Allylic and acrylic substrates may be efficiently transformed by a sequential bichromatic photochemical process into derivatives of levulinates or butenolides with high selectivity when phenanthrene is used as a regulator. Thus, UV-A photoinduced cross-metathesis (CM) couples the acrylic and allylic counterparts and subsequent UV-C irradiation initiates E-Z isomerization of the carbon-carbon double bond, followed by one of two competing processes; namely, cyclization by transesterification or a 1,5-H shift and tautomerization. Quantum chemical calculations demonstrate that intermediates are strongly blue-shifted for the cyclization while red-shifted for the 1,5-H shift reaction. Hence, delaying the double bond migration by employing UV-C absorbing phenanthrene, results in a selective novel divergent all-photochemical pathway for the synthesis of fundamental structural motifs of ubiquitous natural products.
Bibliographical noteFunding Information:
The Israel Science Foundation is gratefully acknowledged for a F.I.R.S.T. grant 1067/15 (OR and NGL) and an individual ISF grant 537/14 (NGL) that funded this research. The Open University is acknowledged for partial nancial support. I. S. gratefully acknowledges funding by European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 678169 “PhotoMutant”).
© The Royal Society of Chemistry 2018.