Methyl iodide → Lithium cyclohexylisopropylamide

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Lithium isopropylcyclohexylamide is prepared by adding 10 mls. of 1.0 molar n-butyl lithium to a solution of 1.41 g. of isopropylcyclohexylamine in 100 ml. of dry tetrahydrofuran. To this solution, cooled to -80° C, there is added a solution of 2.94 g. of ethyl (5-oxo-5H-dibenzo[a,d]cyclohepten-2-yl)acetate (as prepared in Preparation 3 above) in 10 ml. of tetrahydrofuran. The mixture is left for 5 minutes, then 1.42 g. of methyl iodide is added. The reaction mixture is allowed to attain room temperature, then water and ether are added. The ethereal layer is washed with dilute hydrochloric acid and water, dried and evaporated to yield ethyl 2-(5-oxo-5H-dibenzo[a,d]cyclohepten-2-yl)propionate. This ethyl ester is refluxed for 12 hrs. in 5% aqueous potassium hydroxide, followed by acidification with dilute hydrochloric acid and ether extraction to afford d1 2-(5-oxo-5H-dibenzo[a,d]cyclohepten-2yl)propionic acid (m.p. 138°-139° C, 113°-115° C). This mixture of optical isomers can exist in two crystalline forms. The form having the higher melting point is obtained by using chloroform/hexane as the recrystallizing solvent, while the form having the lower melting point is obtained by using acetone/hexane as the recrystallizing solvent.

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