Alkene hydroacylation

Keywords aldehyde, 1-alkene, hydroacylation, RhCl(PPh3)3, microwave irradiation... 

A general catalytic cycle for an intramolecular alkene hydroacylation reaction. 

Scheme 8.20 Asymmetric intermolecular alkene hydroacylation reactions reported by Bolm.

The combination of Ni(COD)2 and l,3-di-ferf-butylimidazol-2-ylidene (ItBu) was demonstrated to effectively catalyse an intramolecular alkene hydroacylation to construct five- and six-membered benzocyclic ketones in good to excellent yields (Scheme 14.71). Al-aryl-substituted NHCs are not effective for this transformation. The reaction is proposed to proceed via a process as shown in Scheme 14.72. Thus, 2-allylbenzaldehyde coordinates to Ni(0)/ItBu to form complex A. The oxidative cyclisation of A gives a nickelacycle intermediate B. B undergoes p-hydride elimination and reductive elimination to produce final product C, along with regeneration of the catalyst. ... 

Alkene-C=X (X=0, NR) Coupling (Reductive Carbonyl-Ene and Reductive Hydroacylation)... 

Tab. 3.27 Solvent-free hydroacylation of 1-alkenes with aldehyde.

A fast and efficient molybdenum-catalyzed asymmetric allylic alkylation under noninert conditions has been reported using MW-accelerated reaction [178]. Inter-molecular hydroacylation of 1-alkenes with aldehydes has been presented as a greener alternative to classical approach using a homogeneous catalyst in toluene. 

During the coverage period of this chapter, reviews have appeared on the following topics reactions of electrophiles with polyfluorinated alkenes, the mechanisms of intramolecular hydroacylation and hydrosilylation, Prins reaction (reviewed and redefined), synthesis of esters of /3-amino acids by Michael addition of amines and metal amides to esters of a,/3-unsaturated carboxylic acids," the 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors, control of asymmetry in Michael additions via the use of nucleophiles bearing chiral centres, a-unsaturated systems with the chirality at the y-position, and the presence of chiral ligands or other chiral mediators, syntheses of carbo- and hetero-cyclic compounds via Michael addition of enolates and activated phenols, respectively, to o ,jS-unsaturated nitriles, and transition metal catalysis of the Michael addition of 1,3-dicarbonyl compounds. ... 

Since the early 1990s, considerable progress has been achieved in the development of catalytic enantioselective intramolecular hydroacylation reactions of alkenes/alkynes that generate five-membered rings. Nonetheless, the vast majority of interesting hydroacylation reactions has not yet proven susceptible to effective asymmetric catalysis. This deficiency represents an exciting opportunity for future investigations in this... 

After extensive screening of various aldehydes to optimize the reaction conditions, it was found that aromatic aldehydes were able to serve as a carbon monoxide source, in which the electronic nature of the aldehydes is responsible for their ability to transfer CO efficiently [24]. Consequently, aldehydes bearing electron-withdrawing substituents are more effective than those bearing electron-donating substituents, with pentafluoro-benzaldehyde providing optimal reactivity. Interestingly, for all substrates tested the reaction is void of any complications from hydroacylation of either the alkene or alkyne of the enyne. Iridium and ruthenium complexes, which are known to decarboxylate aldehydes and catalyze the PK reaction, demonstrated inferior efficiency as compared to... 

The hydrative cyclization involves the formation of a ruthenium vinylidene, an anti-Markovnikov addition of vater, and cyclization ofan acylmetal species onto the alkene. Although the cyclization may occur through a hydroacylation [32] (path A) or Michael addition [33] (path B), the requirement for an electron- vithdra ving substituent on the alkene and lack of aldehyde formation indicate the latter path vay to be the more likely mechanism. Notably, acylruthenium complex under vent no decarbonylation in this instance. 

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... 

Hydroacylation of carbonyls or alkenes by aldehydes is well known. Hydroacylation of an activated ketone (85) by benzaldehyde has now been reported, giving a new asymmetric centre at the ketone carbon (86).257 In a metal-free procedure, the reaction... 

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... 

Acylmetal hydride is formed by the oxidative addition of aldehyde, and hydroacylation occurs by insertion of alkene or alkyne. The Ni-catalysed hydroacylation of internal alkyne 600 with aldehyde gave rise to the v./l-unsaturated ketone 601 [230]. The Ru-catalysed hydroacylation of cyclohexene with aldehyde 602 under CO pressure at high temperature gives the ketone 603 [231]. 

An intermolecular hydroacylation of alkynes or electron-poor alkenes (e.g. CH2= CHCChMe) with /3-thioacetal-substituted aldehydes, catalysed by [(dppe)Rh]C104, has been reported to occur in acetone at 50 °C. The reaction is believed to proceed via a chelated rhodium acyl intermediate.111... 

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. 

Aldehydes also react with alkenes to give hydroacylated products, unsymmetric ketones. Isnard and coworkers reported the first intermolecular hydroacylation, though the yields of the products were low (Eq. 11.20) [61]. 

Usually hydroacylation reactions of alkenes requires CO to suppress decarbonyla-tion of the aldehyde, but this reaction does not require CO. The key intermediate in the catalytic cycle is postulated to be a [Ru(> -al]yl)(acyl)Ln] species. 

Hydroacylation. The formation of ketones from aldehydes and alkenes is catalyzed by Wilkinson s catalyst in the presence of a chelating ligand (e.g., 2-amino-3-picoline). 

The addition of a catalytic amount of Cp2TiCl2 dramatically increases the yield of the hydroacylated ketone formed in the hydroacylation of 1-alkenes with heteroaromatic aldehydes by using Wilkinson s complex and 2-amino-3-picoline as co-catalysts.1264 Cp2TiCl2 catalyzes the reduction of aryl halides by sodium borohydride. The reaction scope and mechanism are solvent dependent.1265... 

Hoffman and Carreira [31] reported a Rh-catalyzed asymmetric intramolecular hydroacylation of pent-4-enal substrates, providing P-substituted cyclopentanones in good yield and excellent selectivity by using chiral spiro phosphoramidite-alkene ligand (R)-29 (Scheme 29). 

Formation of ketones via hydroacylation can be achieved either via transition metal catalyzed hydrocarbonylative coupling of two alkenes ... 

Hydroacylation of Alkenes with Aldehydes Mechanism and Stereochemistry... 

The presence of the hydride acyl intermediate in decarbonylation suggests the possibility of alkene insertion into the metal hydride bond and reductive elimination of a ketone. This was first observed in the intramolecular hydroacylation of 2,3-disubstituted 4-pcntcnals using stoichiometric amounts of Wilkinson s catalyst or in the presence of tin(IV) chloride to give substituted cyclopentanones and stereoisomeric cyclopropanes as side products27. 

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