Thorpe reactions regioselectivity

More general processes rely on variations of the Guareschi-Thorpe reaction [14] where condensations between 1,3-dicarbonyls and cyanoacetamide yield functionalized monocyclic 2(lff)-pyridones (a and b. Scheme 2) [15, 16]. Unless the carbonyls are sufficiently different in reactivity, the reaction suffers from poor regioselectivity. The use of 3-alkoxy or 3-amino enones instead of 1,3-dicarbonyls has proven to be a versatile and reliable synthetic methodology where the 1,4-addition controls the regioselective outcome (c and d. Scheme 2) [17-19]. 

A convenient procedure was developed (1996IZV437, 2000IZV121) for the synthesis of 1,6-naphthyridine derivatives 81 containing the alkylselanyl substituent at position 7. Thus, multicomponent condensation of cyanoselenoacetamide, 2-fur-furylideneacetoacetic ester 82 and alkyl halides was carried out under the action of a two-fold excess of A-methylmorpholine. The reaction involves the Thorpe dimerization of the cyanoselenoamide yielding compound 83, its reaction with a molecule of ester 82 to form adduct 84, regioselective cyclocondensation of the adduct 84... 

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