Novel Methods for the Synthesis of 4‐Arylisoquinolinium Perchlorates and 4‐Arylisoquinolin‐1‐ones

2‐Benzylamino‐1‐phenyl‐ethanones 1 were converted to the corresponding isoquinolinium perchlorates 2 in high yields using 70% HClO₄‐FeCl₃ mixture as a cyclization and oxidation reagent. A mild and high yielding method for the oxidation of perchlorates 2 to isoquinolin‐1‐ones 3 involving the treatment of 2 with KOH and K₃[Fe(CN)₆] in THF‐H₂O two‐phase system at room temperature was developed. Compounds 2a–g were shown to be disproportionate to 3 and the corresponding 1,2‐dihydroisoquinoline 4 in the presence of base, which in turn is oxidized by K₃[Fe(CN)₆] to 2.     

Electronic Absorption Spectroscopy and Photochemistry of Criegee Intermediates

Interest in Criegee intermediates (CIs), often termed carbonyl oxides, and their role in tropospheric chemistry has grown massively since the demonstration of laboratory-based routes to their formation and characterization in the gas phase. This article reviews current knowledge regarding the electronic spectroscopy of atmospherically relevant CIs like CH₂OO, CH₃CHOO, (CH₃)₂COO and larger CIs like methyl vinyl ketone oxide and methacrolein oxide that are formed in the ozonolysis of isoprene, and of selected conjugated carbene-derived CIs of interest in the synthetic chemistry community. Of the aforementioned atmospherically relevant CIs, all except CH₂OO and (CH₃)₂COO exist in different conformers which, under tropospheric conditions, can display strikingly different thermal loss rates via unimolecular and bimolecular processes. Calculated photolysis rates based on their absorption properties suggest that solar photolysis will rarely be a significant contributor to the total loss rate for any CI under tropospheric conditions. Nonetheless, there is ever-growing interest in the absorption cross sections and primary photochemistry of CIs following excitation to the strongly absorbing ¹ππ* state, and how this varies with CI, with conformer and with excitation wavelength. The later part of this review surveys the photochemical data reported to date, including a range of studies that demonstrate prompt photo-induced fission of the terminal O–O bond, and speculates about possible alternate decay processes that could occur following non-adiabatic coupling to, and dissociation from, highly internally excited levels of the electronic ground state of a CI.