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Photochemistry of cyclopentenones : Beyond [2+2] photocycloaddition reactions

Abstract : The aim of this project was to explore the scope and limitations of a tandem photochemical process, consisting of a [2+2] cycloaddition between cyclopentenones and alkenes followed by a Norrish I/γ-hydrogen transfer reaction if the initial bicyclic adduct is formed. Using standard synthetic procedures, a small library of cyclopentenone substrates was prepared. The development of new methods to access substituted cyclopentenones, using organocatalyzed aldolisation conditions, was considered; however, these efforts were unfruitful.The photochemical studies showed that a selection of cyclopentenones and alkenes could react together to furnish cyclobutene aldehydes with average to good yields. The reaction conditions were optimized for the formation of this specific compound type, and some of the limitations as regards substrate diversity were determined. In some cases, control of the regioselectivity of the Norrish-I process was problematic.In course of the study, it was discovered that some of these cyclobutene aldehydes could themselves react photochemically, via an intramolecular Paternò–Büchi reaction, to form hitherto unknown tricyclic oxetanes. This constitutes a one-pot triple photochemical reaction sequence between the starting cyclopenenones and alkenes. Conditions were optimized for this transformation and several examples prepared. The tricyclic core structure was studied in detail, in both solution and the solid state, revealing that the formation had been highly diastereoselective in some examples. Some limitations, arising from steric hindrance and/or use of electron rich alkenes, constituted a limitation of the scope of the process.
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Submitted on : Friday, May 3, 2013 - 1:01:27 AM
Last modification on : Friday, November 27, 2020 - 3:12:26 AM
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  • HAL Id : tel-00820031, version 1



Hendrik Eijsberg. Photochemistry of cyclopentenones : Beyond [2+2] photocycloaddition reactions. Other. Université Paris Sud - Paris XI; Università degli studi (Cagliari, Italie). Facoltà di scienze matematiche, fisiche e naturali. Dipartimento di scienze chimiche (Cagliari, Italie), 2012. English. ⟨NNT : 2012PA112075⟩. ⟨tel-00820031⟩



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