Wu X.-F, * Neumann H, Neumann S, Beller M. * Zhejiang Sci-Tech University, Hangzhou,
P. R of China and Universität Rostock, Germany
A General and Efficient Palladium-Catalyzed Carbonylative Synthesis of 2-Aryloxazolines
and 2-Aryloxazines from Aryl Bromides.
Chem. Eur. J. 2012;
18: 13619-13623
Key words
oxazolines - oxazines - carbon monoxide - multicomponent reaction - palladium catalysis
Significance
Described is the synthesis of oxazolines via a three-component process, in which readily
available aryl bromides, carbon monoxide and 2-chloroethylamine undergo a palladium-catalyzed
carbonylation and a subsequent cyclization to afford 2-aryloxazolines in good yield.
Replacing 2-chloroethylamine with 3-chloropropylamine also works well and in this
case the corresponding
2-aryloxazine derivatives are formed. Notably, both electron-donating and electron-withdrawing
groups are tolerated in this process. However, the scope of the three-component process
was not well investigated, especially for ortho- and meta-substituted aryl bromides.
Comment
Oxazolines and oxazoles are important heterocycles for organic synthesis and materials
chemistry (see Book below). A number of methodologies for the construction of the
oxazoline ring from aryl aldehydes, nitriles, carboxylic acids and related derivatives
have been developed (e.g., S. Takahashi, H. Togo Synthesis 2009, 2329). In comparison with those, the present carbonylation–cyclization strategy
offers a straight-forward way for the synthesis of oxazolines and their analogues
from easily available starting materials. A drawback of this method is the high pressure
required (10 bar).
Book
Oxazoles: synthesis, reactions, and spectroscopy, Part 2; D. C. Palmer, Ed.; Wiley: Hoboken, 2004.
