An unexpected Pummerer rearrangement in the synthetic route to ethyl (2′-hydroxy-4′,5′-methylenedioxyphenyl)acetate: An alternative approach to 2,3-dimethylthio benzofurans

Highlights

• A structural fragment of the antihyperglycemic coumarin subcoriacin is synthesized.

• The CuCl₂ catalyzed hydrolysis of the vinylic dithio derivative affords the ester.

• An unexpected Pummerer reaction proceeds in the absence of CuCl₂ in the hydrolysis.

• This last finding provides an alternative approach to 2,3-dithiomethylbenzofurans.

Abstract

The synthesis of ethyl (2′-hydroxy-4′,5′-methylendioxophenyl)acetate, a fragment of the antihyperglycemic natural coumarin subcoriacin, is reported. We found an expeditious route to the title compound in five steps. Final metal catalyzed acid ethanolysis of the vinylic 1,1-methylthio methylsulfoxide derivative afforded the required aryl acetic ester, but in the absence of metal catalyst, an unexpected Pummerer rearrangement produced the 2,3-dimethylthiofuran derivative as the major product. This last result provides an alternative entry to 2,3-dimethlythiobenzofurans.