Five-membered heterocycles with N and S

Five-membered heterocycles with N and S (Se) atoms 97PF1C190,98PF1C172, 99PHC184. 

Insertion of a C=0, C=S or S=0 group between an amino and a hydroxy function of a 1,2-aminoalcohol produces a five-membered heterocycle with O and N as ring heteroatoms linked by -CO-, -CS- and -SO-groups. Although the reaction proceeds in two steps, it can often be carried out as a one-pot process. 

I. Shinkai, Five-membered Ring Systems with N and S (Se) Atoms, in H. Suschitzky u. E.F.V, Scriven, Progress in Heterocyclic Chemistry, Vol. 1, S. 164, Pergamon Press, Oxford New York Beijing Frankfurt Sao Paulo Sydney Tokyo Toronto 1989. 

Azoles are five-membered heterocycles with an 0, N, or S atom at position 1 and an N atom at position 3. 

Scrutiny of a number of other five-membered C-, N- and S-containing heterocycles (78JCS(P1)1445) with the framework depicted in Scheme 2 has revealed that facile photofragmentation takes place when extrusion of a small inorganic fragment such as N2 (thiatriazole), N20 (thiatriazole 3-oxide), CO, C02, etc. is possible. In these cases formation of nitrile... 

Five-membered heterocycles 206-209, in which two 1-adamantyl groups occupy cis positions, were synthesized from 175 (98BCJ1181).The reaction of tosyl azide with 175 gave 210, which has no tendency to cyclize to 211. These results, together with the fact that compound 173 exists in the ring-opened form, led to the conclusion that, when four-membered rings are constituted by a combination of one S—X (X = N, O, S) and one C—C double bonds, 1,2-dithietes are probably the only species that can adopt a ring-closed structure as the predominant isomeric form. 

Five- to seven-membered O-, N-, and S-heterocycles Acyl ylides with a tethered terminal ester function requisite for the construction of five- to seven-membered heterocycles are very conveniently accessible by reaction of the cumulated ylide ketenylidenetriphenylphosphorane 11 with various carboxylic esters bearing OH-, NHR-, and SH-groups in a-, -, or y-position. 

Some of the important differences in the nuclear magnetic resonance spectra of the /3-n-furanose form in various solvents are shown in Table I. As expected, the chemical shifts are somewhat altered on changing the solvent however, new bands appear with pyridine. In methyl sulfoxide, the mutarotation is very slow, and only one form is seen soon after dissolution. In anhydrous pyridine, the mutarotation is a little faster, so that, in a few minutes, the a- and /S-n-furanose forms are present in equal amounts. With the addition of deuterium oxide, equilibrium between the three forms is rapidly reached. This last spectrum is essentially the same as that of the crude product mentioned earlier. The small values for Jz 4 indicate that all three forms are in fixed conformations and are, therefore, not acyclic. The spectrum of the a-D-pyranose form is closely related to that of (24). The two furanose forms show, overall, a similar spectrum, except that the proton at C-1 of the )3-d anomer shows a relatively large coupling, J = 3.25, of unknown origin. The spectra of many five-membered heterocyclic compounds are anomalous, and not yet fuUy understood. 

---