Efficient synthesis of unsaturated seven-membered rings by an entropy/strain reduction strategy: 2,7-dihydro-1H-azepines, -oxepines, -thiepines, -1H-phosphepine and 1,3-cycloheptadienes

Abstract

Substituted (Z,Z)-1,6-dibromohexa-2,4-dienes, obtained from substituted catechols via the corresponding diols, react with primary amines, lithium sulfide, sodium phenylphosphide and malonic ester enolate under mild conditions to give efficient syntheses of 2,7-dihydro-1H-azepines, 2,7-dihydrothiepines, 2,7-dihydro-1H-phosphepine and cyclohepta-1,3-dienes respectively while the precursor diols yield the 2,7-dihydrooxepines on treatment with toluene-p-sulfonyl chloride.