NOVEL (ALPHA-BETA-EPOXYALKYL)LITHIUM REAGENTS VIA THE LITHIATION OF ORGANYL-SUBSTITUTED EPOXIDES

A series of epoxides bearing unsaturated organyl groups attached directly to the epoxy group was found to have sufficient kinetic acidity to undergo clean lithiation at low temperatures. Epoxides of the type R2C—CH(Un)O,where Un is aryl, vinylic, acetylenic, alkoxycarbonyl, or cyano, were smoothly converted into R2C—CLi(Un)0 by either t-BuLi or LDA in the temperature range of -80 to -115 °C. The resulting (±,β-epoxyalkyl)lithiurn reagents could be transformed into a variety of substituted epoxides, such as R2C—CE(Un)0, where E = D, R3Si, R3Sn, R, RCO, CO2H, or COH(R)2. In cases where Un is acyl, addition to the carbonyl, rather than lithiation, occurred preferentially. Attempted lithiations of aziridines and thiiranes led to extrusion of nitrogen and sulfur, respectively. Even the relatively stable R2C—CLi(Un)0 intermediates generated at <-90 °C underwent carbenoid-like decomposition at higher temperatures to yield isomerization and intermolecular-insertion products. Observation of these processes gives direct corroboration of reaction mechanisms proposed for the base-promoted isomerizations of epoxides. © 1990, American Chemical Society. All rights reserved.