PROCESS FOR THE PREPARATION OF RACEMIC AND OPTICALLY ACTIVE 1,2,3,4-TETRAHYDROISOQUINOLINE-3-CARBOXYLIC ACID AND ITS PRECURSORS

• Main Authors: KAMMERMEIER, BERNHARD, LERCH, ULRICH
• Format: Patent
• Language: English; French
• Published: 10.09.2002
• Edition: 5
• Subjects: CHEMISTRY; HETEROCYCLIC COMPOUNDS; METALLURGY; ORGANIC CHEMISTRY

A process for the preparation of racemic and optically active 1,2,3,4- tetrahydroisoquinoline-3-carboxylic acid is described, in which dihalo-o- xylylenes are cyclized to dicarboxylic acid esters in basic medium using dialkyl N- acylamidomalonates of the formula (CO2R1)2CHNHCOR2, in which R1 is (C1-C4)- alkyl and R2 is H, (C1-C4)-alkyl or (C6-C12)-aryl, decarboxylated by basic hydrolysis and subsequent acid work-up and then reacted in acid medium to give (D,L)-1,2,3, 4- tetrahydroisoquinoline-3-carboxylic acid, or dihalo-o-xylylenes are cyclized in basic medium to give the dicarboxylic acid esters and these are reacted directly without isolation in a one-pot process to give (D,L)-1,2,3,4-tetrahydroisoquinoline- 3- carboxylic acid, if desired the racemic 1,2,3,4-tetrahydroisoquinoline-3- carboxylic acid is reacted with (-)menthol and p-toluenesulfonic acid to give (-)menthy l (D)- or (L)-1,2,3,4-tetrahydroisoquinoline-3-carboxylate, then the diastereomers are separated by column chromatography and subjected to basic hydrolysis to give (D)- or (L)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid, or (D,L)-1,2,3 ,4- tetrahydroisoquinoline-3-carboxylic acid is esterified by means of benzyl alcohol and p-toluenesulfonic acid, reacted with D(-)mandelic acid to give benzyl (D)- 1,2,3,4- tetrahydroisoquinoline-3-carboxylate (D)-mandelate and benzyl (L)-1,2,3,4- tetrahydroisoquinoline-3-carboxylate (D)-mandelate or with L(+)mandelic acid to give benzyl (D)-1,2,3,4-tetrahydroisoquinoline-3-carboxylate (L)-mandelate a nd benzyl (L)-1,2,3,4-tetrahydroisoquinoline-3-carboxylate (L)-mandelate and th en the compounds obtained are separated into the optical antipodes by fractional crystallization in an inert solvent and the enantiomers (D)- or (L)-1,2,3,4- tetrahydroisoquinoline-3-carboxylic acid are liberated by basic hydrolysis, the chiral auxiliary reagent being recovered.