A facile, efficient, and gram‐scale method for the conversion of para‐anisic acid into 3,4,5‐triiodoanisole through a one‐pot C–H iodination/ipso‐iododecarboxylation reaction was investigated. Commercially available benzoic acid was used, which allowed the reaction to be performed on a multigram scale in good yield. This report discloses a practical method for the one‐pot synthesis of hitherto unknown 3,4,5‐triiodoanisole that is catalytic, scalable, efficient, and easy to work up and purify. Potential application of the target compound as a precursor for novel site‐selective metal–iodine exchange and Suzuki–Miyaura cross‐coupling reactions were also explored. 3,4,5‐Trisubstituted anisole derivatives were provided in a highly regioselective fashion; these compounds are useful building blocks in synthesis and indeed are hard to prepare by any other means.
A nonavalent glycodendrimer bearing terminal alpha-d-mannopyranoside units has been synthesized with a convergent approach. Terminal trivalent mannoside dendrons bearing p-halophenyl ethers were prepared by glycosylation of pentaerythritol derivatives having three 2-hydroxyethyl ether substituents. Two efficient routes were developed for the synthesis of the pentaerythritol-based core (17), which has three terminal propargyl ethers. Conditions were found under which the triple Sonogashira coupling reaction of the dendron and the tri-O-propargyl ether (17) proceeded efficiently. The product was deprotected and it and precursors were fully characterized by NMR spectroscopy and FT-ICR mass spectrometry.
Methods were developed to convert dipentaerythritol efficiently into di-O-benzylidene, di-O-cyclohexylidene, di-O-1-ethylpropylidene, and di-O-methylene diacetals. The known di-O-benzylidene acetal, considered to be a single isomer, was shown to be close to a statistical mixture of the cis,cis-, cis,trans-, and trans,trans-isomers. Structures were established by a combination of NMR spectroscopy and X-ray crystallography. Reaction of the di-O-benzylidene acetals with benzyl chloride and potassium hydroxide surprisingly gave good to excellent yields of the monobenzyl ethers. An explanation for this observation was advanced. The dibenzyl derivatives of the di-O-benzylidene acetals were formed by reaction of their dianions with benzyl bromide in DMF. Selective reduction of the di-O-benzylidene acetals with triethylsilane and boron trifluoride etherate gave 2',6'-di-O-benzyldipentaerythritol. A crown ether was formed in modest yield (12%) by reaction of the dianion of the di-O-methylene acetal with α,α'-dibromo-m-xylene in DMF. Key words: dipentaerythritol, pentaerythritol, acetals, dendrimer, selective benzylation, crown ether.
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