-10 with NaND$sub 2$. The optically active cis isomer (+)-14 is prepared from the cis ketone, (-)-17, by an analogous route. Three kinetic experiments on these compounds are carried out. (1) Pyrolysis of (-)-13 and (+)- 13 to effect trans-cis isomerization at 309.5$sup 0$ in the gas phase. This reaction is first-order with a rate constant k/sub i/ = 2.48 x 10$sup -5$ sec$sup -1$. (2) The loss of optical activity from a synthetic equilibrium mixture, ''V'', composed of 50 percent each of (+)-13 and (+)-14, in which the enantiomeric purities of each are identical. This reaction also is first-order with a rate constant k/sub $alpha$//sup eq/ = 4.06 x 10$sup -5$ sec$sup -1$. (3) The decline of optical rotation of the kinetic samples from experiment 1. This reaction is not first-order, because the optical rotations of enantiomerically pure 13 and 14 differ slightly. The ''best-fit'' values are k$sub 1$ = 0, and k$sub 12$ = 0.96 x 10$sup -5$ sec$sup -1$. An assumed isotope effect of 10 percent gives k$sub 13$ = 1.06 x 10$sup -5$ sec$sup -1$. Thus, each rotation of C$sub 1$ is accompanied by a synchronous rotation of C$sub 2$ or C$sub 3$. The result is that expected if the stereomutation pathway passes over a 0.0 trimethylene (''$pi$-cyclopropane''). Ozonolysis of (-)-13 to the acid (-)-18, conversion of the latter to trans-1-benzoylcyclopropane-2-d, and NaND$sub 2$ cleavage of the ketone gives trans-cyclopropane-1,2-d$sub 2$, $alpha$$sub 365$ +0.168$sup 0$ (neat, 1 dm). Pyrolysis of this hydrocarbon at 422.5$sup 0$ results in first-order approach to the trans-cis equilibrium mixture (rate constant k/sub i/) and first-order decline of optical activity (rate constant k/ sub $alpha$/). 69 references (auth)
- Research Organization:
- Yale Univ., New Haven
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-33-025417
- OSTI ID:
- 4026085
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 1 Vol. 98; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)
- Country of Publication:
- United States
- Language:
- English
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