One-pot synthesis of coumarin substituted dihydrofurans

Abstract

Chang and Tsai 20 have developed a new method for the synthesis of 2,3-dihydro furans starting from enones and pyridinum salts. In the present study, a one-pot method for the synthesis of for the synthesis of benzopyran-2-one substituted 2,3-dihydrofurans has been developed using readily available starting materials 3-(2-bromoacetyl)coumarin, pyridine, cyclic 1,3-dicarbonyl compound and aromatic aldehyde. Reaction of 3-(2-bromoacetyl)coumarin, pyridine, dimedone aromatic aldehyde and triethylamine in acetonitrile at RT for about 12 hr gave fused system 3-(3-aryl-6,6-dimethyl-4- ox o-2,3,4,5,6,7-hexahydrobenzofuran-2-carbonyl)-chromen-2-one with good yields. This is a pyridinium ylide mediated one pot reaction. In the first step of the reaction, 3-(2bromoacetyl)coumarin reacts with pyridine to give pyridinium ylide, and the dimedone reacts with aromatic aldehyde to give aryledene intermediate via Knoevengel reaction. In the second step, pyridinium ylide undergoes reaction with aryledene intermediate to give the zwitterionic salt 28 . Further, the zwitterionic salt cyclizes to trans-2,3-dihydrofuran by the elimination of pyridine (Scheme I). The structures of the prepared compounds were confirmed from their spectral and elemental analysis data. The structure of 4 is clearly assigned