Tandem carbocupration/oxygenation of terminal alkynes

chemical reaction: see text]. A direct and general synthesis of alpha-branched aldehydes and their enol derivatives is described. Carbocupration of terminal alkynes and subsequent oxygenation with lithium tert-butyl peroxide generates a metallo-enolate. Trapping with various electrophiles provides alpha-branched aldehydes or stereo-defined trisubstituted enol esters or silyl ethers. The tandem carbocupration/oxygenation tolerates alkyl and silyl ethers, esters, and tertiary amines. The reaction is effective with organocopper complexes derived from primary, secondary, and tertiary Grignard reagents and from n-butyllithium.