Benzopyrylium perchlorates

Benzopyrylium perchlorate, 3-ethyI-reduction, 3, 662 Benzopyrylium salts C NMR, 3, 590 chromene synthesis from, 3, 756 chromone synthesis from, 3, 829 electrophilic substitution, 2, 49 mass spectra, 3, 618 reactions... 

The reaction of sodium azide with 2-benzopyrylium perchlorates 4 gives unstable l-azido-2-benzopyrans 5, which lose nitrogen on heating to give mixtures of 3,1-benzoxazepines 6 and anils 7.25... 

Benzopyrylium perchlorate exhibits maxima at 241, 326 and 349 nm (81JHC1325). Substitution at C-8 results in bathochromic shifts of the lowest and highest absorptions. 

JOC5160). Benzylmagnesium chloride is exceptional as it consistently attacks at C-4 even when this is a ring-fusion atom as in l,3-dimethyl-5,6,7,8-tetrahydro-2-benzopyrylium perchlorate (40) <64LA(678)183>. 

The oxidation of benzopyrylium perchlorate to coumarin is brought about by manganese dioxide in chloroform or acetonitrile (68AC(R)25l). 

Depending on the initial carbonyl derivatives 38, several types of 2-benzopyrylium perchlorates were synthesized they are shown in Scheme 3. 

The reaction of 4-1 dimerization is similar to the primary step of recycli-zation of 2-benzopyrylium salts in acidic nucleophilic media (cf. Section III,C,4,b,i), but the reactive electrophile is the initial cation in this case, and not a proton. Probably for this reason, the 4-1 dimerization of 2-benzopyrylium perchlorates is not observed in acidic nucleophilic media, in contrast to a-1 dimerization (cf. Section III,F,2,b). At the same time, the scope of 4-1 dimerizations is less restricted in terms of structural requirements for 2-benzopyrylium salts in comparison with a a-1 dimerization. Thus, in the latter case, the presence of a methyl group in position 1 of benzo[c]pyrylium cation is compulsory, whereas for 4-1 dimerizations, the nature of the substituent in this position may be different, leading to a variety of 4-1 dimers and, as a consequence, to a wide variety of their transformations. 

Reaction of 2-benzopyrylium perchlorate 79 with hydrazine gives l-aryl-5//-2,3-benzodiazepines 80 <2001RMC243> (Equation 10). 

The l-(hetero)arylvinyl-5//-2,3-benzodiazepines, useful for the treatment of central nervous system (CNS) disorders, are prepared by the reaction of 2-benzopyrylium perchlorates with hydrazine hydrate <2001EPP0726257B1>. 

Reaction of 2-benzopyrylium perchlorate 430 with hydrazine gives l-aryl-57/-2,3-benzodiazepines 431 (Scheme 223) . 1H-Z,3-Benzodiazepines 433 <1994J(P1)3149, CHEC-III(13.04.9.2)150> and analogous thienodiazepines <1980J(P1)1718> are obtained from electrocyclic reaction of diazo derivatives 432 (Scheme 224). 

Treatment of 3,4-dihydro-6,7-dimethoxyisoquinoline hydrochloride with an excess of ethyl vinyl ketone gave the epimers (30) and (31) in variable proportions, depending on the pH of the reaction medium.0-Methylpeyoxylic acid (32 R = H) and 0-methylpeyoruvic acid (32 R = Me) have been prepared and identified as constituents of the amine fraction of peyote. Acylation of 3,4-dimethoxyphenylpyruvic acid with anhydrides in the presence of perchloric acid yielded 2-benzopyrylium perchlorates (33), which were transformed into the corresponding isoquinolines (34) with ammonium acetate in glacial acetic acid. ... 

Chromenes. Benzopyrylium perchlorates such as 1 are reduced by this hydride in high yield to A -chromenes (2). Reduction with formic add and pyridine leads to a mixture of A - and A -chromenes. 

HC104 added gradually to a mixture of 3,4-dimethoxyphenylacetonitrile and excess acetic anhydride, whereupon the product begins to crystallize after 15-30 min. 3-acetamido-6,7-dimethoxy-l-methyl-2-benzopyrylium perchlorate. Y 94%. F.e. s. G.N.Dorofeenko et al., Zh. Org. Khim. 6, 1519 (1970) C.A. 73, 98744. 

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