Pre-functionalizing

Replacement of the hydrophilic acrylamide by the more hydrophobic N-iso-propylacrylamide, in combination with the pre-functionalization of the capillary with (3-methacryloyloxypropyl) trimethoxysilane, afforded a monolithic gel covalently attached to the capillary wall. A substantial improvement in the separations of aromatic ketones and steroids was observed using these fritless hydrogel columns, as seen by the column efficiencies of 160,000 found for hydrocortisone and testosterone [92]. The separations exhibited many of the attributes typical of reversed-phase chromatography and led to the conclusion that, in contrast to the original polyacrylamide-based gels, size-exclusion mechanism was no longer the primary mechanism of separation. 

In principle any pre-functionalized resin can be formed into a plug and the monoliths show good solvent resistance except to e.g. hot toluene or xylene. The size of each plug makes them easily manipulated by a robot and use in scavenging situations seems very attractive. Some applicahons have already been reported [56] and the monoliths will be made available as StratoSphere Plugs via Polymer Laboratories (Church Stretton, UK). 

Alternative approaches for substituted porphyrins have been devised in which pre-functionalized dipyrromethane derivatives 3 are condensed with similar diformyl dipyrromethanes 4 through a "2+2" condensation to form meso-tetraarylporphyrins 5 (Scheme 3). Such condensations are usually catalyzed by acids and the intermediate porphyrinogens are oxidized by air to obtain porphyrins. In a similar "3+1" synthetic approach, tripyrranes 6 are condensed with 2,5-diformylpyrroles to form etioporphyrin 5 (1996CEJ1197). 

The selective functionalization of heterocycles is of particular importance, because of the ubiquity of these structures in natural products and pharmaceutical agents. Direct utilization of a C-H bond [1] of heterocycles is a promising method for the preparation of heterocycles because no pre-functionalization is required. Although Friedel-Crafts acylation is the most commonly used method for introduction of keto functionality on an aromatic ring, it is not often applicable to N-heteroarenes because of deactivation of the Lewis acids by the coordination of N-heteroarenes and the electron-deficient aromatic character of N-heteroarenes. 

The most convenient and most popular analytical methodology to assess enantiomer purity is the direct separation of enantiomers on so-called chiral stationary phases (CSPs). CSPs consist of an (ideally) inert chromatographic support matrix incorporating chemically or physically immobilized SO species. CSPs may be created by a variety of SO immobilization techniques, including (i) covalent attachment onto fhe surface of suitably pre-functionalized carrier materials, (ii) physical fixation employing coating techniques, and (iii) incorporation into polymeric networks by copolymerization, or combinations of these procedures. 

NHS/atnine, maleimide/thiol, and aldehyde/amine couplings (Figure 6) 13). The advantage of reacting the surface with the ligands is that it avoids the need to pre-functionalize antibodies etc with alkyl tails. 

Polystyrene, PEG-PS, and PEGA-based resins pre-functionalized with all the standard linkers required for the production of peptide adds, peptides amides, and protected peptide fragments are commerdally available. 

In 2014, the one-pot synthesis was successfully developed by Wang and co-workers in synthesis of nitrogen-bridged calix[2]arene[2]triazines [43], which had only been obtained by a fragment coupling approach as reported in their previous report [14]. In the presence of DIPEA as a base, the macrocyclic condensation between cyanuric acid chloride 1 and 1,3-phenylene diamines 30 proceeds effectively under very mild conditions to produce the corresponding azacalix[2] arene[2]triazines 31 in 33-54 % yields. It is noteworthy that the one-pot reaction works well for the synthesis of functionalized azacaUx[2]arene[2]triazines when pre-functionalized/M-phenylenediamines are employed (Scheme 14.10). 

However, it is now a common practice to use the commercial, pre-functionalized rubbers for polyamide blending to achieve a more consistent blending process and product properties. The extruder residence time is utilized for achieving the desired degree of grafting and throughput. 

A potentially greener and environmentally benign alternative to the aforementioned strategies is the direct C-H bond functionalization that does not generate hazardous by-products and avoids the pre-functionalization stages [3-6]. While the C - H bonds are highly stable, generally resistant to reactions with acids, bases, electrophiles, and nucleophiles, and consequently, very difficult to be directly... 

Boland S, Foster K, Leech D. A stability comparison of redox-active layers produced by chemical coupling of an osmium redox complex to pre-functionalized gold and carbon electrodes. Electrochim Acta 2009 54 1986-1991. 

The installation of a trifiuoromethyl group is particularly difficult at the late stage of a synthesis, in part because of the harsh protocols typically required for these reactions. Photoredox direct asymmetric a-trifluoromethylation and a-perfluoroaUcylation of carbonyl compounds including ketones, esters, as well as aryls and heteroaryls without first preparing pre-functionalized or trifiuoromethyl-... 

The ideal scenario would be to oxidatively couple two aryl C-H bonds and produce a new biaryl C-C bond. This coupling method, herein known as cross-dehydrogenative-coupling (CDC), requires no pre-functionalization steps and generates fewer by-products as waste (Scheme 6.1). 

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