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

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Abstract
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.

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