Ligand bite angle-dependent palladium-catalyzed cyclization of propargylic carbonates to 2-alkynyl azacycles or cyclic dienamides

Abstract

The regioselectivity of the palladium-catalyzed cyclization of propargylic carbonates with sulfonamide nucleophiles is critically dependent on the bite angle of the bidentate phosphine ligand. Ligands with small bite angles favor attack on the central carbon atom of an allenylpalladium intermediate to afford cyclic dienamide products, whereas the use of those with large bite angles leads to alkynyl azacycles, with high stereoselectivity. A computational analysis of the reaction pathway is also presented. Chomp! The bite angle of bidentate phosphine ligands determined the course of the palladium-catalyzed cyclization of propargylic carbonates with sulfonamide nucleophiles. A small bite angle favored attack on the central C atom of the allenylpalladium intermediate, whereas alkynyl azacycles were formed from attack on the terminal C atom using ligands with a large bite angle. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.