Catalytic and Asymmetric Process via PIII/PV═O Redox Cycling: Access to (Trifluoromethyl)cyclobutenes via a Michael Addition/Wittig Olefination Reaction.

In the present study, we report the first enantioselective and highly efficient phosphine-catalyzed process via a chemoselective in situ phosphine oxide reduction. Starting with 4,4,4-trifluorobutane-1,3-dione and dialkyl acetylenedicarboxylate substrates, highly functionalized fluorinated cyclobutenes were obtained in excellent yields and enantioselectivities. Using the same methodology, CF3-spirocyclobutene derivatives were also synthesized (34 examples, up to 95% ee).