Regio- and stereoselectivity in palladium-catalyzed cycloreductions of 1,6-enynes in the presence of formic acid or triethylsilane

Palladium catalyzed 1,6-enyne cycloreductions in the presence of 1.2 equiv. of formic acid (method A) would involve cycloalkylpalladium formates which proceed via two consecutive steps: beta -elimination of alkylpalladium int ermediates and then reduction at the less hindered olefins regio- and stere oselectivity. Triethylsilane, however, directly reduced the alkylpalladium intermediates to give the corresponding cycloreduced products (method B). ( C) 2001 Elsevier Science Ltd. All rights reserved.