Phosphine-catalyzed [3 + 2] cycloaddition of allenoates with trifluoromethylketones: synthesis of dihydrofurans and tetrahydrofurans.

The triphenylphosphine-catalyzed formal [3 + 2] cycloaddition of allenoates and trifluoromethylketones was realized to give the corresponding dihydrofurans in good yields with excellent γ-regioselectivities. Hydrogenation of the dihydrofurans gave 2,4,4-trisubstituted tetrahydrofurans in good yields with exclusive cis-selectivities.