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′-tetrahydrospiro[cyclohexane-1,1′-[1H]pyrido[3,4-b]indol]-2-yl)alkanones into 2-(4,9-dihydro-3H-pyrido[3,4-b]indol-1-yl)-1 -alkylcyclohexanols

Condensation of 1H-indole-3-ethanamines 1 with cyclic β-keto esters 2 under azeotropic conditions followed by acid-catalyzed ring closure of the resulting enamines 3 gave 2′,3′,4′,9′-tetrahydrospiropiperidine-3,1′,-1H]pyrido3,4-b]indole] -4-carboxylic acid alkyl esters 4 . Condensation of 1 with 2-acylcycloalkanones 8 gave two types of enamines, 10 and 11 , respectively. Enamines 10 on treatment with acid gave 1-(2′,3′,4′,9′-tetrahydro-3H-pyrido3,4-b]indol-1-yl)-1-alkylcyclohexanols 17 . Compounds 17 were further dehydrated to give cycloalkane derivatives 19.