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Oxypalladations

The Pd—C cr-bond can be prepared from simple, unoxidized alkenes and aromatic compounds by the reaction of Pd(II) compounds. The following are typical examples. The first step of the reaction of a simple alkene with Pd(ll) and a nucleophile X or Y to form 19 is called palladation. Depending on the nucleophile, it is called oxypalladation, aminopalladation, carbopalladation, etc. The subsequent elimination of b-hydrogen produces the nucleophilic substitution product 20. The displacement of Pd with another nucleophile (X) affords the nucleophilic addition product 21 (see Chapter 3, Section 2). As an example, the oxypalladation of 4-pentenol with PdXi to afford furan 22 or 23 is shown. [Pg.13]

Phenolic oxygen participates in facile oxypalladation. The intramolecular reaction of 2-hydroxychalcone (105) produces the flavone 106[127]. The ben-zofuran 107 is formed from 2-allyIphenol by exo cyclization with Pd(OAc)2, but benzopyran 108 is obtained by endo cyclization with PdChf S], Normal cyclization takes place to form the furan 109 from 2-(l-phenylethenyl)phe-nol[129]. Benzofuran formation by this method has been utilized in the synthesis of aklavinione (110)[130]. [Pg.35]

The intramolecular oxidative earbonylation has wide synthetie applieation. The 7-lactone 247 is prepared by intramolecular oxycarbonylation of the alke-nediol 244 with a stoichiometric amount of Pd(OAc)2 under atmospheric pres-sure[223]. The intermediate 245 is formed by oxypalladation, and subsequent CO insertion gives the acylpalladium 246. The oxycarbonylation of alkenols and alkanediols can be carried out with a catalytic amount of PdCl2 and a stoichiometric amount of CuCb, and has been applied to the synthesis of frenolicin(224] and frendicin B (249) from 248[225]. The carbonylation of the 4-penten-l,3-diol 250, catalyzed by PdCl2 and CuCl2, afforded in the c -3-hydroxytetrahydrofuran-2-aeetie acid lactone 251[226J. The cyclic acetal 253 is prepared from the dienone 252 in the presence of trimethyl orthoformate as an accepter of water formed by the oxidative reaction[227]. [Pg.54]

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]. [Pg.80]

The mechanism of the rearrangement catalyzed by Pd(fl), typically by PdCl2(RCN)2, is explained by the oxypalladation of an alkene to form 810 as an intermediate, or cyclization-induced rearrangement. As a limitation, no rearrangement takes place when the allylie ester 812 is substituted at the C-2 position of the allyl group, while a smooth rearrangement of 811 takes place[500]. [Pg.401]

The unsaturated c.vo-enol lactone 17 is obtained by the coupling of propargylic acetate with 4-pentynoic acid in the presence of KBr using tri(2-furyl)-phosphine (TFP) as a ligand. The reaction is explained by the oxypalladation of the triple bond of 4-pentynoic acid with the ailenyipailadium and the carbox-ylate as shown by 16, followed by reductive elimination to afford the lactone 17. The ( -alkene bond is formed because the oxypalladation is tnins addition[8]. [Pg.455]

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... [Pg.498]

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]. [Pg.500]

A deuterium-labeling study of a reaction of this type demonstrated syn stereoselectivity in both the oxypalladation and P-elimination, which indicates that the cyclization occurs by internal migration, rather than by an anti nucleophilic capture.113 This particular system also gives products from double-bond migration that occurs by reversible Pd(II)-D addition-elimination. [Pg.712]

Reduced furans are formed in two types of oxypalladation processes on substrate a,ft- and y,<5-unsaturated alcohols. In an unusual reaction, allyl alcohol is converted into 4-methylenetetrahydrofurfuryl alcohol, among other products (Scheme 57)97 the formation of propene is thought to arise by reductive hydrogenolysis of allyl alcohol. [Pg.346]

Chromene acetals 39 are accessible from 2-vinyl-substituted phenols via the allylic acetals 38 through oxypalladation of benzyloxypropa- 1,2-diene and a subsequent Ru-catalysed RCM. 2-Substituted chromenes can be derived from the acetals 39 by conversion into the 1-benzopyrylium salts which are then trapped by nucleophiles (Scheme 26) <00TL5979>. In a like manner, 2-aIkoxychromans have been converted into various 2-substituted chromans by sequential treatment with SnCl4 and a silyl enol ether <00TL7203>. [Pg.324]

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. [Pg.680]

When 1,3-dienes containing a tethered alcohol are subjected to Wacker-type reactions, the initial intramolecular oxypalladation event creates a 7r-allylpalladium species, which can then undergo an additional bond-forming process to effect an overall 1,4-difunctionalization of the diene with either cis- or // -stereochemistry (Scheme 18).399 An array of substrate types has been shown to participate in this reaction to generate both five- and six-membered fused or ro-oxacycles.435-437 Employing chiral benzoquinone ligands, progress toward the development of an asymmetric variant of this reaction has also been recorded, albeit with only modest levels of enantioselectivity (up to 55% ee).438... [Pg.682]

An interesting variant involves the use of an allylic alcohol as the alkene component. In this process, re-oxidation of the catalyst is unnecessary since the cyclization occurs with /Uoxygen elimination of the incipient cr-Pd species to effect an SN2 type of ring closure. Both five- and six-membered oxacycles have been prepared in this fashion using enol, hemiacetal, and aliphatic alcohol nucleophiles.439,440 With a chiral allylic alcohol substrate, the initial 7r-complexation may be directed by the hydroxyl group,441 as demonstrated by the diastereoselective cyclization used in the synthesis of (—)-laulimalide (Equation (120)).442 Note that the oxypalladation takes place with syn-selectivity, in analogy with the cyclization of phenol nucleophiles (1vide supra). [Pg.682]

The phenolic oxygen on 2-allyl-4-bromophenol (7) readily underwent oxypalladation using a catalytic amount of PdCl2 and three equivalents of Cu(OAc)2, to give the corresponding benzofuran 8. This process, akin to the Wacker oxidation, was catalytic in terms of palladium, and Cu(OAc)2 served as oxidant [17]. Benzofuran 10, a key intermediate in Kishi s total synthesis of aklavinone [18], was synthesized via the oxidative cyclization of phenol 9 using stoichiometric amounts of a Pd(II) salt. [Pg.270]

Utimoto et al. synthesized substituted furans using a Pd-catalyzed rearrangement of easily accessible P/y-acetylenic ketones [103]. One plausible pathway is illustrated here using the transformation of p,y-acetylenic ketone 127 to 2,5-disubstituted furan 128. Enolization of 127 is followed by an intramolecular oxypalladation of the resulting enol 129 to form furylpalladium(II) species 130, which is subsequently treated with acid to give furan 128. [Pg.289]

The Pd-catalyzed coupling reaction of the propargyl acetate 53 and 4-pentynoic acid (54) in the presence of potassium bromide produced the unsaturated exo-enol lactone 55 [66], The reaction proceeded via oxypalladation of the triple bond of 54 with an allenylpalladium intermediate, which was formed from Pd(0) and 53 and the carboxylate as shown in Scheme 3.30. [Pg.106]

The oxypalladation method mentioned above was introduced as a crucial step in the synthesis of several natural products. As shown in Scheme 8.51, Metz and coworkers used this strategy in an enantioselective synthesis of ricciocarpin A [122], Other impressive applications including the acetalization-RCM sequence have been employed in the synthesis of the AB ring of ciguatoxin [123] and of the Q-C fragment of laulimalide [124] (Scheme 8.52). [Pg.460]

Palladium-catalyzed reaction of a 3,4-allenol with iodobenzene proceeds through an oxypalladation-reductive elimination sequence to give a 2,3-dihydrofuran efficiently (Scheme 16.8) [13,14],... [Pg.928]

This approach is applicable to cross-coupling reactions of allenoic acids and acrolein, which lead to the synthesis of lactones (Scheme 16.98) [104]. The reaction proceeds via oxypalladation of an allenoic acid to give rise to a vinylpalladium species. [Pg.967]

A development of the last two decades is the use of Wacker activation for intramolecular attack of nucleophiles to alkenes in the synthesis of organic molecules [9], In most examples, the nucleophilic attack is intramolecular, as the rates of intermolecular reactions are very low. The reaction has been applied in a large variety of organic syntheses and is usually referred to as Wacker (type) activation of alkene (or alkynes). If oxygen is the nucleophile, it is called oxypalladation [10], Figure 15.4 shows an example. During these reactions the palladium catalyst is often also a good isomerisation catalyst, which leads to the formation of several isomers. [Pg.324]

Extensive studies on the Wacker process have been carried out in industrial laboratories. Also, many papers on mechanistic and kinetic studies have been published[17-22]. Several interesting observations have been made in the oxidation of ethylene. Most important, it has been established that no incorporation of deuterium takes place by the reaction carried out in D20, indicating that the hydride shift takes place and vinyl alcohol is not an intermediate 1,17]. The reaction is explained by oxypalladation of ethylene, / -elimination to give the vinyl alcohol 6, which complexes to H-PdCI, reinsertion of the coordinated vinyl alcohol with opposite regiochemistry to give 7, and aldehyde formation by the elimination of Pd—H. [Pg.18]


See other pages where Oxypalladations is mentioned: [Pg.33]    [Pg.96]    [Pg.187]    [Pg.499]    [Pg.572]    [Pg.795]    [Pg.351]    [Pg.290]    [Pg.325]    [Pg.55]    [Pg.304]    [Pg.381]    [Pg.537]    [Pg.59]   


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Alcohols oxypalladation

Alkenes oxypalladation

Chlorides oxypalladation

Cyclization oxypalladation

Hydroxyalkenes, intramolecular oxypalladation

Hydroxyalkynes, intramolecular oxypalladation

Intermolecular reactions oxypalladation

Intramolecular oxypalladation

Oxypalladation

Oxypalladation acetalization

Oxypalladation alcohol additions

Oxypalladation alcoholic groups

Oxypalladation alkene-alcohol reactions

Oxypalladation alkene-carboxylic acid reactions

Oxypalladation carboxylic acid/alcohol reactions

Oxypalladation carboxylic acids

Oxypalladation catalytic

Oxypalladation hydroxyalkenes

Oxypalladation organopalladium derivatives

Oxypalladation palladium compounds

Oxypalladation reactions

Oxypalladation, alkene-carboxylic acid

Oxypalladation, reverse

Oxypalladation-dehydropalladation

Oxypalladation-reductive elimination domino

Oxypalladation-reductive elimination domino reactions

Oxypalladations, palladium®) chloride

Phenols oxypalladation

Syn oxypalladation

Takahiro Hosokawa and Shun-Ichi Murahashi 3 Intermolecular Oxypalladation not Accompanied by Dehydropalladation

Vinyl ethers oxypalladation

Wacker oxypalladation

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