Hydrochloric Acid → (S)-7-methoxy-1,2,3,4-tetrahydronaphthalene-2-carboxylic acid

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Reaction Steps

(R)-(+)-α-methylbenzylamine (25.8 ml, 0.2 mol) is added to a solution of 7-methoxy-1,2,3,4-tetrahydronaphthalen-2-carboxylic acid racemate (41 g, 0.2 mol) in acetone (800 ml) and after 2 hours at room temperature the obtained salt is recovered by filtration (45.2 g) and crystallized twelve times from acetone until a product with constant [α] of -20.5° (c=1.4%, CHCl3) is obtained. This product is then taken up in water (30 ml) and the obtained solution is made acidic by the addition of concentrated HCl and extracted with ethyl ether. The organic phase is dried and evaporated to dryness and the obtained residue is crystallised from benzene (20 ml) affording 0.9 g of 7-methoxy-1,2,3,4-tetrahydronaphthalen-2(S)-carboxylic acid; m.p. 133°-135° C.; [α]=-45.1° (c=1.4%, CHCl3). To determine its absolute configuration, the thus obtained product is converted into the corresponding 2-amino-7-methoxy-1,2,3,4 -tetrahydronaphthalene by the Curtius reaction.

Provenance & Evidence