Organo-phosphorus compoundsOrgano-phosphorus compounds S 0080 Regioselective Heterocyclization of Phosphoryl-α-chloroacetaldehydes with 2,3-Diaminopyridine. -(ASADOV, K. A.; BURANGULOVA, R. N.; GUSEINOV, F. I.; GIL'MANOV, R. Z.; PHALJACHOV, I. P.; Chem. Heterocycl. Compd. (N. Y.) 39 (2003) 3, 392-393; Kazan State Technol. Univ., Kazan' 420015, Russia; Eng.) -Staver 45-149

Keywords: 1-amino-4-methylpyridine, α-chlorooxirane, α-hydroxy acid, imidazo[1,2-a]pyridine, heterocyclic carbaldehyde.The presence in α-chloroepoxides of type 1 of a potential aldehyde group -the acetal fragmentpredetermines the high reactivity of these electrophilic reagents. We have shown that acetal-containing α-chlorooxiranes [1] are suitable starting reagents for the synthesis of five-and six-membered heterocyclic carbaldehydes and their derivatives [2][3][4].To widen the synthetic potential of these substrates and to obtain polyheterocycles we have studied the condensation of α-chlorooxirane 1 with the aminopyridine 2. The reaction occurred in boiling isopropanol over 3 h to give the heterocycle 9.The very unexpected formation of compound 9, the structure of which was proved by 1 H NMR and X-ray crystallography, may occur as shown in the scheme (r.p. 1900).Heterocyclization occurs in the first step to form the acetal 3 which is easily converted into the carbaldehyde 4 in the acid medium. An unusual condensation of the polyaminal 5, formed by reaction of the aldehyde 4 with a second molecule of aminopyridine 2, with the product of the rearrangement of α-chlorooxirane -the α-chloro ketone 6 -then occurs, accompanied by the formation of a new carbon-carbon bond. In previous investigations we have shown that heterosubstituted α-chloroacetals in acid media underwent redox processes which led to the synthesis of α-hydroxy acids [5]. Evidently the intermediate α-keto acetal 7 was converted similarly to the hydroxy acid 8. The latter was transformed into the final product 9 by intramolecular condensation. __________________________________________________________________________________________

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