An Expedient New Synthesis of Substituted Carbazoles via α-Oxoketene Acetals through Heteroaromatic Annelation Methodology

Attempted cycloaromatization of α-arylmethyl sulfones with 2-bis(methylthio)methylene-1-teralone: unexpected formation of 2-aryl-3-(methylthio)-4,5-dihydronaphtho[1,2-b]furans

“…In subsequent studies, we have further demonstrated that the stabilized carbanions derived from 3-(cyanomethyl)indole, 4 2-(cyanomethyl)pyrrole, 5 and 2-/3-(cyanomethyl)thiophenes, 6 and 5-(cyanomethyl)pyrazole 7 add to α-oxoketene dithioacetals in exclusive 1,4-addition-elimination fashion to give conjugate adduct which upon subsequent acid-induced aromatization lead to the formation of angularly substituted/annulated benzoheterocycles such as substituted carbazoles, 4 indoles, 5 benzothiophenes, 6 and indazoles, 7 respectively. We have also extrapolated this strategy for the synthesis of few angularly-fused polycyclic hydrocarbons such as benzo [c] …”

α-Oxoketene dithioacetal mediated aromatic annulation: highly efficient and concise synthetic routes to potentially carcinogenic polycyclic aromatic hydrocarbons

“…Thus making use of these methods, a number of polycyclic aromatic hydrocarbons such as benz[a]anthracene, dibenz [a,j]anthracene and the corresponding dibenz[a,h]anthracene were synthesized in good yields. 13,14 In subsequent studies, we have further demonstrated that the stabilized carbanions derived from 3-cyanomethylindole, 2-cyanomethylpyrrole and 2/3-cyanomethylthiophenes add to a-oxoketene dithioacetals in exclusive 1,4-addition -elimination fashion to give conjugate adducts which on subsequent acid induced cycloaromatization lead to the formation of angularly substituted/annulated benzoheterocycles such as carbazoles, 16 indoles 17 and benzothiophenes 18 in highly regiospecific fashion. We have now extrapolated this strategy for the synthesis of a few angularly fused polycyclic aromatic hydrocarbons such as benzo [c]phenanthrene, benzo [c]fluorene, 11-methylcyclopenta[a]phenanthrene, 5-methylchrysene and 1,4-dimethylphenanthrene and the results of these studies are presented in the following section.…”