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.
CITATION STYLE
Sutar, R. L., Sen, S., Eivgi, O., Segalovich, G., Schapiro, I., Reany, O., & Lemcoff, N. G. (2018). Guiding a divergent reaction by photochemical control: Bichromatic selective access to levulinates and butenolides. Chemical Science, 9(5), 1368–1374. https://doi.org/10.1039/c7sc05094a
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