Nitroaldol acceleration

In order to remove a proton from I, we added almost 1 equiv of base to the LLB catalyst. After many attempts, we were finally pleased to find that 1 mol% of second-generation LLB (LLB-II), prepared from LLB, 1 mol equiv of H20, and 0.9 mol equiv of butyllithium efficiently promoted the catalytic asymmetric nitroaldol reactions. Moreover, we also found that the use of LLB-II (3.3 mol%) accelerated these reactions. The use of other bases such as NaO-t-Bu, KO-t-Bu and Ca(0-i-Pr)2 gave less satisfactory results. The results are shown in Table 2 The structure of LLB-II has not yet been unequivocally determined. We propose here, however, that it is a complex of LLB and LiOH a proposed reaction course for its use in an improved catalytic asymmetric nitroaldol reaction is shown at the bottom of Scheme 4. Industrial application of a catalytic asymmetric nitroaldol reaction is being examined. 

Although heterobimetallic complexes afforded nitroaldol adducts in good stereoselectivity, most reactions required a long reaction time even with relatively high catalyst loadings (3-10 mol%). To achieve a more efficient catalysis, a strategy to accelerate the reaction was investigated. A plausible mechanism of catalytic asymmetric nitroaldol reaction is shown in Scheme 13.42. The concentration of intermediate (A) was considered to be rather low in the reaction mixture because of an... 

Scheme 13.43 Acceleration of nitroaldol reaction by second-generation catalyst (LLB f-LiOH).

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