Some reactions of carbenoids with chromone-2-carboxylic esters

Abstract

Ethyl 5-hydroxy-4-oxo-8-propyl-4H-[1]benzopyran-2-carboxylate (3a) reacts with chloroacetone under basic conditions to yield (1α, 1aα, 7aα)- and (1β, 1aα, 7aα)-ethyl 1-acetyl-1,1a,7,7a-tetrahydro-6-hydroxy-7-oxo-3-propylbenzo[b]cyclopropa[e]pyran-1a-carboxylate (4a) and (5a), products of cyclo-propanation of the chromone 2,3-double bond, as well as ethyl 1,7-diacetyl-7, 7a-dihydro-5-propyl-6aH-cyclopropa[b]furo[4,3,2-de][1]benzopyran-6a-carboxylate (6a), representing a novel ring system. The corresponding tetrahydronaphthopyran (3b) gives analogous products (4b), (5b), and (6b). The thiochromone analogue of (3a), (8), gives only the furan annelated product ethyl 2-acetyl-6-propylthio-pyrano[4,3,2-cd]benzofuran-4-carboxylate (9) under similar conditions. The reaction of the chromone (3b) with dimethylsulphoxonium methylide to yield the isomeric naphthofuranones (16a) and (17a) is also described.