Trisiamylborohydride, potassium

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). 

Potassium trisiamylborohydride, 20 605 Potassium winchite, 3 289 Potassium-zirconium carbonate, 26 637 Potato branching enzyme, 12 493 Potatoes, citric acid in, 6 632t Potato fungicide, 13 57 Potato starch, 4 724t Potential energy diagrams, 10 118-119 Potential gum test, 12 400 Potentiated toxic effects, 25 214 Potentiometric measurements, 14 612 Potentiometric titrations, 9 585-58 ... 

Potassium trisiamylborohydride can now be made in a convenient manner and the reaction of cyclic boronic esters possessing a wide variety of sterlc requirements with potassium hydride gives rise to the corresponding borohydrides. These represent a new class of reducing agents whose stability and reactivity have been explored. Copper(I) alkylborohydrldes are obtained from 1 1 mixtures of cuprous chloride and sodium borohydride on reaction with alkenes in THF. 

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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