Geometrical Isomers of the Hydrazones from 2-Formyl- or 2-Acetyl-furans and -thiophenes and 2-Benzothiazolylhydrazine

Abstract

The reaction of 2-formy1-, 2-formy1-5- ethy1-, 2-acety1 rans, 2-formy1-and 2-acetylthiophenes with 2-benzothiazolylhydrazine in refluxing ethanol g4ve -t-he -corLrespgp. ding hyd-e azo-ngg kl)(X=Of R, =R, =H), (2)(X=O, R, =H, R, =CH, ), (3)(X=O, R, =CH, , R, =H), (4)

(X=S, Ri=R2=H) and (5) (X=S, Ri=CHs, R2=H)iJ Erom ea. ch hydrazope mixture, the E- and Z-isomers were separated by fractional recrystallization and column chromatography. The steric configurations of the E and Z-isomers were determined by NMR spectra and their spectral characters were investigated, Moreover, the photoisomerizations between the E-and Z-isomers were studie
ln the NMR spectra, the protons of the 3- and 4-positions of furan rings in (1 E). y(3 E)were shielded more than those of (Z Z). v(3 Z) and the NH protons in (IE), (2E) and (4E)were deshie1ded more than those of the corresponding Z-isomers. But no difference was observed in the NH protons between (3 E), (5 E) and (3 Z), (5 Z). The E- and Z-isomers were isomerized to each other under the irradiation by tungsten lamp at 25eC in a few organic solvents. The ratef constants ki for the isomerization, of (1 Z)tr(1 E) showed the solvent dependence; that is(EtOH CH8CN) k, (cl, -C6H, 2): but k, f(4 Z)(4 E)did not show remarkable solvent dependence. On the other hand, the solvent dependence of the rate constants-1 for the(E)Z isomerizations were opposite to the above tendency.