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.