Homoallylic assistance on the reduction of endo-2,5-dibromotricyclone-[6.2.1.0(2,7)]undeca-4,9-diene-3,6-dione through NaBH4/CeCl3 center dot 6H(2)O:Synthesis and characterization of 5-bromo-12-oxa-pentacyclo[6.2.1.1(6,9).0(2,7).0(2,10)]dodeca-4-en-3-endo-o]

The behavior of the tricyclic compounds 3, 4, and 5 towards reductive syste ms is described. The [4+2] cycloadduct 3, when reduced by NaBN4/CeCl3.6H(2) O led to the isolation of the nortricyclenic compound 8 where;ls the cycloa dduct 4 provided the analog 9. The reduction of norbornenequinone 5 gave th e aromatized compound 10 when performed by sodium dithionite or by NaBH4/Ce Cl3.6H(2)O. The structure and stereochemistry of the hydroxyl group in the compound 8 was determined by NMR and confirmed by X-ray analysis. Also, som e mechanistic considerations concerning the formation of the compounds 8 an d 9 are presented.