Novel organomagnesium reagents in synthesis. Catalytic cyclomagnesiation of allenes in the synthesis of N-, O-, and Si-substituted 1Z,5Z-dienes

An efficient method for the synthesis of valuable N-, O-, and Si-containing 1Z,5Z-diene compounds was developed. The method comprises Cp2TiCl2-catalyzed homo- and cross-cyclomagnesiation of 1,2-dienes by Grignard reagents (RMgR′) to give 2,5-dialkylidenemagnesacyclopentanes in up to 96% yield. This approach was successfully used in the synthesis of 5Z,9Z-dienoic acids, precursors of acetogenins and insect pheromones.