Polyfunctionalized molecules

The naphthalene-catalyzed (3-12%) lithiation of deprotonated chloro phenols and anilides 236 performed with n-butylUthium in THF at 0 or —78 °C, respectively, gave the corresponding functionalized aryllithium intermediates 237 which, by reaction with electrophiles and final hydrolysis, yielded the corresponding polyfunctionalized molecules 238 (Scheme 79) . 

The use of polylithium synthons in synthetic organic chemistry presents the advantage of making possible the simultaneous introduction of various electrophilic fragments in the reaction with electrophiles, in such a way that polyfunctionalized molecules can be directly prepared. 

The chiral aldehyde 88 was decarbonylated to give 89 with overall retention of the stereochemistry [45]. The unsaturated aldehyde in the polyfunctionalized molecule 90 was decarbonylated smoothly to afford alkene 91 [46]. The decarbonylation of aldehydes catalysed by a supported Pd or Rh complex is carried out at high... 

Combinatorial chemistry has proven its usefulness for the synthesis of chemical libraries, with different degrees of complexity embedded in the scaffolds and/or the building blocks used. The synthesis of polyfunctionalized molecules in... 

Mizorokf and Heck reported independently in the early 1970s the first palladium-mediated coupling of an aryl or vinyl halide or triflate with an alkene. This reaction is generally referred to as the Heck reaction. From the first reports on asymmetric intramolecular Heck reactions by Overman and Shibasakf in 1989 the asymmetric Heck reaction has emerged as a reliable method for the stereoselective formation of tertiary and quaternary stereogenic centers by C-C bond formation in polyfunctionalized molecules. ... 

The Nef reaction often represents the key transformation in a reaction sequence in which it is involved. The synthesis of simple aliphatic ketones or aldehydes is probably not the most useful application of the Nef reaction. More important is the access to dicarbonyl compounds for intramolecular cyclization reactions leading to a large variety of carbocycles or heterocycles. However, the method can be capricious and success depends on the structure of the substrate. In order to overcome synthetic drawbacks, several roundabout methods have been devised for application to peculiar polyfunctionalized molecules. The number of modifications of the Nef reaction which can be carried out under a wide variety of conditions clearly reveals that no procedure is of general application. The scope and limitations of the different modifications will be discussed considering the structure of desired carbonyl derivative. 

During the large-scale, high-yield, one-pot synthesis of 4-chloro-3-(hydroxymethyl)pyridine, a starting material for the preparation of several polyfunctionalized molecules that can be linked to cephalosporines, M. Penso and co-workers utilized the combination of direct regioseiective iithiation/formyiation and crossed-Cannizzaro reduction of 4-chloropyridine. ... 

A number of procedures for the hydroxylation and amination of radicals are reported. They offer attractive alternatives to the classical ionic processes. Extremely mild reaction conditions characterize most of these radical procedures. They offer promising perspectives for the synthesis of natural products and other complex polyfunctionalized molecules. 

Some interactions that are generally too weak to drive the self-assembly in solution (dipole dipole, C-H- -n, C-H- halogen, Csp2-H N=C ) efficiently can, however, lead to the organization of molecules into well-defined patterns on a surface, under inert atmosphere (UHV). However, in polyfunctionalized molecules, several weak interactions can often compete and the use of such weak and less directional interactions to organize molecules on surfaces leads to less predictable modes of assemblies. Another complication introduced in surface self-assembly is the existence of subtle molecule-surface interactions. This point was recently emphasized by several related cyano-functionalized porphyrins and the smdy of their different assembly modes on Cu(lll). The antiparallel [C=N/N=C] dipolar interactions and C=N- -H-Cortho weak hydrogen bonds favor the formation of chains from the adsorption of 5,15-bis(4-cyanobiphenyl)porphyrins on a Cu(lll) surface (Figure 40). 

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