2-Benzopyryliums reaction with ammonia

The application of acetic acid catalysis in reaction of 2-benzopyrylium salts with primary amines4, in contrast to the reaction with ammonia, does not lead to a simple result. Thus, if in 30 R3 is not Aik, excluding the alternative formation of a-naphthylamines of type 153, the use of acetic acid catalysis leads to isoquinolinium salts 152 in high yields (89KPS75), whereas without acetic acid, diketones 166 were the only products of interaction between 2-benzopyrylium salts 30 and primary amines. 

The formation of a-naphthylamines 140 and 153 in reactions of 2-benzopyrylium salts with ammonia and primary amines is not always an undesirable process. The synthetic application of a-naphthylamines is connected with the chemistry of benzo[c]phenanthridine alkaloids 132 (78MI1 81H474). 

Similar to the reaction of 2-benzopyrylium salts with ammonia (Section III,C,4,a,i), an excess of competing nucleophiles in reactions with secondary amines is undesirable. Thus, the interactions of l-ethyl-3-methyl-substituted salt 183 with 40% aqueous solution of dimethylamine leads to a-naphthol 189 as the major product (79TH1). 

It is important to realise that 1-benzopyrylium salts cannot be converted into quinolines or quinolinium salts by reaction with ammonia or primary amines (cf. pyryliums to pyridines, 11.1.2.2), whereas 2-benzopyrylinm salts are converted, efficiently, into isoqninolines or isoquinolinium salts, respectively."... 

In preparing 6-alkoxy and 6,7-dialkoxy derivatives, it is convenient to react esters 12 with an acid anhydride in the presence of a Lewis acid or, preferably, perchloric acid to produce a benzopyrylium salt (14), presumably via 13 (70KGS200) (Scheme 2). Reaction of 14 with ammonia gives then the isoquinolinols 15 in high yields, where X = alkoxy, R1 = H, Me, Pr, /-Pr, and R2 = H or alkyl group (88JMC1363). 

The ability of 5-oxoniachrysenes 67 to form stable adducts with ammonia, methyl amine, and hydrazine is not usual for 2-benzopyrylium (cf. Section III,C,2), but is often encountered for 1-benzopyrylium (chro-mylium) salts (51 Mil). At the same time, no rupture of the C6—Cring bond was observed for 2-benzo- or 1-benzopyrylium salts under the conditions used. A remote similarity to C6—Crjng bond rupture may be seen in reactions of 2-benzopyrylium salts with sodium azide (Section III,C,2) or with hydrogen peroxide (Section III,C,4,b,ii). 

The Baeyer pyridine procedure has been extended to the preparation of other six-membered heterocycles, such as quinolines, isoquinolines, and acridines which are obtained by the reactions of the corresponding pyrylium salts with ammonia derivatives. For example, benzopyrylium salt 27 is... 

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