Novel Dimroth rearrangements of the benzotriazole system: 4-amino-1-(arylsulfonyl)benzotriazoles to 4-[(arylsulfonyl)amino]benzotriazoles

Abstract

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Accelerated Discovery in Photocatalysis using a Mechanism‐Based Screening Method

“…Theactivity of complex 6,which has the highest excited state oxidation potential of all six tested photocatalysts,i sh ighly suggestive of an oxidative quenching pathway.E lectronwithdrawing nitrogen substituents may facilitate such amechanism by reducing the reduction potentials of these compounds by stabilizing the ring-opened diazonium form of the benzotriazole. [22] Theq uenching of catalyst 1 by 1H-benzotriazole (Q3)c ould instead proceed through ad ifferent triplet-triplet energy-transfer pathway involving the 2H isomeric form, which has at riplet-state energy comparable to that of 1 (E T (2H-benzotriazole) = 60 kcal mol À1 , E T (1) = 61 kcal mol À1 ). [11,23] Having obtained an overview of the quenching abilities of benzotriazole derivatives,t he next stage of the process involves the development of new visible-light-promoted transformations,w hich exploit the insights provided by "mechanism-based" screening.A sc learly demonstrated in the "quenching evaluation" screen, benzotriazole derivatives which bear electron-withdrawing N-substituents,a ct as efficient oxidative quenchers of reducing photocatalysts.U pon single-electron reduction, the resulting radical anions would be expected to extrude adinitrogen molecule and deliver aryl radical anions in asimilar fashion to that observed with widely employed aryldiazonium salt quenchers.…”

“…[22] Theq uenching of catalyst 1 by 1H-benzotriazole (Q3)c ould instead proceed through ad ifferent triplet-triplet energy-transfer pathway involving the 2H isomeric form, which has at riplet-state energy comparable to that of 1 (E T (2H-benzotriazole) = 60 kcal mol À1 , E T (1) = 61 kcal mol À1 ). Theactivity of complex 6,which has the highest excited state oxidation potential of all six tested photocatalysts,i sh ighly suggestive of an oxidative quenching pathway.E lectronwithdrawing nitrogen substituents may facilitate such amechanism by reducing the reduction potentials of these compounds by stabilizing the ring-opened diazonium form of the benzotriazole.…”

Schnelles Entdecken photokatalytischer Reaktionen durch mechanismusbasiertes Screening

“…Darüber hinaus lässt sich durch das Maß des Quenchings der Substrate mit den jeweiligen Katalysatoren aufgrund der entsprechenden Redoxpotentiale und Tr iplettenergien der Katalysatoren im angeregten Zustand eine Aussage über den Quenchingmechanismus treffen. [22] Das Konzept dieses "Quenching-Evaluations"-Screenings ist in Abbildung 3a dargestellt. Zusätzlich zu dem anfänglich entdeckten Quencher Q3 wurden mehrere strukturell unterschiedliche Benzotriazole untersucht.…”

Microwave-Assisted Regiospecific Synthesis of Pseudohalohydrin Esters

“…The use of a single-mode cavity microwave synthesizer helps to achieve reproducibility, safety, reduced pollution, and simplicity in processing and handling. [25][26][27][28][29][30][31] We found that palladium-catalyzed thermal reaction of Nacylbenzotriazole 1a [32][33][34] with epoxide 3a gave the single regioisomer β-(benzotriazol-1-yl)ethyl ester 4a. Although, as reported 33 recently, thermal isomerization of 1a to 1a′, followed by oxidative addition of 1a′ to palladium(0) gives 1a′′, we found no 1,4-benzoxazine 2a (Scheme 2).…”