Alkenes hydroacylation, intramolecular

A general catalytic cycle for an intramolecular alkene hydroacylation reaction. 

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. ... 

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... 

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). 

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. 

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 . 

An insertion-reductive elimination sequence is involved in the rhodium-catalyzed, intramolecular hydroacylation of 4-alkenals to form cyclopentanes ... 

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... 

The intramolecular hydroacylation of aldehydic olefins is catalyzed by cationic Rh complexes of chelating phosphines in polar nonprotic solvents. The rate decreases with increasing substrate Rh ratio since the substrate complex with the catalyst inhibits the reaction. However, since this complexation also prevents the decarbonylation of the aldehyde, catalyst deactivation decreases, leading to a higher turnover. The only effective catalytic C—H activations are carried out with [RhCl(CO)(PMe3)2] under photolysis which removes CO. Alkanes are converted to alkenes in the order cyclooctane > cyclohexane > n-decane n-hexane. Up to 200 turnovers cyclooctane per hour are observed. In order to generate terminal... 

Compared with asymmetric intramolecular hydroacylation reactions of alkenes, the corresponding intermolecular versions have been relatively less developed. In 2007, Stemmier and Bolm reported the first example of enanti-oselective intermolecular hydroacylation reactions between salicylaldehydes 40 and norbornadiene-type alkenes 41 (Scheme 8.20). It was found that the diastereoselectivity of the reaction could be modulated through changing the chiral ligands. With ferrocene-based bisphosphine ligand L5, the exo-product 42a was obtained exclusively with up to 82% ee. When monodentate phos-phoramidite ligand L6 was employed, the e do-isomer 42b was obtained as major product with moderate enantioselectivity (54% ee). 

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]. 

Intramolecular hydroacylation of 4-aIkenals is a well-established method for producing cyclopentanones in which a C=C bond inserts into the Rh hydride formed by C-H oxidative addition to Rh(I) with chiral ligands and suitable alkenal substrates, useful asymmetric induction is possible. Extension to cyclopentenone synthesis requires a trans addition of Rh—H across the alkyne (see Section 7.2). ... 

Scheme 3.80 Catalytic asymmetric intramolecular hydroacylation with rhodium/phosphoramidite-alkene ligand complexes.

Activation by rhodium complexes has been used to achieve direct exchange of ketone methyl or aryl groups with an aryl group on ArB(OH)2, selective C(CO)-C bond cleavage on reaction of ketones with water, oxidative acylation between secondary benzamides and aryl aldehydes with subsequent intramolecular cyclization to 3-hydroxyisoindolin-l-ones, " cross dehydrogenative coupling to form xanthones from 2-aryloxybenzaldehydes, and activation of the aldehydic C-H bond to achieve hydroacylation of unactivated alkenes by salicylaldehyde derivatives and of vinylsilane by benzaldehyde. ... 

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