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Synthesis of 1,3-oxazoles and benzoxazoles

Recent Literature

Zn(OTf)₂ catalyzed the cyclization of propargyl alcohols with anilines and phenols in toluene at 100°C without additive and gave various indole and benzofuran products with different structures. The cyclization of propargyl alcohols and amides gave oxazoles. Mechanisms for the different substituation patterns are discussed.
M. P. Kumar, R.-S. Liu, J. Org. Chem., 2006, 71, 4951-4955.

The reaction of 1-(methylthio)acetone with different nitriles in the presence of triflic anhydride gave 2-substituted 5-methyl-4-methylthio-1,3-oxazoles in good yield. The methylthio group at the C4 position can easily be removed with Raney nickel. 4-Methylsulfonyl derivatives were prepared by the oxidation of the MeS group with m-CPBA.
A. Herrera, R. Martinez-Alvarez, P. Ramiro, D. Molero, J. Almy, J. Org. Chem., 2006, 71, 3026-3032.

Lawesson’s reagent is an efficient promoter in the solvent-free microwave-assisted synthesis of 2-substituted benzoxazoles and benzothiazoles from carboxylic acids and 2-aminophenol or 2-aminothiophenol, respectively. Various aromatic, heteroaromatic and aliphatic carboxylic acids react under the conditions developed with good yields.
J. A. Seijas, M. P. Vázquez-Tato, M. R. Carballido-Reboredo, J. Crecente-Campo, L. Romar-López, Synlett, 2007, 313-316.

A general method for the formation of benzoxazoles and benzothiazoles via a copper-catalyzed cyclization of ortho-haloanilides is reported. Optimal conditions for cyclization used a catalyst combination of CuI and 1,10-phenanthroline as ligand. The mechanism is believed to proceed via an oxidative insertion/reductive elimination pathway through a Cu(I)/Cu(III) manifold. The rate of reaction of ortho-haloanilides follows the order I > Br > Cl, consistent with oxidative addition being the rate-determining step.
G. Evindar, R. A. Batey, J. Org. Chem., 2006, 71, 1802-1808.