Hydrogen tandem

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). 

Over 75 years research into hydroformylation, the concomitant hydrogenation of aldehydes to alcohols by the effect of Co(I), Rh(I), Ir(I), Ru(II), Pd(II), and Pt(II) catalyst has been described repeatedly. These observations finally led to the development of highly efficient hydroformylation-hydrogenation tandem protocols, which almost completely result in formation of the desired alcohols. 

Cobalt-Catalyzed Hydroformylatlon-Hydrogenation Tandem Reaction... 

A breakthrough was achieved by Slaugh and MuUineaux at Shell, who discovered the beneficial effect of trialkylphosphines such as PEtj, P( Bu)3, or P(Cy)3 on the cobalt-catalyzed hydroformylation-hydrogenation tandem reaction with several olefins as substrates (1- and 2-pentene, 1-butene, propylene, methyl-pentenes, cyclohexenes, dimethyl-butenes, and higher olefins) [31, 36]. Large substituents at the phosphorus, as present in tris(2-ethylhexyl)phosphine, reduce... 

Scheme 5.57 PPhj-directed syn hydroformylation-hydrogenation tandem reaction.

Scheme 5.58 Hydroformylation-hydrogenation tandem reaction using a supramolecular catalyst and a calculated transition state (A).

Scheme 5.59 Decarboxylative hydroformylation-hydrogenation tandem reaction of a,p-unsaturated carboxylic acids.

Polymetallic Systems and Other Metal-Based Catalytic Systems for Hydroformylation-Hydrogenation Tandem Reactions... 

During hydroformylation, acetalization of aldehydes can take place as an undesired side reaction when the hydroformylation is conducted in alcohols as solvent and under the influence of a hydroformylation catalyst with acidic properties. Moreover, when alcohols result in a hydroformylation-hydrogenation tandem reaction (see Section 5.2), acetalization has always been taken into consideration. 

Special hydroformylation protocols allow the one-step production of alcohols (hydroformylation-hydrogenation tandem reaction, see also Section 5.2), which are also of crucial importance as aroma compounds. Acetals, which have similar odors like their aldehydic precursors, maybe produced in the hydroformylation in alcohols as solvent under acidic conditions (hydroformylation-acetalization tandem reaction, see also Section 5.3) [15]. The acetal formed protects the aldehyde toward oxidations, reactions with amines, or aldol condensations. Especially in demanding fragrances, these modifications that may affect the scent impression are not desired. 

Scheme 6.77 Hydroformylation-(aldol condensation)-hydrogenation tandem reaction and...

Scheme 6.107 Hydroformylation-hydrogenation tandem reaction of ethylene oxide.

The dienyne 394 undergoes facile polycyclization. Since the neopentylpalla-dium 395 is formed which has no hydrogen /J to the Pd after the insertion of the disubstituted terminal alkene, the cyclopropanation takes place to form the tt-allylpalladium intermediate 396, which is terminated by elimination to form the diene 397(275]. The dienyne 398 undergoes remarkable tandem 6-e. o-dig. 5-cxo-trig. and -exo-trig cyclizations to give the tetracycle 399 exclu-sively(277]. 

The most recent, and probably most elegant, process for the asymmetric synthesis of (+)-estrone appHes a tandem Claisen rearrangement and intramolecular ene-reaction (Eig. 23). StereochemicaHy pure (185) is synthesized from (2R)-l,2-0-isopropyhdene-3-butanone in an overall yield of 86% in four chemical steps. Heating a toluene solution of (185), enol ether (187), and 2,6-dimethylphenol to 180°C in a sealed tube for 60 h produces (190) in 76% yield after purification. Ozonolysis of (190) followed by base-catalyzed epimerization of the C8a-hydrogen to a C8P-hydrogen (again similar to conversion of (175) to (176)) produces (184) in 46% yield from (190). Aldehyde (184) was converted to 9,11-dehydroestrone methyl ether (177) as discussed above. The overall yield of 9,11-dehydroestrone methyl ether (177) was 17% in five steps from 6-methoxy-l-tetralone (186) and (185) (201). 

The key features of Curran s productive and elegant tandem radical cyclization strategy are illustrated in a retrosynthetic analysis for hirsutene (1) (see Scheme 27). The final synthetic event was projected to be an intermolecular transfer of a hydrogen atom from tri-rc-butyltin hydride to the transitory tricyclic vinyl radical 131. The latter can then be traced to bicyclic tertiary radical 132 and thence to monocyclic primary radical 133 through successive hex-5-enyl-like radical cyclizations. It was anticipated that the initial radical 133 could be generated through the abstraction of the iodine atom from... 

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