Allylation catalytic asymmetric

The catalytic enantioselective addition of vinylmetals to activated alkenes is a potentially versatile but undeveloped class of transformations. Compared to processes with arylmetals and, particularly alkylmetals, processes with the corresponding vinylic reagents are of higher synthetic utility but remain scarce, and the relatively few reported examples are Rh-catalysed conjugate additions. In this context, Hoveyda et al. reported very recently an efficient method for catalytic asymmetric allylic alkylations with vinylaluminum reagents that were prepared and used in Thus, stereoselective reactions... 

More recently, catalytic asymmetric allylations of imines and imine derivatives in aqueous media have been studied. An /V-spiro C2-symmetrical chiral quaternary ammonium salt (5,5)-I-Br (,S, .S )-()-Np-NAS-Br] has been evaluated in the allylation of glycine tert-Bu ester benzophenone Schiff base [Ph2C=NCH2COOCMe3] for synthesis of both natural and unnatural a-amino acids (Eq. 11,45).76... 

Except for a 1976 report in the patent literature (100a), the first true catalytic asymmetric allylic oxidation using copper was reported in 1991 by Muzart (100b). Of the various amino acids investigated as ligands for Cu(II), (S) proline was found... 

CATALYTIC ASYMMETRIC ALLYLATION REACTIONS (S)-1-(PHENYLMETHOXY)-4-PENTEN-2-OL (4-Penten-2-ol, l-(phenylmethoxy)-, (S)-)... 

CATALYTIC ASYMMETRIC ALLYLATION REACTIONS WITH OTHER ALDEHYDES... 

CATALYTIC ASYMMETRIC ALLYLATION REACTIONS (S)-I-PHENYLMETHOXY)-4-PENTEN-2-OL... 

The subject of catalytic asymmetric allylic alkylations has been thoroughly and... 

Scheme 5. Diversity-based approaches used in the late nineties in connection to the development of catalytic asymmetric allylic substitution reactions...

In recent years methods for the catalytic asymmetric allylation have also been developed.14... 

Catalytic asymmetric allylations of aldehydes or ketones are roughly classified into two methods, namely, those using chiral Lewis acid catalysts and those using chiral Lewis base catalysts. The former method uses less reactive allylsilanes or allylstannanes as the allyl source. The latter method requires allyltrichlorosi-lane or more reactive allylmetals. Both processes are applicable to the reactions with substituted allylmetal compounds or propargylation. 

Catalytic asymmetric allylation of aldehydes and ketones with allylsilanes can be achieved by using chiral Lewis acids, transition metal complexes, and Lewis bases. In recent years, much attention has been paid for the chiral Lewis base-catalyzed system using allyltrichlorosilanes. Advances in catalytic asymmetric carbonyl allylation have been described in detail in recent reviews.116,117,117a... 

Practical and efficient asymmetric allylation of aldehydes is successfully promoted by Lewis acid catalysts bearing chiral auxiliaries to afford high levels of enantioselectivity.165 The effective catalysts for asymmetric allylation to benzaldehyde are shown below (Scheme j) 166-176 The catalytic asymmetric allylation of ketones has proved to be a more challenging transformation owing to the significantly low reactivity compared to aldehydes. In 2002, a catalyst based on titanium complex was developed (Equation (51)).A ... 

The first catalytic asymmetric allylation of imines has been reported using allyltri- -butyltin in the presence of a chiral 7r-allylpalladium complex.179 Zirconium is also demonstrated as a metal center for the design of chiral Lewis acid catalysts that are suitable for the activation of bidentate imino compounds.180 Jprgensen reports high enantio-selective allylation of ct-imino esters (Equation (52)).181... 

Catalytic Asymmetric Allylation (CAA) Reactions (S)-1-(Phenylmethoxy)-4-penten-2-ol. 

When catalytic asymmetric allylation was attempted with a catalytic amount of chiral titanium complexes, BINOL-TiCl2 or BIN0L-Ti(0-/-Pr)2 the reaction was found to be slow. The reaction was performed satisfactorily when BIN0L-Zr(0-/-Pr)2 was employed as catalyst in the presence of molecular sieves (Eq. 18) [19a]. 

Rhizoxin is a macrocyclic natural product possessing antibiotic and antifungal properties, and it also exhibits antitumor activity. G.E. Keck and co-workers described a synthetic approach for the construction of this natural product, where they utilized the catalytic asymmetric allylation method as a key strategic element to establish the C13 stereochemistry. ... 

Keck, G. E., Geraci, L. S. Catalytic asymmetric allylation (CAA) reactions. II. A new enantioselective allylation procedure. Tetrahedron Lett. 1993,34, 7827-7828. 

Keck, G. E., Krishnamurthy, D., Grier, M. C. Catalytic asymmetric allylation reactions. 3. Extension to methallylstannane, comparison of procedures, and observation of a nonlinear effect. J. Org. Chem. 1993, 58, 6543-6544. 

Yu, C.-M., Choi, H.-S., Jung, W.-H., Lee, S.-S. Catalytic asymmetric allylation of aldehydes with BINOL-Ti(IV) complex accelerated by I-PrSSiMes. Tetrahedron Lett. 1996, 37, 7095-7098. 

Kii, S., Maruoka, K. Practical approach for catalytic asymmetric allylation of aldehydes with a chiral bidentate titanium(IV) complex. Tetrahedron Lett. 2001,42,1935-1939. 

Keck, G. E., Yu, T. Catalytic Asymmetric Allylation Reactions Using BITIP Catalysis and 2-Substituted Allylstannanes as Surrogates for P-Keto Ester Dianions. Org. Lett. 1999,1, 289-291. 

Keck [89a-c], Tagliavini [89d,e], and Yu [89f] have extensively studied the BINOL-Ti- or binol-Zr promoted reactions of achiral aldehydes with allylstan-nanes. The initial studies employed BINOL and either Ti(Oi-Pr)4 or TiCl2(0/-Pr)2 as the Lewis acid promoter in the reaction of achiral aldehydes with allyltributyl-stannane. The reaction affords good yields of the desired homoallylic alcohol with a high degree of enantioselectivity even with as little as 10 mol% of the chiral catalyst (Scheme 10-49) [89a]. The rate and turnover of the catalytic, asymmetric allylation reaction have also been optimized. It was found that when /-PrSSiMe3 is added to the reaction, a rate acceleration occurs, allowing as little as 1-2% of the catalyst to be used [89 fj. 

Marshall subsequently demonstrated that the efficiency of the crotylation reactions catalyzed by CAB catalyst 459b could be improved by using the more reactive crotylstannanes and employing two equivalents of (CF3C0)20 to aid catalyst turnover [310]. In a comparative study of the catalytic asymmetric allylation and crotylation reactions of cyclohexane carboxaldehyde with allyl- and crotylstannanes 98 and 10, Marshall demonstrated the complementarity between the BINOL-Ti(0-i-Pr)4 catalyst 451 and the CAB catalyst 459b (Table 11-29). 

Of the BINOL/BINAP-metal catalyst complexes, only the allylation procedure described by Keck using the BINOL-Ti(IV) catalyst 451 has been applied in the synthesis of natural products, presumably because it has the most substrate generality and the field is so new. In a preliminary report, Evans disclosed the synthesis of the 4-hydroxy buteneolide terminus 470 of mucocin, where he uses Keck s original catalytic asymmetric allylation procedure to effect conversion of aldehyde 469 to the homoallylic alcohol 470 in good yield and high diastereoselectivity (Scheme 11-36) [312]. 

---