Palladium acetate allylic oxidation

Dialkylindolines and 1,3-dialkylindoles are formed in poor yield (<10%) from the reaction of ethyl- or phenymagnesium bromide with 2-chloro-N-methyl-N-allylaniline in the presence of catalytic quantities of (bistriphenylphosphine)nickel dichloride.72 In a modification of this procedure, the allyl derivatives can be converted by stoichiometric amounts of tetrakis(triphenylphosphine)nickel into 1,3-dialkylindoles in moderate yield72 (Scheme 43) an initial process of oxidative addition and ensuing cyclization of arylnickel intermediates is thought to occur. In contrast to the nickel system,72 it has proved possible to achieve the indole synthesis by means of catalytic quantities of palladium acetate.73 It is preferable to use... 

Another route to the diol monomer is provided by hydroformylation of allyl alcohol or allyl acetate. Allyl acetate can be produced easily by the palladium-catalyzed oxidation of propylene in the presence of acetic acid in a process similar to commercial vinyl acetate production. Both cobalt-and rhodium-catalyzed hydroformylations have received much attention in recent patent literature (83-86). Hydroformylation with cobalt carbonyl at 140°C and 180-200 atm H2/CO (83) gave a mixture of three aldehydes in 85-99% total yield. 

Palladium-catalyzed oxidation of 1,4-dienes has also been reported. Thus, Brown and Davidson28 obtained the 1,3-diacetate 25 from oxidation of 1,4-cyclohexadiene by ben-zoquinone in acetic acid with palladium acetate as the catalyst (Scheme 3). Presumably the reaction proceeds via acetoxypalladation-isomerization to give a rr-allyl intermediate, which subsequently undergoes nucleophilic attack by acetate. This principle, i.e. rearrangement of a (allyl)palladium complex, has been applied in nonoxidative palladium-catalyzed reactions of 1,4-dienes by Larock and coworkers29. Akermark and coworkers have demonstrated the stereochemistry of this process by the transformation of 1,4-cyclohexadiene to the ( r-allyl)palladium complex 26 by treatment... 

In 1997, Backvall and Jonasson published a procedure for the 1,2-oxidation of terminal allenes 7 [5]. In this case the reaction conditions were chosen so that the (vinyl)palladium complex equilibrates back to the allene complex. Using bromide instead of chloride as a nucleophile, the 2-bromo-jt-allyl complex 9 is the major intermediate present in the reaction mixture. A catalytic reaction was developed with the use of 5 mol% palladium acetate and p-benzoquinone (BQ) as terminal oxidant (Scheme 17.5). 

Allylic acetoxylation with palladium(II) salts is well known however, no selective and catalytic conditions have been described for the transformation of an unsubstituted olefin. In the present system use is made of the ability of palladium acetate to give allylic functionalization (most probably via a palladium-x-allyl complex) and to be easily regenerated by a co-oxidant (the combination of benzoquinone-manganese dioxide). In contrast... 

Heterogeneous palladium catalysts proved to be active in the conversion of simple alkenes to the corresponding allylic acetates, carbonyl compounds, and carboxylic acids.694 704 Allyl acetate or acrylic acid from propylene was selectively produced on a palladium on charcoal catalyst depending on catalyst pretreatment and reaction conditions.694 Allylic oxidation with singlet oxygen to yield allylic hydroperoxides is discussed in Section 9.2.2. 

The oxidation of ds-2-hexene (II) catalyzed by palladium acetate proceeds after an induction period of 2-4 hrs shown in Figure 4. Using 0.00163M palladium acetate total inhibition of reaction was observed with 1.08 X 10 5M quinol. 2,4,6-tri (tert-Butyl) phenol (5.60 X 10 5M) only showed the reaction without total inhibition. The formation of the allylic complex IVb proceeds in a similar way to the reaction of I, and it is the major species in the catalyst solutions. The formation of unsatu-... 

A chemo- and highly regio-selective Pd-catalysed allylic oxidation reaction that proceeds via a novel mechanism where two different ligands interact serially with palladium to promote different steps of the catalytic cycle has been reported. Initial formation of a dimeric 7r-allylpalladium acetate complex has been proposed.41... 

Three new chirality centers are formed with high enantio- and complete diastereoselectivity in the course of the reaction of the enol triflate 37 to the bicyclo [3.3.0]octane derivative 38 (Scheme 11) [15]. In this transformation, the intermediate 39, formed by oxidative addition, leads to the cationic palladium-7r-allyl complex 40, which is finally converted to the isolated product 38 by regio- and diastereoselective nucleophilic addition of an acetate anion. The bicyclic product 38 is of interest as a building block for the synthesis of capnellene sesquiterpenes. 

In the oxidation of 2-octenyl acetate, in addition to the normal oxidation, palladium-catalyzed allylic rearrangement and subsequent oxidation took place to give a small amount of 3-acetoxy-2-octanone as a byproduct. Ethers of secondary allylic alcohols also underwent the regioselective oxidation to give the corresponding 3-alkoxy ketones in 30-40% yields. But in this case too, by-products derived from the allylic reanangement a subsequent oxidation were also detected. Results of the oxidation of some allyl ethers are shown in Table 3. °... 

Among oxi tions producing allylic alcohols or their derivatives the modem variants of selenium dioxide oxidations are by far the most popular. Systems based on metal acetates, particularly palladium tri-fluoroacetate, can be very useful and are receiving increasing attention but the Kharasch-Sosnovsky reaction, once very common for allylic oxidation, is now rarely used. Sensitized photooxidation with singlet oxygen, a very well-known procedure, is still somewhat unpredictable and has periu K received less consideration than it deserves. 

An interesting application of the Fujiwara-Moritani/oxidative Heck reaction for the synthesis of benzo furans was recently reported by the Stoltz lab [31]. A variety of allyl phenyl ethers (all containing electron-rich aryl components) react with 10 mol% palladium acetate, 20 mol% ethyl nicotinate, 20 mol% sodium acetate, and one equivalent of benzoquinone at 100°C to provide benzofurans in 52-79% yield (e.g. 16—>17). The mechanism of this transformation begins with arene palladation of Pd(II) followed by olefin insertion, p-hydrogen elimination, and olefin isomerization to the thermodynamically favored benzofuran product. The resulting Pd(0) species is then oxidized to Pd(ll) thus regenerating the active catalyst. 

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