Bisphosphines, nucleophilic

The nucleophile assisted ring-opening reactions of phosphonate bearing phthahmide 13 has been utihzed in the synthesis of mixed primary phosphine-phosphonate and aromatic amide functionahzed primary bisphosphines as out-hned in Scheme 6 [50],... 

A variety of rhodium complexes, including [Rh(CO)2Cl]2 and [Rh(COD)Cl]2 when used in combination with a variety of bisphosphine ligands, will catalyze the ring opening of vinyl epoxides in the presence of aniline nucleophiles [19, 20]. These reactions occur under very mild and neutral conditions (at room temperature or with mild heating) and are highly regio- and stereoselective. In all cases, nucleophilic attack occurs at the allylic epoxide carbon atom and proceeds with inversion of stereochemistry (Scheme 9.11). 

Allyl esters of acetoacetates7-8-9-11 react with Pd° catalysts to generate initially a bisphosphine allylpal-ladium cation, with the 3-ketocarboxylate serving as counterion. Under the reaction conditions the (3-ketocarboxylate decarboxylates, yielding a -Tr-allylpalladium ketone enolate complex. The required nucleophile is thus formed in situ and is capable of Pd-mediated alkylation. A wide spectrum of reactions have been based on this chemistry which will be discussed in later sections. 

The bisphosphines 6 and 8 bearing alkyl substituents on their phosphorus atoms were supported on PS resin by the nucleophilic substitution of the chloromethyl groups on the resin to give 7 and 9, respectively (Scheme 4) [36, 37]. A palladium complex of 7 showed moderate catalytic activity to promote the Heck reaction of iodobenzene with methyl acrylate affording methyl cin-namate. 

A novel de novo synthesis of nucleosides (Scheme 1) involves the conversion of the mwo-compound 1, derived from furan, into the pure enantiomer 2 by two successive allylations using organopalladium intermediates. The first reaction uses 6-chloropurine as nucleophile, in the presence of a chiral bisphosphine. The subsequent elaboration of 2 indicates the use of the substituted malonate as an ingenious CO2H synthon. Use of the enantiomeric catalyst in the first step gives the D-nucleoside. ... 

Such phosphine borane complexes have been tested in the catalytic asymmetric allyhc alkylation of l,3-diphenylpropene-2-yl acetate 120 with dimethyl malonate as nucleophile (Scheme 32). It was fbimd that the enantioselectivities strongly depend on the bite angle which is deeply affected by the nature of the spirocychc spacer and the direction of the coordinating phosphine groups. Representative X-ray stmctures of bisphosphine boranes 122 and 123 are shown in Scheme 32. Bisphosphine 119 afforded up to 74% ee while only 34% and 45% ee were obtained from the reactions using 122 and 123, respectively. 

Four classes of catalysts have been used for the coupling of amines and related nitrogen nucleophiles witii aryl halides. Initially, complexes of the hindered monodentate aromatic tri-ortlio-tolylphosphine catalyzed the reaction of aryl bromides with secondary amines in the presence of an alkoxide or silylamide base. The use of this catalyst for this type of coupling to form C-N bonds was based on an earlier report of the reaction of aryl bromides with tin amides in the presence of a palladium complex of the same ligand as catalyst. - Later, complexes containing aromatic bisphosphines, such as BINAP and dppf, were... 

The regioselectivity of palladium-catalyzed aUylic substitutions with heteroatom nucleophiles is often much different from that of reactions with carbon nucleophiles. In general, reactions of oxygen and nitrogen nucleophiles form more branched product than do reactions of carbon nucleophiles, at least as the kinetic product of substitution. For example, reactions of aryloxide nucleophiles with mono-substituted aUylic carbonates catalyzed by palladium complexes of Trost s ligand form more branched than linear product (Equation 20.32). Reactions of geminaUy disubstituted aUylic acetates with aziridines, hydroxylamine and hydrazine derivatives catalyzed by palladium complexes of bisphosphines form the branched prenyl product as the major isomer (Equations 2033a and 20.33b). " ... 

Jarvo et al. have reported the use of isolated NHCP palladium allyl complexes of the type [(R-2)Pd(i -C3H5)]X (X = C1, OAc, BF ) as catalysts for nucleophihc allylation reactions. They investigated a series of electron-rich monodentate and bidentate ligands (bisphosphines, functionahzed NHCs, monodentate NHCs) for their ability to promote nucleophilic attack of the corresponding palladium allyl complexes on electrophiles in, for example, the conjugate addition of allylboronic esters to a variety of ,p-unsaturated Af-acylpyrroles [15a] as well as the allylation of aldehydes by allylstannanes (Scheme 10.4) [15b]. 

On the other hand, in the nucleophilic attack mechanism an inversion of configuration on the organic reaction was observed. For the particular case of sp carbon atoms in a-sulfoxide systems the mechanism was proposed to be rather similar for both the mono- or bisphosphine catalysts. 

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