Bismuth linker

Beyond RCM and CM strategies, Craig has reported cleavage using Diels-Alder reactions (Scheme 1.16). ° [4 + 2] Cycloaddition (with concomitant aromatization) of the o-quinodimethane precursor (52) with dimethylacetylene dicarboxylate (DMAD), trichlor-oacetonitrile, and benzoquinone provided dimethyl naphthalene-2,3-dicarboxylate (53), 3-(trichloromethyl)isoquinoline (54), and 2,3-naphthoquinone (55), respectively. The diverse products from a single polymer-supported intermediate, such as the bismuth linkers discussed previously, make Craig s multifunctional linker unit attractive for approaches toward diversity-oriented synthesis. 

Scheme 49 Use of a bismuth linker in conjunction with the Suzuki reaction...

First, the experimenter estimates the MW of the oligomer (hydrodynamic measurements, radiation inactivation) and the MW of the subunits (SDS gel electrophoresis of the purified oligomer). She then treats the oligomer with cross-linkers (e.g., from the bismuthate family)... 

Polymer composites were either cast from polymer-salt solutions (from ethyl acetate or acrylate for bismuth halides and methanol for barium bromide), or were made by polymerizing a monomer-salt solution with benzoyl peroxide or azobisisobutyronitrile at 70°C (in a number of cases 2 wt% tetraethyleneglycol diijiethacrylate was added as cross - linker). BiBr ... 

Blocked isocyanates permit making coatings that are stable at ambient temperature when baked, the monofunctional blocking agent is volatilized and the coreactant is cross-linked. An extensive review of blocked isocyanates, their reactions, and uses is available (127). The blocking agents most widely used are phenols, oximes, alcohols, e-caprolactam (hexahydro-2ff-azepin-2-one) [105-60-2], 3,5-dimethylpyrazole, 1,2,4-triazole, and diethyl malonate (propanedioic acid diethyl ester) [105-53-3]. A variety of catalysts are used DBTDL is most widely used but many other catalysts have also been used. Bismuth tris(2-ethyl hexanoate) has been particularly recommended (128). In electrodeposition primers, DBTDL has insufficient hydrolytic stability, and tributyltin oxide is an example of an alternate catalyst (129). Cyclic amidines, such as l,5-diazabicyclo[4.3.0]non-5-ene, are reported to be superior catalysts for use with uretdione cross-linkers in powder coatings (130). 

Scheme 94 Multifunctional cleavage from the bismuth diacetate linker...

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