Potassium trisiamylborohydride reduction

A noteworthy development is the use of KH for complexing alkylboranes and alkoxyboranes to form various boron hydrides used as reducing agents in the pharmaceutical industry. Potassium tri-j -butylborohydride [54575-50-7] KB(CH(CH2)C2H )2H, and potassium trisiamylborohydride [67966-25-0] KB(CH(CH2)CH(CH2)2)3H, are usefiil for the stereoselective reduction of ketones (66) and for the conjugate reduction and alkylation of a,P-unsaturated ketones (67). 

Alkyl borohydrides with even greater steric hindrance but with similar reactivity and selectivity to the Selec-trides, were prepared from trisiamylborane (siamyl = Me2CH2CHMe- s tri-scc-isoamyl, sec. 5.2.A). Lithium trisiamylborohydride [LiBH(CHMeCHMe2)] and the potassium salt [KBH(CHMeCHMe2)], are similar to the L- and the K-Selectrides and are called LS-Selectride and KS-Selectride, respectively. in Bonjoch s synthesis of aeruginosin 298-A, LS-Selectride reduction of 157 gave 158 in 53% yield. 

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