1,3‐Anionic Cycloadditions of Organolithium Compounds: An Initial Survey. New synthetic methods (4)

Abstract

AbstractIn the field of [3 + 2]‐cycloaddition reactions, 1,3‐anionic cycloadditions have now joined 1,3‐dipolar cycloadditions as a second reaction type of major general importance. The cycloaddition in question has been found to occur with 2‐azaallyllithium compounds, allyllithium compounds (with an electron acceptor located on C2), and 1,3‐diphenylpropargyllithium. Compounds with CC, CN, NN, and CS double bonds and those with CC and CN triple bonds were found to be 1,3‐anionophilic. 1,3‐Anionic cycloaddition opens new routes to 1‐aza‐, 1,2‐diaza‐, 1,3‐diaza‐, 1,2,4‐triaza‐, and 1‐thia‐3‐azacyclopentane derivatives, to pyrroles and imidazoles, as well as (and this appears to be of special importance) to cyclopentane derivatives. Currently available data attribute stereospecificity to the 1,3‐anionic cycloadditions, which occupy an interesting intermediate position between 1,3‐dipolar cycloadditions and transition‐metal‐catalyzed cyclizations. A two‐step mechanism has been demonstrated in one case.