3-Bromooxan-2-one → 4-(6,7-dihydro-5H-pyrano[2,3-d][1,3]thiazol-2-yl)-2-propylphenol

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Reaction Steps

A stirred mixture of α-bromo-δ-valerolactone (77% pure; 300 g, 1.3 mol), 4-hydroxy-3-propylbenzenecarbothioamide (229.09 g; 1.2 mol) (Example 504), and absolute ethanol (2.5 L) was gradually heated under nitrogen. A significant gas evolution occurred. When the latter had slowed, the mixture was brought to reflux. After 16 h at reflux, the mixture was cooled to rt, and then concentrated in vacuo. The residue was taken-up in 50% dichloromethane/hexanes, filtered, and the solid triturated and washed with more of the solvent mixture (700 mL total). After washing with hexanes and drying in vacuo, 207.1 g (58%) of the title compound were obtained as a yellow solid. The filtrate was concentrated in vacuo, and the residue chromatographed on silica gel to afford a thick oil containing impure product in which crystals formed. Filtration, trituration, and washing of the solid with ethanol afforded 27.6 g (234.7 g total; 66.1% yield) of opaque, pastel orange crystals, mp 152-154° C.; 1H NMR (DMSO-d6): δ 9.86 (broad exchangeable s, 1H), 7.5 (d, 1H), 7.4 (dd, 1H), 6.8 (d, 1H), 4.2 (t, 2H), 2.7 (t, 2H), 2.5 (t, 2H), 2.0 (m, 2H), 1.5 (m, 2H), 0.9 (t, 3H); LCMS: RT=3.0 min, (M+H)+ 276.

Provenance & Evidence