Selective C(sp3 )-N Bond Cleavage of N,N-Dialkyl Tertiary Amines with the Loss of a Large Alkyl Group via an SN 1 Pathway.

Polar disconnection of the C(sp3 )-N bond of N,N-dialkyl-substituted tertiary amines via ammonium species conventionally favored the loss of the smaller alkyl group by an SN 2 displacement, while selective C(sp3 )-N bond cleavage by cutting off the larger alkyl group is still underdeveloped. Herein, we present a novel Pd0 -catalyzed [2+2+1] annulation, proceeding through an alkyne-directed palladacycle formation and consecutive diamination with a tertiary hydroxylamine by cleaving its N-O bond and one C(sp3 )-N bond, for the rapid assembly of tricyclic indoles in a single-step transformation. Noteworthy, experimental results indicated that large tert-butyl and benzyl groups were selectively cleaved via an SN 1 pathway, in the presence of a smaller alkyl group (Me, Et, i Pr). Under the guidance of this new finding, tricyclic indoles bearing a removable alkyl group could be exclusively obtained by using a (α-methyl)benzyl/benzyl or tert-butyl/2-(methoxycarbonyl)ethyl mixed amino source.