Rhodium catalysts hydroacylation

Hydrogenation of a mixture of styrenes ArCH=CH2 (or reactive alkenes, such as norbornene or ethylene) and symmetric or mixed carboxylic anhydrides [(RC0)20 or (RCO)O(COR )] in the presence of cationic rhodium catalysts ligated by triphenylar-sine (Ph3As), generates hydroacylation products ArCH(Me)COR as single regioiso-mers in high yields.108... 

Various other rhodium catalysts can initiate hydroacylation reactions. Thus, the indenyl complex [075-C9H7)Rh(J72-C2H4)2] is used in intermolecular hydroacylation44. Rhodium zeolites (RhNaX and RhNaY type zeolites) act as bifunctional catalysts for the synthesis of 2-methyl-3-hexanone and 4-heptanone (1 2 ratio) from propene, carbon monoxide and hydrogen53. In this case, the ketones may be formed via hydrocarbonylation (vide supra), however, according to control experiments, rhodium-free zeolites alone catalyze ketone formation from propene and butyraldehyde53. 

Hydroacylation is especially interesting in its intramolecular version, converting unsaturated aldehydes to cyclopentanones. Numerous examples of transition metal catalyzed hydroacylations have been described, mostly with 4-alkenals of various substitution patterns. The reaction is used for the construction of starting materials in prostaglandin synthesis and the preparation of other cyclopentanoid systems. Rhodium catalysts, mainly of the Wilkinson type, are used. The steric course of hydroacylation is believed to occur in a m-addition manner. This was deduced from results of intermolecular alkyne hydroacylation56 (vide supra) and the intramolecular hydroacylation of deuterated E- and Z-isomers of 7,5-unsaturated aldehydes39-5 . 

The asymmetric hydroacylation reaction of 1,5-enal was employed by Castillon and co-workers in the enantioselective synthesis of carbocyclic nucleosides (Scheme 8.14). When compound 31 was treated with a cationic rhodium catalyst, the cyclie ketone 32 could be obtained with up to 95% ee. Starting from an elegantly designed substrate 33, the group of Tanaka and Suemune realized the synthesis of enantioenriched spiro[4.4]nonanediones 36 and 37 via an iterative Rh-eatalyzed asymmetric intramolecular hydroacylation reaction (Scheme 8.15). ... 

In 2008, Willis and co-workers developed a highly enantioselective inter-molecular hydroacylation reaction employing ortfto-S-substituted benzal-dehydes 51 and 1,3-disubstituted allenes 52 (Scheme 8.25). When using a (7 ,/ )-Me-DuPhos-derived cationie rhodium catalyst, excellent yields and ee were obtained. Extension of the substrate scope to a trisubstituted allene led to the product with high ee, but in a disappointingly low yield. It was revealed that the reaction was not a simple kinetic resolution of the racemic allene but rather proceeded by dynamie kinetie asymmetric transformation. 

Synthesis of Aliphatic Ketones from Allylic Alcohols Through Consecutive Isomerization and Chelation-Assisted Hydroacylation by a Rhodium Catalyst [25]... 

In the reactions of sulfanyl aldehydes with aUcenes in the presence of a rhodium catalyst, hydroacylation proceeds via an intramolecular five-membered ring intermediate with the insertion of an alkenyl moiety between the rhodium and carbonyl carbon at the y-position to the coordinating atom [112-114], For example, p-methylsulfanyl aldehyde reacts with an amide alkene to give an intermolecular hydroacylation product with the insertion of an amide alkenyl moiety at a high yield, as shown in Eq. (7.56) [112]. 

At nearly the same time, Jun and coworkers explored a versatile simultaneous hydroacylation and hydrogenation of low-molecular-weight PBD. A novel C—C bond coupling method between a primary alcohol and a 1-alkene in the presence of a rhodium catalyst afforded ketone functionality. The primary alcohol was initially oxidized to an aldehyde by the rhodium catalyst, and subsequent hydroacylation of the aldehyde with... 

Jun CH, Hwang DC. Simultaneous hydrogenation and hydroacylation of vinyl groups in polybutadiene by use of a rhodium catalyst. Polymer. 1998 39 7143-7147. 

Two years later, Bosnich described an extensive study of asymmetric rhodium-catalyzed intramolecular hydroacylation reactions [16]. Like Sakai, Bosnich found that Rh(l)/ BINAP is an unusually effective catalyst for this process, furnishing excellent enantioselectivity for a range of substrates (Eq. 13). Bosnich also reported thaL if the R substituent is a relatively unhindered alkyl (for example. Me) or an aromatic group, lower (< 80% ee) enantioselectivity is observed. 

Optimized reaction conditions call for the use of Wilkinson s catalyst in conjunction with the organocatalyst 2-amino-3-picoline (60) and a Br0nsted add. Jun and coworkers have demonstrated the effectiveness of this catalyst mixture for a number of reactions induding hydroacylation and C—H bond fundionalization [25]. Whereas, in most cases, the Lewis basic pyridyl nitrogen of the cocatalyst ads to dired the insertion of rhodium into a bond of interest, in this case the opposite is true - the pyridyl nitrogen direds the attack of cocatalyst onto an organorhodium spedes (Scheme 9.11). Hydroamination of the vinylidene complex 61 by 3-amino-2-picoline gives the chelated amino-carbene complex 62, which is in equilibrium with a-bound hydrido-rhodium tautomers 63 and 64. 

An indirect method for the hydroformylation of olefins involves formation of the tri-alkylborane (5-12) and treatment of this with carbon monoxide and a reducing agent (see 8-26). Hydroacylation of alkenes has been accomplished, in variable yields, by treatment with an acyl halide and a rhodium complex catalyst, e.g.,587... 

Loupy, A., Chatti, S., Delamare, S., Lee, D.Y., Chung, J.H. and Jun, G.H., Solvent-free chelation-assisted hydroacylation of olefin by rhodium(I) catalyst under microwave irradiation, /. Chem. Soc., Perkin Trans. 1, 2002, 1280-1285. 

Research on intermolecular hydroacylation has also attracted considerable attention. The transition-metal-catalyzed addition of a formyl C-H bond to C-C multiple bonds gives the corresponding unsymmetrically substituted ketones. For the intermolecular hydroacylation of C-C multiple bonds, ruthenium complexes, as well as rhodium complexes, are effective [76-84]. In this section, intermolecular hydroacylation reactions of alkenes and alkynes using ruthenium catalysts are described. 

In 1980, Miller et al. [76] reported the first example of an intermolecular hydroacylation of an aldehyde with an olefin to give a ketone, during their studies of the mechanism of the rhodium-catalyzed intramolecular cyclization of 4-pentenal using ethylene-saturated chloroform as the solvent. Later James and Young [77] reported that the reaction of propionaldehyde with ethylene can be conducted in the presence of RuCl2(PPh3)3 as the catalyst without any solvent at 210 °C, resulting in the formation of 3-pentanone in 2-4% yield (turnover number of 230) (Eq. 49). 

This reaction competes with intramolecular hydroacylation of pent-4-enals to form cyclopen-tanones. In the case of exo- and ent/o-norborn-5-ene-2-carboxaldehyde (4) if treated with Wilkinson s catalyst [tris(triphenylphosphane)rhodium(I) chloride] only decarbonylation occurs. While the exo-aldehyde exo-4 leads to norbornadiene (5), the e fi o-aldehyde endo-4 reacts to form nortricyclene (6 tricyclo[2.2.1.0 ]heptane). These results support organometallic pathways and exclude radical intermediates, since here identical products should be formed. 

Besides hydrocarbonylation of olefins with carbon monoxide, hydroacylation can also be achieved by addition of aldehydes to olefins in the absence of carbon monoxide. This reaction is usually induced by rhodium complexes, mainly of the Wilkinson s catalyst type. Other catalysts are also active, e.g., systems derived from ruthenium complexes. Hydroacylation via aldehyde addition reactions has only rarely been surveyed24. 

The addition of an aldehyde group across an aUcene is a hydroacylation reaction. Whilst there is no hydrogen gas needed for these reactions, the process has some similarity to hydroformylation from a synthetic viewpoint, hence its mention in this chapter. In common with hydroformylations, catalytic asymmetric hydroacylations utilise enantiomerically pure rhodium complexes as catalysts. To date the catalytic asymmetric hydroacylation of alkenes has only been achieved in an intramolecular sense. 4-Substituted pentenal (2.213) and 3,4-disubstituted... 

Hydroacylation of olefins to yield ketones can be achieved by the addition of an aldehyde in the presence of a silver salt or by the addition of an aldimine (29) in the presence of a rhodium(i) catalyst [equation (5)]. ... 

Transition-metal-assisted cyclopentane ring-forming reactions again feature prominently this year. Wilkinson s catalyst brings about the cyclization of 1,6-dienes to methylenecyclopentanes e.g. (37) - (38), whereas cyclopentanones are obtained from the rhodium(i)-catalysed intramolecular hydroacylation of y,5-unsaturated aldehydes e.g. (39) - (40). ... 

Catalytic intramolecular hydroacylations are valuable reactions to create functionalized cyclopentanones. Thus, easily available aldehyde 419 was treated with a chiral rhodium(I) catalyst prepared in situ from phosphoramidite 420-(S)-Ll and [Rh(C2H4)2Cl], silver hexafluoro antimonate, and a phosphine such as MeP(tBu)2 as an activator cyclopentanone 421 was obtained in good yield and with 95% ee. Without the phosphine, no reaction occurred (Scheme 3.80) [131]. 

Lee J-H, Jo E-A, Jun C-H. Modification of polybutadiene chelation-assisted hydroacylation of alpha, omega-diol with a rhodium(I) catalyst. Synlett. 2009 2009 2647-2650. 

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