The 1,5-diaryl-3,3-disubstituted-1,5-pentanedione on reaction with ammonium acetate, phosphorus pentoxide and phosphorus pentasulfide gave respective 1,4-dihydropyridine, 4H-pyran and 4H-thiopyran. Novel spiro heterocycles have been obtained by the cyclocondensation of 4H-thiopyran with hydrazine, hydroxylamine, urea and thiourea.J. Heterocyclic Chem., 39, 649 (2002).As a result of our sustained efforts in the search for new and versatile multi-functional reactive intermediates, recently we have reported the preparation of 1,5-diaryl-3,3-disubstituted-1,5-pentanediones 1 and 2 by the reaction of phenacyl bromide with dimethyl malonate and ethylcyano acetate [1]. The presence of dicarbonyl functionality in 1 and 2 enabled us to incorporate N, O and S as heteroatoms in them [2]. This gave scope for us to design and develop hitherto unknown spiro heterocycles by exploiting the gem diester or cyano ester groups of 1,4-dihydropyridine (3 and 4), 4H-thiopyran (5 and 6) and 4H-pyran (7 and 8). In fact, during the last decade we were actively involved in the syntheses of several spiro-heterocycles [3]. In further development of this synthetic strategy, we have now considered the reactivity of the 2,6-diaryl-4,4-disubstituted-4H-thiopyran(5 and 6) with hydrazine, hydroxylamine, urea and thiourea.The synthetic method involves the reaction of 1,5-diaryl-3,3-dimethoxycarbonyl-1,5-pentanedione (1) or 1,5-diaryl-3-cyano-3-ethoxycarbonyl-1,5-pentanedione (2) with ammonium acetate in acetic acid, phosphorus pentasulfide in xylene and phosphorus pentoxide in dry benzene under reflux conditions to obtain 2,6-diaryl-4,4-dimethoxycarbonyl-1,4-dihydropyridine (3) or 2,6-diaryl-4-cyano-4-ethoxycarbonyl-1,4-dihydropyridine (4), 2,6-diaryl-4,4-dimethoxycarbonyl-4H-thiopyran (5) or 2,6-diaryl-4-cyano-4-ethoxycarbonyl-4H-thiopyran (6) and 2,6-diaryl-4,4-dimethoxycarbonyl-4H-pyran (7) or 2,6-diaryl-4-cyano-4-ethoxycarbonyl-4H-pyran (8) respectively (see Scheme 1 and Table 1) . Displacement of the oxygen atom in 7 or 8 on treatment with excess phosphorus pentasulfide in boiling xylene also gave 5 or 6. The absence of carbonyl absorption (ArCO) around 1690 in IR spectra of 3-8 indicated their formation. Further 3 or 4 showed a band around 3350-3450 for (NH). The 1 H NMR spectra of 3-8 showed a singlet in the region 5.22 -5.86, which accounts for C 3 -H and C 5 -H protons. However in case of 3 and 4 a singlet was observed around 9.02 -9.20 for NH which disappeares on deuteration. The 13 C NMR spectra of 3-8 exhibited resonance signals at 142.15 -152.28 (C 2 and C 6 ), 91.78 -120.54 (C 3 and C 5 ) and 41.24 -45.67 (C 4 ) which also support their structures (Table 3). The cyclocondensation of 5 with hydrazine, hydroxylamine, urea and thiourea in the presence of sodium methoxide resulted in the formation of 7,9-diaryl-8-thia-2,3-diaza-spiro [4,5]deca-6,9-diene-1,4-dione (9), 7,9-