Norbomanone synthesis

Vandewalle et al. have also used oxidative ring opening of one side of a norbomanone to prepare a number of iridoids, culminating in a synthesis and correction of the structure of specionin. At first they described the synthesis of teucrium lactone (425) and a loganin precursor (472) from the Diels-Alder adduct 473 of cyclopentadiene and methyl ( )-crotonate (Scheme 44). The same paper describes the preparation of the all-enafo-isomer 474 of ketone 475, from... 

The transformation of a series of norbomanone derivatives (Fig. 16.5-34) was studied by Roberts and coworkers who determined that both the MOl complement of NADH dependent BVMOs from Pseudomonas putida ATCC 17453 and the NADPH dependent fraction M02 were successful in the resolution of hydroxy, acetoxy and benzyloxy norbomanones11231. Interestingly 25DKCMO and 36DKCMO when separate, displayed notably different reactivity toward the hydroxy and acetoxy derivative, again emphasizing their complementary nature as potential individual biocatalysts. The benzyloxy lactone is an intermediate in the synthesis of the insect antifeedant azadirachtin. 

Enzymes are outstandingly active and highly selective catalysts [332], however, their use in synthesis is often limited by the lack of appropriate cofactors. Reduced nicotinamide cofactors, NADH and NAD(P)H play an important role in many enzyme-catalyzed reactions of practical interest. For example, cyclohexanone and 2-norbomanone was reduced by horse liver alcohol dehydrogenase to afford cyclohexanol, exo-norbomanol (72 %, 38 % e.e.) and enrfo-norbomanol (28 %, 100 % e.e.) on the expense of NADH [333] (Scheme 3.52). 

Vandewalle et al. ( ref 15 ) have demonstrated an dtemative route which starts from the norbomanone 3, whose synthesis has been described in scheme 1, and from its epimer 110 which has been prepared in a similar manner as reported in scheme 23. 

We see this happen three times in Erman and Kretschmar s 0-santalol synthesis. The first is the methylation of the norbomanone enolate... 

R. R. Schmidt, Ch. Beitzke, and A. K. Forrest, Synthesis of 5-deoxy-DL-ribo-hexa-furanuronate derivatives via 7-oxa-norbomanones, J. Chem. Soc., Chem. Commun., 909 (1982). 

---