The effects of neighboring heteroatoms in ring opening of epoxides.

Abstract

In connection with our studies on the roles of heteroatoms (N, S, O) in solvolytic reactions, the effects of the heteroatoms in ring openings of epoxides, methylenecyclohexane epoxide (4), 3-methylene epoxides of tetrahydropyran (5), N-methylpiperidine (6) and tetrahydrothiopyran (7), were examined. All epoxides were synthesized according to Corey's procedure from the corresponding cyclanones. Ring-opening reactions of epoxides were carried out as follows : a) Reduction with lithium aluminum hydride, b) reduction with lithium metal in ethylenediamine, c) reduction with borane-lithium borohydride, d) acetic acid-catalyzed opening, e) hydrochloric acidcatalyzed opening, and f) reaction of 7 with Lewis acid (boron trichloride). No appreciable effects of heteroatoms were observed in the reactions a and b for 4, 5, and 6. The reactions c, d, and f for 7 resulted in the predominant formation of ring-contracted 5-membered ring derivatives. These results strongly suggest that an enormous amount of participation, particularly by the sulfur atom, is also involved in the ring-opening reactions of epoxides as well as that observed in solvolysis.