6-Membered rings heteroatoms

Sulfur containing heterocycles are also common Compounds m which sulfur is the heteroatom m three four five and six membered rings as well as larger rings are all well known Two interesting heterocyclic compounds that contain sulfur-sulfur bonds are hpoic acid and lenthiomne... [Pg.132]

Other six-membered rings with two heteroatoms are also obtained from reaction of diketene with imidates, cyanamides, carbodiimides, isocyanates, oxa2olines, or other multiftmctional compounds. [Pg.478]

When two heteroatoms are present in a saturated six-membered ring their effects are approximately additive. Apart from the case of two a oxygen atoms—in 1,3-dioxane (48) the shift of C-2 is S 95.4 instead of 5 108 which a double shift of 40 p.p.m. would require—predictions of shift made on this basis are usually accurate to within 5 p.p.m. and are generally much closer than this. Observed shifts for a few representative examples are shown in structures (48)-(52). [Pg.15]

Structure of Five-membered Rings with One Heteroatom... [Pg.2]

The reactivity of five-membered rings with one heteroatom to electrophilic reagents has been quantitatively compared in a variety of substitution reactions. Table 2 shows the rates of substitution compared to thiophene for formylation by phosgene and iV,AT-dimethylfor-mamide, acetylation by acetic anhydride and tin(IV) chloride, and trifluoroacetylation with trifluoroacetic anhydride (71AHC(13)235). [Pg.43]