Vinyl compounds fragmentation synthesis

The retrosynthetic approach to welwitindolinone A isonitrile (6) used by the Wood group is shown in Scheme 33. After recognition of the possibility of deriving the vinyl isonitrile fragment from a ketone, the disconnection of 6 to 140 was proposed. A literature report of a samarium (II) iodide-mediated reductive coupling of acrylates with isocyanates to give amides, which could be expected to lead to a new spirooxindole synthesis, prompted the disconnection of 140 to 141. This compound was to be obtained from the readily available cyclohexadiene derivative 143, by way of bicyclic ketone 142. 

The reaction of anomeric sulfones with vinyl magnesium bromide in the presence of zinc bromide allows direct vinylation at the anomeric center. This reaction was the starting point of an approach for the synthesis of the C29 to C51 fragment of altohyrtin A [64]. The C29 to C44 (EF) portion of this compound has been prepared by a stepwise sequence involving anomeric cyanation, using the reaction of anomeric acetate in the presence of BF3-Et20. The anomeric cyanide was then elaborated to the Weinreb amide, which was condensed with an appropriate vinylic carbanion representing the C29 to C37 chain [298]. 

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