Synthesis of isoflavones containing naturally occurring substitution pattern by oxidative rearrangement of respective flavanones using thallium(III)p-tosylate

摘要

Claisen condensation of substituted 2'-hydroxyacetophenones 1a-c with aromatic aldehydes affords respective substituted 2'-hydroxychaIcones 2a-n which on base catalyzed cyclization in pyridine :methanol :water (1:1:1) give respective flavanones 3a-n.The oxidative rearrangement of flavanones with thallium(III) p-tosylate furnishes respective isoflavones 4a-n in overall 62-72% yields starting from 1.The present methodology has been successfully applied for the synthesis of naturally occurring isoflavones such as di-O-methyldaidzein 4a,cabruvin 4b,pseudobabtigenin methylether 4d,5,7-dimethoxyisoflavone 4f,5,7,4'-trimethoxyisoflavone 4g,derrustone 4i,7,8,3',4'-tetramethoxyisoflavone 4l,purpuranin-A 4m and 7,8,3',4',5'-pentamethoxyisoflavone 4n and thus the first synthesis of 4n is reported.