Geometric E→Z Isomerisation of Alkenyl Silanes by Selective Energy Transfer Catalysis: Stereodivergent Synthesis of Triarylethylenes via a Formal anti-Metallometallation.

An efficient geometrical E→Z isomerisation of alkenyl silanes is disclosed via selective energy transfer using an inexpensive organic sensitiser. Characterised by operational simplicity, short reaction times (2 h), and broad substrate tolerance, the reaction displays high selectivity for trisubstituted systems (Z/E up to 95:5). In contrast to thermal activation, directionality results from deconjugation of the π-system in the Z-isomer due to A -strain thereby inhibiting re-activation.

Spatiotemporal Control of Pre-existing Alkene Geometry: A Bio-Inspired Route to 4-Trifluoromethyl-2H-chromenes.

Routes to prepare C4-trifluoromethyl analogues of the 2H-chromene scaffold are scarce: this is particularly striking given the importance of fluorine in pharmaceutical development. To address this limitation, a facile strategy has been developed that is reliant on catalytic, geometric isomerization of easily accessible allylic alcohols (up to >95:5) followed by intramolecular cyclization via Pd catalysis (up to 96%). This concise biomimetic approach emulates the photoisomerization/cyclization cascade inherent to phenylpropanoid biosynthesis.