Phosphine catalysts substitution

The composition of the dimer obtained using the phosphine-free catalyst is close to that obtained with the P(C6H5)3-modified catalyst. Substitution of (i-C3H7)2P-r-C4H9 by (/-C4H9)2P-i-C3H7 leads to a decrease in the yield of 2,3-dimethylbutene from 80.9 to 29.1%. 

Intramolecular Heck reactions.6 Heck intramolecular coupling of alkenyl or aryl iodides substituted by 3-cycloalkenyl group is an attractive route to fused, spiro, and bridged polycyclic products. Coupling is achieved with a Pd-phosphine catalyst such as Pd[P(QH5),]4 in combination with a base, N(C2H5)3 or NaOAc. The coupling tends to produce a mixture of two isomeric alkenes, in which the newly formed bond is allylic or homoallylic to the ring juncture. 

Additional examples of palladium-catalyzed cross-couplings, in particular with allenylzinc compounds, can be found elsewhere [11, 15, 36]. A systematic study comparing several chiral palladium phosphine catalysts in the reaction of 4,4-di-methyl-1,2-pentadienylzinc chloride and iodobenzene revealed that an enantiomeric excess of only 25% was obtained from the best catalyst combination PdCl2 and (R,R)-DIOP [15]. The synthetic value of these transformations of donor-substituted allenes as precursors is documented by the preparation of a/l-unsaturatcd carbonyl... 

One of the major problems with these palladium-phosphine catalysts is in that they are rather unstable under the process conditions and gradual loss of the catalytic activity and precipitation of palladium black can often be observed. The introduction of appropriately substituted DPPP derivatives (Scheme 7.16) not only increased the activity over all previous values but largely improved the stability of the catalysts, as well [57],... 

Amine promoters tend to give higher acetaldehyde rates relative to phosphines. Increasing the temperature to 200 increases the rate to 7.1 M/hr whereas decreasing the pressure to 2000 psig markedly lowers the rate. Lil is a critical component of the catalyst. Substituting Lil with Nal, KI, or CH I results in a substantial loss in catalytic activity. A key step in the postulated reaction mechanism, as outlined in Equations 16-18, is cleavage of methyl acetate by Lil to yield CH I and LiOAc (27). ... 

The second substitution of 1,1-dibromo-l-alkenes involved the Pd-catalyzed crosscoupling reactions of 6-8 obtained as shown in Scheme 37. Quite unexpectedly, the reaction of 6a with MeZnBr in the presence of several Pd-phosphine catalysts produced the expected cross-coupling products of >95% stereoisomeric purity in 76-91% yields, but careful ID NOE analyses have firmly established that the reaction was accompanied... 

The allylic alcohol substitution reaction may also be carried out in DMF solution with sodium bicarbonate as the base at 100 to 125° with palladium-phosphine catalysts, in which case only carbonyl products are formed. With this catalyst combination nonallylic, unsaturated alcohols also react to form carbonyl compounds in good yields. For example, in an extreme case, 9-decen-l-ol and bromobenzene gave some 10-phenyldecanal (40) ... 

RC=CKWG) yields 2,4-di-EWG-substituted pyrroles in the presence of copper catalyst but 2,3-di-EWG-substituted pyrroles in the presence of a phosphine catalyst.74 The 3 + 2-cycloaddition of diazoalkanes to (6 )-3-p-tolylsulfinylfuran-2(5//)-one produces diastereoisomeric pyrazolines in almost quantitative yield and with des >98%. (g) The sulfinyl group is responsible for the complete control of the n-facial selectivity in all these reactions.75 The Rh(II)-catalysed intramolecular 1,3-dipolar cycloaddition reaction of diazoamides (57) with alkenyl and heteroaromatic n -bonds yields pen-tacyclic compounds (59), via the ylide (58), in good to excellent yields and in a (g) stereocontrolled manner (Scheme 15).76... 

The enantioselective hydroaminations of allenes with chiral phosphine catalysts was accomplished with substrates that had a terminal symmetric substitution and with the amines protected as carbamates or sulfonamides. The same symmetric substituents were necessary for the enantioselective transformation nsing chiral counterions. However, very recently, high enantiomeric excesses were reached with trisubstituted asymmetric allenes by a dynamic kinetic enantioselective hydroamination of allenyl carbamates (eqnation 110), even thongh the E/Z ratio of the prodncts was not optimal. 

Hydrogenation reactions that are efficiently controlled by chiral Rh-phosphine catalysts involve those carbon-carbon double bonds substituted with carboxylic and amide groups. They are precursors of a-amino acids, compounds that are very important protein building blocks. The best substrate is (Z)-a-acetamidocinnamic acid 10 ... 

Water-soluble derivatives of alkylidenes 8 and 9 were prepared via phosphine ligand substitution reactions. Exchange of the phosphines in 8a for PhP(p-C6H4S03-Na)2 afforded a water-soluble vinyl alkylidene [20]. This alkylidene was soluble in water, but the triarylphosphine ligands were too small and insufficiently electron-donating to produce an active catalyst [48], Analogous substitution of the phosphines in 9 a for more sterically demanding, electron-rich, water-soluble phosphines yielded ruthenium alkylidenes 10 and 11 (Scheme 2), which were soluble in both water and methanol [49]. 

Reaction of aryl bromides under Heck conditions with 2-vinyloxyethanol and a Pd phosphine catalyst gives products 9 <04SLl56l> while Ru-catalysed cyclisation of 2-allyloxyethanol gives 10 <04SL1203>. Reaction of the corresponding substituted catechol with 1-... 

Reaction of (72) with aryl A -substituted NHC, yielding second-generation metathesis catalysts, was reported in 1999 by Nolan ef a/ and Grubbs ef a/ Substitution of one phosphine in (72) by IMes afforded [Cl2Ru(IMes)(PCy3)(CHPh)] in excellent yields. Even in the presence of a 10-fold excess of IMes, only one phosphine underwent substitution. Since then, this synthetic route has been extended to a number of car-benes, for instance, SIMes, for which the free carbene has been generated in situ from the methanol-protected NHC (14), IPr, SIPr generated either from the terf-butanol-protected... 

The inverse temperature-dependent solubility in aqueous media of polymer-bound palladium(0)-phosphine catalysts, based on the water-soluble polymer poly(Wisopropyl)acrylamide (PNIPAM) 28, was also used to recycle and reuse these catalysts in nucleophilic allylic substitutions (Equation (8)) and cross-coupling reactions between aryl iodides and terminal alkynes (Equation (9)). The catalyst was highly active in both reactions, and it was recycled 10 times with an average yield of 93% in the allylic nucleophilic substitution by precipitation with hexane. ... 

The NHC-coordinated catalysts 2 and 5 also exhibit dramatically improved substrate scope relative to bis(phosphine) catalysts. For example, whereas catalyst 1 is unreactive toward sterically congested substrates and cannot form tetra-substituted RCM products, catalysts 2 and 5 readily form tetra-substituted olefins in five- and six-membered rings systems (Eq. 4.17 E = C02Et) [98,100]. They also mediate CM between terminal olefins and 2,2-disubstituted olefins to form new trisubstituted double bonds [102]. Previously, these transformations could only be accomplished using molybdenum-based catalysts. 

Water-soluble polymer-bound Pd(0)-phosphine catalyst has also been efficiently used in aqueous or mixed aqueous/organic media, the catalyst being recycled by solvent or thermal preparation methods [17]. Amphiphilic resin-supported palladium-phosphine complexes show high catalytic activity in allylic substitution reactions of various allylic acetates with different nucleophiles in aqueous media [18, 19]. Enantiomeric excess up to 98% is obtained using amphiphilic resin-supported MOP ligand or resin-supported P,N-chelating palladium complexes, the catalyst being recyclable [20,21]. The catalyst could be recovered by simple filtration and re-used without any loss of activity and enantioselectivity. 

Scheme 2.115). Among the phosphine catalysts screened, 2,2 -bis(diphe-nylphosphino)-1,1 -binaphthyl (BINAP) CPS was found to be the best catalyst and the corresponding products were obtained with up to 44% ee, which is comparable with those of reported enantioselective methods using chiral tertiary amines under high pressures (Scheme 2.115). For the MBH reaction of substituted pyrimidine 5-carboxaldehyde and other acrylates, the yield and ee were dependent on the bulk of the acrylate. The less bulky acrylate gave the higher yield and ee (Scheme 2.116). 

After screening phosphine catalysts, it was found that the more nucleophilic EtPh2P was the best catalyst for [3 + 2] annulation of allylic compounds, furnishing 2-substituted 1,1-dicyanoalkenes 22 in up to 95% yield (Scheme 4.7). ... 

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