Coupling reactions Williamson

In addition to its uses in photography and medicine, iodine and its compounds have been much exploited in volumetric analysis (iodometry and iodimetry, p. 864). Organoiodine compounds have also played a notable part in the development of synthetic organic chemistry, being the first compounds used in A. W. von Hofmann s alkylation of amines (1850), A. W. Williamson s synthesis of ethers (1851), A. Wurtz s coupling reactions (1855) and V. Grignard s reagents (1900). 

Analogous chemistry (i.e., end functionalization of polymeric organolithiums with l,l-bis(4-tert-butyldimethylsi-loxyphenyl)ethylene) has been utilized for preparation of dendrimacs, a new type of dendritic polymer wherein a key step in the iterative process utilizes the deprotected phenol end groups in polymers as nucleophiles for Williamson ether-type coupling reactions. Hirao and co-workers " have utilized di-monosaccharide-substituted DPEs to prepare well-defined polyisoprenes and polystyrenes labeled at the chain end with monosaccharide residues. 

Most Williamson reactions proceed by the 8 2 mechanism, but there is evidence (see p. 446) that in some cases the SET mechanism can take place, especially with alkyl iodides. Secondary alcohols have been converted to the corresponding methyl ether by reaction with methanol in the presence of ferric nitrate nonahy-drate. Vinyl ethers have been formed by coupling tetravinyl tin with phenols, in the presence of cupric acetate and oxygen. " The palladium-catalyzed coupling of vinyl triflates and phenols has also been reported. ... 

In 1989, Fr chet and co-workers first reported the convergent growth approach [8,9]. In contrast to the divergent growth approach, dendrimer construction is initiated at what will eventually become the outer surface shell of the ideally branched macromolecule and proceeds inward, by a stepwise addition of branching monomers, followed by the final attachment of each branched dendritic sub-unit (or dendron ) to a poly-functional core. This synthesis generated a poly(aromatic ether) dendrimer and a repetitive sequence of Williamson ether coupling and bromination reactions were employed as shown in Scheme 8.1. 

The NAD/NADH couple, as the major source of reducing potential, occupies a position of preeminence akin to that of the adenine nucleotides. Dehydrogenase, catalyzing freely reversible reactions, (e.g., alcohol and lactate dehydrogenases), are subject to rate and direction control by the NAD/NADH ratio. Williamson et al. (1967) proposed a means of determining the NAD/NADH ratio in various intracellular compartments by measuring substrate/product ratios in freeze-clamped tissues that have dehydrogenases that catalyze a reaction at or near... 

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