Tetrahedron p. 4039 - 4062 (1991)
Update date:2022-09-26
Topics: Experimental Induced
Esch, Peter M.
Boska, Ilona M.
Hiemstra, Henk
Boer, Richard F. de
Speckamp, W. Nico
Cationic ?-cyclization reactions of N-(3-alkenyl)-N-(methoxycarbonyl)acetoxyglycine esters induced by tin tetrachloride in dichloromethane are described.Reactions started and quenched with water at -78 deg C mainly yield cis-4-hydroxypipecolic esters, whereas reactions quenched after warm-up to room temperature provide trans-4-chloropipecolic esters as major products.A mechanistic scheme is advanced which adequately explains these results.The essentials are a rapid cationic aza-Cope equilibrium of the incipient iminium cation, and participation of the ester moiety through formation of a relatively stable bicyclic dioxycarbenium cation as pivotal intermediate.
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