Allenes, a class of compounds with unique reactivity, are useful building blocks in chemical syntheses. Selective reduction of allenes is difficult to achieve and can result in a mixture of chiral alkanes and alkene isomers. In this work, a regioselective, palladium-catalyzed method for the semireduction of 1,1-disubstituted allenes has been developed. The reaction proceeds through diboron-mediated activation of water and subsequent formation of a palladium hydride. Thus, the extent of hydrogenation can be controlled through stoichiometric addition of tetrahydroxydiboron. A variety of symmetrical allenes were reduced to yield internal, tri-substituted alkenes in good yields (63-88%). Partial hydrogenation of unsymmetrical allene substrates yielded internal alkenes in up to 72% yield with good <i>Z</i>-selectivity (up to 91:9, Z:E). The preference for Z alkene formation is proposed to result from the steric interaction between the phenyl ring and palladium complex; therefore, the metal attacks on the least hindered face of the allene.

Diboron-mediated semireduction of terminal allenes

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.