Reaction Steps
A 0.1 M solution of N-sulfinyl amino alcohol 32 (0.575 g, 1.53 mmol) in toluene (15.3 mL) with paraformaldehyde (0.917 g, 30.5 mmol) was heated in a sealed vessel at 70° C. with stirring for 50 h. After cooling to rt, the mixture was filtered through Celite, washing the filter cake thoroughly with toluene. The solution was concentrated and purified via HPFC (88:12 to 30:70 CH2Cl2:EtOAc) to afford 0.518 g of tetrahydrooxazine 33 (87%) as a foamy yellow solid. [α]25D=+108.4 (c=1.0, CHCl3). IR (film): 1011, 1076, 1087, 1163, 1195, 1474, 1729, 2957, 2979 cm−1. 1H NMR (500 MHz, CDCl3): δ 1.01 (d, 3H, J=6.8 Hz), 1.02 (d, 3H, J=6.8 Hz), 1.17 (s, 9H), 1.35 (t, 3H, J=7.1 Hz), 2.08-2.16 (m, 1H), 2.28-2.40 (m, 1H), 2.31 (d, 1H, J=14.3 Hz), 3.02 (dd, 1H, J=4.7, 10.1 Hz), 4.37 (q, 2H, J=7.1 Hz), 4.72 (d, 1H, J=11.6 Hz), 5.14 (d, 1H, J=11.6 Hz), 5.20 (dd, 1H, J=2.5, 11.5 Hz), 8.11 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 14.3, 20.5, 20.7, 22.8, 27.5, 32.6, 59.2, 61.3, 62.7, 71.4, 71.6, 127.8, 146.5, 161.3, 173.3. HRMS (FAB) calcd. for C17H29N2O4S2 (M+H): 389.1569. Found 389.1566.
