Studies on indenopyridine derivatives and related compounds. II^†. Stereochemistry of 1-substituted 9-phenyl-1,3,4,4a,9,9a-hexahydro-4-hydroxy-2H-indeno[2,1-b] pyridines and their acetates

Chemical and catalytical reduction of 1-methyl- or 1-benzyl-phenyl-1,3,4,9-tetrahydro-2H-indeno[2,1-b ]pyridin-4-ones (VIIa,b) afforded 1-methyl- or 1-benzyl-9-phenyl-1,3,4,4a,9,9a- hexahydro-4-hydroxy-2H-indeno[2,1-b ]pyridines (IXa,b), which gave the corresponding acetates (Xa,b) by treatment with acetic anhydride and pyridine. Based upon a detailed study of 100 MHz nmr spectra of these compounds, it was concluded that the hydroxy group of IXa,b has an axial configuration taking B/C cis stable form which has the large aromatic group equatorial with respect to the piperidine ring, whereas the acetoxy group of Xa,b is equatorial taking an unfavorable B/C cis unstable form which has the large aromatic group axial with respect to the piperidine ring.