Boronic acids, esters, trifluoroborate salts and MIDA complexes are valuable intermediates for organic synthesis. These alkyl derivatives can be prepared by hydroboration reactions using dialkoxyboranes; such as catecholborane, in catalyzed or uncatalyzed reactions and from coordinated dibromo- or dichloroboranes. The latter reactions are most effectively implemented using Matteson's in situ method reacting an equal molar mixture of BCl3, Et3SiH and alkene. While the reaction proceeds very rapidly with excellent yields and high regioselectivity, the silane by-product, Et3SiCl, adversely affects isolation of the boronic derivatives, lowering yields and purity. We report here a direct and simple one-pot hydroboration of alkenes using the Matteson method and conversion of an alkylhaloborane into a potassium alkyltrifluoroborate salt. Optimization of the reaction conditions in the trifluoroborate salt formation also improved yields. Typical overall isolated yields for the three-step reactions were 89-93%. The alkyltrifluorborate salts can be readily converted to the corresponding boronic acid using a metal catalyzed hydrolysis in essentially quantitative yields.

Simple and high yielding synthesis of alkylboronic derivatives using Matteson in situ hydroboration to form potassium alkyltrifluoroborate salts

248th National Meeting (2014)

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