The synthesis of a bowl-shaped trinuclear circular titanium-based helicate is reported. The strategy allowing access to this neutral architecture is based on a multicomponent self-assembly approach in which the ligands involved in the process are a bis-biphenol strand and 2,2'- bipyrimidine. By reacting the bis-biphenol ligand and 2,2'-bipyrimidine with an equimolar amount [Ti(OiPr)4 ], a bowl-shaped architecture is obtained through the formation of 18 new coordination bonds. This aggregate built from three octahedral TiO4 N2 nodes displays an unusually high stability in solution compared to related species. In addition, by modifying the stoichiometry of the initial components, two assemblies incorporating two titanium centers bridged by a 2,2'-bipyrimidine ligand are obtained. The crystal structures of these species are reported.
The multicomponent coordination chemistry involving Ti(OPr), the ortho-phenylenediamine ligand (opda) and 2,2'-biphenol-based proligands (LH and LH) is described. The proligands LH and LH incorporate two and three 2,2'-biphenol units linked with p-phenylene bridges (p-PLB) respectively. We demonstrate that this selected set of components allows the spontaneous formation of neutral double-stranded helicates. In particular, we report the X-ray crystal structure of a multicomponent helicate formed with L, named Ti(L)(opda). The molecular structure of the helicate shows two inequivalent L ligands. H NMR analysis at variable temperature highlights an intramolecular fluxional phenomenon for this species. An insight into this dynamic behaviour is obtained via the energy profiles of Ti(L)(opda) resulting from the full rotation of the p-PLB rings. Additionally, the thermodynamic parameters associated with the formation of the Ti(L)(opda) complex are modelled and discussed related to the ones linked to the formation of a related monomeric complex.
A general methodology for the stereoselective synthesis of 2-(2-hydroxyalkyl)piperidine alkaloids by ring-rearrangement metathesis of nitroso Diels-Alder cycloadducts is reported. The approach is illustrated by the formal synthesis of porantheridine and the total synthesis of andrachcinidine through a diastereodivergent allylation of an N-alkoxy bicyclic lactam. The asymmetric synthesis of the latter alkaloid provides new insights into the configurational stability of cycloadducts between chloronitroso reagents and cyclopentadiene.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.