Pd-catalyzed conjugate addition

In 1979 Cacchi et reported a Pd-catalyzed conjugate addition of tetraphenyltin to a,/3-unsaturated ketones under a dual-phase system (Scheme 51), and the reaction in Scheme 52 also seems to be in a similar category. °i A more complex reaction was reported by Dceda and Sato using Ni-complex catalyst (Scheme 53). 

Scheme 2.11 Catalytic cycle for Pd-catalyzed conjugate addition of phenylboronic acid to 3-methyl-2-cyclohexenone.

Where possible, it may be most economical to effect a chiral transformation on a pre-formed, pro-chiral ring. Ben Feringa of the University of Groningen prepared (Chem Commun. 2005, 1711) the enone 2 from 4-methoxypyridine 1. Cu -catalyzed conjugate addition of dialkyl zincs to 2 proceeded in up 96% . Pd-mediated allylation of the intermediate zinc enolate led to 3, with the two alkyl subsituents exclusively trans to each other. 

Cho, C. S. Motoffisa, S.-I. Ohe, K. Uemura, S. Shim, S. C. A new catalytic activity of SbCl3 in Pd(0)-catalyzed conjugate addition of aromatics to a,/3-unsaturated ketones and aldehydes with NaBPh and arylboronic adds. 

Yuguchi, M., Tokuda, M., Qrito, K. Pd(0)-Catalyzed conjugate addition of benzylzinc chlorides to a,p-enones in an atmosphere of carbon monoxide Preparation of 1,4-diketones. J. Org. Chem. 2004, 69, 908-914. 

Conjugate addition. The addition of Me SiCN to enones derivatives of glycals is catalyzed by Pd(OAc)2- Five-membered azacycles (lactams, imidazolinones, oxazo-lidinones) that bear a 4-oxoalkylidene group adjacent to the nuclear nitrogen atom are readily available by a Pd-catalyzed intramolecular addition and conjugate addition tandem. °... 

In addition to Zn, B, and Sn—three metal countercations that were found to be highly satisfactory for alkynylafiorf —the Sonogashira alkynylation protocol (Sect IIL2X1) has also proved to be generally tqtpUcable to this case. Some representative examples of Pd-catalyzed conjugate substitution with alkynylmetals and terminal alkynes are summarized in Table 3. 

Pd-catalyzed conjugate substitution, as defined in Scheme 1 of Sect. III.2.15, is nothing more than Pd-catalyzed alkenylation with /3-halo- or /3-metallo-substituted a,/3-unsaturated carbonyl compounds and related derivatives. Since the reaction is closely related to the widely known conjugate addition and since it can serve as the component of a novel and alternative conjugate addition protocol, their special discussion is warranted. 

Some details of the syntheses of natural products via Pd-catalyzed conjugate substitution, such as those of dendrolasin and mokuplalide (Scheme 6 of Sect. III.2.15), are discussed in Sect. III.2.15. These and additional examples are presented in Table 12. 

Scheme 5.27 Pd(ll)-bpy-catalyzed conjugate addition of aryl boronic acids to a,p-unsaturated carbonyl...

Pd- and Rh-catalyzed conjugate additions of arylboronic acids to enones and nitrostyrenes (Hayashi-Miyaura reaction)... 

Lin, S. Lu, X. Cationic Pd(II)/Bipyridine-Catalyzed Conjugate Addition of Arylboronic Acids to P,P-Disubstituted Enones Construction of Quaternary Carbon Centers. Org. Lett. 2010,12,2536-2539. 

Diacetoxylation of various conjugated dienes including cyclic dienes has been extensively studied. 1,3-Cyclohexadiene was converted into a mixture of isomeric l,4-diacetoxy-2-cyclohexenes of unknown stereochemistry[303]. The stereoselective Pd-catalyzed 1,4-diacetoxylation of dienes is carried out in AcOH in the presence of LiOAc and /or LiCI and beiizoquinone[304.305]. In the presence of acetate ion and in the absence of chloride ion, /rau.v-diacetox-ylation occurs, whereas addition of a catalytic amount of LiCl changes the stereochemistry to cis addition. The coordination of a chloride ion to Pd makes the cis migration of the acetate from Pd impossible. From 1,3-cyclohexadiene, trans- and ci j-l,4-diacetoxy-2-cyclohexenes (346 and 347) can be prepared stereoselectively. For the 6-substituted 1,3-cycloheptadiene 348, a high diaster-eoselectivity is observed. The stereoselective cij-diacetoxylation of 5-carbo-methoxy-1,3-cyclohexadiene (349) has been applied to the synthesis of dl-shikimic acid (350). 

Several types of Pd-catalyzed or -promoted reactions of conjugated dienes via TT-allylpalladium complexes are known. The Pd(II)-promoted oxidative difunctionalization reactions of conjugated dienes with various nucleophiles is treated in Chapter 3, Section 4, and Pd(0)-catalyzed addition reactions of conjugated dienes to aryl and alkenyl halides in this chapter. Section 1.1.1. Other Pd(0)-catalyzed reactions of conjugated dienes are treated in this section. 

Recently, elegant synthesis of ruin -MRS carbapenum has been reported. Sequential reaction of nitromethane via conjugate addition-elimination to a,fi-unsanirated esters followed by Pd-catalyzed subsdnidon of the residdng allyl nitro compound with the naphthosultam affords the allyladon product which is an and fEq. 7.20. ... 

Ferrocen-l,l -diylbismetallacycles are conceptually attractive for the development of bimetal-catalyzed processes for one particular reason the distance between the reactive centers in a coordinated electrophile and a coordinated nucleophile is self-adjustable for specific tasks, because the activation energy for Cp ligand rotation is very low. In 2008, Peters and Jautze reported the application of the bis-palladacycle complex 56a to the enantioselective conjugate addition of a-cyanoacetates to enones (Fig. 31) [74—76] based on the idea that a soft bimetallic complex capable of simultaneously activating both Michael donor and acceptor would not only lead to superior catalytic activity, but also to an enhanced level of stereocontrol due to a highly organized transition state [77]. An a-cyanoacetate should be activated by enolization promoted by coordination of the nitrile moiety to one Pd(II)-center, while the enone should be activated as an electrophile by coordination of the olefinic double bond to the carbophilic Lewis acid [78],... 

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