The N-heterocyclic carbene catalyzed stereoselective dimerization reactions of phthalaldehydes produced polyhydroxylated spiro- or fused indenones. The reaction pathways were dictated by the structures of NHC catalysts. Under the catalysis of a imidazole carbene, phthalaldehydes produced dihydroxylspiro[indene-2,1'-isobenzofuran]-3-ones in good to excellent yields, whereas a triazole carbene catalyzed reaction of phthalaldehydes afforded fully cis-trihydroxylindeno[2,1-a]inden-5-ones in high yields. This work not only provides a highly efficient method for the construction of valuable polyhydroxyl substituted indene derivatives that are not easily assembled by other synthetic means but also reflects the versatility of organocatalysis using N-heterocyclic carbenes.

1-Thiocarbamoyl imidazo[1,5-a]pyridinium inner salts, which were obtained readily from the addition of C,N-substituted heterocyclic carbenes imidazo[1,5-a]pyridine-1-ylidenes to isothiocyanates, are powerful ambident nucleophilic zwitterions. They acted as nitrogen nucleophiles toward ethyl propiolate to produce polyfunctionalized pyrrole derivatives in high yields. When treated with dimethyl acetylenedicarboxylate, they behaved exclusively as sulfur nucleophiles to afford fully substituted thiophenes in excellent yields. This work provides highly efficient orthogonal synthesis of polyfunctionalized pyrroles and thiophenes that were not easily obtained by other chemical means.

No abstract

Ring closure reactions O 0130Solvent Controlled Divergent Syntheses of Polysubstituted Pyrroles and Pyrrolo[2,3-b]-1,4-thiazines. -The reaction of arylthiocarbamoyl imidazolium inner salts (I) with ethyl propiolate can take two different pathways depending on the polarity of the solvent. Thus, vinylthiopyrrole derivatives (III)/(IV) are predominantly formed in more polar solvents like butanone or acetone. In less polar solvents like benzene or THF, the formation of pyrrolothiazines (V) is preferred. The reaction mechanism is discussed.

In the presence of IMC, phthalaldehydes undergo efficient dimerization yielding spirocyclic indenones like (II).