The reaction of phenylglyoxal with 2-aminoalcohols. Rearrangement of 2-acyloxazolidines to 2-hydroxy-5,6-dihydro-1,4-oxazines

The reactions of phenylglyoxal hydrate with (R)-phenylglycinol and with (1S,2R)-norephedrine were investigated. The expected 2-benzoyloxazolidines 3 and 2a, respectively are initially formed, and undergo a fast, spontaneous stereospecific rearrangement to the corresponding 2-hydroxy-3-phenyl-5,6-dihydro-1,4-oxazines 4 and 5 respectively. The mechanism of this new rearrangement is discussed. The structures and stereochemistry of 4 and 5 were established by X-ray diffraction analysis.