Biaryl ether moiety

Phenyliodonium salt-induced reactions are also applicable to total syntheses of several natural products having biaryl ether moieties and polycyclic nitrogen heterocycles. 

The intramolecular Ullmann condensation was used by D.L. Boqer and co-workers to form the 15-membered macrocyclic ring of the cytotoxic natural product, combretastatin D-2. This compound possesses unusual meta- and paracyciophane subunits, which are also found in a range of antitumor antibiotics. The first approach where the final step was a macrolactonization was unsuccessful, so the researchers chose to form the biaryl ether moiety as the key macrocyciization step. Methyicopper was found to mediate the cyclization and gave moderate yield of the corresponding biaryi ether. Finaiiy boron triiodide mediated demethylation afforded the natural product. 

Since the early success of Decicco et al. [19] in extending the boronic acid cross-coupling to an intramolecular system, more examples of this approach have appeared in the literature (Scheme 5.5). Snapper and Hoveyda reported a total synthesis of the anti-HIV natural product chloropeptin 1 in which the crucial biaryl ether moiety was constructed via the Cu-mediated reaction (Scheme 5.5) [20]. Thus, treatment of the boronic ester 10 with NalO liberates the boronic acid, which then cyclizes under Cu(OAc)2 to give the biaryl ether 11, a precursor to the final target. In this case, the addition of 10 equiv. of methanol was critical for efficient intramolecular cross[Pg.210]

Encouraged by the success of MUMBIs to synthesize biaryl ether macrocycles, we endeavored to combine this methodology with experience in steroid synthesis to obtain very large macrocycles with both peptide and steroid moieties (Fig. 21). These molecules bear no direct resemblance to any known natural products, but they do display a high degree of structural... 

The structural assignment for yolantinine is not totally convincing since (a) The structure appears to violate the simple rules for biogenetic biaryl ether formation, and (b) the mje 296 ion substituted at C-6 and C-8 cannot arise from the expression ascribed to yolantinine, which incorporates a 6,7-disubstituted tetrahydroisoquinoline moiety. 

In order to explain the stereoselectivity of this reaction, the authors have proposed a plausible transition-state model depicted in Scheme 1.5, in which the bulky biaryl silyl ether moiety exerted steric shielding, resulting in the formation of the observed stereoisomer. This enantioselective addition to vinyl sulfones, in combination with desulfonation, offered a unique, asymmetric entry to a-alkylated aldehydes and their derivatives. 

Molecular recognition processes between amphiphilic biaryl dendrimers 2 (with carboxylic acid moieties) as host compounds and the protein chymotryp-sin as guest were compared with those involving corresponding benzyl ether dendrons 1 (Fig. 4.26) [44]. In the biaryl dendrimers both the carboxylic acid groups of the periphery and those located in the inner shells are available for... 

This section covers the union of two aryl moieties, one of which is a fully alkylated phenol, and the other is either a free phenol or a phenol ether. Clearly, radical dimerization is not operative in such reactions. An early example is to be found in the work of Pitcher and Dietrich (1924) ° who showed that 3,3, 4,4 -tetramethoxybiphenyl was among the products of electrolytic oxidation of veratrole in sulfuric acid using a lead dioxide anode the biaryl was formed in about 20% yield based on reacted veratrole. 

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