Adventures in Coumarin Chemistry

Abstract The cyclization of various nucleophiles, such as 1,3-dicarbonyl compounds, 1,3-bis(silyloxy)-1,3-butadienes, hydrazones, hydroxylamine, amidines, thioglycolic esters, heterocyclic enamines and others, with 4-chlorocoumarins, containing an electron-withdrawing group at position 3, allows for a convenient synthesis of a great variety of benzo[c]coumarins and related fused coumarins. Suzuki–Miyaura reactions of coumarin-derived bis(triflates) result in formation of arylated coumarins with excellent regioselectivity that is controlled by electronic and steric features of the substrate. The combination of Suzuki–Miyaura with lactonization reactions of carba- and heterocyclic substrates allows for the synthesis of benzo[c]coumarins and of other fused coumarins. Domino Michael–retro-Michael–lactonization reactions of 1,3-bis(silyloxy)-1,3-butadienes with chromones provide a convenient access to hydroxylated benzo[c]coumarins. In a related approach, fused coumarins were prepared by domino reactions of heterocyclic enamines with chromone-3-carboxylic acids. 1 Introduction 2 Reactions of 3-Acceptor-4-chlorocoumarins 3 Reactions of Coumarin Triflates 4 Synthesis of Fused Coumarins 5 Conclusions