Diene hydroformylation

In diene hydroformylation with complex (34) and DIOP, the attainable optical yields were critically dependent on the diene. Thus isoprene gave, after oxidation of the aldehyde with Ag20, 3-methylpentanoic acid as major product having an optical purity of 32%. Butadiene, 2,3-dimethylbutadiene and 2-methyl-1-butene all gave optical yields of less than 6%. 369 The hydroformylation by (34) and DIOP of a number of alkenes having C2v symmetry gave best results with m-2-butene, with an optical yield of 27%.370... 

Cyclodimerhation of isoprene to 1,5-dimethylcycloocta-1,5-diene and disproportion with a rhenium oxide catalyst and isobutene produce 2,6-dimethyUiepta-l,5-diene. The diene is hydroformylated to citroneUal, which after hydrogenation produces citroneUol (137). 

Hydroformylation of nitrile rubber is another chemical modification that can incorporate a reactive aldehyde group into the diene part and further open up new synthetic routes to the formation of novel nitrile elastomers with a saturated backbone containing carboxyl or hydroxyl functionalities. 

Rhodium Atom-Derived Catalysts in the Hydroformylation of 1,3-Dienes and in the Hydrosilylation of Aromatic Nitriles... 

We describe here (i) the selective hydroformylation of 1,3-dienes to p,y-unsaturated aldehydes promoted by catalyst A and (ii) the efficient hydrosilylation of aromatic nitriles to A,iV-disilylamines using catalysts B and C. 

The chemo- and regioselectivities of hydroformylation reactions of open chain, conjugated dienes using the usual catalyst are, in most cases, rather low [36]. The rhodium/ mesitylene co-condensate (catalyst A), in the presence of bis(diphenylphosphino)ethane, DPPE, catalyses the hydroformylation of 1,3-butadiene, isoprene, and E,Z)-, 3-pentadiene to the corresponding p,y-unsaturated monoaldehydes, with unusually high chemo- and regioselectivities (Scheme 17). 

Table 5. Hydroformylation of open-chain conjugated dienes by rhodium/mesitylene co-condensate, catalyst A . Substrate...

Many chiral diphosphine ligands have been evaluated with regard to inducing enantioselectivity in the course of the hydroformylation reaction [25,26]. However, a real breakthrough occurred in 1993 with the discovery of the BI-NAPHOS ligand by Takaya and Nozaki [65]. This was the first efficient and rather general catalyst for the enantioselective hydroformylation of several classes of alkenes, such as aryl alkenes, 1-heteroatom-functionalized alkenes, and substituted 1,3-dienes, and is still a benchmark in this area [66,67]. But still a major problem in this field is the simultaneous control of enantio-... 

The asymmetric hydroformylation of a 1,3-diene has been recently used in the course of a total synthesis of the antifungal natural product ambruticin. The retrosynthesis as well as the hydroformylation key step are depicted in Scheme 25 [75]. 

The synthesis, aggregation behavior, and catalytic activity of Rh complexes of Xantphos derivatives (129) with surface-active pendant groups have been described.416 The complex [HRh(CO)(TPPTS)3] was used as a catalyst precursor in the hydroformylation of 1-butene, 1-octene, and styrene under biphasic reaction conditions 417 The two-phase hydroformylation of buta-1,3-diene with [HRh(CO)(TPPTS)3], with excess TPPPS, gives high yields of C5-monoaldehydes.418 The coordination behavior of the catalytic species HRh(130)(CO)2] was studied by HP NMR spectroscopy which showed the desired bis-equatorial coordination of the ligand to the rhodium center.419... 

A method to reduce degradation/deactivation of a phosphite modified rhodium hydroformylation catalyst in the separation system involves feeding a diene such as butadiene to the vaporizer to convert the phosphite-modified rhodium catalyst to a more stable form. [34] In the reactor, the diene is hydrogenated and catalyst activity is restored. 

Butadiene, the simplest conjugated diene, appears to be a promising substrate for the hydroformylation reaction, because the expected product (hexanedial) could be easily converted to useful products. Oxidation would produce adipic acid, hydrogenation hexanediol, and reductive amination hexamethylenediamine. However, this objective has been difficult to realize. 

In some cases, the resulting olefin is not inert and undergoes consecutive hydroformylation. If aliphatic 1,5-dienes are subjected to a hydro-... 

Olefin formation, by reductive elimination of 3-hydroxysulfones, 72, 2 Olefins, hydroformylation of, 56, 1 Oligomerization of 1,3-dienes, 19, 2 Oligosaccharide synthesis on polymer support, 68, 2 Oppenauer oxidation, 6, 5 Organoboranes ... 

Hexahydro-4/f-chromenes are formed from 1,5-dienes in a one-pot process in which a Rh-complex catalyses sequential hydroformylation, carbonyl ene reaction, a second hydroformylation, cyclisation to a lactol and dehydration <99TL7455>. 

Hydroformylation of Other Lower Olefins and Dienes - Lower olefins such as 1-butene or 1,3-butadiene are hydroformylated with acceptable rates using Rh/tppts catalysts according to the RCH/RP process. Hoechst AG Werk Ruhrchemie has developed an attractive new process350 for the hydroformylation of raffinate II, a mixture of 1-butene, cis- and /rbutane derived from the C4 stream of naphtha crackers (after removal of 1,3-butadiene... 

Other additions, such as addition of alkyl halides and carbonyl compounds, are discussed in Chapter 5, whereas Chapter 7 covers addition reactions involving carbon monoxide (hydroformylation, carboxylations). Hydrogen addition is discussed in Chapter 11. The nucleophilic addition of organometallics to multiple bonds is of great significance in the anionic polymerization of alkenes and dienes and is treated in Chapter 13. 

As a result of extensive isomerization, nonconjugated cyclic dienes give complex product mixtures11 when subjected to hydroformylation in the presence of [Co(CO)4]2. In contrast, hydroformylation at the less-hindered double bond usually takes place in the presence of rhodium catalysts to give unsaturated aldehydes68,69 [Eq. (7.8)44] unsubstituted a,co-dienes, in turn, form dialdehydes 70... 

Since conjugated dienes form stable rc-allyl complexes with [Co(CO)4]2, they undergo hydroformylation very slowly to give saturated monoaldehydes in low yields.8 Mixtures of mono- and dialdehydes are usually formed in rhodium-catalyzed hydroformylations.71 72 Saturated monoaldehydes were isolated, however, when 1,3-butadiene and 1,3-pentadiene were hydroformylated in the presence of rhodium dioxide.70... 

Alkenes and Dienes. Alkenes exhibit lower reactivity in metal-catalyzed carboxylation than in hydroformylation. The general reactivity pattern of different alkenes, however, is the same terminal linear alkenes are the most reactive substrates. Cycloalkenes are the least reactive, but strained compounds may react under very mild conditions 128... 

Further novel observations are the hydroformylation of ethylene over graphite nanofiber-supported Rh catalysts,270 the transformation of a mixture of isomeric octenes to Cg-aldehydes,271 and the preparation of linear long-chain dialdehydes by the hydroformylation of linear a,co-dienes.272... 

Cyanide-containing cobalt catalysts, particularly potassium pentacyanocobalta-te(II) K3[Co(CN)5], are used in the reduction of activated alkenes (conjugated dienes).26,31 [Co(CO)4]2 is best known as a hydroformylation catalyst, but hydrogenation is also possible under specific conditions. Phosphine-substituted analogs are more successful. 

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