Microwave-Assisted Synthesis of 2-Aryl-2-oxazolines, 5,6-Dihydro-4H-1,3-oxazines, and 4,5,6,7-Tetrahydro-1,3-oxazepines
María C. Mollo and Liliana R. Orelli*
*Universidad de Buenos Aires, CONICET, Departamento de Química Orgánica, Facultad de Farmacia y Bioquímica, Junín 956, 1113 Buenos Aires, Argentina, Email: lorelliffyb.uba.ar
M. C. Mollo, L. R. Orelli, Org. Lett., 2016, 18, 6116-6119.
DOI: 10.1021/acs.orglett.6b03122 (free Supporting Information)
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Polyphosphoric acid (PPA) esters promote a microwave-assisted procedure for the synthesis of 5- to 7-membered cyclic iminoethers from amido alcohols. 2-Aryl-2-oxazolines and 5,6-dihydro-4H-1,3-oxazines were efficiently prepared using ethyl polyphosphate/CHCl3 in very good yields and short reaction time. Trimethylsilyl polyphosphate under solvent-free conditions enables the synthesis of 4,5,6,7-tetrahydro-1,3-oxazepines.
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Preparation of PPE in CHCl3:
A mixture of P2O5 (150 g), dry chloroform (300 ml) and absolute ether (150 ml) were heated at 60-65ºC with stirring and protected from moisture until complete dissolution of the pentoxide (12-15 h). The solution was allowed to cool, filtered through glass wool and used.
Liliana R. Orelli, October 17, 2017