Gold-catalyzed (4 + 2)-annulations between α-alkyl alkenylgold carbenes and benzisoxazoles with reactive alkyl groups

This work reports new (4 + 2)-annulations of α-alkyl vinylgold carbenes with benzisoxazoles to afford 3,4-dihydroquinoline derivatives with high anti-stereoselectivity. The annulations are operable with carbenes in both acyclic and cyclic forms. This reaction sequence involves an initial formation of imines from α-alkylgold carbenes and benzisoxazoles, followed by a novel carbonyl-enamine reaction to yield 3,4-dihydroquinoline derivatives. This system presents the first alkyl C-H reactivity of α-alkyl gold carbenes with an external substrate.