A Novel Route to Racemic and Nonracemic Products of the Ugi Reaction: Synthesis of Ugi′s Labile α‐Adducts from Iminoaziridines and Carboxylic Acids, and their Transformations

Iminoaziridines ( 11 ) are highly reactive synthetic equivalents for three of the four components in the Ugi four‐component condensation. Thus, iminoaziridines react rapidly with carboxylic acids at temperatures as low as –20°C to afford α‐amino isoimides ( 14 ), which are identical to the elusive α‐adducts of isocyanides in the Ugi reaction. 1,4‐Migration of the acyl group ( O → α‐N ) in 14 furnishes the α‐acylamino amides 15 . Very little, if any, racemisation is observed when carboxylic acids react with nonracemic iminoaziridines [( R )‐ 11 a,c ], which are readily available. Mumm rearrangement by O → N ‐acyl 1,3‐migration to afford α‐amino imides ( 16 e, f ) competes if the O → α‐N 1,4‐shift is slowed down by steric hindrance. The latter acyl shift is catalysed by carboxylic acids while the former is not. The iminoaziridines ( R )‐ 11 a,c react quantitatively and without racemisation with hydrazoic acid to produce the 5‐aminoalkyltetrazoles ( R )‐ 21 a,c .