On the reaction of 2-phenylaminothiazoline withα-halogenoketones

Abstract

It was established that the alkylation of 2-phenylaminothiazoline with substituted phenacyl bromides proceeds at the exocyclic nitrogen atom with the formation of 5-aryl-7-phenyl-2,3-dihydroimidazo[2,1-b]thiazolium bromides. In order to confirm the structure of the last, the reductive desulfurization of one of them (Ar = pchlorophenyl) was accomplished using Raney nickel. It was shown that dequaternization of the resulting 1-phenyl-3-ethyl-4-(p-chlorophenyl)imidazolium bromide to 1-phenyl-4-(p-chlorophenyl)imidazole, identical to the sample obtained by direct synthesis, thereby occurs.In the continuation of investigations into the synthesis and properties of condensed imidazoles with an angular nitrogen atom [1-4], we studied the reaction of 2-phenylaminothiazoline (I) with primary and secondary c~-halogenoketones of the aromatic series (IIa-h). Theoretically, such a reaction can proceed at two nucleophilic centers --the exocyclic or the ring nitrogen atoms --with the final formation, i.e., after cyclization, of 5-aryl-7-phenyl-or 6-aryl-7-phenyl-2,3-dihydroimidazo[2,1-b]thiazolium bromides (structures A and B) correspondingly.It was shown in the work [5] that 2-arylaminothiazolines are only alkylated by alkyl halides at the exocyclic nitrogen atom. Consequently, the products of the reaction of compounds (I) and (IIa-h) should be 2-phenyl-2-acylarylaminothiazoline hydrobromides (structure C), the dehydration of which is accompanied by the formation of the corresponding 5-aryl-7-phenyl-2,3-dilaydroimidazo [2, l-b] thiazolium bromides.

The Chemistry of α-Haloketones and Their Utility in Heterocyclic Synthesis

“…Various ring systems containing the –C(NH 2 )=N– moiety as a part of the ring have been found to condense with α-bromo-ketones to yield condensed imidazo-heterocyclic systems; the ring nitrogen attacks the CH 2 Br unit rather than the primary exocyclic amino group and imidazo[1,2- b ]-pyrazoles [ 254 , 255 ], imidazo[1,2- a ]benzimidazoles [ 256 , 257 , 258 , 259 ], imidazo[2,1- b ]oxazoles [ 260 ], imidazo-[2,1- b ]thiazoles [ 261 , 262 , 263 , 264 , 265 , 266 , 267 ], imidazo[2,1- b ]-1,3,4-thiadiazoles [ 268 , 269 , 270 , 271 , 272 ], imidazo[1,2- d ]tetra-zoles [ 273 , 274 ], are the well-known condensed imid-azo-hetero-cyclic systems thus prepared. A general system-atic preparative route for such fused imidazoles 126 can be presented starting from 124 ( Scheme 34 ).…”

The Chemistry of α‐Haloketones and Their Utility in Heterocyclic Synthesis

“…Various ring systems containing the -C(NH 2 )=N-moiety as a part of the ring have been found to condense with α-bromoketones to yield condensed imidazo-heterocyclic systems; the ring nitrogen attacks the CH 2 Br unit rather than the primary exocyclic amino group and imidazo[1,2-b]pyrazoles [254,255], imidazo[1,2-a]benzimidazoles [256][257][258][259], imidazo[2,1-b]oxazoles [260], imidazo-[2,1-b]thiazoles [261][262][263][264][265][266][267], imidazo[2,1-b]-1,3,4-thiadiazoles [268][269][270][271][272], imidazo [1,2-d]tetrazoles [273,274], are the well-known condensed imidazo-heterocyclic systems thus prepared. A general systematic preparative route for such fused imidazoles 126 can be presented starting from 124 (Scheme 34).…”