We present the results of our study towards the synthesis of 2,3-disubstituted 7-azaindoles by cyclization of 2-pyridylhydrazones of aliphatic and alkylaromatic ketones under the conditions of Fischer reaction, catalyzed by polyphosphoric acid.

The acylation of pyrrolo [1,2-a]pyrazines with acetic anhydride and the acid chlorides of various carboxylic acids has been studied. It has been shown that pyrrole [1,2-a]pyrazines are selectively acylated at the α-position of the pyrrole ring when it is free. Products of the condensation of 1-methylsubstituted pyrrolo [1,2-a]pyrazines have been obtained for the first time in the process of acetylation.In a continuation of a study of the behavior of the pyrrolo[1,2-a]pyrazine system under electrophilic substitution conditions, we have investigated the acylation of alkyl-, aryl-, and hetaryl-substituted pyrrolo-[1,2-a]pyrazines. It was established previously that acetylation of 3,4-dihydropyrrolo[1,2-a]pyrazines with acetic anhydride (in the presence of magnesium perchlorate as a Lewis acid) proceeded selectively at the pyrazine atom N (2) and formed N-acyl-substituted derivatives in 25-87% yield [1].In contrast to the hydrogenated system, acylation of aromatic pyrrolo[1,2-a]pyrazines occurs at the free α-position of the pyrrole ring. For example boiling the pyrrolo[1,2-a]pyrazines 1a-c with acetic anhydride in the presence of tin(IV) chloride or magnesium perchlorate proceeded selectively to give the monosubstituted products 2-4, but the yields of the acyl derivatives did not exceed 14%. N N R N N R Me O (MeCO) 2 O SnCl 4 Mg(ClO 4 ) 2 or 1a-c 2-4 1a, 2 R = Me; 1b, 3 R = Et; 1c, 4 R = Ph Under analogous conditions 1-propylpyrrolo[1,2-a]pyrazine (1d) reacted with the formation of a mixture of two products of acylation in low overall yield (10%) -6-acetyl-1-propylpyrrolo[1,2-a]pyrazine (5) and 6,8-diacetyl-1-propylpyrrolo[1,2-a]pyrazine (6). N N Me N N Me Me O N N Me Me O O Me (MeCO) 2 O SnCl 4 1d 5 6 + __________________________________________________________________________________________

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