Donor bicyclic ring system

The tricyclic ring system containing the fully functionalized CD ring of taxol was prepared from (S)-(+)-carvone by T.K.M. Shing et al. The bicyclic a-hydroxy ketone (4-hydroxy-5-one) was isomerized by an Intramolecular redox reaction in the presence of catalytic amounts of aluminum isopropoxide. This example was a special case where both reactants were in the same molecule the ketone was the oxidant for the Oppenauer oxidation, whereas the secondary alcohol was the hydride donor for the MVP reduction. The conversion to the thermodynamically more stable 5-hydroxy-4-one proceeded in good yield. 

In addition, the same group reported on a synthesis of heptafulvenes and related seven-membered ring systems (e.g., 363) from triafulvene 357 (Scheme 7.80) [91]. A series of donor-substituted 1,3-dienes, when reacted with tria-fulvenes by a Diels-Alder addition, yielded bicyclic methylene cyclopropanes, which were subsequently transformed to 1,6-diphenyl-substituted heptafulvenes or seven-membered ring derivatives. 

Donor-substituted 1-aminomethylcyclopropanes 108 110 and tosylhydrazones of 1-donor-substituted cyclopropyl ketones 111 can undergo ring enlargement to cyclobutanones through deamination. To this purpose, aminomethylcyclopropanes were diazotized with sodium nitrite 108-110 or isopentyl nitrite 109 in acidic medium and tosylhydrazones were decomposed in basic medium.111 The rearrangements proceed via diazonium ions and are especially useful for the construction of bicyclic systems. For examples of these rearrangements see 1,108 2,109 3,109 4,110 5,111 6 and 7.1 1... 

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