Borane-catalyzed hydroboration of substituted alkenes by lithium borohydride or sodium borohydride

In the presence of a catalytic amount of (BH3Me2S)-Me-., TiCl4 or Me3SiCl, LiBH4 or NaBH4 are capable of hydroborating alkenes by following the unusual order of decreasing reactivity: tetramethylethylene > 1-methylcyclohexene > cyclohexene; the key step of the catalytic cycle is the exchange reaction between LiBH4 and the mono- or dialkylboranes resulting from hydroboration of the more substituted alkenes with BH3. (C) 2003 Elsevier Ltd. All rights reserved.