Diisopropylzinc, enantioselective asymmetric

Highly enantioselective asymmetric autocatalytic reactions have been reported using chiral pyrimidyl-lla,b and quinolylalkanols (Scheme 12.2).Uc (5)-2-methyl-l-(2-methyl-5-pyrimidyl)-l-propanol (14b, 99.9% ee) autocatalyses the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde to afford 14b itself of the same configuration with 98.2% ee.ll Moreover 14a shows asymmetric autocatalytic reaction with amplification of ee. Thus, starting from (5)-14a with only 2% ee, four successive autocatalytic reactions afford (5)-14a with 88% ee.ub... 

The first asymmetric autocatalysis with amplification of was observed in the automultiplication of a 5-pyrimidyl alkanol 80 (Figure l)169. When (5)-5-pyrimidyl alkanol 80 with as low as 2% is used as the asymmetric autocatalyst for enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde 88, the of the produced pyrimidyl alkanol (and the initial asymmetric autocatalyst) 80 increases to 10% (Figure 1, 1st run). Consecutive asymmetric autocatalyses using 5-pyrimidyl alkanol 80 with 10% have increased its to 57%, 81% and 88% , successively. During the reactions, the major (S)-enantiomer in the initial asymmetric autocatalyst has automultiplied by a factor of 238, while the slightly minor (R)-enantiomer has automultiplied by a factor of only 16. 

When enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde 89 was examined, simple 2-butanol with low (ca 0.1%) induces a tiny chirality in the initially produced alkanol 81 and the value of the finally obtained alkanol becomes higher (73-76%) due to the asymmetric autocatalysis (Table 2). Note that the value can be further amplified by subsequent asymmetric autocatalysis, as described in the preceding section. Various chiral compounds have been proved to act as chiral initiators. 

Abstract The addition of diisopropylzinc to prochiral pyrimidine carbaldehydes (Soai reaction) is the only known example of spontaneous asymmetric synthesis in organic chemistry. It serves as a model system for the spontaneous occurrence of chiral asymmetry from achiral initial conditions. This review describes the possible kinetic origin of specific experimental features of this reaction. It is shown that generic kinetic models, including enantioselective autocatalysis and mutual inhibition between the enantiomers,... 

We found asymmetric autocatalysis of pyrimidyl alkanol 1 [1-10], Pyrimidyl alkanol 1 acts as asymmetric autocatalyst in the enantioselective addition of diisopropylzinc (/-Pr2Zn) to pyrimidine-5-carbaldehyde 2 to produce more of itself with the same absolute configuration [11] of >99.5% enantiomeric excess (ee) in a yield of >99% (Scheme 1) [12]. Thus, pyrimidyl alkanol 1 automultiplies in... 

A reversal in enantioselectivity has been observed by the combination of a chiral diol and achiral alcohols as a chiral initiator in the asymmetric alkylation of a pyrimidine-5-carbaldehyde using diisopropylzinc. (25,35)-Butane-2,3-diol alone induced (R)-pyrimidyl alkanol, while a mixture of the chiral diol and phenol derivatives induced (5)-pyrimidyl alkanol (Scheme 5). 

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