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A catalytic and enantioselective preparation of the ( S )-4-methyleneproline scaffold is described. The key reaction is a one-pot double allylic alkylation of an imine analogue of glycine in the presence of a chinchonidine-derived catalyst under phase transfer conditions. These 4-methylene substituted proline derivatives are versatile starting materials often used in medicinal chemistry. In particular, we have transformed tert -butyl ( S )-4-methyleneprolinate ( 12 ) into the N -Boc-protected 5-azaspiro[2.4]heptane-6-carboxylic acid ( 1 ), a key element in the industrial synthesis of antiviral ledipasvir.

An Enantioselective Approach to 4-Substituted Proline Scaffolds: Synthesis of (S)-5-(tert-Butoxy carbonyl)-5-azaspiro[2.4]heptane-6-carboxylic Acid