Procedure for (+)-79 to (+)-34
(+)-Cyclobutane ketoester 34. To a recrystallized (1:1 Hexanes-Ethyl Acetate) (+)-79 dissolved in toluene, toluenesulfonic acid (4.0 equivalents) was added, followed by methanol (20 equivalents). This reaction was kept at 105°C in a sealed tube for 12 hours, yielding 50% of (+)-34. Cyclobutane ketoester 34: white needles; m.p. 73-75 °C (ether); Rf = 0.44 (silica gel, 1:1 EtOAc: Hexanes); IR (film) νmax 2957, 1728, 1706, 1439, 1360, 1216 wavenumbers; Proton-NMR (400 MHz, CDCl3) δ 3.76 (s, 6 H), 3.52 (A2B2, J = 9.6, 2.4 Hz, 2 H), 3.41 (A2B2, J = 9.6, 2.4 Hz, 2 H), 2.21 (s, 6 H); 13C NMR (100 MHz, CDCl3) δ 204.8, 171.6, 52.5, 46.3, 38.9, 27.7 ppm.
Reference:
O'Malley, D.P.; Li, K.; Maue, M.; Zografos, A.L.; Baran, P.S. J. Am. Chem. Soc. 2007, 129 (15), 4762-4775.