A convenient synthesis of spironorcamphors

The effects of the base, molar ratio of the reagent, solvent and reaction temperature on the cycloalkylation of norcamphor with 1,4-dibromobutane were explored, and optimum conditions for the preparation of spiro[bicyclo[2.2.1]heptane-2,1′-cyclopentan]-3-one have been established. 3-exo-(4-Bromobutyl)norcamphor was isolated and characterized as a reaction intermediate. A series of spironorcamphors with various ring sizes were obtained in good yields using a 1:1.5:2.5 ratio of norcamphor/α,ω-dibromoalkanes /NaNH2 in Et2O.