Diastereoselective Synthesis of Nitroaldol Derivatives

Abstract

Abstract 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 13 C‐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 ).