Borane, dicyclohexyl hydroboration

Alkenylboronic acids and esters have been prepared by thermal or catalyzed hydroboration of 1-alkynes with catecholborane (HBcat), pinacolborane (HBpin), or dihaloboranes 41-43, followed by hydrolysis to boronic acids or alcoholysis to boronic esters. A convenient alternative to improve chemo- and regioselectivity is the hydroboration of alkynes with dialkylboranes. For selective removal of dummy groups, the oxidation of two cyclohexyl groups was conduced by treatment of l-alkenyl(dicyclohexyl)borane intermediates with Me3N-0 (Equation (7)).116 The... 

Oxime 3, which was derived from L-glucose via stereoselective hydroboration of the exo-olefln of L-j(y/o-hex-5-enopyranoside 2 [12] with dicyclohexyl borane, Swern oxidation of the... 

Alkenylzinc reagents. Hydroboration of pinacolatoborylalkynes with dicyclohexyl-borane affords 1,1-diboryl-l-alkenes. The dicyclohexylboryl group is selectively exchanged on treatment with Me2Zn, and the resulting species show differentiated chemoselectivity such that homologation/functionalization proceed in a desired manner. ... 

Related techniques have been developed to prepare (Z-,Z)- (Z-, )- and ( -, )- dienes. Hydroboration of diacetylenes followed by protonolysis is a convenient route to (Z-,Z)-dienes, as in the conversion of 89 to 90. The requisite symmetrical diacetylenes are prepared by oxidative coupling with oxygen and cuprous chloride, as in the conversion of 1-cyclohexylethyne (78) to 89. Unsymmetrical conjugated dienes can be prepared by formation of a diacetylene ate complex, prepared from disiamylmethoxyborane by sequential reaction with different acetylides. A similar borane route to unsymmetrical diacetylenes uses dicyclohexyl methyl-thioborane. ... 

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