The progress in catalytic organic synthesis with iridium was far behind that with rhodium or palladium in the early 1990s. However, many useful reactions have recently been reported, and iridium catalysts have now been recognized to be useful in organic synthesis. This review covers iridium-catalyzed carbon-carbon and carbon-heteroatom bond formation with particular emphasis on useful reactions for organic synthesis.

New chiral phosphoramidites with an amide moiety were used for iridium-catalyzed asymmetric allylic alkylation reactions. The best results were obtained with a ligand bearing an oxazolidinone moiety. The reaction of cinnamyl acetate with diethyl sodiomalonate without the use of lithium chloride gave the branched product with 94% ee.

[reaction: see text] [Ir(cod)Cl]2/DPPE was found to be a new catalyst for the cycloaddition of alpha,omega-diynes with monoynes to give polysubstituted benzene derivatives in high yields. Internal monoynes as well as terminal monoynes could be used. The reaction tolerates a broad range of functional groups such as alcohol, amine, alkene, ether, halogen, and nitrile. The reaction of 1,6-octadiyne derivatives with 1-alkynes gives ortho products and meta products. The regioselectivity could be controlled by the choice of ligand. The reaction with DPPE was meta selective, with meta selectivity of up to 82%. The reaction with DPPF was ortho selective, with ortho selectivity of up to 88%. We propose a mechanism to account for this regioselective cycloaddition. [Ir(cod)Cl](2)/DPPE also catalyzed the cycloaddition of alpha,omega-diynes with 2,5-dihydrofuran to give bicyclic cyclohexadiene derivatives. The reaction with 2,3-dihydrofuran and n-butyl vinyl ether gave benzene derivatives instead of cyclohexadiene derivatives. We also propose a mechanism to account for this novel aromatization that includes cleavage of the C-O bond.

For Abstract see ChemInform Abstract in Full Text.