Diastereoselective Synthesis of Nitroaldol Derivatives

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°) (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 a-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 mechnisms are discussed. - The configuration of diasteromerically 13C-NMR. Spectroscopy. – Some examples of the preparation of diastereimerically enriched 1,2-aminolcohols by reduction of the correspondence nitro compounds without loss of configurational purity are described (see Schemes 11 and 12).