The formation of the anion from 1-Thiacyclohept-2-ene 1-Oxide and its reaction with substituted benzaldehydes

Abstract

On treatment with bases 1-thiacyclohept-2-ene 1-oxide affords the 2-metallated derivative which rapidly polymerizes, except in the presence of tetramethylethylenediamine when the pale yellow anion is relatively stable in tetrahydrofuran solution at - 78º. The anion reacts rapidly with methyl iodide and with benzaldehyde and gives 2-methyl-1-thiacyclohept-2-ene 1-oxide and 2-(1-hydroxy- 1-phenylmethy1)-1-thiacyclohept-2-ene 1-oxide respectively in high yields. Substituted benzaldehydes react similarly to benzaldehyde and whilst the ratio of diastereomeric products formed is affected by the nature of the substituent, no clear correlation emerges. The reactions are subject to kinetic control and it is proposed that an unfavourable lone-pair, π-cloud electronic interaction is responsible for the diastereoselection.