Reactions of thiophenes with acetylenes in polar solvents; a novel annulation reaction

Addition reactions of heterocyclic compounds. Part 78. Reaction of dimethyl acetylenedicarboxylate with some cyclopent[b]indoles and cyclohex[b]indoles and the crystal structure of (Z)-methyl 1-methoxycarbonylmethyl-11-methoxycarbonylmethylene-12-oxo-1,1a,1b,2,3,4,4a,8,9,9a-decahydro-1b,4a-epoxyethanoindolizino-[2,3,4,5,6-jklm]carbazole-1-carboxylate

“…data) with those of the Reagents: i, ECCE; ii, H20; iii, -MeOH analogue (18), the structure of which has been established 3*6 by X-ray crystallography. A minor product was the acid (8) with spectra very similar to that of the acid previously obtained from the indole (2): and further identified from its reaction with diazomethane which gave compound (9) (see Table 1 for 13C n.m.r.). In 90% aqueous methanol the carbazole (5) gave two (1 + 1 DMAD -CHJ lactones (10) and (19), and two more polar adducts C and D (see later) which were the major products.…”

1,5-Dipolar cyclizations

“…In the nonpolar medium, formation of the two new bonds in the [2 + 2] cycloaddition may be concerted. 171 1,5-Dipolar Cycllzatlons droindolizine 441 initially formed loses the elements of nitrous acid and furnishes the observed product 442. Heating 442 in concentrated sulfuric acid affords the dearoylated product 444 which was independently prepared by heating the pyridinium salt 443 with sodium hydroxide.…”

Conjugated Azomethine Ylides

“…This pro-cess is illustrated using 3-pyrrolidinothiophene (15) as the starting enamine. [16] The reaction with dimethyl acetylenedicarboxylate (DMAD) in methanol leads to the formation Scheme 3. of an azomethine ylide, which tautomerises to the vinyl azomethine ylide 17. The 1,5-electrocyclization of this dipole produces the corresponding tricyclic heterocyclic ring system 18 (Scheme 3).…”