Control of Dynamic sp3-C Stereochemistry

Stereogenic sp3-hybridized carbon centres are fundamental building blocks of chiral molecules. Unlike dynamic stereogenic motifs, such as sp3-nitrogen centres or atropisomeric biaryls, sp3-carbon centres are usually fixed, requiring intermolecular reactions to undergo configurational change. Here, we report the internal enantiomerization of fluxional carbon cages and the consequences of their adaptive configurations for the transmission of stereochemical information. The sp3-carbon stereochemistry of the rigid tricyclic cages is inverted through strain-assisted Cope rearrangements, emulating the low-barrier configurational dynamics typical for sp3 nitrogen inversion or conformational isomerism. This dynamic enantiomerization can be stopped, restarted, or slowed by external reagents, while the configuration of the cage is controlled by neighbouring, fixed stereogenic centres. As part of a phosphoramidite–olefin ligand, the fluxional cage acts as a conduit to transmit stereochemical information from the ligand while also transferring its dynamic properties to chiral-at-metal coordination environments, influencing catalysis and ligand exchange energetics.

Configurational change in Indo-European coordinate constructions

This chapter presents a case study of word order change in coordinate constructions across a wide range of Indo-European languages. Early Indo-European languages had two available patterns of coordination at their disposal: one in which the coordinating particle was placed in first and another in which it was placed in the second position with respect to the second coordinand (‘Wackernagel effect’). Diachronically, the two competing configurations reduce to a single winning one, namely the head-initial one that all contemporary Indo-European languages retained. This is accounted for as the result of the loss of ‘Wackernagel movement’ and the development of a lexicalized J(unction)-morpheme. Resting on the notion of Junction, the analysis succeeds in explaining the bimorphemicity signature of initial conjunctions by deriving the morpheme count as a fusional exponent of two functional heads. The analysis stands on the assumption that narrow- and postsyntactic processes operate in derivationally delimited chunks, qua phases.