Insect antifeedants intermediate

The potent biological activity (insect antifeedant, antitumour, antifungal) of warburganal (35) has stimulated considerable synthetic interest in this compound. Three total syntheses of this compound have been recorded in the period under review. " The synthesis by Tanis and Nakanishi has additional flexibility since the key intermediate diol (34) can be used in the syntheses of cinnamolide (36), drimenin (37), and polygodial (38). Both norisoambreinolide (39 R = O) and isoambrox (39 R = H2) have been synthesized from (40), the product of the stannic chloride-catalysed cyclization of farnesyl phenyl sulphone. Yahazunol (41), a bicyclofarnesyl hydroquinone, has been identified in the brown seaweed... 

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. 

A nice example of the foregoing stratagem is seen in equation (17) enone (6) undergoes copper(I)-catalyzed reaction with vinylmagnesium bromide from its less-hindered face to give an enolate that reacts with formaldehyde from the opposite face to provide decalone (7), an intermediate in the synthesis of insect antifeedants. Yoshida and coworkers have used this method for the stereospecific generation of tetrasubstituted thioamide enolates, which undergo remarkably stereoselective aldol reactions (equation 18). ° The stereochemistry of this process is discussed in Section 1.6.3.6. 

A key intermediate 829 in the construction of the decalin part of azadirachtin 831, an antifeedant insect growth regulatory and reproductive effective substance from the Neem tree Azadirachta indica, has been prepared by carbonylation of the alcohol with methyl chloroformate, affording carbonate 829 in 70% yield [613]. 

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