Various Multicomponent Synthesis

Catalytic multicomponent synthesis of highly substituted pyrroles has been described. A one-pot reaction uses DBU with the commercially available thiazolium salt 513 to produce the necessary nucleophilic zwitterionic catalyst in situ, which promotes a conjugate addition of acylsilanes (sila-Stetter) and unsaturated ketones to generate 1,4-dicarbonyl compounds in situ. Subsequent addition of various amines promotes a Paal-Knorr reaction, affording the desired polysubstituted pyrrole compounds in a one-pot process in moderate to high yields (Scheme 129) <2004OL2465>. Microwave heating dramatically reduced the reaction time (from 16 h to 30 min), but offered no improvement in yields. 

The economics of the various methods that are employed to sequence multicomponent columns have been studied. For example, the separation of three-, four-, and five-component mixtures has been considered (44) where the heuristics (rules of thumb) developed by earlier investigators were examined and an economic analysis of various methods of sequencing the columns was made. The study of sequencing of multicomponent columns is part of a broader field, process synthesis, which attempts to formalize and develop strategies for the optimum overall process (45) (see Separation systems synthesis). 

Partially hydrogenated quinoline cores are also present in some important bioactive compounds. For example, the 4-aza-analogs of Podophyllotoxin, a plant lignan that inhibits microtubule assembly, revealed to be more potent and less toxic anticancer agents. In 2006, Ji s group reported a green multicomponent approach to a new series of these derivatives, consisting of the reaction of either tetronic acid or 1,3-indanedione with various aldehydes and substituted anilines in water under microwave irradiation conditions (Scheme 26) [107]. For this efficient and eco-friendly transformation, the authors proposed a mechanism quite similar to the one that was postulated for the synthesis of tetrahydroquinolines in the precedent section. 

Pyridine and its partially or totally unsaturated derivatives such as tetrahydropy-ridines, DHPs, and piperidines are ubiquitous cores found in numerous natural product skeletons and in synthetic compounds of primary interest for synthetic chemistry, agrochemistry, or pharmacology. Among the various methodologies available for the synthesis of these compounds, multicomponent approaches have attracted much attention in the last few years. Most of these sequences are initiated by a Michael addition. 

Cyclization of imidoyl azides 150 into 1,5-disubstituted tetrazoles 5 (Equation 10) is widely used both in the laboratory and on an industrial scale. Imidoyl azides form in situ in the course of various multistage processes, and sometimes in the multicomponent reactions (MCRs). The problems related to generation of imidoyl azides and also to electrocyclization of these intermediates into 1-mono- and 1,5-disubstituted tetrazoles are of crucial importance for the tetrazole chemistry. These problems are traditionally treated at length in basic reviews <1984CHEC(4)791, 1996CHEC-II(5)621>. The traditional methods for the synthesis and cyclization of imidoyl azides into tetrazoles were broadly employed and further refined in more recent works <1997MI1375>. Several new methods based on this approach have also been developed. 

This review highlights recent studies of synthetic, covalently linked multicomponent molecular devices which mimic aspects of photosynthetic electron transfer. After an introduction to the topic, some of the salient features of natural bacterial photosynthetic reaction centers are described. Elementary electron transfer theory is briefly discussed in order to provide a framework for the discussion which follows. Early work with covalently linked photosynthetic models is then mentioned, with references to recent reviews. The bulk of the discussion concerns current progress with various triad (three-part) molecules. Finally, some even more complex multicomponent molecules are examined. The discussion will endeavor to point out aspects of photoinitiated electron transfer which are unique to the multicomponent species, and some of the considerations important to the design, synthesis and photochemical study of such molecules. 

NIL patterns were also used for the assembly of nanoparticles via supramole-cular host-guest interactions.95 The NIL-patterned substrate was functionalized with CD SAMs via a three-step synthesis process. The fabrication of 3D nanostructures was achieved by the alternating assembly of multivalent guest-functionalized dendrimers and CD-fnnctionalized Au nanoparticles.88 This methodology can be applied to various nanoparticles, regardless of their size and core material. For instance, CD-functionalized silica and polystyrene nanoparticles were adsorbed onto NIL-patterned CD SAMs with preadsorbed guest-fnnctionalized dendrimers.60 92 Recently, Huskens et al. demonstrated the supramolecular LbL assembly of 3D multicomponent nanostructures of nanoparticles by alternating assembly steps of complementary ferrocenyl-functionalized silica nanoparticles and different kinds of host-fnnctionalized nanoparticles (see Fig. 13.8).66... 

Abstract The photochemical properties of transition metal complexes, such as those of iridium(III) or ruthenium(II), can be exploited in various ways to generate charge-separated (CS) states, in relation to the mimicry of the natural photosynthetic reaction centres, or to set multicomponent compounds or assemblies in motion. The first part of the present chapter summarizes the work carried out in our groups (Bologna and Strasbourg) in recent years with iridium(III)-terpy complexes (terpy 2,2,6,6"-terpyridine). The synthesis of multicomponent iridium(III) complexes in reasonable yields has been... 

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