Synthesis of 2,2-dialkyl 1-vinylboronates using the ruthenium-catalyzed Alder-ene reaction

ORGN 501

Daesung Lee, dlee@chem.wisc.edu and Eric C. Hansen. Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave, Madison, WI 53706
The ruthenium-catalyzed Alder-ene reaction between alkynyl boronates and terminal alkenes was investigated. The reactions proceed under mild conditions and a strong directing effect of the boron substituent was found to offer complete regioselectivity for the branched isomer, culminating in the formation of 2,2-dialkyl 1-vinylboronates. Complete stereoselectivity was also observed except in cases where an allylic heteroatom was present in the alkene substrate, in which case an E/Z mixture of the vinyl boronate was obtained. The products generated are useful substrates for transition metal-mediated coupling reactions, such as the Suzuki-Miyaura coupling, allowing efficient access to a variety of substructures found in important natural products.