Synthesis of 6-alkoxy-3-aryl-6-trimethylsilyloxy-5,6-dihydro-4H-1,2-oxazines and their acid-catalysed hydrolysis leading to 3-aryl-5,6-dihydro-4H-1,2-oxazin-6-ones and/or 4-aryl-4-(hydroxyimino)butyric acid esters

The cycloaddition of α-nitrosostyrene and its ring-substituted derivatives, which are generated by the reaction of α-chloroacetophenone oxime and its ring-substituted derivatives with K2CO3 in tetrahydrofuran, with ketene trimethylsilyl acetals proceeds to afford 6-alkoxy-3-aryl-6-trimethylsilyloxy-5,6-dihydro-4H-1,2-oxazines. These oxazines are susceptible to hydrochloric acid-catalysed hydrolysis affording 3-aryl -5,6-dihydro-4H-1,2-oxazin-6-one and/or 4-aryl-4-(hydroxyimino)butyric acid esters.