Cobalt carbonyl hydride synthesis

Remarkably few examples of this type of ring construction are available. The cobalt carbonyl hydride catalyzed hydroformylation of A/,A/ -diallylcarbamates has provided 3-pyrrolidinones (Scheme 61a) (81JOC4433). The pyrrole synthesis shown in Scheme 61b depends on Michael addition of ethyl a-lithioisocyanoacetate to ethyl a-isocyanocrotonate (77LA1174). 

T,he hydroformylation reaction or oxo synthesis has been used on an industrial scale for 30 years, and during this time it has developed into one of the most important homogeneously-catalyzed technical processes (I). A variety of technical processes have been developed to prepare the real catalyst cobalt tetracarbonyl hydride from its inactive precursors, e.g., a cobalt salt or metallic cobalt, to separate the dissolved cobalt carbonyl catalyst from the reaction products (decobaltation) and to recycle it to the oxo reactor. The efficiency of each step is of great economical importance to the total process. Therefore many patents and papers have been published concerning the problem of making the catalyst cycle as simple as possible. Another important problem in the oxo synthesis is the formation of undesired branched isomers. Many efforts have been made to keep the yield of these by-products at a minimum. 

Silicon and germanium hydrides react with cobalt, manganese and rhenium carbonyls affording complexes having a silicon (or germanium)-metal bond. These reactions, described previously for inactive compounds have been used in the synthesis of optically active silyl and germyl-transition metals ... 

The formal conjugate addition of a hydride to a,f(-unsaturated carbonyl compounds with a subsequent aldol reaction of the in situ formed enolate has been frequently employed in organic synthesis. A broad range of procedures have been developed using various metals (e.g., rhodium, cobalt, iridium, mthenium, copper) and different reductants (typically silanes, boranes, or elemental hydrogen) [37]. 

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