反应详情

Following the general procedure for the methylenation of lactols by Wittig-olefination (Description 4, Method A), 100 g (280 mmol) of methyltriphenylphosphonium bromide was reacted overnight at room temperature with 270 mL (270 mmol) of a one molar (1.0 μl) solution of potassium tert-butoxide (KOtBu) in 350 mL of anhydrous tetrahydrofuran (THF). The phosphorane was subsequently reacted in situ at ca. 0° C. (icebath) with 29.7 g (134 mmol) of (2R/S)(3R/S)-4,4-dimethyl-3-phenylmethoxy)oxolan-2-ol (2b) dissolved in 150 mL of anhydrous tetrahydrofuran (THF). After work-up and isolation, followed by repeated titration of residual triphenylphosphine oxide (Ph3PO) with methyl tert-butyl ether (MTBE) and hexane (Hxn) mixtures, i.e. MTBE/Hxn˜1:2 (v/v) at ca. −20° C. (freezer), the crude product was obtained. Purification by silica gel column chromatography using ethyl acetate (EtOAc) and hexane (Hxn) mixtures as eluent (EtOAc/Hxn=1:4→EtOAc/Hxn=1:3→EtOAc/Hxn=1:2) provided 18.0 g (61% yield) of the title compound (2) as a colorless liquid. Rf=0.63 (EtOAc/Hxn=1:3). MS (ESI) m/z: 221.1 (M+H)+, 243.1 (M+Na)+. The analytical data was consistent with the proposed structure, to the corresponding material (1) obtained starting from enantiopure D-pantolactone, and with the data reported in the literature (Mandel et al., Org. Lett. 2004, 6(26), 4801-4803; and Ito et al., Synthesis 1993, 137-140).

1. customat ca. −20° C.
2. customthe crude product was obtained
3. customPurification by silica gel column chromatography