1,1-Disubstituted-2,3,4,9-Tetrahydro-1H-pyrido[3,4-b]indolecarboxylic Acid Esters and Ketones. The Base Catalyzed Transformation of 1-(2′,3′,4′,9′-Tetrahydrospirocyclohexane-1,1′-[1H]pyrido[3,4-b]-indol]-2-yl)alkanones into 2-(4,9-Dih