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Zwitterionic 1,3‐Shift Intermediates in the Interconversions of (Thio)carbamoyl Isocyanates and Carbamoyl Iso(thio)cyanates, R 2 N–CX–NCO ⇌ R 2 N–CO–NCX, and in Carbamoylketenes R 2 N–CO–CH=C=O
Author(s) -
Koch Rainer,
Wentrup Curt
Publication year - 2013
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201300975
Subject(s) - ketene , chemistry , zwitterion , thio , medicinal chemistry , reactive intermediate , activation barrier , isocyanate , reaction intermediate , stereochemistry , molecule , organic chemistry , catalysis , polyurethane
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 ketene ⇌ ketene 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 ketene ⇌ ketene interconversion is expected well below room temperature with an activation barrier of ca. 10 kcal/mol.