ChemInform Abstract: Recyclization of Pyrrolo(1,2‐a)pyrazinium (I) into 8‐Aminoindolizine (III). A New Synthesis of the Indolizine System.

Chemistry of heterocyclic compounds at the Department of Organic Chemistry, Chemical Faculty, M. V. Lomonosov State University. (Review)

“…One of the most interesting recent results was the discovery of an unusual cycloaddition in such systems [201][202][203] with the experimental detection of a stable intermediate 14. [204][205][206]. This heterocyclic system is interesting in that it contains two nitrogen atoms, each of which is capable of participating in recyclization.…”

Cyclotransformation of Azinium Salts into Hydrogenated Cyclic Alkylamino Ketones

“…The exocyclic carbon atom must have at least two hydrogen atoms required for consecutive reduction of aromaticity of the transformation products, which are either carbocycles or heterocycles. In previous work, we have shown that pyrrolo [1,2-a]pyrazinium alkyl iodides containing methylene group at position 1 are converted by the action of alcoholic alkylamines into 8-alkylaminoindolizines [3], while isoquinolinium alkyl iodides are converted to 1-alkylaminonaphthalenes [4]. The nucleophilic transformation of azacycles containing an α-methine substituent was not examined due to the above reasons.…”

“…A study of the transamination of starting pyrrolo [1,2-a]pyrazinium alkyl iodides 2 and isoquinolinium alkyl iodides 5 showed the feasibility of the complete exchange of the alkylamine fragment at C (6) in the resultant tetrahydroindolizinone derivatives 3 and at C (3) in tetralones 6. When R 2 ≠ Me at the nitrogen atom in the starting azinium salt and R 3 ≠ Me in the alkylamine, the yields of the corresponding recyclization products are reduced and the products of the dealkylation of the starting salts to give nitrogenous bases are enhanced.…”

“…In addition to signals for the pyrrole ring protons, signals were found for the protons of two ethyl groups of imine C2, while signals for protons of the methylimine and ethylamino groups were detected for the minor product, C1 (see Experimental). In all likelihood, the initial attack of the nucleophile occurs at C (3) along with attack at α-carbon atom C (1) . However, we cannot evaluate the preference for nucleophilic attack at C (1) or C (3) of the azine ring using the ratio of integral intensities of the protons in the abovementioned spectrum of imines C1 and C2 since intermediates A1 and B3 and imine C1 in the case of a large excess of alkylamine should undergo transamination.…”

“…In all likelihood, the initial attack of the nucleophile occurs at C (3) along with attack at α-carbon atom C (1) . However, we cannot evaluate the preference for nucleophilic attack at C (1) or C (3) of the azine ring using the ratio of integral intensities of the protons in the abovementioned spectrum of imines C1 and C2 since intermediates A1 and B3 and imine C1 in the case of a large excess of alkylamine should undergo transamination. Such ring transformation is undoubtedly general in nature since it has been demonstrated for the pyrrolo [1,2-a]pyrazine and isoquinoline systems and is a new method for the preparation of tetrahydroindolizinones and tetralones, including spirocyclic products 3f,e, and 6c, containing an alkylamino group.…”