Abstract
Irradiation of (E)-4-(2-(2-naphthyl)vinyl)pyridine (1a) and (E)-4-(2-(1-naphthyl)vinyl)pyridine (1b) with a 250 W high-pressure mercury lamp in acidic solution afforded synHT dimers in high stereoselectivities. Similar results were obtained by visible light irradiation. On the other hand, when the reactions were carried out under neutral conditions, the stereoselectivities were very low, and the yields were decreased by visible light irradiation. Comparison of the UV-vis spectra between the acidic and the neutral conditions elucidated that the red shift was observed in acidic solutions. These results show that HCl plays essential roles not only in the preorientation of substrates through cation-π interactions, but also in the changes in the absorption properties of substrates that enable visible light reactions.
Highlights
Controlling the association mode of substrate alkenes during [2 + 2] photodimerization is a key subject in organic photochemistry [1,2,3,4], as it is essential for the regio- and stereoselective formation of cyclobutane dimers
Various approaches for the alignment of molecules have been developed using a variety of organized media [5], organic crystals [6,7,8,9,10], metal–organic frameworks [11,12], metal complexes [13,14], and supramolecular systems [15,16]
We reported that a cation-π interaction [17] between a pyridinium salt and a benzene ring plays an essential role on the product distribution in the [2 + 2] photodimerization of styrylpyridines [18,19,20]
Summary
Controlling the association mode of substrate alkenes during [2 + 2] photodimerization is a key subject in organic photochemistry [1,2,3,4], as it is essential for the regio- and stereoselective formation of cyclobutane dimers. We reported that a cation-π interaction [17] between a pyridinium salt and a benzene ring plays an essential role on the product distribution in the [2 + 2] photodimerization of styrylpyridines [18,19,20] This preorientation process is responsible for various stereoselective photodimerization reactions in solution, and in crystals [21,22]. It has been reported that the size of the π-system is significantly correlated with the strength of the cation-π interactions; for example, the interaction energy of a sodium cation with naphthalene is 2–3.5 kcal/mol larger than that with benzene [23,24] This prompted us to investigate the [2 + 2] photodimerization of naphthylvinylpyridines having more extended π-systems than those of styrylpyridines.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
