Heteroarylboronates in Rhodium-Catalyzed 1,4-Addition to Enones

Rhodium­(I)-catalyzed 1,4-addition of aryl and alkenylboronic acids to α,β-unsaturated carbonyl compounds is well established, but the transfer of heteroaryl residues in this reaction remains underdeveloped. We have studied heteroaryl MIDA and pinacol boronates as alternatives to the labile boronic acid counterparts. Under racemic conditions, 12 adducts with heteroaryl residues, among them unsubstituted 3- and 4-pyridinyl, 2-furanyl, thienyl, and pyrrolyl groups, were obtained in moderate to excellent yields. The enantioselective version of the reaction proved highly sensitive to the electronic character of the heteroaryl substituents, with boronates carrying electron-rich residues giving modest to high yields but consistently high enantiomeric excesses

Cycloalkene Carbonitriles in Rhodium-Catalyzed 1,4-Addition and Formal Synthesis of Vabicaserin

Cycloalkenes with exocyclic acceptor substituents still remain challenging substrates for enantioselective rhodium-catalyzed 1,4-addition. Cycloalkene carbonitriles and carboxylates have been investigated, and a highly diastereo- and enantioselective protocol for 1,4-addition to cyclopentene and cycloheptene carbonitrile has been developed. This new asymmetric transformation was subsequently applied in the asymmetric formal synthesis of the drug candidate Vabicaserin