Entry into Lithium Ynolates from α,α,α-Tribromomethyl Ketones: Synthesis of Cyclobutenes via the [2+2] Cycloaddition with α,β-Unsaturated Carbonyls

This study reports the synthesis of cyclobutene derivatives in good yields via the [2 + 2] cycloaddition between lithium ynolates and alpha,beta-unsaturated carbonyls. The ynolates are generated from alpha,alpha,alpha-tribromomethyl ketones and tert-butyl lithium via a simple and novel method, which does not produce any harmful byproducts, such as lithium alkoxide, which induces a polymerization reaction with alpha,beta-unsaturated carbonyls.