Unexpected formation of 3,3a,4,7a-tetrahydrobenzofuran-2,5-diones as well as arene carboxylic acids upon formal double exo nucleophilic addition of R1R2C−COO− to anisolechromium tricarbonyl complexes

Abstract

Bis(trimethylsily)ketene acetals of the general structure 2 (R1 = H, Me, R2 = Me, Et, Pri, CMe=CH2) react at –78 °C in the presence of ButOK with a series of arenechromium tricarbonyl complexes 3 to give as expected, after oxidation with I2 followed by silica gel chromatography, arylcarboxylic acids 7. In the case of anisolechromium tricarbonyl 8, besides the m-methoxyarylcarboxylic acids, tetrahydrobenzofuran-2,5-diones 11, are formed as the result of a double nucleophilic addition.