Conversion of 7-Methoxy-3,4-dihydro-2H-1-benzopyran-2-one into the corresponding dimethyl ortho ester

Article abstract of DOI:10.1016/S0040-4020(97)00007-0

7-Methoxy-3,4-dihydro-2H-1-benzopyran-2-one 2 was converted into 3-(2'-tert-butyldimethylsilyloxy-4'-methoxyphenyl)-N-methyl-N-phenylpropanamide 25 and reaction of this with methyl trifluoromethanesulfonate, followed by reaction with sodium methoxide, gave 2,2,7-trimethoxy-2H- 1-benzopyran 1a in 55% overall yield from 25. A similar methylation/methoxide sequence using 3-(2'-benzyloxy-4-methoxyphenyl)-N-methyl-N-phenylpropanamide 18 gave a mixture which contained trimethyl 3-(2'-benzyloxy-4'-methoxyphenyl)orthopropanoate 20a and reaction of this mixture with a solution of sodium in tert-butanol gave a product in which 2,2,7-trimethoxy-2H-1-benzopyran 1a was detected, but not isolable.