Ethanol → (R)-(+)-methyl 3,4-dihydro-6-hydroxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-carboxylate

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Reaction Steps

A solution of 2g(8 mmoles) of optically pure (R)-(+)-3,4-dihydro-6-hydroxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-carboxylic acid; [α]D25 + 65.84° (c 1.18, C2H5OH) and 0.1g of p-toluenesulfonic acid monohydrate in 40 ml of methanol was stirred and refluxed for 3.75 hr. After cooling, the solution was diluted with water and worked-up with ether in the usual manner (the ether extracts were additionally washed with saturated aqueous sodium bicarbonate solution) giving 2g (94.7%) of (R)-(+)-3,4-dihydro-6-hydroxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-carboxylic acid methyl ester as a colorless solid, mp 132°-134.5°; [α]D25 + 61.4° (c 4.91, CH3OH). The analytical specimen was obtained by recrystallization of a sample from aqueous methanol as a colorless solid, mp 133.5°-135°; [α]D25 + 61.85° (c 5.07, CH3OH).

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