Bicyclic dihydropyridone

Halide substituted isoxazolines 371a-f gave bicyclic dihydropyridones 374 after rearrangement. Methoxycarbonyl substituted isoxazolines 371g-k gave the lactams 375, whereas carbonyl substituted isoxazolines 373a-e gave pyrroles 376 (Scheme 51). 

Methyl acrylate reacts with the enediamine 230 to yield the spiro-tetrahydroimidazo-pyridone 232 via the transient intermediate 231120. The reaction with methyl propiolate gives an analogous intermediate 233, which, however, is stable. It is transformed into the bicyclic dihydropyridone 234 by the action of methanol121 (equation 98). 

Asymmetric synthesis of dihydropyridones. 8-Phcnylmcnthol has been used frequently as a chiral auxiliary, but this derivative (1) is more effective as the chiral auxiliary for cnantioselcctivc reactions of N-acylpyridinium salts with organomctallic reagents. Thus 2, prepared by reaction of 4-methoxy-3-(triisopropylsilyl)pyridine with the chloroformate of 1 reacts with the Grignard reagent 3 to give an adduct that on acidic deprotection provides the dihydropyridone 4 in 94% dc. Conversion of the alcohol to a chloride [P(CftH5)j and NCS] followed by treatment with sodium methoxide in methanol cleaves the chiral auxiliary as the methyl carbonate (94% yield) and at the same time effects cyclization to form the chiral bicyclic dihydropyridone 5 in 84% yield. 

Photolysis of enaminones 432 gives tricyclic tetrahydropyridones 433 in good yields. Ring-opening of 433 affords bicyclic dihydropyridones 434, Scheme 119. Both 433 and 434 are useful synthons for the preparation of triquinanes and various sesquiterpenes (92TL7347). 

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