Diastereoselectivity enantiopure applications

The conjugate addition of activated nitrogen nucleophiles, such as hydroxylamine and hydrazine derivatives, to a,/3-unsaturated bicyclic lactam 284 gave the corresponding /3-amino product 285 in good yield and excellent diastereoselectivity. These products can be manipulated to afford enantiopure /3-aminopyrrolidinones of potential application as conformationally constrained, substituted glutamate templates (Equation 45) <2001J(P1)2997>. 

Basing on this investigation, 5-17 has been cycloadded to numerous chiral dienophiles in order to increase the asymmetric induction [430]. The use of chiral oxazolidinones allowed to obtain induced diastereoselectivities up to 92 % de. On the other hand, the complementary application of enantiopure, chiral thia- 1,3-butadienes introduced by Fishwick et al. has yielded very promising results [431]. Upon in situ generation of the chiral heterodiene 5-22 from 5-21, a completely exo-selective cycloaddition occurred in the presence of cyclopente-ne leading to the fused thiopyran 5-23 as a single diastereomer (Fig. 5-7). 

Moreover, a wide series of enantiopure A, A -disubstituted cw-a-aminocy-cloalkanols could be prepared by application of this methodology starting from the corresponding dialkylaminocycloalkanones in quantitative yields and diastereoselectivities >98% de in all cases of substrates (Scheme 2.36). ... 

Trans-N,N-didecyl diaminocyclohexane was also applied by Cheng et al. to the asymmetric aldolisation of pyruvic derivatives with benzaldehydes, providing the corresponding aldol products with excellent syn diastereoselectivities and enantioselectivities of up to 99% ee (Scheme 2.31). It is important to note that enantioselectivities of up to 99% ee combined with syn diastereoselectivities of up to 90% de were also observed in the case of using aliphatic aldehydes, albeit with low yields (<32%). A synthetic application of this methodology was found in the synthesis of enantiopure furanoses, which are important precursors for the synthesis of bioactive compounds. 

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