A new route to poorly available 5-alkoxyindolizines has been developed by reaction of oxazolo[3,2-a]pyridinium salts with sodium alkoxides; the structures of three indolizines and one parent salt have been confirmed by X-ray diffraction analysis.The indolizine ring is isomeric and isostructural to indole, and substituted indolizines are frequently prepared as bioisosters of biologically active indole derivatives. A well-known class of psychotropic indole compounds (e.g., psillocine, psylocibine and pindolole) belongs to the family of 5-hydroxy(alkoxy)indoles. An isostructural class of indolizines bearing 5-OR group (A in Scheme 1) may serve as the biomimetics of such indoles. This class can be designed by a mental rearrangement of the indole ring nitrogen into bridgehead positions.The entire class of 5-alkoxy(hydroxyl)indolizines is poorly investigated since there is lack of synthetic methodologies leading to this scaffold. Rare examples of preparation of the members of class A include their synthesis from pyrrole derivatives 1-3 and by means of photolytic C-5 oxidation of the indolizine ring. 4 Structure B with the desired motif was prepared via 1,3-dipolar cycloaddition. 5 The most common strategy to indolizine ring (the Chichibabin cyclization) failed for the case of 6-methoxy-2-picoline. 6 It is, however, possible to annelate the pyrrole ring to pyridine by condensation of the Guresci pyridone with α-bromoketones 7,8 leading to 5-indolizinones C, which are stable tautomers of desired 5-hydroxyindolizines D. We found 9 that pyridone-like derivatives C can be converted into 5-chloroindolizines E, which react with MeONa leading to 5-methoxy-6-cyanoindolizines F. However, simple 5-alkoxyindolizines A (without other substituents in the pyridine ring) remain unknown.We reported an efficient strategy [10][11][12] to build the indolizine ring by a somewhat unusual conversion of oxazolo[3,2-a]-pyridinium salts G (route a in Scheme 2). This reaction allowed us to prepare 5-dialkylaminoindolizines H. Recently, 13 this methodology has attracted attention in industrial chemistry as a source of a library of 5-substituted indolizines with potential bioactivity. However, only secondary amines are suitable for such a transformation, and with primary amines (route b) salts I were formed instead of indolizines. Therefore, it is unclear which other nucleophiles are suitable for this new strategy of indolizine synthesis from oxazolopyridines. Furthermore, the ring system of salts G may undergo alternative modes of ring opening depending on the group R and the nature of the nucleophile. Thus, salts G with R = H react with secondary amines with pyridine ring opening (route c 11 ), whereas with alkoxide the C(2)-O bond cleavage was observed (route d 14 ). In this paper, we studied the direction of the reaction of salts G (R = Me) with alkoxides to test the synthesis of 5-alkoxyindolizines A.

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The title compound, C12H9ClN2O2, was synthesized and characterized by 1H NMR and IR spectrocopy and X‐ray diffraction techniques. The chlorobenzoyl fragment in the structure is almost flat, whereas the carbonyl group is almost perpendicular to the pyrimidine ring plane.

An unusual example of the recyclization of the tricyclic 6,7,8,9 tetrahydrooxazo lo[3,2 a]quinolinium system into the 8,9 dihydro 7H pyrrolo[3,2,1 ij]quinoline system was discovered. The reaction is a topological modification of the known conversion of oxazo lo[3,2 a]pyridinium salts into indolizines. The structural feature of this transformation is a change of the annelation type in the tricycle from the angular one to peri fusion of three rings.