An anomalous addition of chlorosulfonyl isocyanate to a carbonyl group: the synthesis of ((3a S ,7a R , E )-2-ethyl-3-oxo-2,3,3a,4,7,7a-hexahydro-1 H -isoindol-1-ylidene)sulfamoyl chloride.

In this study, we developed a new addition reaction of chlorosulfonyl isocyanate (CSI), starting from 2-ethyl-3a,4,7,7a-tetrahydro-1 H -isoindole-1,3(2 H )-dione. The addition reaction of CSI with 2-ethyl-3a,4,7,7a-tetrahydro-1 H -isoindole-1,3(2 H )-dione resulted in the formation of ylidenesulfamoyl chloride, whose exact configuration was determined by X-ray crystal analysis. We explain the mechanism of product formation supported by theoretical calculations.