Electrophilic grafting

The synthesis and characterization of a series of dendrigraft polymers based on polybutadiene segments was reported by Hempenius et al. [15], The synthesis begins with a linear-poly(butadiene) (PB) core obtained by the sec-butyllithium-initiated anionic polymerization of 1,3-butadiene in n-hexane, to give a microstructure containing approximately 6% 1,2-units (Scheme 3). The pendant vinyl moities are converted into electrophilic grafting sites by hydrosilylation with... 

In recent years, a number of structurally distinct compounds targeting the proteasome have reached the clinic, amongst others the covalent and irreversible inhibitor carfilzomib [5]. The structure of carfilzomib is based on that of the natural product, epoxomicin, that also features the epoxyketone electrophilic trap. Indeed, numerous natural product proteasome inhibitors with a distinguishing electrophile grafted onto a peptidic core have been described over the years, including lactacystin, syringolin A (SylA), and fellutamide B. An important class of synthetic covalent proteasome inhibitors is represented by the peptide vinyl sulfones, whereas numerous noncovalent proteasome inhibitors have been discovered as well (e.g., TMC 95A). 

Anionic grafting methods (vide infra) can be applied to the synthesis of comb-shaped polymers. As an example, a polystyrene backbone is partially chloromethylated (under mild conditions) and used as an electrophilic deactivator for a living polystyrene 89). The grafting onto process yields well defined species that have been characterized accurately. The branches are distributed randomly along the backbone 90). 

The electrophilic functions most commonly used in grafting onto processes are ester 141 144), benzylic halide 145,146) and oxirane, 47). Other functions such as nitrile or anhydride could be used as well. The backbone is a homopolymer (such as PMMA) or a copolymer containing both functionalized and unfunctionalized units. Such species can be obtained either by free radical copolymerization (e.g. styrene-acrylonitrile copolymer) or by partial chemical modification of a homopolymer (e.g. 

G. Forat, J.-M. Mas, L. Saint-Jalmes (Rhone-Poulenc Chimie). Method for Grafting a Substituted Difluoromethyl Group to a Compound Containing an Electrophilic Group with Microwave Irradiation. PCT International Application WO 5, 609,1998 (FR Application 96/ 9,754, 1 Aug 1996) Chem. Abstr. 1998, 128, 166999u. 

For cationic SIP, limitations when applied to surfaces are also evident. Like anionic polymerization, SIP on particles has been abundantly reported by several groups, most notably on work by Tsubokawa et al. The use of nanoparticles has also been widely reported. The same assumptions were made for cationic polymerization based on the grafting of electrophiles on surfaces and the reactivity of nucleophilic monomers for cationic polymerization. 

The reactions of 1,2-thiazine 1,1-dioxides with electrophiles can often lead to a mixture of products due to competing addition at C-4 and C-6. A selective Friedel-Grafts-type acylation of the C-6 position of the 1,2-thiazine 1,1-dioxo ring was observed in reaction of 3,5-dimethyl-1,2-thiazine 1,1-dioxide 71 with anhydrides, such as acetic anhydride, furnishing compound 45 (Equation 18) <1999JPR37>. 

It is evident that this type of grafting is restricted to those monomers which are polymerizable by a cationic mechanism moreover, electrophilic substitution on the aromatic nucleus must be possible. Nevertheless, alkylvinyl ethers, isobutene and iV-vinylpyrrolidone could not be grafted on polystyrene, polyvinyltoluene or poly- >-methoxystyrene. The limitation of the method to the system styrene/poly-/j-methoxystyrene is very surprising and not well understood until now. 

The same TBD 2 was also grafted to silica but by means of a different electrophilic linker [3-(glycidyloxy)propyl]trimethoxysilane was first grafted and then TBD reacted with the oxirane group to give the hydroxy guanidine (Figure 9). 

Another interest in the introduction of snch gronps lies in the opportunity to take advantage of the nucleophilicity (amines) of these side-gronps for further functionalizing polysiloxanes. Conversely, methods for grafting a nucleophilic molecule on electrophilic side-gronps on polysiloxanes are based essentially on the... 

A variation for grafting of sugar units on aminopolysiloxanes has been described, by using an acetyl-protected glucosyl isothiocyanate as the electrophilic carbohydrate reagent, followed by a deprotection step [39]. The aminopropylpolysi-loxane is prepared by redistribution of aminopropyl-D with decamethyltetrasiloxane,... 

POMs have potential for forming hybrid materials due to nucleophilic surface oxygen atoms at the vacant site of them, which allow the covalent grafting of electrophilic group... 

Shilov and coworkers discovered the oxidation of methane to methanol by mixtures of Pt and Pt, and aroused the Holy Graft-pursuing for electrophilic C H activation and subsequent alkane oxidation. The diimine complexes of Pt(II) methyl are indeed found to facilitate smooth benzene activation, resulting in formation of methane via Pt (Me)(Ph)(H) intermediates (Scheme 10). Such Pt(II)/Pt(IV) involved C-H activation reactions have been widely extended to a variety of nitrogen-donor ligands, whose electronic and steric effects shed light on the reaction mechanisms (see Section 7.1). 

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