The Mannich Reaction. 1-Alkyl-3,3-diphenyl-4-piperidinones, 1,6'-Dialkyl-3',4',5',6',7',8'-hexahydro-5,5,8',8'-tetraphenylspiropyranopyridin>-4-ones and Their Derivatives

Article abstract of DOI:10.1021/jo00211a023

Condensation of 1,1-diphenyl-2-propanone with methyl- and ethylamine hydrochloride and a large excess of paraformaldehyde in refluxing methanol gave 1-alkyl-3,3-diphenyl-4-piperidinones (1) as the main isolable products.When the reaction was carried out at 120 deg C, there resulted dimeric compounds 1,6'-dialkyl-3',4',5',6',7',8'-hexahydro-5,5,8',8'-tetraphenylspiropyrano<3,2-c>pyridin>-4-ones (4) as the major products.Reduction of the dimer 4a (alkyl = methyl) gave 3',4',5',6',7',8'-hexahydro-1,6'-dimethyl-5,5,8',8'-tetraphenylspiropyrano<3,2-c>pyridin>-4-ol (10) which, on treatment with hot hydrobromic acid, was transformed into the tetracyclic ketal decahydro-2,8-dimethyl-4,4,6,6-tetraphenyl-4a,9a-epoxy-2H,7H-oxepino<3,2,c:6,7,c'>dipyridine (11).