“…Recrystallization from ethyl acetate/ether yielded 3.0 g (54%) of 12a: mp 165-167 °C; NMR (CDC13) 1.69 (s, 3 ), 2.17 (d, J = 0.9 Hz, 3 H), 3.64 (dd, J = 14.7, 7.5 Hz, 1 H), 4.52 (dd, J = 14. 6,5.7 Hz, 1 H), 4.84-4.92 (m, 2 ), 5.05 (dd, J = 17.9,12.1 Hz, 2 H), 5.55-5.67 (m, 1 ), 6.30 (s, 1 ), 7.07-7.12 (m, 2 ), 7.30-7.44 (m, 5 H), 7.56 (t, J = 7.4 Hz, 1 ), 7.71 (d, J = 7.6 Hz, 2 ), 7.81 (s, 1H). Homonuclear NOE irradiation of the C-3 methyl protons ( 2.17) resulted in a 17% enhancement in the Hc-2 signal at A pure sample of 12b was isolated from a reaction in which 12a and 12b were treated with BBr3.…”