Tandem Isomerization-Hydroformylation Reactions

Scheme 5.4 Simplified mechanisms for two cycles of tandem isomerization-hydroformylation reaction (HF = hydroformylation Iso = isomerization only the most important relationships are depicted equilibria are not indicated).

Tandem Isomerization-Hydroformylation Reactions 393 Table 5.2 Product formation in relation to the syngas pressure. ... 

Tandem Isomerization-Hydroformylation Reactions with Consecutive Steps... 

Behr, A., Obst, D., Schulte, C., and Schosser, T. (2003) Highly selective tandem isomerization-hydroformylation reaction of trans-4-octene to n-nonanal with rhodium-BIPHEPHOS catalysis. J, Mol, Catal, A-Chem, 206, 179-184. 

Metal enolates have played a Umited role in the metal-catalyzed isomerization of al-kenes . As illustrated in a comprehensive review by Bouwman and coworkers, ruthenium complex Ru(acac)3 (51) has been used to isomerize a wide range of substituted double bonds, including aUylic alcohols (131), to the corresponding ketones (132) (equation 38) . The isomerization of aUylic alcohols affords products that have useful applications in natural product synthesis and in bulk chemical processes. An elegant review by Fogg and dos Santos shows how these complexes can be used in tandem catalysis, where an alkene is subjected to an initial isomerization followed by a hydroformylation reaction ... 

In 2013, Nozaki s group reported a dual Rh/Ru catalyst based on a combination of Rh(diphosphite), Shvo s catalyst, and Rug(CO)j2 in the isomerization-hydroformylation-hydrogenation tandem reaction [108]. 

One year later, the same research group reported a similar dual Rh/Ru catalyst based on a combination of a Rh(diphosphite), Shvo s catalyst, and Ru3(CO)j2 in the isomerization-hydroformylation-hydrogenation tandem reaction (Scheme 5.41) [21]. With methyl oleate, 53% yield of the terminal alcohol was observed. With unmodified internal olefins (2-decene, 2-tridecene, 4-octene), even higher regioselectivities in favor of the terminal alcohol could be achieved Ub up to 12). 

In conclusion, the applicability of the transition metal catalyzed hydroformylation of easily accessible functionalized or non-functionalized unsaturated compounds is expanded by its implementation in reaction sequences, tandem reactions or domino reactions. The hydroformylation can be combined with simple functional group transformations, such as reduction or isomerization, or with C,0-, C,N- and, most importantly, C,C-bond forming reactions. It can be expected that more interesting examples and applications will be presented in the future. 

In mixtures of acychc olefins, besides terminal compounds, also internal and branched compounds are present. Since in several cases the production of terminal aldehydes is desired, hydroformylation with prior isomerization is targeted (see Section 5.1). This tandem reaction can be achieved by the proper choice of metal, ligand, and reaction conditions [8]. High branched selectivity is predominantly achieved by using an internal olefin together with a catalyst with low isomerization properties and high hydroformylation activity. 

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