Ring expansion of thiochroman-4-one and isothiochroman-4-one with ethyl diazo(lithio)acetate to tetrahydrobenzothiepin β-oxoesters

Abstract

When thiochroman-4-one (1) and isothiochroman-4-one (3) were treated with ethyl diazo(lithio)acetate, ethyl 2,3-dihydro-4-hydroxy-1-benzothiepin-5-carboxylate (2) and ethyl 1,3-dihydro-4-hydroxy-2-benzothiepin-5-carboxylate (4), respectively, were formed. An improved procedure for the two-step addition–ring expansion sequence is described. The preparation of 2,3-dihydro-1-benzothiepin-4(5H)-one (7) and of 1,3-dihydro-2-benzothiepin-4(5H)-one (8) from the esters (2) and (4), respectively, is reported. Deoxygenation of (7) and (8) to 2,3,4,5-tetrahydro-1-benzothiepin (9) and 1,3,4,5-tetrahydro-2-benzothiepin (10) by Caglioti reduction is described.