Dialyzable Carbosilane Dendrimers as Soluble Supports for the Functionalization of Pyridine Fragments via Palladium-Catalyzed Coupling Reactions

Phosphine-Free Cross-Coupling Reaction of Halopyridines with Arylboronic Acids in an Ionic Liquid: Water Mixture

Palladium acetate-catalysed Suzuki reaction of halopyridines and arylboronic acids has been investigated in room-temperature ionic liquids in the absence of the phosphine ligand. A significant effect of water on the efficiency of the Suzuki reaction in ionic liquids was observed. The mixture of ionic liquid and water significantly enhanced the rate of the coupling reaction. The separation of the product was easily performed by extraction with diethyl ether and the Pd(OAc)2–[bmim][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate) can be reused six times with only a small loss of reactivity.

Carbosilane dendrimeric carbodiimides: site isolation as a lactamization tool

The convergent syntheses of three generations of carbosilane dendrimeric carbodiimides are described. The wedge-type building blocks were synthesized in a divergent way, starting from allyl chloride and a repetitive sequence of hydrosilylation with HSiCl3 and a Grignard reaction with allylmagnesium bromide. Hydrogenation of the terminal double bonds led to inert and stable wedges. The chloride substituent at the focal point was transformed into several functional groups that eventually led to dendrimeric structures with a carbodiimide core. The extent of the site isolation effect of the dendrimers was studied with dilution experiments monitored by FT-IR spectroscopy on the corresponding dendrimeric ureas. These studies showed that only the first generation self-aggregates via hydrogen bonding, while the second and the third do not, implying isolation of core-bound moieties. The dendrimeric carbodiimides mediated lactamization reactions to obtain homodiketopiperazines.

An Efficient Route to Well-Defined Macrocyclic Polymers via “Click” Cyclization

Polystyrene macrocycles have been prepared from ATRP precursors by modification of the terminal bromide to an azide, followed by "click" cyclization with a pendant alkyne from the initiator. This route offers exceptional control over the size and polydispersity of the macrocyclic polymers, as well as providing tolerance to a number of functional groups.