The four isomers of 9-butylphosphabicyclo [3.3. 1] nonane, s-PhobPBu, where Bu= n-butyl, sec-butyl, isobutyl, tert-butyl, have been prepared. Seven isomers of 9-butylphosphabicyclo [4.2. 1] nonane (a 5-PhobPBu, where Bu= n-butyl, sec-butyl, isobutyl, tert-butyl; a 7-