Dyotropic rearrangements in natural product total synthesis and biosynthesis

Some recent examples of dyotropic rearrangements involved in complex natural product total synthesis and biosynthesis are highlighted.

Synthesis of (+)-discodermolide by catalytic stereoselective borylation reactions

The marine natural product (+)-discodermolide was first isolated in 1990 and, to this day, remains a compelling synthesis target. Not only does the compound possess fascinating biological activity, but it also presents an opportunity to test current methods for chemical synthesis and provides an inspiration for new reaction development. A new synthesis of discodermolide employs a previously undisclosed stereoselective catalytic diene hydroboration and also establishes a strategy for the alkylation of chiral enolates. Furthermore, this synthesis of discodermolide provides the first examples of the asymmetric 1,4-diboration of dienes and borylative diene-aldehyde couplings in complex-molecule synthesis.

Total synthesis of discodermolide: optimization of the effective synthetic route

An efficient and modulable total synthesis of discodermolide (DDM), a unique marine anticancer polyketide is described including related alternative synthetic approaches. Particularly notable is the repeated application of a crotyltitanation reaction to yield homoallylic (Z)-O-ene-carbamate alcohols with excellent selectivity. Advantage was taken of this reaction not only for the stereocontrolled building of the syn-anti methyl-hydroxy-methyl triads of DDM, but also for the direct construction of the terminal (Z)-diene. Of particular interest is also the installation of the C13=C14 (Z)-double bond through a highly selective dyotropic rearrangement. The preparation of the middle C8-C14 fragment in two sequential stages and its coupling to the C1-C7 moiety was a real challenge and required careful optimization. Several synthetic routes were explored to allow high and reliable yields. Due to the flexibility and robust character of this approach, it might enable a systematic structural variation of DDM and, therefore, the elaboration and exploration of novel discodermolide structural analogues.

Dinuclear zinc-catalyzed asymmetric desymmetrization of acyclic 2-substituted-1,3-propanediols: a powerful entry into chiral building blocks

The asymmetric acylation of meso-2-substituted-1,3-propanediols by using an amphoteric chiral dinuclear zinc catalyst is described. It is has been demonstrated that both 2-alkyl- and 2-aryl-1,3-propanediols can be desymmetrized in high yields and enantioselectivities by using the same family of ligands. Given that both antipodes of the chiral catalyst are available, both enantiomers of the desymmetrized product can be obtained from the same starting material. The synthetic utility of the desymmetrized products has been demonstrated by the synthesis of several chiral building blocks with high enantiomeric purities.