Enantioselective crossed intramolecular [2+2] photocycloaddition reactions mediated by a chiral chelating Lewis acid
Thomas Rigotti1, Daniel P Schwinger1, Raphaela Graßl1
1School of Natural Sciences, Department Chemie, Catalysis Research Center (CRC), Technische Universität München 85747 Garching Germany thorsten.bach@ch.tum.de +49 89 28913315 +49 89 28913330.
Abstract:
In intramolecular [2+2] photocycloaddition reactions, the two tethered olefins can approach each other in a straight or in a crossed fashion. Despite the fact that the latter reaction mode leads to intriguing, otherwise inaccessible bridged skeletons, there has so far not been any enantioselective variants thereof. This study concerned the crossed [2+2]-photocycloaddition of 2-(alkenyloxy)cyclohex-2-enones to bridged cyclobutanes. It was found that the reaction could be performed with high enantioselectivity (80-94% ee) under visible light conditions when employing a chiral rhodium Lewis acid as a catalyst (2 mol%).
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