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A novel multicomponent reaction of o-phenylenediamines with aldehydes and isonitriles yields 1,4-dihydroquinoxalines. These intermediates are unstable under reaction conditions. They undergo oxidation with DDQ to furnish 33-54% isolated yields of the respective quinoxalines. This reaction is general for aromatic 1,2-diamines. Monoalkylated aryl 1,2-diamines lead to stable 1,4-dihydroquinoxalines.

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A novel synthetic protocol toward imidazo[1,2-a]quinoxalines has been developed. It includes two isocyanide-based multicomponent reactions sequentially introducing four diversity elements to the final products.

A four-center, three-component Ugi-type reaction of a variety of keto acids, Boc-or Cbz-protected hydrazine, and isocyanides offers a simple and high-yielding access to cyclic products containing an N-aminolactam unit. The latter are shown to form consistently an intramolecular hydrogen bond leading to a -turn-like secondary structure. The possibility of integrating such N-aminolactam units (without disruption of the folded structure) into pseudotripeptide fragments is demonstrated.The successful use of keto (as well as aldehydo) carboxylic acids as bifunctional inputs for isocyanide-based multicomponent reactions (IMCR) was demonstrated by Harrimann 1 and Ugi. 2 This four-center, three-component process was found to provide a simple and efficient (as well as atom-economical) entry into novel dipeptoid lactam structures. The strategy has been aggressively exploited to give rise to a wide variety of novel small-and medium-size lactamtype heterocyclic scaffolds 3 and validated, in general, the use of bifunctional reagents in IMCR as a source of significant product diversity. 4

A number of N a -alkyl,N b -acylhydrazines have been synthesized via the Ugi reaction of N-acylhydrazones with an isocyanide and trifluoroacetic acid. The trifluoroacetic acid acted as a 'silent partner' and becomes removed upon basic workup of the reaction. These compounds have been efficiently modified further via reductive alkylation to produce N a ,N a -dialkyl,N b -acylhydrazines. The two groups of novel hydrazinopeptide motifs have been shown by simple 1 H NMR spectroscopic experiments to display two different secondary structure patterns. These observations were confirmed by X-ray crystallographic analysis. Combining the hydrazone and carboxylic acid moieties in one reaction precursor offers the opportunity for an 'intramolecular' hydrazino-Ugi reaction, which was also demonstrated.

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