The effects of neighboring heteroatoms in ring opening of epoxides.

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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.

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