Bismuth polymer-supported

Mg(ll), Ca(ll), and Zn(ll) Lewis Acids, Boron(lll) Lewis Acids, Al( ,Lgwis cids, Ga(lll) Lewis Acids, ln(llljrtewis Acids, Si(IV) Lewis Acids, Sh(ll) and Sn(IV) Lewis Acids, Bismuth(lll) Lewis Acids, Scandium and Yttrium Lewis cids. Lanthanide Lewis Acid, Titanium Lewis Acid, Zr(IV) and Hf(IV) Lewis Acids, llransition Metal Lewis Acids, Cu(l) anc u(ll) Lewis Acids, Ag(l) and Au(l) Lewis Acids, Polymer-supported Metal... 

Bismuth chloride was found to be very efficient to catalyze the benzimidazole cyclization on soluble polymer support by microwave irradiation. In the absence of microwave, it took 2 hours to complete the reaction by conventional heating instead of 4 minutes (Equation 26) [44]. 

The use of polymer-supported bismuth catalysts for organic synthesis is highly attractive since this approach combines the advantages of the relative nontoxicity of bismuth salts with their easy separation and recyclability after reaction [131]. For example, microencapsulated Bi(0Tf)3 xH20 in polystyrene has been successfully reported for the methoxymethylation of alcohols, allylation of aldehydes, Michael-type and aldol reactions as well as Baeyer-Villiger oxidations [132]. 

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. 

The condensation of formaldehyde on acetylene requires an extremely active and highly selective catalyst system to prevent explosions due to the use of excessively high acetylene partial pressures and the undesirable formation of cuprene, a polymer of acetylene. The catalyst used today is copper acetylide, deposited on a magnesium silicate support containing bismuth. Operations are -conducted at low pressure (0.1.10 Pa -absolute) and at relatively moderateiemperature (95°C) in a continuously fed system. 

The Reppe process is a method that was developed in the 1940s and typical manufacturers include BASF, Ashland, and Invista. Cu-Bi catalyst supported on silica is used to prepare the 1,4-butynediol by reacting formaldehyde and acetylene at 0.5 MPa and 90-110 C (Eq. (10.2)). The copper used in the reaction is converted to copper(I) acetylide, and the copper complex reacts with the additional acetylene to form the active catalyst. The role of bismuth is to inhibit the formation of water-soluble acetylene polymers (i.e., cuprenes) from the oligomeric acetylene complexes on the catalyst [5a]. The hydrogenation of 1,4-butynediol is accom-pUshed through the use of Raney Ni catalyst to produce 1,4-butanediol (Eq. (10.3)). The total yield of 1,4-butanediol production is 91% from acetylene [5b]. Since acetylene is a highly explosive compound, careful process control is necessary. 

Thiophenes are generally obtained by sulfuration of 1,4-dicarbonyl compounds (Paal s)mthesis). The preparation of the highly substituted 2-(4-bromophenyl)-5-(3,4-dimethoxyphenyl)-3,4-dimethylthiophene from the respective 1,4-diketone represents a recent example. This type of reaction can be performed as a solid-phase synthesis with polymer-bound diketones (132) and LR (eq 44). Trifluoroacetic acid releases the thiophene (133) from the solid support. Bismuth triflate in 1,3-dialkylimida-zolium fluoroborate has been utilized as a catalytic ionic liquid system for the synthesis of thiophenes from 1,4-diketones and LR with significantly improved yields. 

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