Eliminations tetrakis palladium

Diynes.1 In the presence of tetrakis(triphenylphosphine)palladium(0), (Z)-l,2-dichloroethylene couples with a terminal alkyne to form a (Z)-chloroenyne, which undergoes anti-elimination of HC1 to give a 1,3-diyne on treatment with Bu4NF. 

The procedure described here incorporates a number of modifications to the Suzuki coupling that result in a sound, efficient and scaleable means of synthesizing biaryls. First, the catalytic use of palladium acetate and triphenylphosphine to generate palladium(O) eliminates the need for the expensive air and light sensitive tetrakis(triphenylphosphine)palladium(0). No purification of reagents is necessary, no special apparatus is required, and rigorous exclusion of air from the reaction mixture is not necessary. Furthermore, homo-coupled products are not present in significant levels (as determined by 500 MHz 1H NMR). 

Several perfluoroalkyl iodides add to alkenes in the presence of 1 mol % of tetrakis(triphenylphos-phine)palladium(O) at room temperature in fair to good yields forming fluoroalkyl iodides.52 Palladium hydride elimination is less favorable than substitution of the palladium by iodide in these examples. This is due to the reaction proceeding by an unusual radical chain mechanism (equation 17). 

Reaction of bis(disilanyl)dithiane 32 with the corresponding palladium(O)-isonitrile complex affords a four-membered cyclic bis(silyl)palladium(II) complex 34 quantitatively together with the formation of a disilane (Eq. 15) [30]. The formal intramolecular metathesis of the two Si-Si bonds of 32 may proceed through initial formation of tetrakis(silyl)Pd(IV) complex, corresponding to the platinum complex 33. The double oxidative addition of the two Si-Si bonds may be followed by reductive elimination of the disilane with accompanying formation of four-membered bis(silyl)palladium complex 34, due to difficulty in reductive elimination leading to formation of a three-membered cyclic disilane. 

Oxidative addition of palladium(O) species into unsaturated halides or triflates provides a popular method for the formation of the a-bound organopalladium(II) species. It is important to use an unsaturated (e.g. aryl or alkenyl) halide or tri-flate, as (3-hydride elimination of alkyl palladium species can take place readily. Oxidative addition of palladium(0) into alkenyl halides (or triflates) occurs stere-ospecifically with retention of configuration. The palladium is typically derived from tetrakis(triphenylphosphine)palladium(0), [Pd(PPh3)4], or tris(dibenzylidene-acetone)dipalladium(O), [Pd2(dba)3], or by in situ reduction of a palladium(II) species such as [Pd(OAc)2] or pd(PPh3)2Cl2]. 

The role of palladium in organic synthesis continues to be explored and exploited. Enol stannanes are monoalkylated by allylic acetates in the presence of tetrakis(triphenylphosphine)palladium, Enol stannanes give higher selectivity for monoalkylation than enolate ions or silyl enol ethers. High regioselec-tivity is observed for alkylation at the less substituted end of the allyl moiety. Olefins, after complexation to palladium(ll), alkylate enolate anions. The organopalladium product may be converted into saturated ketones, or into enones by /3-elimination, or acylated with carbon monoxide (Scheme... 

The elimination of benzoic acid from the benzyloxycarbonyl compounds (206) is catalysed by tetrakis(triphenylphosphine)palladium, giving ( , )-dienoic carbonyl compounds (207). ... 

One of the most synthetically useful reactions involving organopalladium intermediates is that between rr-allyl complexes and relatively stable carbanions such as those derived from malonate esters and jS-ketoesters. The tt- allyl complexes can be synthesized separately and used in stoichiometric amount or they can be generated in situ by reaction of allylic acetates with a catalytic amount of tetrakis (triphenylphosphine)palladium. In the catalytic version of the reaction, the tt-allyl complex is formed by reaction of the allylic acetate and the Pd(0) species which is regenerated in the elimination step. 

TT-Allyl palladium species are involved in a number of useful reactions which result in allylation of nucleophiles. These reactions can be applied to carbon-carbon bond formation with relatively stable carbanions, such as those derived from malon-ate esters and j8-ketoesters. The 7r-allyl complexes can be synthesized and used in stoichiometric amount" or they can be generated in situ by reaction of an allylic acetate with a catalytic amount of tetrakis(triphenylphosphine)palladium. The reactive Pd(0) species is regenerated in an elimination step. 

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