Synthesis of substituted 2-aroyl-3-methylchromen-4-ones from isovanillin via 2-aroyl-3-methylchroman intermediates

Abstract

The synthesis of substituted 2-aroyl-3-methylchromen-4-one from isovanillin is described. O-Allylphenol ( 2) prepared from isovanillin ( 1) was allowed to react with various α-bromoacetophenone ( 3) to produce 2-(2-allyl-3,4-dimethoxy)phenoxy-1-aroylethanones ( 4). The resultant 4 were treated with 2 equiv of potassium tert-butoxide to afford the substituted 2-aroyl-3-methylchromans ( 5) through an isomerization of an allylic double bond and a carbanion–olefin intramolecular 6- endo- trig cyclization reaction. Subsequently, resultant 5 were oxidized with DDQ to yield the title compound 6, in good over-all yields.