Preface for the special issue of ISRIUM‐2015 in Honolulu, Hawaii, USA

Abstract

The International Symposium on Reactive Intermediates and Unusual Molecules (ISRIUM-2015) was held in Honolulu as part of the International Chemical Congress of Pacific Basin Societies (Pacifichem) in 2015. The ISRIUM-2015 was the 33rd of a series of roughly annual meetings that were started in 1978 in Geneva (organized by Professors Charles Jefford and Curt Wentrup). The Journal of Physical Organic Chemistry has devoted so far 4 special issues to the ISRIUM conferences in 2010, 2012, 2013, and 2014. Now, the Journal offers a new ISRIUM special issue containing papers delivered at the December 2015 Honolulu conference. There were 36 oral presentations by scientists from 6 different countries, as well as 34 posters in a separate poster session. This special issue of the Journal of Physical Organic Chemistry includes 10 papers, including 1 mini review article and 9 original research articles. Professor Robert Moss and his coworkers describe in detail the chemistry of extremely reactive carbenes,1 in which the phenomena of negative activation energies are discussed for addition reactions of reactive carbenes with alkenes. Oxidations of allenes bearing 1,8-diphenoxy or diaryloxyacridene moieties are performed by the research group of Professor Yohsuke Yamamoto to generate persistent triplet carbenes. They isolate a cyclized compound that is characterized by X-ray analysis.2 The research group of Professor Wolfram Sander reports the generation of a new sextet ground-state molecule, the 2,4,6-trichloro-1,3-dinitrenophenoxyl radical, in the UV photolysis of the corresponding diazido precursor in argon at 5 K.3 They found that the sextet molecule is formed in a stepwise fashion, with the triplet nitrene, the quartet nitreno radical, and the quintet dinitrene as intermediates that are detected by electron paramagnetic resonance spectroscopy. Chemists in Hiroshima, Japan, describe a first report on the regioselective formation of a bicyclic oxetane derivative in the photochemical [2 + 2] cycloaddition, or so-called Paternó-Büchi reaction of benzophenone with 2-siloxypyrole.4 They propose that the relative stability of intermediary triplet diradicals plays an important role for the regioselectivity. Professor Anna Gudmundsdottir and coworkers find the photochemical transformation of 3,5-diphenylisoxazole to an azirine in argon.5 Further irradiation was found to produce the corresponding ylide in the low-temperature matrix conditions. The formation of the azirine from the isoxazole is proposed to occur via a triplet nitrene intermediate, which is confirmed by theoretical calculations. Professor Hiroshi Ikeda and coworkers report luminescence from an excited-state biradical generated by irradiation of benzopheone-substituted cyclopropanes. The excited state is proposed to be generated from an adiabatic process of higher electronically excited states.6 Professor Weston Borden and coworkers computationally predict the low-lying electronic states of dioxatrimethylenemethane (DOTMM), H2CCO2, and the photoelectron spectrum of its anion.7 They find that DOTMM has a triplet ground state. An open-shell singlet state is found to lie very close in energy to the triplet state. However, the open-shell singlet is predicted to be a transition-state structure leading to barrierless formation of α-lactone. Professor Masayoshi Nakano and coworkers report a theoretical investigation of curved π-conjugated fullerene flakes,8 in which they discuss open-shell character, aromaticity, and third-order nonlinear optical properties of fragments of C60 fullerene. Professor Torsten Linker et al9 discuss the decomposition of anthracene endoperoxides. Interestingly, they observed not only homolytic O–O but also C–O bond cleavages in the thermolyses. In general, barbaralanes and semibullvalenes are fluxional molecules renowned for their exceedingly low–Cope rearrangement activation barriers and their close approach to homoaromaticity. However, Professor Richard Williams and coworkers find that 4,6-barbaralanedicarboxyl-2,8-dicarboxylic anhydride and 1,5-dimethyl-4,6-semibullvalenedicarboxy-2,8-dicarboxylic anhydride are unusual barbaralanes and semibullvalenes that are locked as the closed tautomers and do not undergo Cope rearrangement.10 This total lack of the Cope rearrangement was demonstrated through variable-temperature 13C nuclear magnetic resonance spectroscopy and computational studies. The reactive intermediates community looks forward to the next ISRIUM conference, organized by Professor Dasan M. Thamattoor, which will be in Sorrento Italy in 2017. We hope that readers of this special issue of the Journal of Physical Organic Chemistry will attend that meeting. Finally, the guest editors especially wish to acknowledge the invaluable assistance of Dr Sarah Ryan, Managing Editor, and Dr Peter Creaton, Journals Publishing Manager from Wiley, in the preparation of this issue.