Catalysis BINOL

Terminal alkynes such as 4-phenylbutyne undergo nickel(II)-catalysed reaction with dialkylaluminium hydride to give vinylaluminium reagents (84), which react with aldehydes to give enantioselective formation of a-substituted secondary allylic alcohols, via Hg-BINOL catalysis. The vinylaluminium alkyl groups are chosen in such away that the reagent does not just directly reduce the aldehyde. 

The 2-pyrones can behave as dienes or dienophiles depending on the nature of their reaction partners. 3-Carbomethoxy-2-pyrone (84) underwent inverse Diels-Alder reaction with several vinylethers under lanthanide shift reagent-catalysis [84] (Equation 3.28). The use of strong traditional Lewis acids was precluded because of the sensitivity of the cycloadducts toward decarboxylation. It is noteworthy that whereas Yb(OTf)j does not catalyze the cycloaddition of 84 with enolethers, the addition of (R)-BINOL generates a new active ytterbium catalyst which promotes the reactions with a moderate to good level of enantio selection [85]. 

The structure of the active catalyst and the mechanism of catalysis have not been completely defined. Several solid state complexes of BINOL and Ti(0-/-Pr)4 have been characterized by X-ray crystallography.158 Figure 2.4 shows the structures of complexes having the composition (BIN0Late)Ti2(0-/-Pr)6 and (BINOLate)Ti3(O-/-Pr)10. 

Enantioselective catalysis of S alkylation has been achieved.91 A BINOL-phosphoramidite catalyst (o-methoxyphenyl analog) similar to that in Entry 3 in Scheme 8.7 gave good results. 

Fig. 10.2. Structures of complexed aldehyde reagent (a) and transition structure (b) for enantios-elective catalysis of the carbonyl-ene reaction by BINOL-Ti(IV). Reproduced from Tetrahedron Lett., 38, 6513 (1997), by permission of Elsevier.

Over the last few years several examples have been reported in the field of asymmetric catalysis that are based on the interaction of two centers.6,119 Recently, Shibasaki and coworkers have developed an asymmetric two-center catalyst. Scheme 3.14 shows preparation of optically active La binaphthol (BINOL). This catalyst is effective in inducing the asymmetric nitro-aldol reaction, as shown in Scheme 3.15. 

The self-assembly of a chiral Ti catalyst can be achieved by using the achiral precursor Ti(OPr )4 and two different chiral diol components, (R)-BINOL and (R,R)-TADDOL, in a molar ratio of 1 1 1. The components of less basic (R)-BINOL and the relatively more basic (R,R)-TADDOL assemble with Ti(OPr )4 in a molar ratio of 1 1 1, yielding chiral titanium catalyst 118 in the reaction system. In the asymmetric catalysis of the carbonyl-ene reaction, 118 is not only the most enantioselective catalyst but also the most stable and the exclusively formed species in the reaction system. 

Takaya and co-workers in 1993 were the first to report on asymmetric hydroformylation using phosphite-phosphine ligands [59]. In an attempt to combine the effectiveness of the BINOL chemistry for asymmetric catalysis and the effectiveness of the phosphite moiety for asymmetric hydroformylation, they developed the (.R,S)-BINAPHOS ligand 3, which turned out to be very efficient (Fig. 6). 

Table 6 Reaction of Chan s diene with aldehydes under BINOL-Ti(OzPr)4 catalysis...

This chapter focuses on several recent topics of novel catalyst design with metal complexes on oxide surfaces for selective catalysis, such as stQbene epoxidation, asymmetric BINOL synthesis, shape-selective aUcene hydrogenation and selective benzene-to-phenol synthesis, which have been achieved by novel strategies for the creation of active structures at oxide surfaces such as surface isolation and creation of unsaturated Ru complexes, chiral self-dimerization of supported V complexes, molecular imprinting of supported Rh complexes, and in situ synthesis of Re clusters in zeolite pores (Figure 10.1). 

The role of multicomponent ligand assembly into a highly enantioselective catalyst is shown in the enantioselective catalysis for the carbonyl-ene reaction (Table 8.9). The catalyst is prepared from an achiral precatalyst, Ti(0 Pr)4 and a combination of BINOL with various chiral diols such as TADDOL and 5-Cl-BIPOL in a molar ratio of 1 1 1 (10mol% with respect to the olefin and glyoxylate) in... 

In the neutral BIPHEP-Pt complex, the axial chirality of BIPHEP moiety is controlled by chiral diol BINOL as shown in Scheme 8.29. However, the diastereo-meric purity is not high enough (95 5). Therefore, recrystallization is essential to obtain the single BIPHEP-Pt diastereomer and subsequent enantiomer. It has thus been required that complete chirality control of both neutral and cationic BIPHEP-Pt complexes without recrystallization and its application to asymmetric Lewis acid catalysis (Scheme 8.32)." Interestingly, both enantiopure (5)- and (7 )-BIPHEP-Pt complexes can be obtained quantitatively through the... 

Other successful H-bond catalysis apphcations have been introduced by Schaus and Sasai involving asymmetric Morita-Bayhs-Hilhnan (Scheme 11.13c) and aza-Morita-Baylis-Hillman reactions (Scheme 11.13d), respectively. Intriguingly, derivatized BINOL systems 33 and 34 provided optimal selectivities. 

Keywords Asymmetric catalysis BINOL Dicarboxylic acids A-Triflyl phosphoramides Phosphoric acids Strong chiral Brpnsted acids... 

List and coworkers reasoned that BINOL phosphates (specific Brpnsted acid catalysis) could be suitable catalysts for an asymmetric direct Pictet-Spengler reaction [26], Preliminary experiments revealed that unsubstituted tryptamines do not undergo the desired cyclization. Introduction of two geminal ester groups rendered the substrates more reactive which might be explained by electronic reasons and a Thorpe-Ingold effect. Tryptamines 39 reacted with aldehydes 40 in the presence of phosphoric acid (5)-3o (20 moI%, R = bearing 2,4,6-triisopropyI-... 

Two years later, Terada and coworkers described an asymmetric organocatalytic aza-ene-type reaction (Scheme 28) [50], BINOL phosphate (7 )-3m (0.1 mol%, R = 9-anthryl) bearing 9-anthryl substituents mediated the reaction of A-benzoylated aldimines 32 with enecarbamate 76 derived from acetophenone. Subsequent hydrolysis led to the formation of P-amino ketones 77 in good yields (53-97%) and excellent enantioselectivities (92-98% ee). A substrate/catalyst ratio of 1,000 1 has rarely been achieved in asymmetric Brpnsted acid catalysis before. 

Akiyama and coworkers extended the scope of electrophiles applicable to asymmetric Brpnsted acid catalysis with chiral phosphoric acids to nitroalkenes (Scheme 57). The Friedel-Crafts alkylation of indoles 29 with aromatic and aliphatic nitroalkenes 142 in the presence of BINOL phosphate (7 )-3r (10 mol%, R = SiPhj) and 3-A molecular sieves provided Friedel-Crafts adducts 143 in high yields and enantioselectivities (57 to >99%, 88-94% ee) [81]. The use of molecular sieves turned out to be critical and significantly improved both the yields and enantioselectivities. 

Until 2006, a severe limitation in the field of chiral Brpnsted acid catalysis was the restriction to reactive substrates. The acidity of BINOL-derived chiral phosphoric acids is appropriate to activate various imine compounds through protonation and a broad range of efficient and highly enantioselective, phosphoric acid-catalyzed transformations involving imines have been developed. However, the activation of simple carbonyl compounds by means of Brpnsted acid catalysis proved to be rather challenging since the acid ity of the known BINOL-derived phosphoric acids is mostly insufficient. Carbonyl compounds and other less reactive substrates often require a stronger Brpnsted acid catalyst. 

The last few years have witnessed major advances in the use of small organic molecules as organic acid catalysts in asymmetric catalysis [1], Selected examples of such organic acid catalysts include urea and thiourea [2], TADDOL [3], BINOL [4], and phosphoric acid derived from BINOL [5] (Figure 2.1). 

The Rawal group next applied diol catalysis to the enantioselective vinylogous Mukaiyama aldol (VMA) reaction of electron-deficient aldehydes [105]. Screening of various known chiral diol derivatives, including VANOL, VAPOL, BINOL, BAMOL, and TADDOL, revealed that 38a was the only catalyst capable of providing products in acceptable levels ofenantioselection (Scheme 5.55). Subsequent to this work, Scettri reported a similar study of TADDOL-promoted VMA reactions with Chan s diene [106]. 

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