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Theoretical Studies on Cycloaddition Reactions between 1‐Aza‐2‐azoniaallene Cations and Isocyanates
Author(s) -
Wei MeiJu,
Fang DeCai,
Liu RuoZhuang
Publication year - 2004
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.200400343
Subject(s) - chemistry , substituent , isocyanic acid , cycloaddition , isocyanate , medicinal chemistry , activation barrier , polar effect , reaction mechanism , solvent effects , solvent , catalysis , organic chemistry , polyurethane
The mechanisms of the title reactions between 1‐aza‐2‐azoniaallene cations and isocyanic acid or isocyanates have been theoretically explored at the B3LYP/6‐31++G** level. It was found that all of these reactions proceed in asynchronous but concerted pathways. The substituent effects are also obvious; e.g., the presence either of an electron‐withdrawing chlorine substituent on the 1‐aza‐2‐azoniaallene cation or of an electron‐releasing methyl substituent on the isocyanate both favor the cycloaddition reactions. For the [1,2]‐shift reactions, all the substituents lower their activation barrier, especially Cl substituents on the 1‐aza‐2‐azoniaallene cation, but when Cl substituents are present on the 1‐aza‐2‐azoniaallene cation the rearrangement product is not as stable as others. In addition, solvent effects with the PCM model are also reported, and a model reaction has been investigated at the MP2/6‐31+G* and QCISD/6‐31+G* levels as well as by DFT. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)