Ketenimine N-functionalization of thiazolidine-2,4-diones with acetylenes and isocyanides

The zwitterionic 1:1 intermediates formed in the reaction between alkyl isocyanides and dialkyl acetylenedicarboxylates are trapped by 2,4-thiazolidine-2,4-diones to afford N-functionalized 2,4-dioxothiazolidines containing a ketenimine moiety.