The reaction of N-[6-methyl-2-oxo-4(2H)-pyranyl]-substituted carbodiimides 3, generated by the treatment of [6-methyl-2-oxo-4(2H)-pyranyl] iminotriphenylphosphorane (1) with isocyanates 2 in situ, with 1-(1-pyrrolidinyl) cyclopentene (4) in refluxing toluene or dioxane gave cyclopenta [d] pyrano [4,3-b] pyridine derivatives 5. A similar reaction of 3 with 1-(1-pyrrolidinyl) cyclohexene (6) afforded pyrano [4,3-b] isoquinoline derivatives 7 and 8. Compound 8 corresponds formally to the adduct of 7 and isocyanate 2.