ALPHA-SUBSTITUTED PHOSPHONATES .64. PHOSPHONO-SUBSTITUTED IMIDAZOLES AND OTHER HETEROCYCLES FROM DIETHYL [(2,2-DICHLORO-1-ISOCYANO)-ETHENYL]PHOSPHONATE

The reaction of diethyl [(1-isocyano-2,2-dichloro)-ethenyl]phosphonate (1) with mono- and bifunctional aliphatic and aromatic amines and thi ols has been studied. Because 1 is a push-pull olefine, a nucleophilic attack can take place at the halide-substituted carbon atom. On the o ther hand, 1 possesses with the isocyano group a further reactive cent re, which is able to undergo typical isocyanide reactions. With second ary and ethylene-bridged bifunctional nucleophiles the substitution of the chloro atoms of 1 furnishes ketene N,N-, N,S- and S,S-acetals (8, 12, 14). By treating 1 with primary amines imidazoles 6 are obtained, an alpha-addition of an amino function to an isocyano group under mil d conditions being involved. The isocyano-substituted cyclic ketene N, N-acetal 12 a inserts acceptor-substituted isocyanides forming the fus ed pyrazines 18. The structure of 18 a is corroborated by X-ray crysta l structure analysis.