Nitrosoaldol reaction

In 2002, Yamamoto and Momiyama reported an unusual aldol-like reaction with silyl enol ethers and nitrosobenzene in the presence of a catalytic amount of TESOTf (nitrosoaldol reaction).29 Usually, nucleophiles react with nitrosobenzene without Lewis acid to give the N adduct predominantly. In contrast, they reported that the reaction of silyl enol ethers and nitrosobenzene catalyzed by TESOTf afforded the 

TABLE 9.12. O-Nitrosoaldol Reaction Using Tin Enolates and Nitrosobenzene 

Entry Enolate Yield/ee (%) Entry Enolate Yield/ee (%) 

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. 

After their discovery, several other groups reported nitrosoaldol reactions using different catalysts including acid catalysts and organocatalysts.31 

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Although the asymmetric nitrosoaldol reaction was achieved with high enantioselectivity, the use of a stoichiometric amount of organostannane was unacceptable. In... 

Yamamoto et al. reported the asymmetric (9-nitrosoaldol reaction using silyl enol ethers in the presence of the silver catalyst.32 In order to achieve this reaction, they developed a novel combination of silver and a chiral phosphite derived from BINOL. The disilanyl enol ether was used to ensure high yield and enantioselectivity. The reaction was conducted with disilanyl enol ether and nitrosobenzene in the presence of AgBF4 and the chiral phosphite ligand in THF to produce the O adduct with high regio- and enantioselectivity (Table 9.14). In addition, a chiral silyl enol ether could be used as a substrate. The reaction was conducted with chiral silyl enol... 

TABLE 9.14. 0-Nitrosoaldol Reaction Using Silyl Enol Ethers and Nitrosobenzene... 

SCHEME 11.7. A -Nitrosoaldol reaction of a-branched aldehydes promoted by prolinamide 10. 

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