Boronic derivatives are important intermediates in organic synthesis. The Suzuki-Miyaura coupling reaction combines sp2 vinyl, aryl and heteroarylboronic derivatives with other sp2 halides and tosylates in a metal catalyzed reaction. Recently, new catalysts have been developed that couple sp3 alkylboronic derivatives. In contrast to the number of methods developed to prepare sp2 boronic derivatives, including those compatible with functional groups (FG), routes to alkylboronic compounds are far more limited. Only a few methods exist to prepare alkylboronic derivatives, and inclusion of most functional groups requires protection/deprotection. We have developed a simple hydroboration approach to prepare alkylboronic derivatives containing unprotected functional groups. The dialkylboranes, R'2BH, used in these hydroborations show significant differences in their reactivity towards hydroboration versus reduction of a functional group. In some cases, only hydroboration of a terminal alkene is observed with no indication of any reduction. The resulting mixed organoboranes, R'2BRFG may include ketones, esters and nitriles as functional groups. The secondary, R', auxiliary groups are removed by a two-group reductive alkylation with quinone. The boronic ester is then directly converted into a potassium alkyltrifluoroborate complex and isolated in good to excellent yields. This new procedure expands the types of functionalized alkylboronic derivatives for use in organic synthesis without needing to protect and deprotect these groups.

Synthesis of primary alkyltrifluroborate salts containing unprotected functional groups via hydroboration reactions

248th National Meeting (2014)

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