Pyrazoles hydrazines, review

Equimolar amounts of acetylmethylacetylene and phenylhydrazine refluxed 3 hrs. in alcohol containing some HCl 3,5-dimethyl-l-phenylpyrazole. Y 15-85%. F. e., also isomers in different ratios depending on the solvent, s. G. Coispeau, J. Elguero, and R. Jacquier, Bl. 1970, 689 pyrazoles from hydrazines, review, s. ibid. 1970, 2717. 

The chlorine-containing salt formed during a Vilsmeier reaction loses dimethyl-amine on treatment with hydrazine. Fused pyrazoles have been reviewed [3902]. 

Compound 12 cyclizes with hydrazine to give a pyrazoline which can be dehydrogenated to afford pyrazole 12. Many trifluoromethylated pyrazoles are known as described in an excellent review (ref. 27). Alcohols U can be methylated using NaH/TfOMe. These methyl ethers could not be hydrolyzed to the corresponding Mosher acid. As the hydroxyl is now protected by an alkyl group, the thioamide moiety can be chlorinated to give the amide chloride 14- This unstable compound was directly cyclized with benzothiazole (Scheme 35). 

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]. 

There are numerous condensation reactions involving a hydrazine derivative and a difunctional substrate that lead to pyrazoles or pyrazolines. These reactions have been reviewed elsewhere. Typical of reactions involving participation by the hydrazone group are examples involving the ring opening of aziridines or epoxides. The stereochemistry of such... 

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