Reaction Steps
Following a general procedure,50 a mixture of 4-Ts (9.00 g, 23.3 mmol) and 1,1-dimethoxy-4-methyl-3-penten-2-one (11.1 g, 69.9 mmol, 3 equiv) was treated with DBU (10.5 mL, 69.9 mmol). The reaction mixture was stirred for 15 min under argon. A saturated solution of cold aqueous NH4Cl (50 mL, 0° C.) was added. The mixture was extracted with ethyl acetate (100 mL). The organic layer was washed with brine, dried (Na2SO4), concentrated and dried overnight under high vacuum. Addition of diethyl ether (50 mL) to the resulting solid, trituration, and filtration afforded a pale brown solid (11.0 g, 86%): mp 114-115° C.; 1H-NMR δ 1.22 (s, 3H), 1.27 (s, 3H), 1.85 (s, 3H), 2.42 (s, 3H), 2.64, 2.74 (AB, 2J=19.0 Hz, 2H), 3.15 (ABX, 2JAB=15.4 Hz, 3JBX=1.8 Hz, 1H), 3.32 (ABX, 2JAB=15.4 Hz, 3JAX=11.7 Hz, 1H), 3.41 (s, 3H), 3.43 (s, 3H), 4.37 (s, 1H), 5.19 (ABX, 3JAX=11.7 Hz, 3JBX=1.8 Hz, 1H), 7.28 (s, 1H), 7.31 (d, J=8.1 Hz, 2H), 7.59 (d, J=8.1 Hz, 2H); 13C NMR δ 0.7, 21.9, 23.8, 24.0, 25.9, 36.8, 44.2, 55.28, 55.29, 94.4, 104.9, 105.9, 122.6, 125.1, 125.9, 126.7, 130.5, 135.9, 145.6, 203.2; Anal. Calcd for C22H29BrN2O7S: C, 48.44; H, 5.36; N, 5.14. Found: C, 48.70; H, 5.30; N, 5.17.
