Stereochemistry of nucleophilic reductions of 2-methyl-4-t-butylcyclohexanones. Further support for the linear combination of SSC and PSC stereochemical models

Abstract

trans-2-Methyl-4-t-butylcyclohexanone reacts with lithium aluminum hydride, lithium trimethoxyaluminium hydride and methyl-lithium with equal stereoselectivity of axial attack (i.e. 95 ± 1%). This is attributed to the equal steric strain control (SSC) of these three reagents in the absence of product stability control (PSC) brought about by the equal stability of its two secondary alcohol products (i.e. ΔG°= 0 and Δπ=aΔG°= 0).

Also presented for comparison are the stereochemistries of the reactions of 4-t-butylcyclohexanone, 2-methylcyclohexanone, cis-2-methyl-4-t-butylcyclohexanone and 2,2-dimethyl-4-t-butylcyclohexanone. In these three systems, the stereochemical courses of addition are controlled by SSC(Δδ) and PSC(Δπ) simultaneously, i.e. Δ(ΔG^‡)=Δδ+Δπ.