Abstract
Exploitation of the synthetic route to optically active (R) (-)-4a-methyl-4, 4a, 9, 10-tetrahydro-2 (3H)-phenanthrone ((R) (-)-6a) and its 7-methoxy derivative ((R) (-)-6b) from optically active (R)-2-cyclohexenones ((R) (+)-1) or (S) (+)-δ-ketoaldehydes ((S) (+)-2) were attempted. (R) (+)-1 and (S) (+)-2 could be obtained by the asymmetric synthesis via the enamines prepared from L-proline-derived pyrrolidines ((S)-5) and dl-2-arylpropionaldehydes (dl-4). Base-catalysed cyclization of (S) (+)-2, followed by ketalization and Jones oxidation, gave (S) (-)-cyclohexanone ((S) (-)-7). The same compounds could be also prepared from (R) (+)-1 by successive epoxidation, ketalization, reduction, and Jones oxidation. Addition of N, N-dimethyl lithioacetamide 1, 4-diazabicyclo [2, 2, 2] octane complex to (S) (-)-7, followed by reduction with Vitride and cyclization with polyphosphoric acid, afforded (R) (-)-6a, 85% optically pure, and (R) (-)-6b, [α]20D-223° (ethanol). Detailed studies on reaction products and conditions, and preliminary experiments with racemic compounds were also carried out.
