Palladium chloride-Benzoquinone

The elegant asymmetrization methodology of a meso compound, achieved in high enantioexcess under chiral environment, was the highlight of the total synthesis of (+)-pancratistatin (94) reported by Trost and Pulley (31]. The synthesis commenced with ( )-conduritol-A (130), obtained from p-benzoquinone, (Scheme 18) which was converted into the acetonide 131 and thence, via the dialkoxide to the cis-bis carbonate 132 (Scheme 19). The chiral n-ailyl palladium complex A formed on treatment erf 132 with the catalyst generated from chiral bis-amide 133 and n-allyl palladium chloride underwent azide substitution from the less hindered face of the molecule to provide the monocarbonate 134 in excellent yield and with high optical induction. 

To overcome the problems encountered in the homogeneous Wacker oxidation of higher alkenes several attempts have been undertaken to develop a gas-phase version of the process. The first heterogeneous catalysts were prepared by the deposition of palladium chloride and copper chloride on support materials, such as zeolite Y [2,3] or active carbon [4]. However, these catalysts all suffered from rapid deactivation. Other authors applied other redox components such as vanadium pentoxide [5,6] or p-benzoquinone [7]. The best results have been achieved with catalysts based on palladium salts deposited on a monolayer of vanadium oxide spread out over a high surface area support material, such as y-alumina [8]. Van der Heide showed that with catalysts consisting of H2PdCU deposited on a monolayer vanadium oxide supported on y-alumina, ethene as well as 1-butene and styrene... 

Analogously, in the presence of silica-supported palladium catalysts, benzene is oxidized under ambient conditions to give phenol, benzoquinone, hydroquinone and catechol [37b]. Palladium chloride, used for the catalyst preparation, is believed to be converted into metallic palladium. The synthesis of phenol from benzene and molecular oxygen via direct activation of a C-H bond by the catalytic system Pd(OAc)2-phenanthroline in the presence of carbon monoxide has been described [38]. The proposed mechanism includes the electrophilic attack of benzene by an active palladium-containing species to to produce a a-phenyl complex of palladium(ll). Subsequent activation of dioxygen by the Pd-phen-CO complex to form a Pd-OPh complex and its reaction with acetic acid yields phenol. The oxidation of propenoidic phenols by molecular oxygen is catalyzed by [A,A"-bis(salicylidene)ethane-l,2-diaminato]cobalt(ll)[Co(salen)] [39]. 

Oxidation of olefins to ketones by palladium chloride and an inorganic (cupric ions) or organic (benzoquinone) co-oxidizer is an effective method which has been applied for a long time. It was used in the regioselective preparation of a lipidic ketone, from an olefinic azide, without disturbance of the latter group (Fig. 35) 38... 

In a lOOmL round-bottomed flask fitted with a magnetic stirrer is placed a mixture of palladium (II) chloride (89mg, O.Smmol), p-benzoquinone (5.94g, 55mmol) and 7 1 dimethylformamide/water (20mL). To the solution, t-decene [substitute safrole for this compound) (7.0g, 50mmc4) is added in 10 min and the mixture is stirred at room temperature for 7h. The solution is poured into cold 3 normal hydrochloric acid (lOOmL) and extracted with 5 portions of ether. The extracts are combined and washed with three portions of 10% aqueous sodium hydroxide solution and a portion of brine, and then dried After removal of the solvent, the residue is distilled to give 2-decanone [P2P] yield 6.1g (78%). 

In 1981, a stereoselective palladium-catalyzed 1,4-diacetoxylation of 1,3-dienes with p-benzoquinone (BQ) as the oxidant was reported33. It was found that chloride ions can be used as a stereochemical switch. Thus, in the absence of chloride ions trans diacetoxylation takes place, whereas in the presence of a catalytic amount of chloride ion (as added LiCl) a cis diacetoxylation takes place (Scheme 4). In both cases the reaction is highly 1,4-regioselective. The explanation for... 

The mechanism of this new reaction is shown in Scheme 14. Coordination of the diene to palladium(II) makes the diene double bond electrophilic enough to be attacked by the allylsilane. The attack by the allylsilane takes place on the face of the diene opposite to that of the palladium (anti). This is the first example of an anti attack by an allylsilane on a 7T-(olefin)metal complex. Benzoquinone (BQ)-induced anti attack by chloride ion produces the product 58. 

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). 

Presumably a 2 -oxy-2-aminobiphenyl is intermediate in the conversion of 292 with ammonia at 135°C to 1,3,6,8-tetranitrocarbazole. The p-benzoquinones 293 (R = H, Me or OMe) gave 294 on reduction with hydrogen-palladium-acid and 295 on reduction with sulfur dioxide. Compound 294 on oxidation with iron(III) chloride and compound 295 on reduction with hydrogen-nickel produced the 3-hydroxycarbazoles 296. ... 

METHYL KETONES AUyltrimethyl-silane, Bis(acetonitrilo)chloronitro-palladium (11). Dicarb ony lbis( triphenyl-phosphine)nickel. Dichloro-dicyano-benzoquinone. Hydrogen peroxide-Palladium acetate. Meldrum s acid. Palladium r-butyl peroxide trilluoro-acctate. Palladium tl) chloride. 

The vinyl substitution reaction often may be achieved with catalytic amounts of palladium. Catalytic reactions are carried out in different ways depending on how the organopalladium compound is generated. Usually copper(II) chloride or p-benzoquinone is employed to reoxidize palladium(0) to palla-dium(II) in catalytic reactions when methods (i) or (ii) are used for making the organopalladium derivative. The procedures developed for making these reactions catalytic are not completely satisfactory, however. The best catalytic reactions are achieved when the organopalladium intermediates are obtained by the oxidative addition procedures (method iii), where the halide is both the reoxidant and a reactant. Reviews of some aspects of these reactions have been published.u-le... 

A. cis-1-Acetoxy-4-chloro-2-cyclohexene. A 1-L, one-necked, round-bottomed flask equipped with a magnetic stirring bar is charged with 200 mL of acetic acid, 5.1 g (0.12 mol) of lithium chloride, 12.2 g (0.12 mol) of lithium acetate dihydrate, 0.67 g (3 mmol) of palladium acetate, and 12.9 g (0.12 moi) of p-benzoquinone. The contents of the flask are stirred at room temperature until all components are dissolved, and 300 mL of pentane is added. To the pentane phase of the biphasic system formed is added 4.82 g (60 mmol) of 1,3-cyclohexadiene (Note 1). The reaction mixture is stirred at a moderate rate (Note 2) at room temperature and after 4 hr, 2.87 g (33 mmol) of manganese dioxide (Note 3) is added. After the flask is stirred for another 4... 

Benzoquinone 6 was reported as one of a new class of amino alcohol-derived benzoquinones tested in the palladium-catalyzed 1,4-dialkylation of 1,3 dienes. These ligands were prepared by reaction of 1 with C2-symmetric l,4-diallyloxy-2,5-benzenedicarboxylic acid chloride followed by allyl deprotection.29... 

A series of palladium(O) mono-imidazolylidene complexes have also been prepared and used for the Heck reaction of aryl chlorides in [NBu4]Br.29 The authors report that two of their catalysts, (1,3-dimesi-tylimidazolylidene)(naphthoquinone)palladium(0) and (1,3-dimesitylimida-zolylidene)(benzoquinone)palladium(0) (Fig. 5) remain stable throughout the reaction and will couple even non-activated aryl chlorides in good yields. Clearly, the authors believe that the imidazolylidene complex is responsible for this activity. 

Diacetoxylation of 1,3-dienes.1 Palladium-catalyzed oxidation of 1,3-cyclo-hexadiene with benzoquinone (used in catalytic amounts with Mn02 as the external oxidant) in acetic acid gives a 1 1 mixture of cis- and trans-, 4-diacetoxy-2-cyclohexene. Addition of LiCl or LiOAc has a profound effect on the stereochemistry. Oxidation in the presence of lithium acetate results in selective fraws-diacetoxylation, whereas addition of lithium chloride results in selective cw-diacetoxylation (equation I).2... 

OXIDATIVE CYCLIZATION Benzene-selenenyl chloride. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone. Palladium(ll) chloride-CopperCH) chloride. 

The reaction conditions are similar to those employed in the diacetoxylation reaction, with the difference that the halide concentration (usually CI ) has been increased. Thus, palladium-catalyzed oxidation of 1,3-dienes with / -benzoquinone in the presence of lithium chloride and lithium acetate gives l-acetoxy-4-chloroalk-2-enes [78]. For example cyclohexa-1,3-diene and cyclohepta-1,3-diene afforded the corresponding chloroacetates 58a and 58b in good yield and >98% cis selectivity [Eq.(41)]. Cycloocta-1,3-diene gave a 61% yield of acetoxychlorination product (>98% cis), but in this case a 3 1 mixture of 1,4-and 1,2-addition products was formed. A number of substituted cyclic conjugated dienes work well, and, in all cases tried, the reaction proceeds with >97-98% cis selectively [52,78-81]. 

In the catalytic cycle of the palladium-benzoquinone-based 1,4-oxidation of 1,3-dienes, benzoquinone is reduced to hydroquinone. The diacetoxylation reaction is conveniently performed with p-benzoquinone in catalytic amounts, employing Mn02 as the stoichiometric oxidant. In this process, the hydroquinone formed in each cycle (cf. Scheme 8-6) is reoxidized to p-benzoquinone by MnO,. For example, the catalytic reaction of cyclohexa-1,3-diene using catalytic amounts of both Pd(OAc)2 and p-benzoquinone with stoichiometric amounts of Mn02 in acetic acid in the presence of lithium acetate afforded a 93% yield of rranj-l,4-diacetoxycyclohex-2-ene (>91% tram) [51b]. The corresponding reaction in the presence of lithium chloride gave ci5-l,4-diacetoxycyclohex-2-ene in 79% yield (>96% cis). 

Palladium-catalyzed reaction of dienol 80 in acetone in the presence of acetic acid and benzoquinone resulted in an intramolecular 1,4-oxyacetoxylation (Scheme 8-28) [107], The stereochemistry of the reaction can be controlled via a slight variation of the ligand environment. Thus, under chloride-ion-free conditions, a rrawj-oxyacetoxylation occurs. Usually this reaction is highly stereoselective (>98% tram addition), except m = n = 2 in Scheme 8-28, where the tramlcis ratio is 75 25. When the reaction is run in the presence of a catalytic amount of chloride, the stereochemistry is reversed and now a 1,4-cts-oxyacetoxylation takes place. The effect of the chloride is the same as discussed above, i.e., it blocks the coordination of acetate so that cis migration by acetate cannot occur. 

Dehydrooenation 1,4-Benzoquinone. Chloranil. o-Chloranil. Copper chromite. Copper-Chromium oxide. Diethyl azodicarboxylate. 2,3-Dichloro-3,6-dicyano-I,4-benzoquinone. DIphenylpIcrylhydrazyl, N-Lithioethylenediamlne. Mercuric acetate. Nickel catalyst. Oleic add, Palladium. Perbenmic acid. Potassium l-butoxide. Pyrldinium hydrobromide per-bramlda, Balinlum. Selenium dioxide. Sodium borohydride. Sulfdr (sm 1,2-Naphthalic anhydridli preparation). Tetracyanoethylene. Thionyl chloride. Trityl perchlorate. 

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