Tautomeric equilibrium in trifluoroacetaldehyde arylhydrazones

Novel Trifluoromethylated Spiro-1,3,4-thiadiazoles via [3+2]-Cycloadditions of 2,3-Diphenylcyclopropenethione with Selected in situ-Generated Nitrile Imines Derived from Trifluoroacetonitrile

“…The comparison of the reactivity of 1 and diphenyl nitrile imine 14 evidenced that the presence of the CF 3 -group is necessary to achieve sufficient electrophilicity to perform the formation of the Trifluoroacetaldehyde arylhydrazones were prepared by heating methanolic solutions of excess fluoral hydrate with the appropriate hydrazine in a closed ampoule at 75 °C overnight in the presence of freshly activated molecular sieves 4Å following our earlier report. 26 Hydrazonoyl bromides 12 were obtained by treatment of the above mentioned hydrazones with N-bromosuccinimide (NBS) in dry DMF as described. 4c 2,3-Diphenylcyclopropenethione 7was prepared by thionation of the respective ketone with…”

First (3+2)-Cycloadditions of Thiochalcones as C=S Dipolarophiles: Efficient Synthesis of 1,3,4-Thiadiazoles via Reactions with Fluorinated Nitrile Imines

“…As the precursor, the corresponding hydrazonoyl bromide 7a, readily accessible from fluoral-derived hydrazone 8a was applied (Scheme 2, Figure 2). 10,14 The reaction was performed in anhydrous THF, at room temperature, using a slight excess of bromide 7a in the presence of Et 3 N as a base. The progress of the reaction was monitored by TLC until the starting 2a was fully consumed.…”

“…22 Trifluoroacetaldehyde arylhydrazones 8 were prepared by heating methanolic solutions of the appropriate hydrazine and excess fluoral hydrate in a closed ampoule at 75 °C overnight in the presence of 4 Å molecular sieves according to literature protocols. 14,23 Hydrazonoyl…”

“…Calcd for C 22 H 17 F 3 N 2 S 2 (430.1): C,61.38;H,3.98;N,6.51;S,14.90. Found: C,61.40;H,3.92;N,6.48;S,14.94. 2-(3′,4′-Methylenedioxyphenyl)-2-styryl-3-p-tolyl-5-trifluoromethyl-2,3-dihydro-1,3,4-thiadiazole (9f) Reaction time 5 h; CC (SiO 2 , PE/CHCl 3 , 9:1); yellow oil; yield: 94 mg (20%).…”

“…,59.18;H,3.84;N,6.27;S,14.36. Found: C,59.12;H,3.98;N,6.21;S,14.31. 5-trifluoromethyl-2,3dihydro-1,3,4-thiadiazole (9k) Reaction time 3 h; CC (SiO 2 , PE/CHCl 3 , 9:1); yellow oil; yield: 366 mg (88%).…”