Hexatriene-l,6-distannanes

At that time, we strived for the first total synthesis of a polyunsaturated natural product named xerulinic acid (22 Scheme 4). We envisaged using the hexatriene-l,6-distannane trans,trans,trans-lS (Fig. 5) as a Cg linchpin for joining the Z-configured y-(hromomethylidene)butenolide 20 and the polyunsaturated bromoalkyne 23 by sequential Stille couplings. 

FIG. 5 The first hexatriene-l,6-distannanes that we prepared stereoselectively were trans,cis. 

The first application of our hexatriene-l,6-distannane trans,trans,trans-lH (Fig. 5) in natural product synthesis was in our total synthesis of the polyunsaturated y-alkyUdenebutenolide dUiydroxerulin. ... 

Moreover, Paterson et al. employed our hexatriene-l,6-distannane tram,cis,trans- % in a natural product synthesis (Scheme 5). Its first C-Sn bond was engaged in 59% yield in a Stille coupling with the cis-iodoalkene 24. The second C-Sn bond Stille coupled with another cis-iodoaUcene 25 in 65% yield. 

SCHEME 4 The first total synthesis of the fungal dye xerulinic acid (22) was highly convergent. Its Ci8 backbone stemmed from the symmetric hexatriene-l,6-distannane trans,trans,trans-18/ a Negishi coupling with the bromobutenolide 20, and an ensuing Stille coupling with the... 

SCHEME 5 Sequential Stille couplings of the symmetric hexatriene-l,6-distannane trans,cis, by the Paterson group in the very last phase of their total syntheses of spirangiene A and its methyl ester. 

SCHEME 6 Sequential Stille couplings of our unsymmetric hexatriene-l,6-distannane rrans,rrans, -19. " The reactivity order of the C-Sn bonds is such that the sterically least hindered C-Sn bond couples first. This was exploited in our laboratory for realizing the first total synthesis of the carotenoid natural product pyrrhoxanthin. ... 

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