Olefins hydroacylation

A highly efficient olefin hydroacylation known as the Stetter reaction resulted from the discovery that an activated olefin could intercept the putative acylanion intermediate of the classical benzoin reaction. Metal cyanides and heterocyclic carbenes are commonly employed catalysts for the Stetter reaction. Chiral heterocyclic carbenes as well as chiral metallophosphites have been developed as catalysts to provide 1,4-dicarbonyl compounds with high levels of enantiomeric purity. ... 

A recyclable system for the directed rhodium-catalyzed hydroacylation of olefins was reported using a homogeneous phenol and 4,4 -dipyridyl solvent system at 150 °C. High yields were obtained even after eight cycles and the ketone product was obtained after decantation (Equation (132)).115... 

Based on Watanabe s intermolecular hydroacylation of olefins with aldehydes,348 Kondo and Misudo developed the first ruthenium-catalyzed hydroacylation of 1,3-dienes with aldehydes (Scheme 71). Usually, palladium-mediated hydroacylations of 1,3-dienes with aldehydes give tetrahydropyran and/or open-chain homoallylic alcohol derivatives.350 However, in the present ruthenium-catalyzed transformations, the corresponding /3,7-unsaturated... 

Recent Advances in Rhodium(l)-Catalyzed Asymmetric Olefin Isomerization and Hydroacylation Reactions... 

Rhodium( )-Catalyzed Asymmetric Hydroacylation of Olefins and Alkynes with Aldehydes I 85... 

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... 

Addition of tin and mercury hydrides to unsaturated ketones 5-22 Free-radical addition of aldehydes or ketones to olefins 5-24 Hydroacylation of alkenes... 

Rhodium-catalyzed hydroacylation of appropriately substituted olefinic aldehydes gives cyclopentanone and cyclohexanone, respectively (Scheme 13) [49]. 

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. 

Hydrido(trialkylsilyl)silyllithiums, preparation, 3, 424 Hydroacylations, olefins, 10, 142 Hydroalkoxylations and etherification, 10, 672 in etherification, 10, 683 Hydroaluminations for C-E bond formation characteristics, 10, 857 chemoselectivity, 10, 859 mechanism, 10, 858 overview, 10, 839-870 stereoselectivity, 10, 861 total synthesis applications, 10, 865 characteristics, 3, 275 process and examples, 9, 268 via Ti(IV) complexes, 4, 658 Hydroaminations actinide-catalyzed, 4, 237 in aminations... 

The hydroacylation of olefins with aldehydes is one of the most promising transformations using a transition metal-catalyzed C-H bond activation process [1-4]. It is, furthermore, a potentially environmentally-friendly reaction because the resulting ketones are made from the whole atoms of reactants (aldehydes and olefins), i.e. it is atom-economic [5]. A key intermediate in hydroacylation is a acyl metal hydride generated from the oxidative addition of a transition metal into the C-H bond of the aldehyde. This intermediate can undergo the hydrometalation ofthe olefin followed by reductive elimination to give a ketone or the undesired decarbonyla-tion, driven by the stability of a metal carbonyl complex as outlined in Scheme 1. 

An interesting example is the hydroiminoacylation reaction, a good alternative to hydroacylation reactions, using aldimines as a synthetic equivalent to aldehydes (Scheme 4) [4]. The rhodium-catalyzed hydroiminoacylation of an olefin with aldimines produced a ketimine which could be further acid-hydrolyzed to give the ketone. The reaction proceeded via the formation of a stable iminoacylrhodi-um(III) hydride (this will be discussed in the mechanism section), production of which is facilitated by initial coordination of the rhodium complex to the pyridine moiety of the aldimine. This hydroiminoacylation procedure opened up the direct... 

A primary alcohol and amines can be used as an aldehyde precursor, because it can be oxidized by transfer hydrogenation. For example, the reaction of benzyl alcohol with excess olefin afforded the corresponding ketone in good yield in the presence of Rh complex and 2-amino-4-picoline [18]. Similarly, primary amines, which were transformed into imines by dehydrogenation, were also employed as a substrate instead of aldehydes [19]. Although various terminal olefins, alkynes [20], and even dienes [21] have been commonly used as a reaction partner in hydroiminoacylation reactions, internal olefins were ineffective. Recently, methyl sulfide-substituted aldehydes were successfully applied to the intermolecu-lar hydroacylation reaction [22], Also in the intramolecular hydroacylation, extension of substrates such as cyclopropane-substituted 4-enal [23], 4-alkynal [24], and 4,6-dienal [25] has been developed (Table 1). 

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). 

Later, they also reported an intermolecular hydroacylations of 1,3-dienes with aromatic aldehydes yielding the corresponding j8,y-unsaturated ketones (Eq. 51) [79]. This reaction does not require a CO atmosphere. The addition of formyl C-H bond in formic acid esters and amides to olefins and conjugate... 

The use of C-H bonds is obviously one of the simplest and most straightforward methods in organic synthesis. From the synthetic point of view, the alkylation, alkenylation, arylation, and silylation of C-H bonds are regarded as practical tools since these reactions exhibit high selectivity, high efficiency, and are widely applicable, all of which are essential for practical organic synthesis. The hydroacylation of olefins provides unsymmetrical ketones, which are highly versatile synthetic intermediates. Transition-metal-catalyzed aldol and Michael addition reactions of active methylene compounds are now widely used for enantioselective and di-astereoselective C-C bond formation reactions under neutral conditions. 

Lenges CP, Brookhart M. Co(I)-catalyzed inter- and intramolecular hydroacylation of olefins with aromatic aldehydes. J Am Chem Soc 1997 119(13) 3165—3166. 

The use of a formyl group as a directing functionality is challenging because, in the case of the low-valent transition metal-catalyzed reaction of aldehydes with an olefin, aldehydes are prone to undergo decarbonylation or hydroacylation of the olefins. The following protocol to suppress the decarbonylation, one being steric and the other electronic in nature, can be used. In the case of the reaction of 1-methylin-dole-3-carboxaldehyde with ethylene, the ethylation product is also obtained in quantitative yield (Eq. 9.5) [13]. 

Tischchenko-type dimerization of aldehyde is catalyzed by dihydridorutheni-um(II) complexes. In this reaction, aldehyde is initially consumed to reduce Ru(II) to give Ru(0), to which aldehyde oxidatively adds to give a hydrido(acyl)mtheni-um(II) active intermediate affording esters [15]. Hydroacylation of olefins [16] and dienes [17] is also catalyzed by ruthenium complexes (Scheme 14.5). 

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 method of transition metal induced hydroacylation of olefins with aldehydes has its origins in the observation that aldehydes are decarbonylated by Wilkinson s catalyst31. Mechanistically, decarbonylation is believed to start with an oxidative addition of a low valent transition metal unit to the aldehyde C —H bond. This individual step has been observed in several cases32 " 37. The resulting metal acyl hydride system can then be decarbonylated to form a new C - H bond upon reductive elimination, steps which are also well known. 

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