Arylation asymmetric

Furthermore, the second Mizoroki-Heck reaction of the thus-obtained 58 with iodoben-zene yields 61, which is then hansformed into enantiopure diphenyltetrahydrofuran 62 by hydrogenation and C—S cleavage with Raney-Ni G igure 7.20). The complete asymmetric induction might be rationalized by assuming a chelate model (59- 60) similar to that 

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The reaction of a halide with 2-butene-1,4-diol (104) affords the aldehyde 105, which is converted into the 4-substituted 2-hydroxytetrahydrofuran 106, and oxidized to the 3-aryl-7-butyrolactone 107[94], Asymmetric arylation of the cyclic acetal 108 with phenyl triflate[95] using Pd-BINAP afforded 109, which was converted into the 3-phenyllactone 110 in 72% ee[96]. Addition of a molecular sieve (MS3A) shows a favorable effect on this arylation. The reaction of the 3-siloxycyclopentene 111 with an alkenyl iodide affords the. silyl... 

Asymmetric aryl isocyanate dimers, ia which the C=0 group of oae molecule reacts with the C=N group of another, have been postulated as labile iatermediates ia the formation of carbodiioiides (17) upoa heating isocyanates. 

So far, there is only one report describing the use of chiral NHC-metal complexes in catalytic asymmetric arylation of imines. This was achieved by using C -symmetric cationic NHC-Pd diaquo complex 20 (Scheme 7.6) [38]. The arylation of a variety of A-tosylimines with different arylboronic acids was carried out under mild conditions. The presence of electron-withdrawing or electron-donating substituents on both partners did not seem to affect the reaction and the corresponding chiral diarylamines were obtained in good to excellent yields and high enantiomeric excess. 

The new method for asymmetric arylation was applicable to a host of aryl halides, to provide a diverse array of 2-arylpyrrolidines in good yield and 92% ee, regardless of the nature of the aryl bromide component. This sequence offers a number of advantages over existing methods, and represents the most convenient and practical synthesis of enantiopure 2-aryl pyrrolidines and 2,5-diarylpyrrolidines. 

The asymmetric arylation of ketone enolates represents an attractive method for the preparation of optically active carbonyl compounds with a stereogenic quaternary center at the a-position to the carbonyl group. Such types of compounds are important intermediates for natural product synthesis. Replacement of BINAP by 109 provides... 

Figure 3.46. Scope of Rh/48-catalyzed asymmetric arylative cyclization of alkynals with arylboronic acids.

The catalytic asymmetric arylation (Heck reaction) of 2,3-dihydrofuran to give (/J)-2,3-di-hydro-2-phenylfuran which, upon Jones oxidation, yields (/ )- 2 (for assignment, see p 439)80. 

Another limitation of the protocols described so far related to the aryl moiety itself. Until this stage only phenyl groups had been transferred onto (aromatic) aldehydes, which significantly restricted the substrate scope. In order to expand the applicability of the process, alternative aryl sources had to be found. This problem was solved in 2002, when we discovered that simple boronic acids 40 could also be applied in the transmetallation process [49]. For the first time the catalyzed asymmetric aryl transfer allowed a high degree of flexibility in the substitution pattern of the substrates. A wide variety of aryl boronic acids is commercially available alternatively, specific derivatives can easily be synthesized, selected examples of which (with benzaldehyde 37b as the aryl acceptor) are shown in Scheme 2.1.2.10. 

The success of the asymmetric aryl transfer from boronic acids also relied on another important phenomenon. The presence of catalytic amounts (10 mol%) of DiMPEG (MW = 2000) increased the enantioselectivity of the process significantly [49]. For example, without DiMPEG the reaction between benzaldehyde 37b and 1-naphthylboronic acid 40c gave the corresponding diarylmethanol 27g with 31% ee in 56% yield, whereas in the presence of the polyether, 27g was obtained in 85% ee and 91% yield (Scheme 2.1.2.12) [49]. 

For a general review of catalyzed asymmetric aryl transfer reactions, see C. Bolm, J. P. Hildebrand, K. Muniz, N. Hermanns, Angew. Chem. 2001, 113, 3382 Angew. Chem. Int. Ed. 2001, 40, 3284. 

E. Asymmetric Aryl Transfer Reaction to Carbonyl Compounds. 566... 

The chiral phosphine 31 or 32-rhodium complex catalyzed the addition of arystannanes 30 to N-sulfonylimines 29 to give diarylmethylamines 33 with high enantioselectivity (75-96% ee) [21]. The choice of the chiral monoden-tate phosphine ligand is essential for their catalytic asymmetric arylation. With chelating bisphosphine ligands the arylation was very slow. The authors hypoth-... 

Transition Metal-Catalyzed Asymmetric Arylation of Enolates. 167... 

Buchwald has designed a hindered dialkylphosphino-binaphthyl ligand (3) that is much more active than the original ligand for asymmetric arylation of ketone enolates. Reactions occur at room temperature using only 2 mol % catalyst with enantioselectivities up to 94% [41]. Additionally, the Buchwald group has developed an electron-rich monodentate ligand (4) capable of vinylation of ketone enolates with up to 92% ee [42]. 

Asymmetric amplification, in diisopropylzinc additions, 2, 386 Asymmetric arylation, phenols with lead triacetates, 9, 399 Asymmetric carboalumination, Zr-catalyzed, alkenes, 10, 272 Asymmetric carbonyl-ene reaction, characteristics, 10, 559 Asymmetric catalysis... 

Intermolecular a-arylation of the ketone 399 with o-tolyl bromide (398) gives 400 under selected conditions using f-BuONa or KN(SiMe2)2 as suitable bases, and BINAP or DPPF (XLIX) as a bulky ligand [194], Furthermore, asymmetric arylation of the ketone 402 with the bromide 401 gave 403 with 98% ee efficiently by using chiral BINAP [195]. 

Matsumura, S. Maeda, Y. Nishimura, T. Uemura, S. Palladium-catalyzed asymmetric arylation, vinylation, and allenylation of tert-cyclobutanols via enantioselective C—C bond cleavage./. Am. Chem. Soc. 2003, 125, 8862-8869. 

The asymmetric arylation of aldehydes in the presence of a catalytic amount of chiral amino alcohol111 or of chiral tertiary aminonaphthol112 has been described. The reactive arylzinc species have been generated in situ from a boron-zinc exchange instead of employing the more expensive diphenylzinc. The chiral diaryl carbinols have been obtained in high yields and ees. 

Table I. Catalytic Asymmetric Arylation of 2,3-Dihydrofuran with Aryl Triflatesa...

Table III. Catalytic Asymmetric Arylation of 2,3-Dihydrofuran with Phenyl Triflate (la) Promoted by [Pd (fl)-BINAP 2] Catalysta...

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