Mesoionic compounds synthesis

Pyrazolino[2,3-c][l,2,3]triazoles, 5, 702 Pyrazolium hydroxide, l,2-dimethyl-3,5-diphenylanhydro-4-hydroxy-IR spectra, 5, 201 Pyrazolium salts dequatemization, 5, 269 H NMR, 5, 185 hydrogen exchange at ring carbon, 5, 245 mesoionic compounds, 5, 171 nitrodebromination, 5, 237 reactivity, 5, 217 reduction, 5, 68, 243 synthesis, 5, 156 UV spectra, 5, 199 Pyrazolium salts, amino-reactions, 5, 262 Pyrazolium salts, bromo-nucleophilic displacements, 5, 266 Pyrazolium salts, 1,2-dimethyl-deuteration, 5, 175, 245 hydrogen exchange, 5, 71 acid-catalyzed, 5, 239 reactions... 

These results prompted them to attempt the stereoselective synthesis of the IV-phenylsulfonyl substituted spiro- (3-lactams 150, 151 (Scheme 36) from the N-(phenylmethyIe ne )be n ze nesulfonamide and the ketene valence tautomer of the bicyclic mesoionic compounds such as (2 S,4/ )-4-acetyloxy or benzoyloxy-IV-acyl-prolines 149 in the presence of acetic anhydride [109]. The presence of the stereocenter in position 4 of the cyclic amino acid 149 was found to be sufficient to ensure complete stereoselectivity on the spiranic C-4. 

In connection with these results, and as an extension of their studies toward the reactivity of new bicyclic mesoionic compounds and their usefulness in the synthesis of condensed heterocycles, they further reported the stereoselective synthesis of spiro-(3-lactams 153, 154 (Scheme 36) by reactions of imines with mesoionic compounds or ketenes generated from A-acyl-thiozolidine-2-carboxylic acids 152 [110]. 

The synthesis of various heterocyclic systems via 1,3-dipolar cycloaddition reactions of 1,3-oxazolium-5-oxides (32) with different dipolarophiles was reported. The cycloaddition reactions of mesoionic 5H,7H-thiazolo[3,4-c]oxazolium-l-oxides (32), which were prepared from in situ N-acyl-(/J)-thiazolidine-4-carboxyIic acids and N,N -dicyclohexylcarbodiimide, with imines, such as N-(phenylmethylene)aniline and N-(phenylmethylene)benzenesulfonamide, gave 7-thia-2,5-diazaspiro[3,4]octan-l-one derivatives (33) and lH,3H-imidazo[ 1,5-cJthiazole derivative (35). The nature of substituents on imines and on mesoionic compounds influenced the reaction. A spirocyclic p-lactam (33) may be derived from a two-step addition reaction. Alternatively, an imidazothiazole (35) may be obtained from a typical 1,3-dipolar cycloaddition via a tricyclic adduct (34) which loses carbon dioxide and benzenesulfinic acid. [95T9385]... 

The synthesis of thiazoIo[3,2-a]-[I]benzothieno[2,3-t/]pyrimidin-3(2//)-ones (323) is accomplished in two ways. The first involves direct condensation of thione with a-chloroester, while the second, the cyclization of the acid through a mesoionic compound, is affected as illustrated in Scheme 76 [81IJC(B)538]. 3-MethyI(phenyl)-4-oxo-5,6,7,8-tetrahydro[l]benzothi-eno[2,3-c/]pyrimidine-2-thiones (322a,b) react with ethyl a-chlorophe-... 

Sydnones, like miinchnones (see p 129), are mesoionic compounds. The synthesis of the first example, namely 3-phenylsydnone 1, was achieved by Earl and Mackney at the University of Sydney. It was carried out by cyclodehydration of A-nitroso-A-phenylglycine with acetic anhydride ... 

Mesomeric zwitterions like Munchnones, which are known as mesoionic compounds, also occur in other heterocyclic systems [276], Munchnones show the reactivity of 1,3-dipoles for instance, they react with acetylenes via the products 62 of a 1,3-dipolar cycloaddition to give pyrroles 63 after cycloreversion of 62 by loss of CO2 Huisgen pyrrole synthesis). 

The first synthesis of a l,2,3,4-oxatriazolium-5-amenate derivative (83, R=Ri=C, H5) was reported by Busch et al. as early as 1896 [144]. The product was obtained by the nitrosation of the diphenylthiosemicarbazide precursor 119. The real structure remained unclear until 1971, when Christophersen et al. [145] assigned the correct mesoionic structure to the compound. These authors prepared a series of mesoionic... 

Matsuda et al. <1995H(41)2777> described an efficient synthesis of mesoionic [l,2,4]triazolo[4,3-A]pyridazines 390 and 391. The starting compound for the synthesis is the A-aminotriazole 389, which can be treated either with ethyl 2-chloro-3-ethoxyacrylate to yield 390 or with ketene dithioacetals to afford 391. The reactions proceed in good to high yield. 

Molina et al. were able to prepare the mesoionic thiadiazole (292) from iminophosphorane 297 and carbon disulfide. As Scheme 106 shows, 298 reacts with a,w-dihalo compounds to form dimer 299 [91JCS(P1)1159]. The synthesis of the mesoionic thiazolo[2,3-6][l,3,4]thiadizole is described in (92T1285). 

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