Compound 16 has an ent-1b-hydroxy group and a C-3 carbonyl group, and its puckering 
parameters for the A ring are given by Q = q2 = 0.728 D, q3 = -0.004 D, and 2 = 90.3º. Therefore 
A ring is as twist boat conformation (f2 = 89.0º) with C-3 and C-10 apexes below the mean 
plane. Compound 17 also has a carbonyl group at C-3, but the C-1 hydroxyl group is in an ent-a 
arrangement. In this case, the A ring conformation is similar to a chair (Q = 0.475 D, q3 = -0.416 
D, and 2 = 140.5º) with C-3 apex above the mean plane. However, there is a significant 
distortion from the chair (q2 = 0.229) towards a combination of an inverted boat and a twist boat 
(f2 = 140.5º). For products 16 and 17, the theoretical and experimental coupling constants are in 
concordance with the different arrangements of the hydroxyl groups on C-1.