An operationally simple E → Z isomerization of activated dienes, based on the β-ionyl motif intrinsic to retinal, is reported using inexpensive (−)-riboflavin (vitamin B 2 ) under irradiation at 402 nm. Selective energy transfer from photoexcited (−)-riboflavin to the starting E-isomer enables geometrical isomerization. Since the analogous process with the Z-isomer is inefficient, microscopic reversibility is circumvented, thereby enabling a directional isomerization to generate the contrathermodynamic product (up to 99% yield, up to 99:1 Z/E). Prudent choice of photocatalyst enables chemoselective isomerization to be achieved in both inter-and intramolecular systems. The principles established from this study, together with a molecular editing approach, have facilitated the development of a regioselective isomerization of a truncated triene based on the retinal scaffold. Letter pubs.acs.org/OrgLett
Photochemical generation of nitrile imine species and subsequent reaction with boronic acid derivatives furnishes a new C–C bond without transition metal catalysis.
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