Synthesis, Structure, and Cyclocondensation of the 4,4,4-Trifluoro-3,3-dihydroxy-2-methyl-1-(thien-2-yl)-1-butanone with Hydroxylamine and Hydrazine

Abstract

The synthesis of 4,4,4-trifluoro-3,3-dihydroxy-2-methyl-1-(thien-2-yl)butan-1-one (3) through acylation of 1,1-dimethoxy-1-(thien-2-yl)propane (1) with trifluoroacetic anhydride and its reactions with hydroxylamine and hydrazine was investigated. X-ray structural analysis of new trifluoromethyl-substituted dielectrophile 3 revealed that this hydrate exists as a racemate with inter- and intramolecular O-H·O bonds. The crystal structure shows alignment along axis b of pair molecules with the same configuration of the O2-H·O1 bond. For 5(3)-trifluoromethyl-4-methyl-3(5)-(thien-2-yl)-1H-pyrazole (4), obtained via cyclocondensation of precursor 2 and hydrazine hydrochloride, X-ray structural analysis indicated that its rings are almost planar (torsion angle N2-C5-C6-C7–5.4°) and that S1 at the thienyl moiety is anti-periplanar to N2 (torsion angle N2-C5-C6-S1 176.01); no disorder effect was observed for the thienyl ring.