Polar tagging in the synthesis of monodisperse oligo(p-phenyleneethynylene)s and an update on the synthesis of oligoPPEs

Abstract

SummaryOne important access to monodisperse (functionalized) oligoPPEs is based on the orthogonality of the alkyne protecting groups triisopropylsilyl and hydroxymethyl (HOM) and on the polar tagging with the hydroxymethyl moiety for an easy chromatographic separation of the products. This paper provides an update of this synthetic route. For the deprotection of HOM protected alkynes, γ-MnO2 proved to be better than (highly) activated MnO2. The use of HOM as an alkyne protecting group is accompanied by carbometalation as a side reaction in the alkynyl–aryl coupling. The extent of carbometalation can be distinctly reduced through substitution of HOM for 1-hydroxyethyl. The strategy of polar tagging is extended by embedding ether linkages within the solubilising side chains. With building blocks such as 1,4-diiodo-2,5-bis(6-methoxyhexyl) less steps are needed to assemble oligoPPEs with functional end groups and the isolation of pure compounds becomes simple. For the preparation of 1,4-dialkyl-2,5-diiodobenzene a better procedure is presented together with the finding that 1,4-dialkyl-2,3-diiodobenzene, a constitutional isomer of 1,4-dialkyl-2,5-diiodobenzene, is one of the byproducts.

Improving the accuracy of Cu(ii)–nitroxide RIDME in the presence of orientation correlation in water-soluble Cu(ii)–nitroxide rulers

“…99 To enable the attachment of the nitroxide it was equipped with an amino group through Sonogashira-Hagihara coupling with p-iodoaniline. To ease the separation of the target compound from the accompanying oxidative alkyne dimerization product the polar tagging strategy [98][99][100] was applied. Reaction of the amino functionalised spacer 4 with the N-acylpyridinium salt 6, which was preformed but not isolated, 101 83 The protonation degree at pH 7 given with the formula of PyMTA-nitroxide 19 is based on the data for diethylenetriaminepentaacetic acid (DTPA) which is structurally similar to PyMTA.…”

Phenylene Ethynylene‐Tethered Perylene Bisimide Folda‐Dimer and Folda‐Trimer: Investigations on Folding Features in Ground and Excited States

“…Compound 7 was previously synthesized by a different route; [14b] however, the present pathway using a polar tagging strategy [16] resulted in significantly higher yield. In the next step, 12-tricosanyl-substituted [17] (first mentioned as "swallowtailed" [18] alkyl substituents for smaller branched alkyl chains www.chemeurj.org attached to steroids by Louw et al) perylene-3,4:9,10-tetracarboxylic acid-3,4-anhydride-9,10-imide 8 [19] was treated with 3-iodoaniline to obtain PBI 9 in a yield of 97 % in analogy to the literature-known reaction of symmetric 3,5-diiodoaniline with 8 affording PBI 12, [14a] which was used to build up the inner PBI moiety in folda-trimer 3.…”

“…Compound 7 was previously synthesized by a different route; [14b] however, the present pathway using a polar tagging strategy [16] resulted in significantly higher yield. In the next step, 12-tricosanyl-substituted [17] (first mentioned as "swallowtailed" [18] alkyl substituents for smaller branched alkyl chains Figure 1.…”

Synthesis of Homoditopic Ligands with an Incrementable Rodlike Backbone

“…This has been achieved with bis-terpyridine (bis-Tpy) oligomers with ethynylthiophene, [20] ethynylnaphthalene [21] or phenylene-ethynylene [22][23][24] repeat units. [33] We have chosen the so-called bidirectional approach, [34,35] which is well suited to the synthesis of symmetrical OPE linkers. [30,31] Such systems, in which the ligand-ligand distance can be easily tailored, are also very useful for controlling the size of host-guest cavities or the porosity of MOFs.…”

“…Discrete OPE oligomers with up to 16 phenylene-acetylene repeat units, equipped with diverse solubilizing moieties, have been prepared by using different strategies that have been recently reviewed. [33] We have chosen the so-called bidirectional approach, [34,35] which is well suited to the synthesis of symmetrical OPE linkers. To improve its efficiency, we decided to derivatize only one phenyl ring out of two with small poly(ethylene glycol) (PEG) chains so that the OPE spacer can be quickly elongated (four repeat units added in one step) while maintaining good solubility in organic solvents.…”