KEYWORDSQuinuclidin-3-one (1) was used as a versatile intermediate for the synthesis of fused and spiro quinuclidine and its C-nucleosides. The reaction of 1 with formalin and secondary amines namely; morpholine, piperidine, and piperazine afforded the corresponding Mannich bases 2-4 in acid medium. Quinuclidino[3,2-b]pyran 5 has been synthesized via a selective cyclocondensation reaction between Mannich base of quinuclidinone hydrochloride 2 and malononitrile. The transformation of 1 with formalin and methylamine in molar ratio (1:20:2) afforded the spiro compound 7. Ring expansion of 2 under Schmidt reaction conditions gave the 1,3-diazabicyclo[3.2.2]nonanone derivative 6. Eventually, the synthesis of C-nucleosides 10, 12-14 were achieved by using aldohexoses and aldopentose catalyzed by zinc chloride, while, the bis-quinuclidine derivative 15 was obtained by using sodium carbonate. Newly synthesized compounds were characterized by IR, 1 H NMR, and mass spectral data.