Synthesis of Alkanes RH

The Rh-BIPHEPHOS-catalyzed cyclohydrocarbonylation has also been successfully applied to the rapid synthesis of a variety of l-azabicyclo[X.Y.O]alkane amino acids, which serve as conformationally restricted dipeptide surrogates for enzyme inhibitors and receptor antagonists, directly from dehydrodipeptide substrates (Scheme Reaction... 

Direct borylation of hydrocarbons catalyzed by a transition metal complex has been extensively studied by several groups and has become an economical, efficient, elegant, and environmentally benign protocol for the synthesis of a variety of organoboron compounds. The Rh-, Ir-, Re-, and Pd-catalyzed C-/H borylation of alkanes, arenes, and benzylic positions... 

Preparation. The synthesis of alkylzinc alkoxides and aryloxides is achieved by an alkane elimination process in the simple reaction of a dialkylzinc compound, R2Zn, with one equivalent of an alcohol, R OH (equation 18). This reaction proceeds either in hydrocarbon solvents or neat solution, to give essentially quantitative yields of the desired products. The volatility of the RH side product helps to drive the equilibrium to the right. The formation of relatively strong Zn-O and C-H bonds, at the expense of breaking the O-H and a relatively weak Zn-C bond also guarantee favorable reaction energetics. 

Undoubtedly, the synthetic value of the Rh-catalyzed alkyl borylation reaction follows from the fact that it can selectively deliver a functional group, such as an alcohol, an amine or an alkene, at the terminus of an alkyl chain during the synthesis of more complex structures. With the proper substituent at boron, this process can extrude the same borane reagent that was used in the alkane functionalization step to allow recycling of the main group reagent for large-scale synthesis. 

Structure promoters can act in various ways. In the aromatization of alkanes on Pt catalysts, nonselective dissociative reaction paths that lead to gas and coke formation can be suppressed by alloying with tin. This is attributed to the ensemble effect, which is also responsible for the action of alkali and alkaline earth metal hydroxides on Rh catalysts in the synthesis of methanol from CO/H2 and the hydroformylation of ethylene. It was found that by means of the ensemble effect the promoters block active sites and thus suppress the dissociation of CO. Both reactions require small surface ensembles. As a result, methanol production and insertion of CO into the al-kene are both positively influenced. 

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