Allylation double palladium-catalyzed

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... 

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. 

When the allylic substituent is the source of chirality, then palladium-catalyzed substitutions can lead to good asymmetric induction (Schemes 16 and 17).109 In this example, the geometry of the double bond in the substrate controls the stereochemical outcome of the reaction. 

The palladium-catalyzed silylboration of typical allenes exhibited a strong tendency to occur at the internal double bond giving allylsilanes, which undergo allylation of aldehydes in the presence of a Lewis acid (Equation (44)).254 257 The selectivity can be varied by changing the substituents, but the boron atom always added to the central carbon. Enantioselective silylboration of terminal monosubstituted allenes was demonstrated by double asymmetric induction using chiral silylboranes and chiral catalysts (Equation (45)). 

It is very well known that jr-allyl palladium complex 1, which is a key intermediate for the Tsuji-Trost type allylation, has an electrophilic character and reacts with nucleophiles to afford the corresponding allylation products. We discovered that bis 7r-allyl palladium complex 2 is nucleophilic and reacts with electophiles such as aldehydes [27] and imines [28-32] (Scheme 2, Structure 2). We have also shown that bis 7r-allyl palladium complex 2 can act as an amphiphilic catalytic allylating agent it reacts with both nucleophilic and electrophilic carbons at once to produce double allylation products [33]. These complexes incorporate two allyl moieties that can bind with different hapticity to palladium (Scheme 3). The different complexes may interconvert by ligand coordination. The complexes 2a, 2b and 2c are called as r]3,r]3-bisallypalladium complex (also called bis-jr-allylpalladium complex), r)l,r)3-bis(allyl)palladium complex, -bis(allyl)palladium complex, respectively. Bis zr-allyl palladium complex 2 can easily be generated by reaction of mono-allylpalladium complex 1 and allylmetal species 3 (Scheme 4) [33-36]. Because of the unique catalytic activities of the bis zr-allyl palladium complex 2, a number of interesting cascade reactions appeared in the literature. The subject of the present chapter is to review some recent synthetic and mechanistic aspects of the interesting palladium catalyzed cascade reactions which in-... 

The palladium-catalyzed reaction of 1 1 mixture of allyl chloride 11 and allyl stannane 3a with alkylidene malonitriles e.g., 4a resulted into the double-allylated product 95 (Scheme 29) [33]. The mechanism of this reaction is... 

The stereospecific insertion of 2-monosubstituted alkenyl carbenoids was successfully employed in the preparation of 1-alkyl-1-zircono-dienes. The Z and E carbenoids of 1-chloro-l-lithio-l,3-butadiene (69 and 70, respectively) are generated in situ fromE- andZ-l,4-dichloro-2-butene [53] (Scheme 25). Inversion of configuration at the carbenoid carbon during the 1,2-metalate rearrangement stereospecifically yields terminal dienyl zirconocenes 71 and 72 [54] (Scheme 25). As the carbenoid-derived double bond is formed in 9 1=Z E for 69 and >20 1=E Z isomeric mixtures for 70, the metalated dienes 71 and 72 are expected to be formed with the same isomeric ratio. Carbon-carbon bond formation was achieved by palladium-catalyzed cross-coupling with allyl or vinyl halides to give the functionalized products with >95 5 stereopurity [55-57]. 

Palladium-catalyzed hydrostannation of isoprene was used for in-situ generation of allylstannane 9, which was trapped by an aldehyde to give alcohol 10 [Eq.(4)] [20]. It was suggested that an intermediate HPdSn(OAc)Cl2 is formed. The authors proposed two mechanisms for the hydrostannation, one according to Scheme 8-1 where Nu = Sn(OAc)Cl2 and another where insertion of the double bond into the palladium-tin bond is followed by reductive elimination from a (jr-allyl)palladium hydride. 

The stereochemistry of the dialkoxylation arises from two external attacks by the alcohol, one on the r-diene complex and the second on the intermediate 7r-allyl complex. This is in accordance with the other palladium-catalyzed 1,4-syn additions discussed above. Also, the 1,4-dialkoxylation of acyclic 1,3-dienes was stereoselective. For example, the reaction of ( , )-2,4-hexadiene gave the d,l products 38 by a 1,4-syn addition. The double bond was exclusively of E configuration (equation 18),... 

A more versatile palladium-catalyzed formylation of organic halides takes place using tributyltin hydride and carbon monoxide (equation 7). The reaction works for a variety of substrates — aryl, benzyl and vinyl iodides, vinyl triflates and allyl halides. Reaction conditions are mild (1-3 bar CO, 50 °C), and a variety of functional groups can be tolerated. With unsymmetrical allyl halides formylation is regio-selective, taking place at the less-substituted allylic position with retention of geometry at the allylic double bond. 

Dilactones can be synthesized by a palladium-catalyzed stereospecific intramolecular double cycliza-tion of 3-hydroxy-4-pentenoic acids (Scheme 21). The cis stereochemistry of the reaction is rationalized by assuming that attack of Pd" on the alkene is directed by the allylic OH group, forming the intermediate (12). 

Palladium catalyzed hydrogenation of 3/3-acetoxy- or 3/3-hydroxy-A- -steroids affords 5-10% of the corresponding 3-desoxy steroids. The hydrogenation can be catalyzed by 70% perchloric acid. 3/3-Acetoxy-5a-steroids are resistant to hydrogenolysis hence the reaction probably involves partial isomerization of the A -double bond to the Apposition, followed by hydrogenolysis of the allylic group.40... 

Cooper et al. reported that the cascade reaction of the palladium-catalyzed cyclization and the Barbier-type allylation of the 1,3-diene-aryl iodide 514, the aldehydes 515, and indium gave the heterocycles 516 in good yields (Scheme 154).220b The reaction proceeds through oxidative addition of a C—I bond of 514 to Pd(0) and subsequent insertion of a double bond of 517 to give the jr-allylpalladium intermediate 518. Transmetalation of the jr-allylpalladium 518 with indium leads to the allylindium complex 519, and the following reaction with the aldehydes 515 gives 516. 

Burke and Jiang reported that the palladium-catalyzed diastereoselective double allylation of the diol bis(allylic acetate) 613 using (R,R) DPPBA 607 afforded the bis-tetrahydrofuran core 614 in 97% yield (Scheme 187).265 The resulting diene 614 was further transformed into a known intermediate 615 for the synthesis of uvaricin. They demonstrated that palladium (0)-catalyzed desymmetrization of the C2 diol 616 with Trost s ligand 607 afforded the tetrahy-drofuran 617 diastereoselectively (Scheme 188).266 The product 617 was manipulated to the F ring of halichondrin B (618). 

A similar palladium-catalyzed cyclocarbonylation reaction with norbornene and norbornadi-ene gives products of cis-exo attack with an E configuration at the exocyclic double bond, independent of the stereochemistry of the starting allylic compound52. 

MBH diene adducts have also been employed successfully in a palladium-catalyzed asymmetric allylic alkylation reactions with various phenols in good regio- and enantioselectivity. These high enantioselectivities are even more substantial considering the ambiguity introduced by the additional double bond in the allylic system (Scheme 3.139). ... 

Total syntheses of diterpenoid hydrokempenones have been accomplished by Paquette et al.,f using the Pd-catalyzed [3 + 2] cycloaddition methodology. One example is outlined on Scheme 43 and describes the synthesis of an isomeric compound 208 of 3/3-hydroxy-7/3-kemp-8(9)-en-6-one, a defense secretion agent of the neotropical species Nasutitermes octopilis. 3-AUcoxy-2-cyclohexenone 204 was efficiently functionalized and transformed to bicylic adduct 205 via a Robinson annulation reaction. Reduction of the double bond followed by condensation of dimethyl carbonate and oxidation gave the keto ester 206, which was treated with [2-(acetoxymethyl)-3-allyl]trimethylsilane, palladium acetate, and triisopropyl phosphite in refluxing tetrahydrofuran to afford a 98% yield of 207. Substituted methylenecyclopentane 207 was then functionalized by stereoselective reduction and protections, and final closure was done under basic conditions after an ozonolysis step. A modified Barton-McCombie reaction produced the desired tetracyclic adduct 208. 

A. Yamamoto, Bull. Chem. Soc. Jpn., 1995, 68, 433-446. Palladium-Catalyzed Double and Single Car-bonylation of Aryl Halides and Allylic Compounds. 

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