Palladium-catalysed reactions allylic compounds

With 1-alkoxyallenes as proelectrophiles, the palladium-catalysed asymmetric allylic alkylation proceeds with 1,3-dicarbonyl compounds as pronucleophiles with excellent regioselectivity good enantioselectivity (82-99% ee) was obtained with the Trost lig- and. The pH of the medium proved crucial for the reactivity and selectivity. By using the more acidic Meldrum s acids, the reactions required a co-catalytic amount of a Brpnsted acid, such as CF3CO2H. On the other hand, the less acidic 1,3-diketones failed to react under these conditions but the reaction proved to occur in the presence of the weaker benzoic acid, suggesting the need for general base catalysis. Indeed, a mixture of Et3N and PhCOiH proved to be optimal (93-99% ee). A mechanistic model to rationalize these results has been developed.88... 

Palladium-catalysed chemo- and enantio-selective oxidation of allylic esters and carbonates has been achieved using nitronates as nucleophilic oxidants. The products, o /3-unsaturalcd carbonyl compounds, were obtained in excellent yields and ees. The mechanism in Scheme 5 has been suggested for the reaction.108... 

An excellent review21 outlining the mechanism of diphenylphosphinobenzoic acid-based palladium-catalysed asymmetric substitution of allyl compounds with nucleophiles has been published. The mechanistic model developed for these reactions allows one to predict the stereochemistry of the product(s). 

The palladium-catalysed coupling of allylic esters with carbanions has now been extended to include other reactions. The allylic carbonate 299 couples with the nitro compound 300 to give the expected product 301 in good yield. 

When an organometallic derivative of indole is required for a coupling reaction, boronic acids are to be preferredalthough 2-zinc and 2-stannyl derivatives can be used. The palladium-catalysed coupling of 6-bromo or 6-iodoindoles with allyl and heteroaryltin compounds does not require masking of the indole iV-hydrogen. ... 

The Wacker reaction provides a method for the preparation of 1,4-dicarbonyl compounds, by formation of an enolate, allylation with an allyl halide, followed by palladium-catalysed oxidation of the terminal alkene. The product 1,4-dicarbonyl compounds can be treated with base to promote intramolecular aldol reaction (Robinson annulation - see Section 1.1.2) to give cyclopentenones. Thus, in a synthesis of pentalenene, Wacker oxidation of the 2-aUyl ketone 115 gave the 1,4-diketone 116, which was converted to the cyclopentenone 117 (5.115). ... 

Negishi and his co-workers have developed several approaches to allylated arenes involving cross-coupling reactions. Preliminary studies established that aryl-aluminium, zirconium, or zinc compounds readily undergo palladium-catalysed cross-coupling with allylic halides or acetates (Scheme 19). Later in the year it was shown that allylic alcohol derivatives containing OAlR2,... 

The palladium-catalysed decarboxylation of /3-ketocarboxylates is an attractive new method for the production of allylically substituted compounds " (Scheme 10). The reaction is thought to involve Pd enolate complexes as intermediates. 

Substitution reactions of allylic nitro compounds often lead to rearranged products, as in palladium(0)-catalysed aminations and alkylations. Thus treatment of the nitro ester 419 with piperidine in the presence of tetrakis(triphenylphosphine)palladium yields a mixture of the unrearranged and rearranged amines 420 (R = piperidin-l-yl) and 421... 

Other organic processes facilitated by metal carbonyl clusters include a palladium carbonyl catalysed Diels-Alder reaction the selective reduction of aromatic nitro compounds using rhodium and ruthenium phosphine-carbonyls aza- and oxa-carbonylations of allyl phosphates by rhodium carbonyls Michael reactions of alkoxy-alkenones using iron... 

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