Tandem Carbocupration/Oxygenation of Terminal Alkynes

Significance

α-Branched aldehydes were synthesized via a tandem carbocupration of terminal alkynes followed by sequential oxygenation of the intermediate vinyl copper species with lithium tert-butyl peroxide. Trapping the metal enolate with TMSCl, acetic anhydride or benzoic anhydride gave the corresponding enol derivatives as a single regio- and stereoisomer. Addition of Br₂ or t-BuOCl to the intermediate metallo-enolate generated the α-haloaldehyde. Functional groups tolerated include esters, silyl ethers, benzyl ethers, and tertiary amines. The reaction was successful using primary, secondary and tertiary Grignard reagents and also n-butyllithium.