4-Toluenesulfonyl chloride → (R)-(2,3-Dihydrobenzo[b][1,4]dioxin-2-yl)methyl 4-methylbenzenesulfonate

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Reaction Steps

Toluene-4-sulphonyl chloride (4.2 g) was added at -10° C. under nitrogen to a stirred solution of (S)-1,4-benzodioxan-2-ylmethanol (3.3 g) in pyridine (50 ml) The mixture was allowed to warm to ambient temperature and was stirred for a further 60 hours, then poured onto ice-water (200 ml). The product was extracted into ethyl acetate (3×200 ml) then the combined extracts were washed with dilute hydrochloric acid (100 ml), and water (100 ml), dried over magnesium sulphate, and the solvent removed in vacuo. The resulting orange oil (5.84 g), which solidified slowly on standing, was purified by crystallisation from an ether and petroleum ether (b.p. 40°-60° C.) mixture to yield two batches of a white crystalline solid (2.4 and 1.2 g). The 2.4 g batch was recrystallised 3 times from ethanol, the solid obtained becoming each time less rich in the desired (R)-isomer of the product and was therefore discarded. The mother liquors from these 3 recrystallisations now contained predominantly the desired (R)-isomer of the product so they were combined, the solvent removed in vacuo and the residue recrystallised from ethanol to yield white crystals of (R)-1,4-benzodioxan-2-ylmethyl toluene-4-sulphonate (1.2 g); m.p. 105°-107° C.

Provenance & Evidence