[OH:1][C:2]1[C:3]([CH3:18])=[C:4]([CH3:17])[C:5]2[O:10][C@@:9]([CH3:14])([C:11]([OH:13])=[O:12])[CH2:8][CH2:7][C:6]=2[C:15]=1[CH3:16].[CH2:19](O)C.O.C1(C)C=CC(S(O)(=O)=O)=CC=1.CCOCC>CO.O>[CH3:19][O:12][C:11]([C@@:9]1([CH3:14])[CH2:8][CH2:7][C:6]2[C:15]([CH3:16])=[C:2]([OH:1])[C:3]([CH3:18])=[C:4]([CH3:17])[C:5]=2[O:10]1)=[O:13]A solution of 2 g(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 0.1 g 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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