Synthetic approaches to the deoxyhumulones; some new 2,2-dimethylchromens from phloroacetophenone

Abstract

Condensation of 3-hydroxy-3-methylbutanal dimethyl acetal with phloroacetophenone (2′,4′,6′-trihydroxyacetophenone) in the presence of pyridine gave a mixture of 6- and 8-acetyl-2,2-dimethylchromen-5,7-diols (XI) and (XII), respectively, 6,8-diacetyl-2,2-dimethylchromen-5,7-diol (X), and 6-acetyl-2,2,8,8-tetramethyl-2H,8H-benzo[1,2-b,3,4-b′] dipyran-5-ol (II; R = Me). Also isolated were two complex isomeric products (XIII) and (XIV), resulting from condensation of (II; R = Me) with (XII). In the presence of pyridinium hydrochloride, an increase in the yield of compound (II; R = Me) and the condensation products (XIII) and (XIV) was achieved, with a corresponding decrease in the amounts of compounds (X), (XI), and (XII).