Multifunctional amphiphilic siloxane architectures using sequential,metal‐free click ligations

Polysiloxanes or silicones are a class of macromolecules widely used in commerce because of their exceptional properties. Their derivatization leads to functional silicones with added value and properties, such as surfactants and liquid crystals, among many others. However, most silicone surfactants are monofunctional, owing to the synthetic challenges associated with the introduction of multiple functional groups onto the hydrolytically sensitive siloxane backbone. Thus, general routes to surface active silicones with multiple and different functional groups are not available. Herein, a synthetic strategy is reported that permits sequential derivatization of silicones with hydrophiles including oligo(ethylene oxides), carboxylic acids, and bromoalkylesters using a simple metal‐free Click reaction: the process benefits from mild conditions, extremely high yields and does not generate any by‐products, allowing the facile preparation of di‐ and trifunctional silicones that could not be readily obtained using traditional methods. The products exhibit amphiphilic characteristics as demonstrated through interfacial tension measurements that yielded the critical aggregation concentration of selected compounds. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Chemoenzymatic Synthesis of All Four Diastereomers of 2,6‐Disubstituted Piperidines through Stereoselective Monoamination of 1,5‐Diketones

The regioselectivity of various enantiocomplementary ω‐transaminases was evaluated for the stereoselective monoamination of designated 1,5‐diketones; excellent conversions, enantio‐ and regioselectivities were observed. The resulting amino‐ketones underwent spontaneous intramolecular ring closure to afford Δ1‐piperideines, which served as precursors for the cis‐ and anti‐piperidine scaffold as demonstrated for the synthesis of the alkaloids dihydropinidine and epi‐dihydropinidine. Key to the success of accessing the trans‐piperidines was a Lewis acid mediated conformational change of the Δ1‐piperideines in the reduction step. Thus, all four diastereomers of 2,6‐disubstituted piperidines could successfully be prepared.     

P-C bond formation via P-H addition of a fluoroaryl phosphinic acid to ketones

The synthesis, structure and reactivity of the fluoroaryl phosphinic acid HF₄C₆-P(O)HOH is reported and compared to a sterically comparable yet non-fluorinated analog with similar size. The fluoroaryl phosphinic acid undergoes reversible P-H addition to the carbonyl functionality of ketones under formation of a P-C bond which is retained in the resulting α-hydroxy phosphinic acid. The latter shows an extended 2D hydrogen bonded network in the solid state.     

Self-assembly of tert-butyl silanetriol in solution and aggregation with tetrahydrofuran

tert-Butyl silanetriol behaves like a surfactant and self-assembles in aqueous and tetrahydrofuran (THF) solutions. Micelle formation was studied with pulsed field gradient stimulated spin echo (PFG-SSE) NMR, while multilayer lamellar vesicles can be concluded from small/wide angle X-ray scattering measurements in concentrated solutions at elevated temperature. The significant interaction between tert-butyl silanetriol and THF is further highlighted by a crystal structure featuring a 3:1 adduct of silanetriol and THF.