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Borenium ion catalyzed hydroboration of alkenes with N-heterocyclic carbene-boranes.

ABSTRACT: Treatment of alkenes such as 3-hexene, 3-octene, and 1-cyclohexyl-1-butene with the N-heterocyclic carbene (NHC)-derived borane 2 and catalytic HNTf(2) (Tf = trifluoromethanesulfonyl (CF(3)SO(2))) effects hydroboration at room temperature. With 3-hexene, surprisingly facile migration of the boron atom from C(3) of the hexyl group to C(2) was observed over a time scale of minutes to hours. Oxidative workup gave a mixture of alcohols containing 2-hexanol as the major product. A similar preference for the C(2) alcohol was observed after oxidative workup of the 3-octene and 1-cyclohexyl-1-butene hydroborations. NHC-borenium cations (or functional equivalents) are postulated as the species that accomplish the hydroborations, and the C(2) selective migrations are attributed to the four-center interconversion of borenium cations with cationic NHC-borane-olefin ?-complexes.

SUBMITTER: Prokofjevs A

PROVIDER: S-EPMC3405176 | biostudies-literature | 2012 Jul

REPOSITORIES: biostudies-literature

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Borenium ion catalyzed hydroboration of alkenes with N-heterocyclic carbene-boranes.

Prokofjevs Aleksandrs A Boussonnière Anne A Li Linfeng L Bonin Hélène H Lacôte Emmanuel E Curran Dennis P DP Vedejs Edwin E

Journal of the American Chemical Society 20120716 29

Treatment of alkenes such as 3-hexene, 3-octene, and 1-cyclohexyl-1-butene with the N-heterocyclic carbene (NHC)-derived borane 2 and catalytic HNTf(2) (Tf = trifluoromethanesulfonyl (CF(3)SO(2))) effects hydroboration at room temperature. With 3-hexene, surprisingly facile migration of the boron atom from C(3) of the hexyl group to C(2) was observed over a time scale of minutes to hours. Oxidative workup gave a mixture of alcohols containing 2-hexanol as the major product. A similar preference ...[more]

PMID: 22713106

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