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AuBr 3 ‐Catalyzed Chemoselective Annulation of Isocyanates with 2 H ‐Azirine
Author(s) -
Wu Yufeng,
Tian Bing,
Witzel Sina,
Jin Hongming,
Tian Xianhai,
Rudolph Matthias,
Rominger Frank,
Hashmi A. Stephen K.
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201804765
Subject(s) - annulation , azirine , catalysis , chemistry , organic chemistry , ring (chemistry)
Abstract The chemoselective cyclization of isocyanates with 2 H ‐azirine was achieved with AuBr 3 as catalyst. This transfer sets the stage for the synthesis of aromatic oxazole‐ureas in a tandem process. The addition of a catalytic amount of phosphite enhances the process enormously. The reaction can also be performed in a one‐pot process using benzoyl azide instead of isocyanate under the same conditions. A detailed study on the role of the phosphite that was applied as an additive revealed that only non‐coordinated phosphite can reduce gold(III) and that gold(I) coordinated phosphite is not oxidized. Accompanied by the reduction of gold, HBr is generated in situ, which turned out to be the actual promotor in combination with the remaining AuBr 3 . The positive effect of acid can be explained by a strong N–Au coordination, which tends to break more easily in the presence of small amount of protic acid in the reaction solution.