Enantio- and Diasteroselective Preparation of \u3cem\u3eβ\u3c/em\u3e-Hydroxycarbonyls Using \u3cem\u3eO\u3c/em\u3e-Silyl Protected Cyanohydrins and Epoxides

A β-hydroxycarbonyl is formed as a product in the aldol addition, a carbon-carbon bond-forming reaction of great importance. In the aldol reaction, an enolized carbonyl reacts with a ketone or aldehyde. The reaction can potentially create as many as two new chiral centers, and enantio- and diasteroselective control of the reaction is often critical. Useful stereoselective variants of the aldol addition have been developed, each with its own set of drawbacks and limitations. We have developed a new alternative method for the formation of β-hydroxycarbonyls via the reaction of O-silylated cyanohydrins with epoxides. Previous research on the project consisted of optimizing the reaction conditions for aryl-substituted cyanohydrins (R = Ar) and determining the scope of the reaction with respect to epoxide and cyanohydrin. Current research has been focused on reacting alkyl-substituted cyanohydrins (R = alkyl). Reaction conditions with an alkyl substituent were optimized to avoid an undesired cyclization of product and retro-Brook rearrangement. A subsurface quenching technique was used alongside 0 °C reaction conditions to discourage formation of the undesired by-products. Silicon protecting groups such as tert-butyldimethylsilyl and triisopropylsilyl were explored to examine the effect of the steric bulk of the protecting group on suppressing the undesired side-reactions. After successful epoxide attack on the cyanohydrin, the silicon protecting group was removed using TBAF to yield a β-hydroxycarbonyl