Potassium selectride

Synthetically useful stereoselective reductions have been possible with cyclic carbonyl compounds of rigid conformation. Reduction of substituted cyclohexanone and cyclopentan-one rings by hydrides of moderate activity, e.g. NaBH (J.-L. Luche, 1978), leads to alcohols via hydride addition to the less hindered side of the carbonyl group. Hydrides with bulky substituents 3IQ especially useful for such regio- and stereoselective reductions, e.g. lithium hydrotri-t-butoxyaluminate (C.H. Kuo, 1968) and lithium or potassium tri-sec-butylhydro-borates or hydrotri-sec-isoamylborates (=L-, K-, LS- and KS-Selectrides ) (H.C. Brown, 1972 B C.A. Brown, 1973 S. Krishnamurthy, 1976). 

Alkylborohydrides are also used as reducing agents. These compounds have greater steric demands than the borohydride ion and therefore are more stereoselective in situations in which steric factors come into play.72 These compounds are prepared by reaction of trialkylboranes with lithium, sodium, or potassium hydride.73 Several of the compounds are available commercially under the trade name Selectrides .74... 

Replacement of hydrogen by alkyl groups gives compounds like lithium triethylborohydride (Super-Hydride ) [100], lithium tris sec-butyl)borohydride [101] (L-Selectride ) and potassium tris sec-butyl)borohydride (K-Selectride ) [702], Replacement by a cyano group yields sodium cyanoborohydride [103], a compound stable even at low pH (down to 3), and tetrabutylammonium cyanoborohydride [93],... 

Notes Selective reducing agent. The potassium and sodium Selectrides are also available. Will convert C-X to C-H, with I>Br>Cl. 

For the synthesis of the 11-thia-prostanoid analog of the F-series 138, the ketone 131 was reduced with potassium tri-sec.-butylborohydride (K-Selectride), followed by using the methods described above. 

Lithium and potassium tri-sec-butylborohydride (L- and K-Selectride) selectively reduce the olefin of many a,g-unsaturated carbonyl compounds.79 The intermediate enolate anions may also be trapped by electrophiles, providing a regiospecific reductive alkylation of a,g-unsaturated carbonyl compounds. 

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