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Issue 7, 2019

Photoelimination of nitrogen from adamantane and pentacycloundecane (PCU) diazirines: a spectroscopic study and supramolecular control

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Abstract

Photochemical reactivity of pentacycloundecane (PCU) and adamantane diazirines was investigated by preparative irradiation in different solvents, laser flash photolysis (LFP) and quantum chemical computations. In addition, formation of inclusion complexes for diazirines with cucurbit[7]uril, β- and γ-cyclodextrin (β- and γ-CD) was investigated by 1H NMR spectroscopy, isothermal microcalorimetry and circular dichroism spectroscopy, followed by the investigation of photochemical reactivity of the formed complexes. Diazirines undergo efficient photochemical elimination of nitrogen (ΦR > 0.5) and deliver the corresponding singlet carbenes. Singlet carbenes react in intra- and intermolecular reactions and we found a rare singlet carbene pathway in CH3OH involving protonation and formation of a carbocation, detected due to the specific rearrangement of the pentacycloundecane skeleton. Singlet diazirines undergo intersystem crossing and deliver triplet carbenes that react with oxygen to form ketones which were isolated after irradiation. Our main finding is that the formation of diazirine inclusion complexes with β-CD and γ-CD changes the relative ratio of singlet vs. triplet pathways, with singlet carbene products being dominant from the chemistry of the irradiated complexes. Our combined theoretical and experimental studies provide new insights into the supramolecular control of carbene reactivity which has possible applications for the control of product distribution by solvent effects and the choice of constrained media.

Graphical abstract: Photoelimination of nitrogen from adamantane and pentacycloundecane (PCU) diazirines: a spectroscopic study and supramolecular control

Supplementary files

Article information


Submitted
13 Mar 2019
Accepted
22 May 2019
First published
22 May 2019

Photochem. Photobiol. Sci., 2019,18, 1806-1822
Article type
Paper

Photoelimination of nitrogen from adamantane and pentacycloundecane (PCU) diazirines: a spectroscopic study and supramolecular control

T. Šumanovac, M. Alešković, M. Šekutor, M. Matković, T. Baron, K. Mlinarić-Majerski, C. Bohne and N. Basarić, Photochem. Photobiol. Sci., 2019, 18, 1806 DOI: 10.1039/C9PP00124G

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