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The Grignard compound was prepared under an argon atmosphere from 4.00 g of 2-bromo-6,7,8,9-tetrahydro-9,9--dimethyl-5H-benzocycloheptene, as described in EP-A2-0315071, and 456 mg of Mg shavings in 20 ml of absolute tetrahydrofuran. After carrying out the metallation a vigorous CO2 stream was introduced at -10° C. The mixture was hydrolyzed with dil. HCl, extracted with ether and washed with a small amount of water. The acid was then purified by extraction in lN NaOH, acidification to pH 1 (HCl) and re-extraction in ether. After washing with water, drying over Na2SO4 and evaporating there were obtained 2.64 g of 6,7,8,9--tetrahydro-9,9-dimethyl-5H-benzocycloheptene-2-carboxylic acid as colorless crystals of melting point 155° C.-156° C.

1. additionwas introduced at -10° C
2. extractionextracted with ether
3. washwashed with a small amount of water
4. customThe acid was then purified by extraction in lN NaOH
5. extractionacidification to pH 1 (HCl) and re-extraction in ether
6. washAfter washing with water
7. dry with materialdrying over Na2SO4
8. customevaporating there