Phosphane catalyzed

Some cases are known in which Diels-Alder reactions of electron-deficient allenes and dienes compete with [2 + 2]-cycloadditions (see also Section 7.3.7) [12, 151, 335, 336]. Recently, a phosphane-catalyzed [4 + 2]-annulation starting from allenic ester 337 and N-tosylaldimines 338 was published [337]. However, the formation of the tetrahydropyridines 339 isolated in excellent yields is explained by a multi-step mechanism and only resembles a Diels-Alder reaction. 

The palladium-catalyzed reactions of the substituted MCP, 1-methylene-2-vinylcyclopropane (22), have been investigated in great detail.In addition to the product variability resulting from the formation of different regioisomers, isomers with respect to the configuration at the double bonds are formed in this reaction. Thus, a rearrangement product 3-methylenecyclopen-tene (23), together with five major dimerization products 24-26, result from the palladium/ phosphane-catalyzed reaction. 

Revisiting the SiiCle Cleavage of Group 14 Element Phosphanes Phosphane-Catalyzed Rearrangements... 

In 2(X)3, an interesting intramolecular organocatalytic [3-h2] dipolar cycloaddition of an enynoate (19) catalyzed by PBUj was developed by Krische and his coworker in the total synthesis of ( )-hirsutene (21), Scheme 3.6 [12], The inlramolecular phosphane-catalyzed [3+2] dipolar cycloaddition provides a concise approach to the hnear tiiquinane hirsutene, whereby three contiguous stereo-genic centers are created and controlled in a single reaction step. 

Scheme 3.6 Intramolecular phosphane-catalyzed [3 + 2] cycloaddition of electron-deficient 1,7-enynes...

The phosphane catalyzed [3+2] cycloaddition between aUenoates and activated alkenes have attracted extensive attention since its discovery [95, 96]. Recently, in 2009, Krische and his co-worker reported a phosphane-catalyzed [3+2] cycloaddition of ethyl-2,3-butadienoate 237 with an enone 238 to give the cis-fused cyclopenta[c]pyran 239. They applied this methodology to the total synthesis of the iridoid p-glucoside (+)-geniposide 240, Scheme 3.77 [97], Alternatively, phosphane-catalyzed [3+2] annulation of aUenoates with aldehydes, affording 2-alky-lidenetetrahydrofurans, was reported by He and his co-workers [98]. 

SCHEME 11.43. Chiral bifunctional thiourea-phosphane-catalyzed allylic amination of MBH acetates and carbonates with phthalimide. 

In 2005, Yamamoto and coworkers [97] reported the copper-cat2ilyzed (Cu O, 5mol%) reaction of electron-deficient isocyanides with electron-deficient intern2d 2dkynes to selectively give 2,4-di-substituted pyrroles (Scheme 9.34) [97]. However, on using a phosphane-catalyzed (dppp,... 

Scheme 9.34 Cu- or phosphane-catalyzed click-chemistry leading to 2,4- or 2,3-di-substituted pyrroles, as described by Yamamoto and coworkers [97].

A phosphane-catalyzed [4 - -1] annulation between nitroalkenes and Morita-Baylis-Hillman carbonates was performed by He and co-workers. " The authors claimed the in situ formation of an allylic phosphorus ylide as an active intermediate. Allenoates and enones were able to form cyclopentenes via two cycloaddition reactions they underwent a [3 -F 2] or a [2 -F 4] process in the presence of catalytic phosphines or amines, respectively (Scheme 15). To explain such a different reactivity, Huang, Lankau and Yu, carried out M06-2X/6-31- -G calculations to study the role of ylide intermediates. ... 

Tetrasubstituted phosphinous amides of the type R2NPPh2 have been successfully arylated at phosphorus by the action of bromobenzene, in a process catalyzed by NiBr2, to give the aminophosphonium bromides [R2NPPh3] Br [109]. Other representative members of this class form phosphane-borane complexes [62], are aminated at phosphorus by chloramine to yield bis(amino)phos-phonium salts [110] and have been claimed to be protonated at phosphorus by ethereal tetrafluoroboric acid, as determined by NMR analysis [111]. 

Many chiral phosphorus ligands have shown excellent reactivities and enantio-selectivities in the Rh-catalyzed hydrogenation of itaconic acids or esters. Some successful (>95% ee) hydrogenations of itaconic acid or its dimethyl ester with different chiral phosphorus ligands are listed in Table 26.7. High reactivity is observed with electron-rich phosphane ligands such as BICHEP [7c[. 

Reetz,M.T. and Westermann, E., Phosphane-free palladium-catalyzed coupling reactions thedecisive role of Pd nanoparticles, Angew. Chem. Int. Ed., 39, 165, 2000. 

The intramolecular hydroamination of substrates 170 is catalyzed by a Pd(0) catalyst which is generated in situ from a Pd(II) precursor and a phosphane. One equivalent of acetic acid has to be added for efficient catalysis this is a hint of a hydropallada-tion mechanism. Meguro and Yamamoto obtained good yields of the vinyltetrahy-dropyrroles or the vinylhexahydropyridines 171 in that way (Scheme 15.53) [109]. 

More attention has been devoted to aromatic and heteroaromatic substrates since first reported in 1983 [40]. The results are shown in Table 2 [25, 41-51]. All these reactions were run with nickel complexes associated with a phosphane or bpy ligand. Depending on the experimental conditions, the polymers were either precipitated during the electrolysis or deposited as films at the surface of the electrode. The method is also convenient to prepare copolymers from a mixture of two aryl dihalides. A mechanistic investigation on the nickel-bpy catalyzed polymerisation has been reported very recently [52]. 

The first publications to describe the phosphane oxide-catalyzed carbodi-imide synthesis from isocyanate appeared in 1962. In this case iminophos-phoranes were recognized as important intermediates. The first mechanistic studies also appeared at this time. Scheme 24 depicts the proposed two-step mechanism (62JA3673, 62JA4288 66CJC2793). 

Catalytic enantioselective synthesis of 4,4-dimethyl-l-phenyl-l,2-pentadiene from 4,4-dimethyl-1,2-pentadiene and iodobenzene using 0.4 to 1 mol % of palladium complexes containing chiral phosphane ligands as the catalyst for the enantioselective cross coupling134 is the only example of substoichiometric transition metal catalyzed enantioselective allene synthesis. 

Hashimoto has shown that the addition of phosphane sulfides results in higher yields and faster conversions for PKR under atmospheric pressure of CO. This mild promoter provided high TONs, and can be applied to catalyze an intermolecular PKR under 1 atm of CO. ... 

Following the success with cobalt and rhodium, Shibata reported Ir(i)-based enantioselective catalytic reaction. Right after their observation that the efficiency of [IrCl(COD)]2-catalyzed PKR substantially increased by addition of a phosphane co-ligand, they moved directly to use chiral phosphanes and examined the enantioselectivity. " TON and TOE of the reaction were low and the number of examples was limited. Typically, the reaction required a fair amount of Ir(i) catalyst [IrCl(COD)]2 (0.1-0.15 equiv.) and (reaction time. However, this has remained as the best in terms of enantioselectivity to date. Moreover, this catalytic system provided the first asymmetric intermolecular reaction as well. 

The trimerization of cyclopentadiene (6) is catalyzed by a homogeneous bifunctional palladium-acid catalyst system.7 The reaction gives trimers 7 and 8 as a 1 1 mixture in 70% yield with bis(acetylacetonato)palladium(II) [Pd(acac)2] or with bis(benzylideneacetone)-palladium(O) as the palladium component of the catalyst. As the phosphorus component, phosphanes like trimethyl-, triethyl-, or triphenylphosphane, and triisopropylphosphite or tris(2-methylphcnyl)phosphite, are suitable. A third component, an organic acid with 3 < pK < 5, is necessary in at least equimolar amounts, in the reaction with cyclopentadiene (6), as catalytic amounts are insufficient. Acids that can be used are acetic acid, chloroacetic acid, benzoic acid, and 2,2-dimethylpropanoic acid. Stronger acids, e.g. trichloroacetic acid, result in the formation of poly(cyclopentadiene). The new catalyst system is able to almost completely suppress the competing Diels-Alder reaction, thus preventing the formation of dimeric cyclopentadiene, even at reaction temperatures between 100 and 130°C. 

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