Cyclopropanation of N-Substituted 2-Oxochromene-and 6-Bromo-2-oxochromene-3-carboxamides with Zinc Enolates Derived from l-Aryl-2,2-dibromoalkanones

摘要

Zinc enolates derived from l-aryl-2,2-dibromoalkanones react with N-cyclohexyl-2-oxochromene-3-carboxamides to give N-cyclohexyl-1-alkyl-1-aroyl-2-oxo-1 a,7b-dihydrocyclopropa[c]chromene-1 a-carbox-amides mainly as cis isomers with respect to the substituents in positions 1 and la.Reactions of the same zinc enolates with N-benzyl-2-oxochromene-3-carboxamide and N-benzyl-6-bromo-2-oxochromene-3-carboxamide lead to formation of l-aryl-2-benzyl-and l-aryl-2-benzyl-6-bromo-l-hydroxy-9c-alkyl-l,2,9b,9c-tetrahydro-5-oxa-2-azacyclopenta[2,3]cyclopropa[l,2-a]naphthalene-3,4-diones.The reaction of zinc enolates with N-aryl-2-oxochromene-3-carboxamides in a weakly polar solvent(diethyl ether or ethyl acetate)affords mixtures of cis-N-aryl-l-aroyl-l-alkyl-2-oxo-la,7b-dihydrocyclopropa[c]criromene-la-carboxamides and their cyclic isomers,9c-alkyl-1,2-diaryl-1-hydroxy-1,2,9b,9c-tetrahydro-5-oxa-2-azacyclopenta[2,3]cyclopropa[ 1,2-a]naphthalene-3,4-diones,the latter prevailing.N-Substituted 1-alkyl-1-aroyl-2-oxo-la,7b-dihydrocyclopropa[c]chromene-la-carboxamides in which the aroyl group on C~1 and the carboxamide group on C~(1a)are arranged trans are formed by reactions of zinc enolates with the corresponding 2-oxochromene-3-carboxamides in the presence of hexa-methylphosphoric triamide.