β-Quaternary α-Amino Acids via Iridium-Catalyzed Branched and Enantioselective Hydroalkylation of 1,1-Disubstituted Styrenes

A cationic Ir(I)-complex modified with the chiral diphosphine DM-SEGPHOS mediates the hydroalkylation of diverse α-methyl styrenes with N-aryl glycine derivatives. The processes occur with complete branched selectivity and high enantioselectivity. Styrenes possessing higher α-alkyl substituents also participate to provide the targets with moderate to excellent levels of diastereoselectivity. The products are readily advanced to β-quaternary α-amino acids that are inaccessible or cumbersome to access by other means. In broader terms, the study demonstrates how catalyst controlled C─H additions across alkenes can be used to execute the by-product-free construction of contiguous acyclic trisubstituted and quaternary centers.