Addition reactions to alkenyl- and alkynylboron compounds

The catalyzed hydrogenation of alkenylboronic esters was used for the diastereoselective synthesis of alkylboronic esters 276446 (Equation (75)). The hydrogenation of a pyrrolboronic acid provided a prolineboronic acid, which was then resolved by HPLC to give an optically active boronic ester 277447 (Equation (76)). 

Potassium 1-alkenyltrifluoroborates permitted alkene epoxidation with oxone or m-CPBA with excellent conversions without cleavage of the G-B bond (Equation (77)).448 

Arylboronic acids possessing an ortho-1-alkenyl or 2-alkenyl group underwent preferential bromoetherification with NBS in aqueous THF, whereas the B-C bond cleavage predominated under basic pH s (Equation (78)).449 

The radical addition to 1-alkenyl or 1-alkynylboronic esters or amides took place extremely smoothly because the boron atom stabilizes the resulting ct-radical intermediates. Bu3SnH and PhSH predominated the trans-addition products 287 in the addition to 1-alkynylboronic amides at 90 °G, whereas Bu3SnH and Ph2Ph produced the m-addition products 288 at 0°C ( 98% Equation (82)).455 Intramolecular addition to 1-alkenylboronic esters has been demonstrated in boron-tethered radical cyclization that provided 1,3- or 1,4-alkanediols 290 via oxidative workup (Equation (83)).456 Inter- and intramolecular additions of alkyl radical457 and sulfonyl radical458 have also been studied. 

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