THE INFLUENCE OF LITHIUM COMPLEXING AGENTS ON THE REGIOSELECTIVITY OF REDUCTIONS OF SUBSTITUTED 2-CYCLOHEXENONES BY LiAlH4 and LiBH4

Article abstract of DOI:10.1016/0040-4020(80)80205-5

A reversal of regioselectivity of LiAlH4 or LiBH4 reduction of 2-cyclohexenone induced by addition of <2.1.1>-cryptand to the reaction medium is accompanied by a rate decrease.In the absence of the cryptand, carbonyl attack predominates (C1:C3=86:14 with LiAlH4 in THF).In the presence of the cryptand, double bond attack is favoured (C1:C3=14:86).This effect is larger with LiAlH4 than with LiBH4.This trend is general in the case of five substituted 2-cyclohexenones.Using 12-crown-4 as a Li+ coordinator, a change in regioselectivity occurs but it is less pronunced than with the cryptand.