Asymmetrische <i>Michael</i>‐Additionen. Stereoselektive Alkylierung chiraler, nicht racemischer Enolate durch Nitroolefine. Herstellung enantiomerenreiner γ‐Aminobuttersäure‐ und Bernsteinsäure‐Derivate

Abstract

Asymmetric Michael ‐Additions. Stereoselective Alkylation of Chiral, Non‐racemic Enolates by Nitroolefins. Preparation of Enantiomerically Pure γ‐Aminobutyric and Succinic Acid Derivatives Chiral, non‐racemic lithium enolates ( E , F , G ) of 1,3‐dioxolan‐4‐ones, methyl 1,3‐oxazolidin‐4‐carboxylates, methyl 1,3‐oxazolin‐4‐carboxylates, 1,3‐oxazolidin‐5‐ones, and 1,3‐imidazolidin‐4‐ones derived from ( S )‐lactic acid ( 2a ), ( S )‐mandelic acid ( 2b ), and ( S )‐malic acid ( 2c ), or from ( S )‐alanine ( 10 ), ( S )‐proline ( 11 ), ( S )‐serine ( 12 ), and ( S )‐threonine ( 13 ), are added to nitroolefins. Michael adducts ( 3 – 9 , 14 – 18 ) are formed (40–80%) with selectivities generally above 90% ds of one of the four possible stereoisomers. Conversions of these nitroalkylated products furnish the α‐branched α‐hydroxysuccinic acids 28 and 29 , the α‐hydroxy‐γ‐amino acid 25 , the α,γ‐di‐amino acid 32 , the substituted γ‐lactames 19 – 22 , and the pyrrolidine 23 . The relative and absolute configuration of the products from dioxolanones and nitropropene are derived by chemical correlation and NOE measurements indicating that the steric course of reaction is to be specified as 1k , ul ‐1,3. The mechanism is discussed.