Synfacts 2006(2): 0163-0163  
DOI: 10.1055/s-2005-924805
Bioorganic Chemistry and Organocatalysis
© Georg Thieme Verlag Stuttgart · New York

Mechanism of Phosphine-Catalyzed Cyclo-Oligomerization of Isocyanates

Contributor(s): Benjamin List, Nolwenn J. A. Martin
Z. Pusztai, G. Vlád, A. Bodor, I. T. Horváth*, H. J. Laas, R. Halpaap, F. U. Richter*
Eötvös University, Budapest, Hungary and Bayer Material Science AG, Leverkusen, Germany
Further Information

Publication History

Publication Date:
23 January 2006 (online)

Significance

The mechanism of the tri-n-butylphosphine-catalyzed cyclo-oligomerization of alkylisocyanates 1 (R = n-Bu, n-Hex) to give products 3-5 is elucidated using NMR spectroscopy. The authors propose the reaction to be initiated by the nucleophilic attack of the phosphine to the carbonyl group of the isocyanate moiety, followed by reaction with another isocyanate leading to the zwitterionic intermediate A. Intramolecular nucleophilic attack on the carbonyl group of A affords uretdiones 3 and the reaction of A with another isocyanate, followed by intramolecular nucleophilic attack on its carbonyl group results in the formation of isocyanurates 4 and iminooxadiazinediones 5. Intermediate A as the key intermediate of this reaction has been characterized for the first time.