Norbornadiene epoxidation

Asymmetric hydrogenolysis of epoxides has received relatively little attention despite the utility such processes might hold for the preparation of chiral secondary alcohol products. Chan et al. showed that epoxysuccinate disodium salt was reduced by use of a rhodium norbornadiene catalyst in methanol/water at room temperature to give the corresponding secondary alcohol in 62% ee (Scheme 7.31) [58]. Reduction with D2 afforded a labeled product consistent with direct epoxide C-O bond cleavage and no isomerization to the ketone or enol before reduction. 

If the dienophile (norbornadiene) is chlorinated instead, either via the reaction of hex with vinyl chloride followed by dehydrochlorination, or directly with acetylene, to give 1,2,3i4, 7 7-hexachlorobicyclo( 2.2.1 J] hepta-2,5-diene (hexachloronorborn-adiene B, Figure 3)i this compound reacts with cyclopentadiene to give isodrin (C precursor of the epoxide, endrin) having the opposite (endo-,endo-) stereochemistry to aldrin (and dieldrin), respectively (12). Isodrin has not found commercial use but endrin has been widely used in tropical and sub-tropical agriculture - to control cotton pests, for example. 

Different facial selectivities also exist in the epoxidation of norbornadiene, to give the epoxide 4 and diepoxide 5, respectively, where appreciable differences in nonbonded steric interactions in the two diastereomeric transition states would not be expected. 

Yamabe, S., Kondou, C., Minato, T. A Theoretical Study of the Epoxidation of Olefins by Peracids. J. Org. Chem. 1996, 61, 616-620. Marchand, A. P., Ganguly, B., Shukla, R., Krishnudu, K., Kumar, V. S., Watson, W. H., Bodige, S. G. Experimental and theoretical investigations into the stereoselectivities of peracid promoted epoxidations of substituted norbornenes and norbornadienes. Tetrahedron 1999,55, 8313-8322. 

The origin of the three 5-membered rings in this synthesis is notable. Two of the rings were purchased in the form of starting materials (cyclopentadiene and norbornadiene). The final ring was constructed from a 1,6-difunctional intermediate, keto-epoxide 55. 

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