The Transannular Cyclization and Hydrogen Shift in the Chlorination of 1,5-Cyclooctadiene and cis-Cyclooctene with Antimony(V) Chloride

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Abstract
The slow addition of SbCl5 to a CCl4 solution of 1,5-cyclooctadiene or cis-cyclooctene gives an isomeric mixture of endo- and exo-2, anti-8-dichlorobicyclo[3.2.1]octanes (1 and 2) or an isomeric mixture of trans- and cis-1,4-dichlorocyclooctanes (12 and 13) respectively in a good yield. The former reaction involves the transannular cyclization, while the latter is accompanied by the transannular hydrogen shift. The addition of 1,5-cyclooctadiene to a CCl4 solution of SbCl5 (reverse addition) affords endo-2,6- and endo, exo-2,6-dichlorobicyclo[3.3.0]octanes (6 and 7) as additional products, besides 1 and 2. In the case of cis-cyclooctene, however, a reverse addition produces only chlorocyclooctane. It has been revealed that a mixture of 6 and 7 is readily isomerized to a mixture of 1 and 2 by the interaction with SbCl5. The 1,4-chlorination of cis-cyclooctene which gives 12 and 13 also occurs with VCl4, SeCl4, PhICl2, and PCl5, although the selectivity and the yield are low compared to the case of SbCl5.