Some Chlorine Derivatives of Norbornane (Bicyclo[2.2.1]heptane)

Abstract

The endo-cis and trans-5,6-dichloronorbornenes were prepared by the respective additions of cis- and trans-dichlorocthylene to cyclopentadiene. The sterochemical assigments were confirmed by dipole moment studies. The cis-dichloride was inert to hydrolysis while the trans isomer was hydrolyzed to 3,5-dihydroxynortricyclene. Hydrogenation of the dichloride isomers gave the endo-cis- and trans-2,3-dichloronorbornanes. Contrary to expectations based on preferential trans-elimination of hydrogen halide, the saturated cis-dichloride appeared to dehydrohalogenate somewhat less readily than the trans isomer, although the reaction was slow in both cases. Both isomers gave the same dehydrohalogenation product, 2-chloronorbornene, the structure of which was confirmed by oxidation to cis-cyclopentane-1,3-dicarboxylica cid and hydrolysis to norcamphor. Chlorination of norbornene at - 75º gave nortricyclyl chloride and syn-7-exo-2-dichloronorbornane. The structure of the latter was assigned (in preference to exo-cis-2,3-dichloronorbornane)because of the compound's relative inertness to dehydrohalogenating reagents. endo-cis-2,3-Dichloronorbornane was not readily hydrolyzed, but trans-2,3-dichloronorbornane and syn-7-exo-2-dichloronorbornane hydrolyzed to anti- and syn-7-exo-Z-norborneol, respectively. The syn-isomer also was obtained by addition of hypochlorous acid to norbornene. The structures of the chloro alcohols were inferred from their modes of formation and oxidation to chlorine-containing dicarboxylic acids which were presumed to be, respectively, trans- and cis-2-chloro-cis-cyclopentane-1,3-dicarboxylic acids. These acids were different from trans-and cis-4-chloro-cis-cyclopentane-1,3-dicarboxylic acids obtained by oxidation of exo- and endo-dehydronorbornyl chlorides, respectively. The assignments of the syn and anti configurations to the ketones were confirmed by dipole moment measurements. The syn and anti-chlorohydrins were converted by pyrolysis of their carboxylic acid esters in low yield to syn- and anti-7-chlorotiorbornenes. Each of the latter substances on hydrogenation gave the same compound, 7-chloronorbornane.

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