Rhodium-Catalyzed Highly Enantio- and Diastereoselective Alkenylation of ß,γ-Unsaturated Butenolides via Dynamic Kinetic Resolution.

A rhodium-catalyzed highly enantio- and diastereoselective alkenylation of ß,γ-unsaturated butenolides is reported. The use of a chiral diene ligand, (S,S)-Ph-bod, enables the facile synthesis of chiral butyrolactones in high yields with extremely high enantioselectivities (>99% ee in all cases) and high diastereoselectivities (up to >20:1 dr). The key process of the reaction involves the isomerization of ß,γ-unsaturated butenolides to racemic α,ß-unsaturated butenolides and the subsequent dynamic kinetic resolution through ligand-controlled, enantioselective alkenylation with an alkenylrhodium species that is generated in situ via 1,4-rhodium migration.

Highly Enantioselective Synthesis of Monofluoroalkenes by Rhodium-Catalyzed Asymmetric Arylation/Defluorination of Allyl Difluorides.

The reaction of readily available E-allyl difluorides (R1CH = CHCF2COR2) containing a CF2COR2 moiety with arylboronic acids catalyzed by a chiral diene-rhodium complex gives high yields of chiral monofluoroalkenes (R1ArC*HCH = CFCOR2) with perfect enantioselectivity (enantiomeric excess (ee) of > 99% in all cases) and high level of Z/E selectivity (up to 20:1). The reaction is proposed to proceed through enantioselective arylrhodation of the E-allyl difluorides forming a ß,ß-difluoroalkylrhodium intermediate, followed by stereoselective ß-fluoride elimination. The CF2COR2 moiety plays a key role in activating the E-allyl difluorides toward arylrhodation/defluorination in executing the catalytic cycle, and it serves as a handle for further functionalization.