Studies on the esterifications of 9-(hydroxyimino)-4-methyl-8,9-dihydrofuro[2,3-h]chromen-2-one with acid chlorides under different conditions

The esterifications of 9-(hydroxyimino)-4-methyl-8,9-dihydrofuro[2,3-h]chromen-2-one (4) with acid chlorides afforded normal oxime-esters 3a-e in 35-78% yields in presence of excessive 4-dimethylaminopyridine as the acid scavenger, whereas the reactions gave unexpected 8-substituted products N-(8-chloro-4-methyl-2-oxo-2H-furo-[2,3-h]chromen-9-yl)amides (5a-c) and 4-methyl-2,9-dioxo-8,9-dihydro-2H-furo[2,3-h]chromen-8-ylcarboxyloates (6d-e) by using excessive acid chlorides. The structures of 10 new compounds were determined by 1H NMR, 13C NMR, MS and HRMS, and the possible mechanism for the formation of unexpected products 5a-c and 6d-e was also proposed.