Ugi four-component

In Ugi four-component reactions (for mechanism, see Section 1.4.4.1.) all four components may potentially serve as the stereodifferentiating tool65. However, neither the isocyanide component nor the carboxylic acid have pronounced effects on the overall stereodiscrimination60 66. As a consequence, the factors influencing the stereochemical course of Ugi reactions arc similar to those in Strecker syntheses. The use of chiral aldehydes is commonly found in substrate-controlled syntheses whereas the asymmetric synthesis of new enantiomerically pure compounds via Ugi s method is restricted to the application of optically active amines as the chiral auxiliary group. 

If ammonia or an amine is also added to the mixture (in which case the reaction is known as the Ugi reaction, or the Ugi four-component condensation, abbreviated 4... 

P., Warrington, B., Wong, S., A microreactor device for the Ugi four component condensation (4CC) reaction, in Ramsey,... 

N-Hydro-2/C-(a-AcyloxyallFour component Condensation (4CC)... 

Such a strategy follows the philosophy of resin capture, as introduced by Armstrong and Keating Keating TA, Armstrong RW. Postcondensation modifications of Ugi four-component condensation products 1-isocyano-cyclohexane as a convertible isocyanide. Mechanism of conversion, synthesis of diverse structures, and demonstration of resin capture. J Am Chem Soc 1996 118 2574-2583. See also Brown SD, Armstrong RW. Synthesis of tetrasubstituted ethylenes on solid support via resin capture. J Am Chem Soc 1996 118 6331-6332. 

The application of the one-pot Ugi four-component reaction by stirring a mixture of the aldehyde 486, benzyl amine 487, isocyanide 479, and acrylic acid 385 in methanol at room temperature for 36 h afforded the triene 488 as a 74 26 mixture of amine rotational isomers in 80% combined yield. The triene 488 on heating in DMSO at 120 °C for 12 h underwent cycloaddition to give the tricyclic compound 489 as a single diastereomer in 98% yield (Scheme 111). 

An elegant two-step solution-phase methodology was developed for the synthesis of the benzodiazepine-2,5-diones (93 e.g. R1 = PhCH R2 = Me, R3 = Me, R4 = H, R5 = Me, 32%). The first step was a Ugi four-component reaction followed in the second step by a palladium-mediated intramolecular IV-arylation reaction. This methodology has considerable scope for further application in heterocyclic synthesis <06TL3423>. 

Y. Li, X. Zhang, S. Chu, K. Yu, and H. Guan, Synthesis of cluster mannosides via a Ugi four-component reaction and their inhibition against the binding of yeast mannan to concanavalin A, Carbohydr. Res., 339 (2004) 873-879. 

The first solid-phase application of the Ugi four-component condensation, generating an 18-member acylamino amide library, was presented in 1999 by Nielsen and Hoel [53]. The authors described a library generation utilizing amino-functionalized PEG-polystyrene (Tentagel S RAM) as the solid support (Scheme 7.36). A set of three aldehydes, three carboxylic acids, and two isonitriles was used for the generation of the 18-member library. 

Furthermore, multicomponent reactions can also be performed under fluorous-phase conditions, as shown for the Ugi four-component reaction [96], To improve the efficiency of a recently reported Ugi/de-Boc/cyclization strategy, Zhang and Tempest introduced a fluorous Boc group for amine protection and carried out the Ugi multicomponent condensation under microwave irradiation (Scheme 7.84). The desired fluorous condensation products were easily separated by fluorous solid-phase extraction (F-SPE) and deprotected by treatment with trifluoroacetic acid/tet-rahydrofuran under microwave irradiation. The resulting quinoxalinones were purified by a second F-SPE to furnish the products in excellent purity. This methodology was also applied in a benzimidazole synthesis, employing benzoic acid as a substrate. 

Multicomponent reactions (MCR), in which three or more reactions combine to give a single product, have lately received much attention. The Ugi four-component condensation in which an amine, an aldehyde or ketone, a carboxylic acid, and an isocyanide combine to yield an ot-acylamino amide, is particularly interesting, because... 

Perhaps the most useful and most widely employed multicomponent reaction in this context is the Ugi four-component reaction (U4CR and variations, Fig. 11), where an isonitrile, an aldehyde, an amine, and a carboxylic acid react to form a single product [65, 66]. The principal product is a dipeptide or dipeptide derivative and a high degree of diversity can be introduced by substituents (each of the four components can be varied), subsequent reactions, or by other reaction paths, which can lead to a vast varia-... 

Keating TA, Armstrong RW (1995) Molecular diversity via a convertible isocyanide in the Ugi four-component condensation. J Am Chem Soc 117 7842-7843... 

Lindhorst T, Bock H, Ugi I (1999) A new class of convertible isocyanides in the Ugi four-component reaction. Tetrahedron 55 7411-7420... 

Rikimaru K, Yanagisawa A, Kan T, Fukuyama T (2004) A versatile synthesis of a-amino acid derivatives via the ugi four-component condensation with a novel convertible isonitrile. Synlett 1 41-44... 

Seike H, Sorensen EJ (2008) A synthesis of the tricyclic core structure of FR901483 featuring an Ugi four-component coupling and a remarkably selective elimination reaction. 

Bonnaterre F, Bois-Choussy M, Zhu JP (2006) Rapid access to oxindoles by the combined use of an Ugi four-component reaction and a microwave-assisted intramolecular Buchwald-Hartwig amidation reaction. Org Lett 8 4351-4354... 

Wu JL, Jiang Y, Dai WM (2009) Assembly of l,3-dihydro-2H-3-henzazepin-2-one conjugates via Ugi four-component reaction and palladium-catalyzed hydroamidation. Synlett 1162-1166... 

Trifilenkov AS, Ilyin AP, Kysil VM, Sandulenko YB, Ivachtchenko AV (2007) One-pot tandem complexity-generating reaction based on Ugi four component condensation and intramolecular cyclization. Tetrahedron Lett 48 2563-2567... 

Faggi C, Marcaccini S, Pepino R, Pozo MC (2002) Studies on isocyanides and related compounds synthesis of l,4-benzodiazepine-2,5-diones via Ugi four-component condensation. Synthesis 18 2756-2760... 

Marcaccini S, Miliciani M, Pepino R (2005) A facile synthesis of 1, 4-benzodiazepine derivatives via Ugi four-component condensation. Tetrahedron Lett 46 711-713... 

Umkehrer M, Kalinski C, Kolb E, Burdack C (2006) A new and versatile one-pot synthesis of indol-2-ones by a novel Ugi-four-component-Heck reaction. Tetrahedron Lett 47 2391-2393... 

Dai WM, Shi JY, Wu JL (2008) Synthesis of 3-arylideneindolin-2-ones from 2-aminophe-nols by Ugi four-component reaction and Heck carbocyclization. Synlett 2716-2720... 

Faggi et al. describes the synthesis of a 1,6-dihydro-6-oxopyrazine-2-carboxylic acid derivative via the Ugi four-component reaction (Scheme 8) [28]. Arylglyoxals 44, an amine 45, benzoylformic acid 46, and an isocyanide 47 afforded the Ugi intermediate 48, which was cyclized in a [5+1] fashion with ammonium acetate to give the final product 49 in good yields. 

Scheme 8 Synthesis of a l,6-dihydro-6-oxopyrazine-2-carboxylic acid derivatives via the Ugi four-component reaction and two representative 3D conformation of 49A (cyan) and 49B (blue). Yield shown represents yield over all steps...

---