Allyl acetates palladium-catalyzed

Based on the above-mentioned stereochemistry of the allylation reactions, nucleophiles have been classified into Nu (overall retention group) and Nu (overall inversion group) by the following experiments with the cyclic exo- and ent/n-acetales 12 and 13[25], No Pd-catalyzed reaction takes place with the exo-allylic acetate 12, because attack of Pd(0) from the rear side to form Tr-allyl-palladium is sterically difficult. On the other hand, smooth 7r-allylpalladium complex formation should take place with the endo-sWyWc acetate 13. The Nu -type nucleophiles must attack the 7r-allylic ligand from the endo side 14, namely tram to the exo-oriented Pd, but this is difficult. On the other hand, the attack of the Nu -type nucleophiles is directed to the Pd. and subsequent reductive elimination affords the exo products 15. Thus the allylation reaction of 13 takes place with the Nu nucleophiles (PhZnCl, formate, indenide anion) and no reaction with Nu nucleophiles (malonate. secondary amines, LiP(S)Ph2, cyclopentadienide anion). 

Reduction of iV-(3-bromopropyl) imines gives a bromo-amine in situ, which cyclizes to the aziridine. Five-membered ring amines (pyrrolidines) can be prepared from alkenyl amines via treatment with N-chlorosuccinimide (NCS) and then BusSnH. " Internal addition of amine to allylic acetates, catalyzed by Pd(PPh3)4, leads to cyclic products via a Sn2 reaction. Acyclic amines can be prepared by a closely related reaction using palladium catalysts. Three-membered cyclic amines (aziridines)... 

Chiral phosphinous amides have been found to act as catalysts in enantio-selective allylic alkylation. Horoi has reported that the palladium-catalyzed reaction of ( )-l,3-diphenyl-2-propenyl acetate with the sodium enolate of dimethyl malonate in the presence of [PdCl(7i-allyl)]2 and the chiral ligands 45 gave 46 in 51-94% yields and up to 97% ee (Scheme 38). It is notorious that when the reaction is carried out with the chiral phosphinous amide (S)-45a, the product is also of (S) configuration, whereas by using (R)-45b the enantiomeric (R) product is obtained [165]. 

The hydrolytic DKR of allyl esters has been studied as a DKR of esters. The first DKR was accomplished through Pd-catalyzed racemization and enzymatic hydrolysis of allylic acetates in a buffer solution. However, the DKR under these conditions was limited to cyclohexenyl acetates to give symmetrical palladium-allyl intermediates. Among them, 2-phenyl-2-cyclohexenyl acetate 9 was the only substrate to have been resolved with good results (81% yield, 96% ee). 

Allylic carbonates are better electrophiles than allylic acetates for the palladium-catalyzed allylic alkylation.77 Reaction of Eq. 5.54 shows the selective allylic alkylation of a-nitro ester with allylic carbonates without affecting allylic acetates.78... 

Allyl acetates are more commonly used as electrophiles for the palladium-catalyzed allylic alkylation than allylic nitro compounds.20 However, the reaction of allylic nitro compounds has found wider applications. Allylic nitro compounds are readily available by nitration of alkenes. The regio- and stereoselective introduction of electrophiles and nucleophiles into alkenes is possible as outlined in Eq. 7.19. In fact, this strategy is applied to the synthesis of terpenoids.21... 

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... 

The chloroacetoxylation reaction is synthetically useful since the chloride can be substituted with either retention [Pd(0)-catalyzed reaction] or inversion (Sjv2 reaction) by a number of nucleophiles. In this way both the cis and trans isomers are accessible and have been prepared from a number of allylic acetates (Schemes 5 and 6). In a subsequent reaction the allylic acetate can be substituted by employing a copper- or palladium-catalyzed reaction. The latter reactions are stereo specific. 

If the side chain with the nucleophile is situated in the 1-position of the conjugated diene, a palladium-catalyzed spirocyclization occurs. In this case stereoselective oxa-spirocyclizations were obtained from the diene alcohols 59 and 60 (equation 23 -25)58. The reaction worked well for the formation of a tetrahydrofuran and tetrahydropyran in the spirocyclization. In the absence of chloride ions 59 gave high yields of the acetoxy oxaspirocyclic compound 61 via a 1,4-anti addition across the diene (equation 23). In the presence of stoichiometric amounts of LiCl a 1,4-syn oxychlorination took place and allylic chloride 62 was obtained (equation 24). Under chloride-free conditions, cyclohep-tadiene alcohol 60 afforded oxaspirocyclic acetate 63 (equation 25). 

Another approach is based on the palladium-catalyzed intramolecular carbocyclization of the allylic acetate moiety with the alkene moiety (Scheme 96). After the formation of a 7t-allylpalladium complex, with the first double bond the intramolecular carbometallation of the second double bond occurs to form a new C-C bond. The fate of the resulting alkylpalladium complex 393 depends on the possiblity of /3-elimination. If /3-elimination is possible, it generates a metallated hydride and furnishes the cycloadduct 394. This cyclization could be viewed as a pallada-ene reaction, in which palladium replaces the hydrogen atom of the allylic moiety.231... 

For the synthesis of heterocycles, an efficient strategy has been introduced utilizing the dual transition metal sequences (Scheme 6).11,lla The key issue is the compatibility of the two catalyst systems. Jeong et al. studied the one-pot preparation of bicyclopentenone 35 from propargylsulfonamide 33 and allylic acetate.11 This transformation includes two reactions the first palladium-catalyzed allylation of 33 generates an enyne 34 and the following Pauson-Khand type reaction (PKR) of 34 yields a bicyclopentenone 35. The success of this transformation reflects the right combination of catalysts which are compatible with each other because the allylic amination can be facilitated by the electron-rich palladium(O) catalyst and the PKR needs a Lewis-acidic catalyst. Trost et al. reported the one-pot enantioselective... 

Allylphosphonium salts are synthesized by substitution of allyl halides with PPh3. The use of allyl alcohol, allyl acetate, or nitropropene with a palladium catalyst has also been reported.19 It is shown in this study that the organophosphorous compounds can be obtained by a palladium-catalyzed addition to an allene. A notable aspect of this method is that it can control the stereochemistry of the phosphonium salt, and that (Z)-allylphosphonium salts have been obtained in pure form for the first time. 

The mechanism of the Zn chloride-assisted, palladium-catalyzed reaction of allyl acetate (456) with carbonyl compounds (457) has been proposed [434]. The reaction involves electroreduction of a Pd(II) complex to a Pd(0) complex, oxidative addition of the allyl acetate to the Pd(0) complex, and Zn(II)/Pd(II) transmetallation leading to an allylzinc reagent, which would react with (457) to give homoallyl alcohols (458) and (459) (Scheme 157). Substituted -lactones are electrosynthesized by the Reformatsky reaction of ketones and ethyl a-bromobutyrate, using a sacrificial Zn anode in 35 92% yield [542]. The effect of cathode materials involving Zn, C, Pt, Ni, and so on, has been investigated for the electrochemical allylation of acetone [543]. 

The first iridium catalysts for allylic substitution were published in 1997. Takeuchi showed that the combination of [fr(COD)Cl]2 and triphenylphosphite catalyzes the addition of malonate nucleophiles to the substituted terminus of t -allyliridium intermediates that are generated from allylic acetates. This selectivity for attack at the more substituted terminus gives rise to the branched allylic alkylation products (Fig. 4), rather than the linear products that had been formed by palladium-catalyzed allylic substitution reactions at that time [7]. The initial scope of iridium-catalyzed allylic substitution was also restricted to stabilized enolate nucleophiles, but it was quickly expanded to a wide range of other nucleophiles. 

Palladium-catalyzed allylation using nucleophiles with allylic halides, acetates, carbonates, etc. via intermediate allylpalladium complexes, and typically with overall retention of stereochemistry. 

Blechert reported a skillful method of cross-enyne metathesis. Solid-supported alkyne 139 is reacted with alkene in the presence of Ic to give 140. For cleavage of 1,3-diene from solid-supported product 140 having an allyl acetate moiety, palladium-catalyzed allylic substitution is used. Thus, 140 is treated with Pd(PPh3)4 in the presence of methyl malonate to afford three-component coupling product 141 in good yield ... 

Palladium-catalyzed, Allylic Amination. Allylic substitution of mono-saccharidic hex-2-enopyranoside 4-acetates with secondary amines in the presence of tetrakis (triphenylphosphine)palladium(O) liad led to a large variety of 4-aminated 2-enosides, with retention of configuration (56-58). The method was applied to the disaccaridic enoside 1 to give, with benzylmethylamine or dibenzylamine, the 4-amino sugar derivatives g in yields of 92 and 67% (46). Studies concerning hydrox-ylation of t)ie double bond and subsequent deprotection are incomplete. 

A-Alkylhydroxylamines react with substituted allyl acetates (e.g. 15, equation 11) in palladium catalyzed addition-elimination reactions giving the corresponding A-alkyl, A-allylhydroxylamines 16. The reaction proceeds with high regioselectivity but complete racemization. A similar reaction with 0-acyl hydroxamic acids has been carried out using allylic a-alkoxycarbonyloxyphosphonates. ... 

Treatment of the (—)-menthone-derived 2/7-1,3-benzoxazin-4(3//)-one 202 with triflic anhydride gave the triflate 203 in quantitative yield. Palladium-catalyzed cross-coupling of 203 with 2-pyridylzinc halide resulted in formation of an approximately 3 1 mixture of the 4-(2-pyridyl)-2//-l,3-benzoxazine 204 and a 4-imino-l,3-benzodioxane derivative 205 (Scheme 36). Compound 205 was formed by the isomerization of 203, which occurred with complete retention of stereochemistry. The 4-(2-pyridyl)-l,3-benzoxazine derivative 204 was applied in enantioselective allylic alkylations of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate as a chiral ligand inducing a 62% ee in the product <2005JOM(690)2027>. 

Benzamido allylic acetates 242 and 243 undergo palladium-catalyzed cychza-tion to oxazolines. Excellent yields and very high diastereoselectivity is observed for the conversion of several acyclic primary and secondary benzamido aUyhc acetates to tran -5-vinyl substituted oxazolines 244. The diastereoselectivity of the reaction is determined by the the steric interactions between the R group and the hydrogen of the 7i-allylpalladium complex in the transition state, trans-Oxazolines are obtained since transition state A is favored over transition state B (Scheme 8.66). 

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