Pyrazolo[1,5-a]pyridines (3) and pyrano [4,3-d]pyrazolo [1,5-achieved from the reaction of 2 with polarised ketene dithioacetals (5) and arylidenemalononitrile, respectively. An a]pyridines (4) have been synthesized from the reaction of pyran-2-one (1) and 5-aryl-3-cyanomethyl-1H-pyrazole (2) analogous reaction of 1 with 2-cyanomethyl-1H-benzimidazole (8) has also afforded the fused heterocycles 9 and 10. through carbanion-induced ring transformation reactions. A regioselective synthesis of highly functionalized polysub-The cyano function in 9 has been exploited for acid-catalysed cyclization with thiosemicarbazide to obtain 11 in high yield. stituted pyrazolo[1,5-a]pyridines (6, 7) has also been Azolo[a]pyridines, being isosteric with purines, display Scheme 1 diverse pharmacological activities, such as antihypertensive [1] [2] , antithrombotic [1] , cardiotonic [1] , antineoplastic [3] and anti-HIV activity, [3] depending upon the type and position of the substituents present in the molecular skeleton.
Heteroarenes such as pyrazolo[1,5-a]pyridines have been prepared previously either by the reaction of N-aminopyridinium salts [4] and acid chloride, or by the reaction of Naminopyridinium ylides with dipolarophiles [5] [6] [7] . They have also been obtained in low yields by the thermal decarboxylation [8] of 2,6-diazatricyclo[5.2.1.0 2,6 ]deca-4,8-diene-3,10-diones. Alternatively, the oxidation of pyrazolinones in the presence of cyclopentadienone [8] also affords heteroarenes. Recently, a new synthesis of these compounds, by the reaction of 5-amino-4-cyano-3-cyanomethyl-1H-pyrazole with cinnamonitrile, has been reported [9] . However, under similar reaction conditions, an interaction between arylidenemalononitrile and 5-aryl-3-cyanomethyl-1H-pyrazole (2) failed to yield pyrazolo[1,5-a]pyridines. Instead 3-aryl-2-(5aryl-1H-pyrazol-3-yl)acrylonitrile was isolated as a result of a retro Michael reaction, while heating in DMF in the presence of K 2 CO 3 afforded polysubstituted pyrazolo[1,5-a]pyridine (7) with a yield of 21%.
Recently, pyrido[1,2-a]benzimidazoles have been prepared either by the ring transformation [10] reaction of pyrylium salts with 2-cyanomethyl-1H-benzimidazole (8), or by the cyclocondensation of 8 with 3-oxo esters [3] . These synthetic routes do not offer much scope for substituent variation and structural modification because of the limited choice of reagents used. Our synthetic strategy is based on the reaction of ambiphilic nucleophiles with the properly functionalized pyran-2-ones 1, which have three different sets of 1,3-electrophilic centres in their molecular skeleton: [ ] CDRI Communication No. 5523.