Zwitterionic 1,3-Shift Intermediates in the Interconversions of (Thio)carbamoyl Isocyanates and Carbamoyl Iso(thio)cyanates, R_2N–CX–NCO≒R_2N–CO– NCX, and in Carbamoylketenes R_2N–CO–CH=C=O

摘要

Cyclic zwitterionic intermediates 3 have been located as reactive intermediates in the thermal 1,3-shifts of dimethylamino and N- piperidinyl groups in carbamoyl isocyanates, carbamoyl isothiocyanates and carbamoylketenes at the B3LYP, M06-2X and MP2 computational levels of theory. The zwitterion formed in the course of the ketenehketene rearrangement shows the highest stabilization (by about 3–5 kcal/mol). The interconversions of carbamoyl isocyanates and isothiocyanates should occur readily at or near room temperature with activation barriers in the range 23–30 kcal/ mol, and the ketenehketene interconversion is expected well below room temperature with an activation barrier of ca. 10 kcal/mol.