BINAP-AgOTf

In addition, this silver-BINAP catalyst has been applied to the crotylation reaction between aldehydes and 2-butenylstannanes (Scheme 9.1).3 The addition of (E)-2-butenylstannane to benzaldehyde in the presence of 20 mol% AgOTf/BINAP gave the corresponding adduct with 94% ee with a high anti syn ratio. In contrast to other... 

Aldol reactions. A combination of AgOTf, (/ )-BINAP, and RjSnOMe promotes a diastereoselective-enantioselective aldol reaction of enol trichloroacetates with aldehydes. ... 

Asymmetric allylation. Allylation of aldehydes with allytributyltin in the presence of AgOTf-BINAP furnishes homoallylic alcohols with good ee. Other combinations, such as BINAP and AgNOj, AgClO, AgOCOCFj, or other chiral phosphines with AgOTf, are inferior. 

Shibasaki has examined catalysis of a complex, prepared in situ from PdCl2, AgOTf, (R)-or (S)-BINAP, 4 A molecular sieves, and H20, in the aldol addition reaction of enolsilanes by (Eq. 8B2.5) [13]. Under these conditions, aryl methyl ketone-derived trimethylsilyl enolates add to benzaldehyde and hydrocinnamaldehyde, affording adducts with up to 73% ee. 

It should be added that an analogous, previously developed [15], metal-catalyzed synthesis, based on use of BINAP-AgOTf as catalyst, is also available. This effi-... 

Attempts to develop enantioselective protocols for the aza-Diels-Alder reaction were reported simultaneously with those described above. A first contribution in this area was the report by the. Mrgensen group,85 who studied the influence of salts of copper, silver, palladium, and zinc. Copper(I) perchlorate provides optimal yields and enantioselectivity, but complexes of BINAP (87) and Tol-BINAP (203) with AgSbF6, AgOTf, and AgC104 were able to catalyze the reaction, albeit with low enantioselectivity (Scheme 2.52). 

In 1996, Yamamoto and Yanagisawa reported the allylation reaction of aldehydes with allytributyltin in the presence of a chiral silver catalyst.2 They found that the combination of silver and a phosphine ligand accelerates the allylation reaction between aldehydes and allyltributyltin. After this discovery, they screened several chiral phosphine ligands and found that chiral silver-diphosphine catalysts can effect the reaction in an enantioselective fashion (Table 9.1).2 For example, when benz-aldehyde and allyltributyltin were mixed in the presence of 5 mol% of AgOTf and (S)-2,2 -bis(diphenylphosphino)-1,1 -binaphthyl (BINAP), the corresponding homoallyl alcohol was obtained with 96% ee and 88% yield (Table 9.1). Generally, the reaction with aromatic aldehydes afforded the corresponding homoallyl alcohols in excellent... 

To overcome this limitation, Yamamoto and coworkers investigated the reaction conditions and found that the use of KF and %-crown-6 in the presence of AgOTf and BINAP was effective in promoting the allylation reaction (Table 9.6).11 Thus, the reaction was conducted with aliphatic aldehydes and allytrimethoxysilane in the presence of catalyst to give the corresponding adducts with satisfactory yields and high enantioselectivities. Moreover, this catalytic system can be applied to the reaction between aromatic aldehydes and allyltrimethoxysilane. 

More recently, the catalyst that was prepared from AgOTf and Tol-BINAP was applied to the synthesis of 2,3-dihydrobenzofnrans. The reaction of 2,3-dihydroben-zoxasilepine and an aromatic aldehyde was carried out in the presence of the silver catalyst, KF, and 18-crown-6 to give tra s-2,3-disubstituted 2,3-dihydrobenzofuran... 

In 1997, Yamamoto, Yanagisawa, and others reported the asymmetric reaction catalyzed by a BINAP-AgOTf catalyst (Table 9.7).16 The reaction was conducted with tributyltin enolate and aldehydes in the presence of the BINAP-AgOTf catalyst to afford the corresponding adduct with high enantioselectivity. The observed... 

In addition, the combination of KF and 1 H-crown-6 in the presence of BINAP-AgOTf, which was effective in accelerating the allylation reaction using allyltrimethoxysilane, could be used for the aldol reaction (Scheme 9.11).20 Thus, the reaction with the silyl enol ether derived from cyclohexanone and benzaldehyde in the... 

This catalytic system could be applied to the enantioselective hydroxymethylation of silyl enol ethers with aqueous formalin (Scheme 9.12).21 Doyle and coworkers have successfully applied the catalyst system of BINAP-AgOTf, KF, and %-crown-6 for Mukaiyama aldol reaction of a-diazo silyl enol ether (Scheme 9.13).22... 

In contrast, the reaction of tributyltin enol ethers and nitrosobenzene in the presence of a 1 2 mixture of BINAP and AgOTf in ethylene glycol diethyl ether afforded the N adduct predominantly with high enantioselectivity (Table 9.13). Momiyama and Yamamoto have determined the structures of silver-BINAP complex by an X-ray analysis and a 31P NMR study3015. 

Enantioselective aldol reaction of tin enolates with aldehydes catalyzed by BINAP-AgOTf complex has been accomplished. This reaction proceeds through a cyclic transition state with the aid of chiral silver complex (Equation (67)).221... 

The use of Lewis acid drastically changes the regioselectivity. The highly enantioselective and O-selective nitroso aldol reactions of tin enolates with nitrosobenzene have been developed with the use of (i )-BINAP-silver complexes as catalysts. AgOTf and AgCICL complexes are optimal in the O-selective nitroso aldol reaction in both asymmetric induction (up to 97% ee) and regioselection (0/N= > 99/1), affording amino-oxy ketone. The product can be transformed to a-hydroxy ketone without any loss of enantioselectivity (Equation (71)).224... 

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