New synthesis with acetylene biscobalthexacarbonyl complex (2)

Abstract

Following our previous review of this issue, chemistry of acetylene biscobalthexacarbonyl complex is discussed with special reference in the synthesis of natural and unnatural products. The first example is to do with protein phosphatase inhibitors; thus, okadaic acid and tautomycin are known as strong inhibitors to these enzymes with high specificity of the enzyme type. Hybrid molecules are discussed as unnatural product having enantiomeric spiro moieties. These syntheses have been achieved via enantio-switching method from the same D-glucose derivatives; namely, alkynylation of silylacetylene to sugars provides sugar acetylenes, which are convertible with or without epimerization into α or β heteroolefins leading to enantiomer to each other. Heteroconjugate addition on pyranose ring can provide either syn or anti adduct by switching the chelational anchor and metals of the nucleophile. Pauson-Khand reaction is demonstrated on the sugar acetylenes to provide tricyclic compounds with definite stereoisomer. A macrocyclic ring closure is a specific example of the cobalt complex with C-C bond formation in the critical step. Cobalt chemistry and sugar acetylene chemistry made it possible to provide both of the enantiomers of left end segments of ciguatoxin. This line also discussed to the potential methodology directed toward other portion of this marine natural toxin. These endo-cyclic complexes have reductively been decomplexed into the olefins or vinylsilanes.