Pyrazole, 1-amino-3,5-dimethyl-, reaction

The imonium salt (199), obtained from ynamines and phosgeneimonium chloVide, underwent ready reaction with monosubstituted hydrazines to give the 3,5-bis(dimethyl-amino)pyrazole (200) (68T4217, 69T3453). Similarly, the adduct (201), resulting from the addition of phosgene to ynamines, likewise reacted with sym-disubstituted hydrazines to give pyrazoles (202). With hydroxylamine derivatives the isoxazolinone (203) was obtained. 

A microwave-assisted three-component coupling reaction of 5-amino-3-phenyl-pyrazole, a cychc 1,3-dicarbonyl compound and an aromatic aldehyde has been described by Chebanov and co-workers [121]. Depending on the apphed reaction conditions a series of 4-aryl-3-phenyl-l,4,6,7,8,9-hexahydro-l// pyrazolo[3,4-h] quinolin-5-ones 80, 9-p-tolyl-6,6-dimethyl-2-phenyl 5,6,7,9-tetrahydro-pyrazolo [5,l-h]quinazolin-8-ones 81, or 4-aryl-5a-hydroxy-4,5,5a,6,7,8-hexahydropyra-zolo[4,3-c]quinolizin-9-ones 82 can be formed (Scheme 61). 

Most of these reactions were carried out with 4-amino-l,2-dihydro-l,5-dimethyl-2-phenyl-3/f-pyrazol-3-one (4-aminoantipyrine). The acid chlorides were prepared separately or generated in situ from the corresponding carboxylic acid in the presence of the aminopyrazol-3-ones. 

Butler has described that the treatment of l-ethoxycarbonylmethyl-2,3,4,5-tetraarylpyrazolium salts with base in the presence of DM AD (dimethyl acetylenedicarboxylate) affords l-(2 -amino-vinylpyrroles) and pyrrolo[l,2-a] pyrazines <93JCS(Pl)883> a mechanism has been proposed for this unexpected behavior. Reaction of l,3,4,5-tetraaryl-2-methylpyrazolium salts (141) with ethoxide base produces the fragmentation of the pyrazole ring with formation of 1,2-bisimines (142) the mechanism is represented in Scheme 2 <94JCR(S)12>. In both cases the structures of the resulting products were supported by x-ray determinations. 

The fluorescence quantum yields of pyrene-1-carboxaldehyde in water and methanol are 0.98 and 0.07/ an effect attributed to solvent effects on 7c,n and n,n states. Cycloaddition reactions of 1-naphthonitrile to 1,2-dimethyl-cyclopentene are attributed to both and Lj, states.It is pointed out that although dual fluorescence is known, this is the first example of divergent reaction from two nearly isoenergetic singlet states. An analysis of the u.v. spectra of some acyl pyridines, including a theoretical examination of the molecular geometry, and excited states of bipyrimidine compounds have also been made. Photo tautomerism and the fluorescence of the cation of 4-amino-pyrazole[3,4-iflpyrimidine, an analogue of adenine, has been published by Wierzchowski et Intramolecular heteroexcimer formation in... 

Condensation of syn- or anti-27 with hydrazine afforded new pyrazole derivatives 28 with a stereodefined and protected amino diol side chain [64]. The preparation of push-pull substituted unsaturated monosaccharide derivatives and their use in the synthesis of nucleoside analogs have been reviewed [65]. Thus, the 2-formyl pentose glycals were transformed to the corresponding acyclo-C-nucleosides 29 [66]. Similarly, the benzy-lated 2-formylglycals reacted with hydrazine derivatives to afford the substituted l,2,4-tri-0-benzyl-lC-(lH-pyrazol-4-yl)-D-tetritols the deprotection of which was achieved with Pd/H2 to yield the lC-( 1-methyl-lH-pyrazol-4-yl)-D-tetritols [67]. 3-0-Benzyl-6-deoxy-l,2-0-isopropylidene-o -D-xylo-hept-5-ulofuranurono-nitrile was reacted with f, N-dimethylformamide dimethyl-acetal in THF to furnish the (E)-3-0-benzyl-6-deoxy-6-dimethyl-aminometh-ylene-l,2-0-isopropylidene-Q -D-xylo-hept-5-ulofuranurono-nitrile as a major product, and on treatment with carbon disulfide and methyl iodide under basic conditions afforded 3-0-benzyl-6-deoxy-l,2-0-isopropylidene-6-[bis(methylsulfanyl)methylene]-a-D-xylo-hept-5-ulofuranurono-nitrile. Further reaction with hydrazines yielded the reversed pyrazole-C-nucleoside analogs [68]. 

In the literature, several methods have been reported for the synthesis of 5-amino p5rrazole derivatives. Hasseneen and coworkers [18] have prepared pyrazole derivatives by the reaction of nitrile imine with fumaronitrile. Jachak and co-workers [19] also reported the synthesis of 4-cyano pyrazole derivatives by starting with cyanoacetaldehyde, DMF-DMA (N,N-Dime-thylformamide dimethyl aceta) and hydrazines. 

One-pot four-component reactions of carbonyl compounds, hydrazines, malononitrile, and P-ketoesters mediated by meglumine (13T9931), cetyltri-methylammonium chloride in aqueous medium (13SC1721), or in the absence of catalyst under ultrasound irradiation in water (13JHC1174) are versatile routes for the synthesis of pyrazole-fused 2-amino-3-carbonitrile-4f/-pyrans. Quinohnone-fiised 3-nitro-4H-pyrans result from the ZnCl2-cat-alyzed three-component reaction of 4-hydroxy-l-methylquinolin-2(lH)-one, nitroketene N,S-dimethyl acetal, and various aromatic aldehydes, in excellent yields (Scheme 14) (13TL3248). 

PROBLEM 23.39 Reaction of A -phenylalanine (1) with nitrous acid affords A -nitroso amino acid (2), which on treatment with acetic anhydride yields sydnone (3). Sydnones belong to a class of compounds known as mesoionic compounds. These compounds cannot be satisfactorily represented by Lewis structures not involving charge separation. The name sydnone derives from the University of Sydney where the first examples were prepared in 1935. Reaction of 3 and dimethyl acetylenedicarboxylate (DMAD) gives pyrazole (4). Propose mechanisms for the formations of 2, 3, and 4. Hint. For the formation of 4, it may be helpful to consider the other possible Lewis structures for sydnone 3. 

---