Chlorovinyl ketoacetals

To synthesize isomeric 3-substituted isoxazoles (301) the reaction of ethylene acetals of )3-ketoaldehydes (300) (readily available from -chlorovinyl ketones (57IZV949)) with hydroxylamine was employed. Owing to the comparative stability of the dioxolane group, this reaction gave exclusively 3-substituted isoxazoles (301) (60ZOB954). The use of noncy-clic, alkyl S-ketoacetals in this reaction resulted in a mixture of 3- and 5-substituted isoxazoles (55AG395). 

Soon it was found that good yields of many 1-azaquinolizinium salts could be obtained by adding either the ketoacetal (250) or a /3-chlorovinyl ketone (254) to an acidic solution of 2-aminopyridine (58DOK(l 18)297). This simple one-pot reaction was extended by the use of additional ketoacetals as well as j8-diketones (253) and malonaldehyde diacetal (Scheme 124). Table 14 illustrates the scope of this [3 + 3] addition mode of the 1-azaquinolizinium synthesis. 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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