2-Benzopyrilium salts. 28. Conversion of 1-methyl-2-benzopyrilium salts into substitute chrysenes in basic media

Hypoxia-Protective Azaphilone Adducts from Peyronellaea glomerata

“…The interesting configurations of 1 and 2 could be explained by their biosynthetic origin (Supporting Information Scheme S1). Generally, oxonium intermediates (such as 1a and 2a ) are thermodynamically unstable and would rapidly rearrange to give ring cleavage products, thus preventing subsequent reactions. − However, in this case, the crucial hemiketal intermediates 1b and 2b are proposed to trap these, allowing them to react with carboxyl moieties to form γ-lactone rings. − The simultaneous isolation of 1 and 2 suggests that the [4+2]-cycloaddition is a pivotal step in the formation of both of their skeletons. This is the first direct evidence that oxa-[4+2]-cycloadditions can generate enantiomeric skeletons.…”

2-[2-(1-benzoyl-4-methyldibenzo- thienyl-2)benzo[b]thienyl-3]phenyl- 1-ethanone – a new product of the reaction of 1-methyl-3-phenylbenzo- thieno[2,3-c]pyrilium perchlorate with nucleophilic reagents

“…Subsequent intramolecular cyclization of compound 3, in contrast to its benzoid analogs [7], occurs exclusively in acid media, for example, on boiling compound 3 in toluene in the presence of p-toluenesulfonic acid.…”

“…Assuming that the mechanism of formation of compound 3 may be analogous to the formation of chrysenes from 1,3-dimethylbenzo[c]pyrylium perchlorate, we proposed to obtain dimers of analogous structure from perchlorate 1 under conditions of hydrolysis (sodium acetate-water) as described in [7]. However we isolated a mixture of 2-acetyl-3-phenacylbenzo[b]thiophene (6) (42% yield), 4-hydroxy-3-phenyldibenzothiophene (7) Further study of the reaction of 2-acetyl-3-phenacylbenzo[b]thiophene (6) with alkalis, primary and secondary amines showed that just this compound was the precursor of dibenzothiophene 3.…”

“…In papers on the recyclization of 1,3-dimethylbenzo[c]pyrylium perchlorate with alkali the following sequence was described for the formation of chrysenes: pyrylium → dimer → chrysene; and the side process: pyrylium → 1,5-dicarbonyl compound →naphthol. So the authors considered the formation of chrysene from 1,5-dicarbonyl compounds was impossible [7].…”