1,2,4,5-Tetrahydro-4-methyl-7,8-methylenedioxy-5-oxo-3-benzothiepin-2-carboxylic acid → (2S,4R)-(+)-1,2,4,5-tetrahydro-4-methyl-7,8-methylenedioxy-5-oxo-3-benzothiepin-2-carboxylic acid

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Reaction Steps

In 340 mL of methanol was suspended 20.00 g of a racemic mixture, 1,2,4,5-tetrahydro-4-methyl-7,8-methylenedioxy-5-oxo-3-benzothiepin-2-carboxylic acid (content 100%; trans compound 87.1%, cis compound 12.9%). To the suspension was added 11.01 g (1 equivalent) of (1S,2R)-norephedrine at room temperature (25° C.), followed by stirring for 1 hour. The resulting crystals were collected by filtration, washed with 80 mL of cold methanol, and dried over one night at room temperature under reduced pressure to afford 10.39 g of substantially pure (2S,4R)-1,2,4,5-tetrahydro-4-methyl-7,8-methylenedioxy-5-oxo-3-benzothiepin-2-carboxylic acid.(1S,2R)-norephedrine salt as colorless crystals [HPLC area percentage: (2R,4R):(2S,4S):(2S,4R):(2R,4S)=0%:0.7%:94.2%:4.0%].

Provenance & Evidence