Chlorides oxypalladation

The isoflavone 406 is prepared by the indirect a-phenylation of a ketone by reaction of phenylmercury(II) chloride with the enol acetate 405, prepared from 4-chromanone[371]. A simple synthesis of pterocarpin (409) has been achieved based on the oxypalladation of the oriho-mercurated phenol derivative 408 with the cyclic alkene 407[372,373]. 

The first step of the reaction is the oxypalladation of the triple bond with PdCl2 as shown by 228 to form the alkenylpalladium species 229, and the Pd is displaced with proton to regenerate Pd(TI) species and the lactone 224. The alkenylpalladium species 229 can be utilized for further reaction. When allyl chloride (230) is added, double bond insertion is followed by elimination of... 

Propargylic alcohol, after lithiation, reacts with CO2 to generate the lithium carbonate 243, which undergoes oxypalladation. The reaction of allyl chloride yields the cyclic carbonate 244 and PdC. By this reaction hydroxy and allyl groups are introduced into the triple bond to give the o-allyl ketone 245[129]. Also the formation of 248 from the keto alkyne 246 with CO2 via in situ formation of the carbonate 247 is catalyzed by Pd(0)[130]. 

Early mechanistic studies have indicated that the oxypalladation step in the Wacker process proceeds through an <37z/z-pathway,399 although recent deuterium-labeling experiments have shown the viability of a yy/z-mechanism involving insertion of a metal-coordinated oxygen into the alkene.400,401 For example, with excess chloride ion present, the Wacker-type cyclization of a deuterated phenol system occurred in a primarily //-pathway, whereas the oxypalladation step favored a yy/z-mode in the absence of excess chloride ion (Scheme 16). Thus, either mechanism may be operative under a given set of experimental conditions. 

In an analogous reaction the acetoxypalladation adduct of 1,5-cyclo-octadiene reacted in acetic acid, containing traces of chloride in the presence of Pb(OAc)4, to give 2,6-cwinsertion into the second double bond, and trans elimination of Pd(II) with OAc ... 

These workers also allowed /8-hydroxyethyl mercuric chloride to react to form supposedly the oxypalladation adduct postulated in the Pd(II) oxidation they obtained acetaldehyde as the product (34). 

It is comparable with the empirical rate Eq. (9.11). In this sense, these kinetics support Henry s mechanistic ideas of a sy -oxypalladation step, at least at low chloride ion concentration. 

As mentioned earlier, the oxypalladation step is discussed controversially. Thus, Backvall et al. [22] reacted -(ethylene)-ii2 (C2H2D2) with palladium chloride and cupric chloride under extreme conditions, that is, extremely high chloride ion concentration as cupric and lithium chlorides. Under such conditions, 2-chloroethanol is formed as the main product besides some acetaldehyde [23] this is not the normal product of the Wacker reaction. In this study, the formation of cz s-l,2-dideuterioethylene oxide, evidently via t/zreo-l,2-dideuterio-chloroethanol, suggests trans-addition of water (antz -hydroxypalladation). 

The selective oxidation of ethylene to acetaldehyde with Pd VCu° chloride solutions has attained major industrial importance (Wacker process). This reaction can be regarded as an oxidative olefin substimtion (oxypalladation). Once again the in-... 

From hydroxyalkenes derived from (/ )-(-)- or (5)-(+)-phenethyIamme and/or (5 )-(+)-lactic acid or (li , 25)-(-)-ephedrine, optically active tetrahydro-l,4-oxazines have been synthesized by using either MeOH or H2O as the nucleophile (Scheme The diastereoselectivities observed are high. In this case, the use of excess amounts of copper salts makes the reaction catalytic even in the absence of Oj. Interception of the Pd—C bond in oxypalladation adduct by chloride ion yields 2-chloromethyl-l,4-oxazines as shown in Scheme 30. ... 

The palladium(II)-catalyzed olefin carbonylation reaction was first reported more than 30 years ago in studies by Stille and co-workers and James et al. The reaction of carbon monoxide with cis- and tra 5-but-2-ene in methanol in the presence of palladium(II)-chloride and copper(II)-chloride yielded threo- and eryt/zro-3-methoxy-2-methyl-butanoate, respectively. The transformation that was based on the well-known Wacker process for oxidation of ethylene into acetaldehyde in water " is now broadly defined as the Pd(II)-catalyzed oxycarbonylation of the unsaturated carbon-carbon bonds. This domino reaction includes oxypalladation of alkenes, migratory insertion of carbon monoxide, and alkoxylation. Since the development of this process, several transformations mediated by palladium(II) compounds have been described. The direct oxidative bisfunctionalization of alkenes represents a powerful transformation in the field of chemical synthesis. Palladium(II)-promoted carbonylation of alkenes in the presence of water/alcohol may lead to alkyl carboxylic acids (hydrocarboxylation), diesters [bis(aIkoxycarbonyla-tion)], (3-alkoxy carboxylic acids (alkoxy-carboxylation), or (3-alkoxy esters (alkoxy-carbonylation or alkoxy-alkoxy-carbonylation). Particularly attractive features of these multitransformation processes include the following ... 

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