Multicomponent assemblies

A multicomponent assembly of pyrido-fused tetrahydroquinolines has been accomplished by Lavilla and coworkers in a one-pot process by the interaction of dihydroazines, aldehydes, and anilines (Scheme 6.242) [425], The reactions were conducted with 20 mol% of scandium(III) triflate as a catalyst in dry acetonitrile in the presence of 4 A molecular sieves, employing equimolar amounts of the building blocks. This protocol provided the cycloadducts shown in Scheme 6.242 in 80% yield as a 2 1 mixture of diastereoisomers following microwave irradiation at 80 °C for 5 min. The same reaction at room temperature required 12 h to reach completion. 

Severin and coworkers reported (146) the reaction of tris(2-aminoethyl)amine and 4-formylphenylboronic acid with penta-erythritol to give, via multicomponent assembly, the boronic acid based macrobicyclic cage 35 (Fig. 25). The cage has the form of an ellipsoid with a diameter of 20.5 A and binds two Cud) ions in a fashion similar to the smaller tren-based cryptands. The reversible formation of boronic esters has also been employed to build other hollow structures such as nanotubes (147) and porous covalent organic frameworks (148,149). 

Christinat, N. ScopeUiti, R. Severin, K. Multicomponent assembly of boronic acid based macrocycles and cages. Angew. Chem. Int. Ed. 2008, 47, 1848-1852. 

Fleming and coworkers have developed a number of such multicomponent assembling reactions using alkyl halides, aldehydes, ketones and acid chlorides as electrophiles for post-functionalization of carbomagnesiation . The stereoselectivity of the reaction with electrophiles is not only generally high but also highly dependent on the nature of electrophiles. 

Scheme 8.8 Schematic representation of a multicomponent assembly fixing two phosphites in space to form a chelating bidentate ligand.

Radicals add to unsaturated bonds to form new radicals, which then undergo addition to other unsaturated bonds to generate further radicals. This reaction sequence, when it occurs iteratively, ultimately leads to the production of polymers. Yet the typical radical polymerization sequence also features the essence of radical-induced multicomponent assembling reactions, assuming, of course, that the individual steps occur in a controlled manner with respect to the sequence and the number of components. The key question then becomes how does one control radical addition reactions such that they can be useful multicomponent reactions Among the possibilities are kinetics, radical polar effects, quenching of the radicals by a one-electron transfer and an efficient radical chain system based on the judicious choice of a radical mediator. This chapter presents a variety of different answers to the question. Each example supports the view that a multicomponent coupling reaction is preferable to uncontrolled radical polymerization reactions, which can decrease the overall efficiency of the process. 

In the context of MCRs the novelty of a reaction and the chemical backbone structures accessible from it can also be understood in terms of combining otherwise known reactions into a multicomponent assembly of starting materials that, via a domino process [23], yield a product. Although neither the individual reactions forming the MCR nor the product might be novel, in terms of creating a synthetically useful process we suggest that such MCRs should also be considered novel reactions as they create chemical innovation. 

The photochemical and other properties must be retained when the chiral molecular switch is incorporated in a polymer or acts as a part of a multicomponent assembly. 

In comparison with the fabrication of alkynyl- or alkenyl-linked multicomponent assemblies, there are few examples dedicated to aryl-Pcs. Such attempts are mainly based on Suzuki or Stille couplings. Hence, Odobel et al. [80] reported the construction of a Pc macrocycle carrying a trimethyltin function, thus allowing... 

The amine function in Pcs was also found to be versatile as it allows for the facile incorporation of other photoactive or electroactive species. In particular such amino-functionalized Pcs can be easily reacted with perylene dianhydride to undergo formation of the corresponding diimides such as 18 (Fig. 13) [90-92], The Pc building blocks, carrying either a spacered amino or an anilino group, respectively, were thus implemented into the perylene structure by melting of the two components in imidazole to result in the construction of the corresponding multicomponent assemblies. The pathway toward such structures can also be performed by first introduction of the phthalonitrile to the perylene followed by the formation of the macrocycle [93],... 

As part of an effort to build covalently linked multicomponent assemblies for light-chemical energy conversion schemes, the Pt(diimine)(tdt) chromo-phore has been incorporated into bimetallic complexes with platinum(II) and mthenium(II) diimine chromophores using dipyridocatecholate (dpcat) or... 

Multicomponent assemblies in which a photoredox-active metal-polypyridine unit is combined with electron acceptors and/or donors show very rich photo-induced electron transfer reactivity [38]. Such species are often called molecular dyads (triads, tetrads. ..). Electron transfer usually occurs from an excited metal-polypyridine unit M to an attached acceptor ... 

The possibility of efficient multicomponent assembly of carbon chains is illustrated by the following equation. ... 

In biology, many molecular motors or machines play essential roles. These systems are multicomponent assemblies undergoing large amplitude geometrical changes or leading to the locomotion of one of the components,... 

Figure 1.9.2. Convergent multigeneration/multicomponent assembly strategy...

Multicomponent assembly strategies with single functional group liberation... 

Multicomponent assembly strategy with cyclisation-assisted cleavage... 

Diversity generation that is neither due to multicomponent assembly nor thermally spontaneous, but is based on photoinduced changes within a single molecule, is found in the selection of a receptor molecule for arginine... 

Functionalized acetylenes as versatile building-blocks for the multicomponent assembling of polysubstituted furans and pyrroles 07H(73)87. 

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