Pulo’upone synthesis

Camphor sultam derivatives have proved to be effective chiral auxiliaries in many different types of asymmetric reactions. As shown in Scheme 5-44, chiral camphor sulfam can be applied in the synthesis of (—)-pulo upone precursor 151 using an intramolecular Diels-Alder reaction. A Wittig reaction of 148 with 147 connects the chiral auxiliary to the substrate, and subsequent intramolecular Diels-Alder reaction via transition state 150 affords product 151. Compound 151 already has the stereochemistry of (—)-pulo upone 153.72... 

Of these three highly diastereoselective methods for accomplishing asymmetric IMDA reactions, the a-hydroxy ketone protocol" [trienes (154) and (155)] is the least convenient owing to the greater difficulty of triene preparation, the moderate reactivity of the trienes, and the destructive removal of the auxiliary. Consequently, the auxiliary systems developed by Evans and Oppolzer are more likely to find application in natural products synthesis. Indeed, Oppolzer has recently applied the IV-acyl sultam methodology to the asymmetric total synthesis of (-)-pulo upone (Figure 43). °... 

Oppolzer, W., Dupuis, D., Poli, G., Raynham, T.M., and Bemardinelli, G. (1988) Enantioselective synthesis and absolute configuration of (—)-pulo upone by asymmetric intramolecular Diels—Alder reaction. Tetrahedron Lett., 29, 5885-5888. 

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