'Atypical Ugi' tetrazoles.

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Reaction Mechanisms

Background:

• The Ugi tetrazole reaction is a multicomponent reaction utilizing amino acid-derived isocyano amides, azides, carbonyl compounds, and amines.
• Classical Ugi products are well-established, but the formation of isomeric products has not been widely reported.

Purpose of the Study:

• To investigate the surprising formation of two constitutional isomers during the Ugi tetrazole reaction.
• To characterize and elucidate the mechanism behind the formation of both classical and atypical Ugi products.

Main Methods:

• Synthesis and separation of 22 different isomorphic examples of Ugi reaction products.
• Characterization of the constitutional isomers using analytical techniques.
• Mechanistic studies to propose a pathway for the concomitant formation of both isomers.

Main Results:

• The Ugi tetrazole reaction, under standard conditions, produces two distinct constitutional isomers (A and B).
• Isomer A represents the classical Ugi product, while isomer B is an atypical Ugi product with a migrated tetrazole heterocycle.
• Successful synthesis and separation of 22 pairs of these isomers confirmed their formation.

Conclusions:

• The Ugi tetrazole reaction can concurrently produce two constitutional isomers, challenging previous assumptions.
• A proposed mechanism explains the simultaneous formation of the classical and atypical Ugi products.
• This finding expands the scope and understanding of Ugi-type multicomponent reactions.