Synthesis of spiro-Annelated Isochromanones by Ring Expansion of Benzocyclobutenones in the Presence of Lithium Diisopropylphosphide

Abstract

spiro-Annelated isochromanones are prepared by treatment of benzo-cyclobutenone with lithium diisopropylphosphide - borane adduct (LDP-BH 3 ), which is easily accessible by metalation of the air stable diisopropylphosphane-borane adduct. The reaction takes place at very mild reaction conditions and involves an oxyanion driven ring opening. As a substituted example the synthesis of the first trifluoromethyl-substituted isochromanone derivative is reported.