Diastereoselective Synthesis of Nitroaldol Derivatives

Article abstract of DOI:10.1002/hlca.19820650402

Three methods are described by which diastereomerically enriched nitroaldols and their O-silylated derivatives can be prepared. threo-Nitroaldols prevail up to 10:1 over the erythro-isomers if doubly deprotonated nitroaldols 28 are quenched with acetic acid (THF/HMPT or DMPU, -100 deg C) (see Scheme 5 and Table 2).O-Trimethyl- or O-(t-butyl)dimethylsilylated (TBDMSi) erythro-nitroaldols can be obtained by protonation of the corresponding lithium nitronates (35, 39) in THF at low temperature (see Schemes 6 and 7).The erythro-O-TBDMSi-nitroaldol derivatives are also formed in the fluoride catalyzed addition of TBDMSi-nitronates (40-45) to aldehydes (see Schemes 8 and 9).In the latter reaction no 1,2-asymmetric induction is observed if α-branched silylnitronates or aldehydes are employed (see 48/49 and 50/51). - The stereochemical course of the reactions leading to erythro-O-TBDMSi-nitroaldols follows topological rules of broad applicability (see Scheme 10); possible mechanisms are discussed.- The configuration of erythro/threo-nitroaldols is determined by chemical correlation (see 24-26) and by 13C-NMR. spectroscopy. - Some examples of the preparation of diastereomerically enriched 1,2-aminoalcohols by reduction of the corresponding nitro compounds without loss of configurational purity are described (see Schemes 11 and 12).