Ionic liquid-supported synthesis aldehyde

Synthesis of thiazolidinones [PEG -RMIM]X ionic liquids have been used for rapid synthesis of a small library of amido 4-thiazolidinones from amine, aldehyde, and mercaptoacid components (Scheme 7.22) [74]. In an initial feasibility study, acid-functionalized benzaldehydes were first coupled to the [PEG -RMIM]X ionic liquids. Imines were formed by reaction of the supported aldehydes with primary amines. The reactions were run in open vessels. Optimum results were obtained by irradiating the reaction mixture with low power at 100 °C for 20 min. The imines were then condensed with mercaptoacids to give the desired thiazolidinones which were then cleaved from the ionic liquid support by amide formation. Microwave irradiation was again used in this cleavage step. The procedure entailed addition of a small amount of solid potassium tert-butoxide to a premixed mixture of the amine and supported thiazolidinone and microwave exposure for 10-20 min at 100 or 150 °G depending on the amine used. In another study, a series of one-... 

Since the first publication, amine-catalyzed Diels-Alder reactions of a,/ -unsaturated aldehydes have been investigated in much detail [15, 26-33]. Catalyst immobilization studies on solid support [26, 27], as well as in ionic liquids [29], have shown advantages for amine recycling, while partially maintaining good levels of asymmetric induction [34]. The use of this reaction in total synthesis has allowed the rapid preparation of (+)-hapalindole Q, a tricyclic alkaloid natural product containing four contiguous stereocenters (Scheme 3.2) [28]. 

A novel and efficient ionic liquid synthesis of DHPMs has been developed by Bazureau and co-workers [92] in which ionic liquid-phase bound acetoacetate was reacted with (thio)urea and a suitable aldehyde in the presence of HCl affording ionic liquid-phase supported 3,4-dihydropyrimidine-2-(thi)ones 43. The desired 3,4-dihydropyriinidme-2-(thi)one was easily cleaved from the ionic liquid-phase by transesterification under mild conditions in good yield and with high purity. Advantageously, the ionic liquid-phase linked DHPM could be crystallized from the excess of (thio)urea (Scheme 32). 

A novel and efficient task-specific ionic liquid synthesis of Biginelli compounds has been developed. Ionic liquid phase-bound acetoacetate reacted with urea or thiourea and various aldehydes in the presence of a cheap catalyst to afford ionic liquid phases supported 3,4-dihydropyrimidine-2-(thi)ones. The desired 3,4-dihydropy-rimidine-2-(thi)ones were easily cleaved from the ionic liquid phase by transesteri-flcation under mild conditions in good yields and high purity. The task-specific ionic liquid technology represents an attractive alternative to the classical solid- and... 

Of the inorganic supports, best results were reported for a mesoporous MCM-41 [337]. Support on ionic-liquid phases has been studied by different groups with variable results [338, 339], Of the non-conventional organic polymers, non-covalent immobilization on poly(diallyldimethylammonium) is notable [340], Catalysts 133 (15 mol.%) promoted the aldol reaction of acetone and benzaldehydes to afford the corresponding (i-hydroxyketones in 50-98% yields and 62-72% ee, which are clearly lower than those reported for other polymer-supported systems. Recycling of the catalysts was possible at least six times without loss of efficiency. More recently, proline has been attached to one DNA strand while an aldehyde was tethered to a complementary DNA sequence and made to react with a non-tethered ketone [341], To date, the work has focused more on conceptual development than on the analysis of its practical applications in organic synthesis. 

Labrini et al. (2005) have reported a rapid synthesis of 2,5-disubstituted-1,3,4-thiadiazoles via the one pot condensation reaction of aromatic aldehydes, hydrazine, and sulfur in ethanol under microwave irradiation. Microwave-assisted synthesis of 2-aminothiophene-3-carboxylic derivatives (Gewald synthesis) has been reported by Hu et al. (2006) under microwave conditions using a functional ionic liquid as a soluble support. 

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