Hydroacylation of alkenes

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 

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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. 

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... 

The let rail uoroborate salt 3 can effect hydroacylation of 1-alkenes. ... 

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. ... 

Hydroacylation of Alkenes with Aldehydes Mechanism and Stereochemistry... 

Here catalysis involves the formation of a ruthenium vinylidene, an anti-Markovnikov addition of water (368), and cyclization of an acylmetal species onto the alkene. Although cyclization may occur via hydroacylation (Scheme 52, path A) (460-462) or the Michael addition reaction (Scheme 52, path B) (463,464), the requirement for an electron-withdrawing substiment on the alkene and the absence of aldehyde formation suggest path B to be the more likely mechanism (465,466). Trost discovered that the use of the cationic mthenium catalyst CpRu(MeCN)3+PFg is tolerant of 1,2-di-and trisubstimted alkenes and promotes cyclization of 1,6- and 1,7-enynes to five- and six-membered ring products (467). In a number of examples, the mthenium reaction is complementary to the Pd-catalyzed cyclization described above, selectively forming the 1,4-diene over the traditional 1,... 

Jim et al. [24] reported the above reaction in an article entitled Chelation-Assisted Intermolecular Hydroacylation Direct Synthesis of Ketone from Aldehyde and 1-Alkene in 1997 [24]. They also reported on the reaction mechanism, as shown in Scheme 7.1 [24]. 

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... 

In 2009, Tanaka and co-workers achieved Rh-catalyzed highly enantioselective intermolecular hydroacylation reactions of aliphatic aldehydes 48 with 1,1-substituted acrylamides 49 by using a cationic Rh/QuinoxP complex as the catalyst (Scheme 8.24a). Unfortunately, the reaction of simple benzaldehyde with acrylamide 49a was sluggish and the enantioselectivity was moderate, but utilizing (i ,R)-Me-DuPhos as the ligand could improve both yield and enantioselectivity (Scheme 8.24b). When cyclopentene-substituted amide 49b was subjected to the standard reaction conditions, a thermodynamically stable hydroacylation product 50b was generated with excellent diastereoselectivity (>99 1 dr) and enantioselectivity (97% ee), although dramatically reduced reactivity was observed (5% yield) (Scheme 8.24c). This report represents the first example of an asymmetric hydroacylation reaction of a trisubstituted alkene. 

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