Synthesis and Conversions of Substituted o-[(Trimethylsilyl)methyl]benzyl p-Tolyl Sulfones to o-Quinodimethanes and Products Thereof

Abstract

Use of o-[(trimethylsilyl)methyl]benzyl p-tolyl sulfone (3) for synthesis and cycloaddition of substituted o-quinodimethanes has been investigated. Sulfone 3 is prepared from 2-methylbenzyl alcohol (4) by reactions with n-BuLi and chlorotrimethylsilane to form o-[(trimethylsilyl)methyl]benzyl alcohol (7) which phosphorus tribromide converts to o-[(trimethylsilyl)methyl]benzyl bromide (8). Displacement of 8 with sodium p-toluenesulfinate yields 3. Sulfone 3 is alkylated at its α-sulfonyl position upon deprotonation with n-BuLi followed by methyl iodide, ethyl, butyl, allyl, and benzyl bromides, and 5-bromo-1-pentene, respectively. Acylations occur using acid chlorides. Dialkylation occurs upon further reaction with n-BuLi and an alkyl halide. 1,4-Eliminations of α,α-dialkyl sulfones 11 with tetrabutylammonium fluoride (TBAF) give α,α-dialkyl-o-quinodimethanes (29); 3 is therefore a synthon for the o-quinodimethane-α,α-dianion (34). o-Quinodimethanes 29 undergo (1) cycloaddition with acrylonitrile, acrylate esters, and alkyl fumarates to yield 1,1-disubstituted-tetrahydronaphthalenes (30) and (2) 1,5-sigmatropic rearrangements of hydrogen to give styrenes (32). The stereochemistries of the various cycloadditions reveal significant mechanism information.