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Unexpected Reactions of Terminal Alkynes in Targeted "Click Chemistry'' Coppercatalyzed Azide-alkyne Cycloadditions

Ali TH, Heidelberg T, Hussen RSD, Tajuddin HA

Curr Org Synth, 2019;16(8):1143-1148.
PMID: 31984920 DOI: 10.2174/1570179416666191105152714

BACKGROUND: High efficiency in terms of reaction yield and purity has led to the extensive utilization of copper-catalyzed azide-alkyne cycloaddition (CuAAC) in various fields of chemistry. Its compatibility with low molecular weight alcohols promotes the application in surfactant synthesis to tackle the miscibility constraints of the reactants.
OBJECTIVE: For the tuning of surfactant properties, double click coupling of the antipode precursors was attempted. Failure of the CuAAC to provide the targeted product in combination with unexpected reaction outputs led to an investigation of the side reaction.
METHODS: The CuAAC-based coupling of sugar azide with propargyl building block in the presence of copper- (I) catalyst exclusively led to the mono-coupling product in a respectable yield of almost 80%. Besides the unexpected incomplete conversion, the loss of the remaining propargyl group, as indicated by both NMR and MS. On the other hand, application of substantial amounts of CuSO4 under reducing conditions in refluxing toluene/water furnished the alkyne dimer in a moderate yield of 43%, while no change of azide compound was noticed.
RESULTS: The Cu(I)-catalyst applied for azide-alkyne cycloadditions enables the homo-coupling of certain terminal alkynes at a higher temperature. Moreover, aromatic propargyl ethers may be cleaved to furnish the corresponding phenol. The copper-catalyzed coupling appeared highly sensitive towards the alkyne compound. Only selected derivatives of propargyl alcohol were successfully dimerized.
CONCLUSIONS: The observed failure of the Huisgen reaction for the synthesis of sugar-based surfactants may indicate non-recognized constrains of the reaction, which could affect its wide application in bioconjugation. The temperature requirement for the alternative dimerization of terminal alkynes renders this side reaction nonrelevant for typical click couplings, while narrow substrate diversity and moderate yield limit its synthetic application.
Fulltext Secondary bonding in di-methyl-bis-(morpholine-4-carbodi-thio-ato-κ(2)S,S')tin(IV): crystal structure and Hirshfeld surface analysis

Zaldi NB, Hussen RSD, Lee SM, Halcovitch NR, Jotani MM, Tiekink ERT

Acta Crystallogr E Crystallogr Commun, 2017 Jun 01;73(Pt 6):842-848.
PMID: 28638641 DOI: 10.1107/S2056989017006855

The title compound, [Sn(CH3)2(C5H8NOS2)2], has the Sn(IV) atom bound by two methyl groups which lie over the weaker Sn-S bonds formed by two asymmetrically chelating di-thio-carbamate ligands so that the coordination geometry is skew-trapezoidal bipyramidal. The most prominent feature of the mol-ecular packing are secondary Sn⋯S inter-actions [Sn⋯S = 3.5654 (7) Å] that lead to centrosymmetric dimers. These are connected into a three-dimensional architecture via methyl-ene-C-H⋯S and methyl-C-H⋯O(morpholino) inter-actions. The Sn⋯S inter-actions are clearly evident in the Hirshfeld surface analysis of the title compound along with a number of other inter-molecular contacts.
Fulltext trans-Di-chlorido-bis-(dimethyl sulfoxide-κO)bis-(4-fluoro-benzyl-κC(1))tin(IV): crystal structure and Hirshfeld surface analysis

Amin NABM, Hussen RSD, Lee SM, Halcovitch NR, Jotani MM, Tiekink ERT

Acta Crystallogr E Crystallogr Commun, 2017 May 01;73(Pt 5):667-672.
PMID: 28529772 DOI: 10.1107/S2056989017005072

The Sn(IV) atom in the title diorganotin compound, [Sn(C7H6F)2Cl2(C2H6OS)2], is located on a centre of inversion, resulting in the C2Cl2O2 donor set having an all-trans disposition of like atoms. The coordination geometry approximates an octa-hedron. The crystal features C-H⋯F, C-H⋯Cl and C-H⋯π inter-actions, giving rise to a three-dimensional network. The respective influences of the Cl⋯H/H⋯Cl and F⋯H/H⋯F contacts to the mol-ecular packing are clearly evident from the analysis of the Hirshfeld surface.
Renewable resources-based approach to biantennary glycolipids

Tabandeh M, Salman AA, Goh EW, Heidelberg T, Hussen RSD

Chem Phys Lipids, 2018 05;212:111-119.
PMID: 29409839 DOI: 10.1016/j.chemphyslip.2018.01.011

A new synthesis approach towards biantennary lipids of Guerbet glycoside type was developed based on oleic acid as sustainable resource. Functionalization of the double bond provided access to primary alcohols with α-branched C19-skeleton. Formulation studies with corresponding lactosides indicated formation of vesicles with high assembly stability. A relatively narrow bimodal size distribution of the latter, which turns into a narrow unimodal distribution of small vesicles upon addition of an ionic cosurfactant, suggests potential for a vesicular drug delivery system.