Herstellung chiraler elektrophiler Glycin‐ und (E)‐2,3‐Dehydroaminosäure‐Derivate aus 2‐t‐Butyl‐3‐methyl‐4‐oxo‐1‐imidazolidincarbonsäure‐t‐butylester (Boc‐BMI)

Preparation of Chiral Electrophilic Glycine and (E)‐2,3‐Dehydroamino Acid Derivatives from t‐Butyl 2‐t‐Butyl‐3‐methyl‐4‐oxo‐1‐imidazolidinecarboxylate (Boc‐BMI) Boc‐BMI, the compound specified in the title, is brominated under radical‐chain conditions (NBS/AIBN) to give trans‐bromo‐BMI 2, which is highly reactive in nucleophilic substitutions [see the 5‐carbo‐ and ‐hetero‐substituted (N, O, S, P) 2‐t‐butyl‐3‐methylimidazolidinones 4 – 23 and Tab. 1]. The substitutions occur preferentially with inversion of the configuration, the mechanism being not clear at all. – The Boc‐BMI dimethyl phosphonate 23 (Michaelis‐Arbusov product from 2) reacts with aldehydes (15 examples) to give preferentially (E)‐5‐alkylidene‐imidazolidinones, chiral α‐aminoacrylic acid derivatives which are available in either the R or the S form, see 24 – 38 (Tab. 2). Best yields and highest (E) selectivities (> 25:1), with short reaction times, are obtained by using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene. (DBU)/LiBr in dry THF in a very special variant of the Horner olefination. α‐Branched, racemic aldehydes may give alkylidene derivatives with efficient kinetic resolution (38). Some speculations are made about the mechanism and the observed stereochemical outcome of the reaction (I, J, K). A comparison is made with other chiral electrophilic glycine (A – C) and α,β‐dehydroamino acid derivatives (D, E), as well as with other methods for the preparation of enantiomerically pure methylenedioxolan‐, ‐oxazolidin‐, and ‐imidazolidinones (H), containing an α,β‐unsaturated carbonyl system.