Norrish’ type I and II reactions and their role in the building of photochemical science

Abstract

The highly inspiring work by Professor Norrish has exerted a consistent influence on chemistry and, in particular, on photochemistry, where he was one of the first scientists, along with Gilbert N. Lewis, able to develop a viable concept of excited states and their rate of reaction. However, having him listed among the authors of two name reactions, known as Norrish Type I and Type II, plus a subcase of the latter that is the Yang cyclization, is not coherent. Indeed, Norrish had no interest in organic synthesis, while this is a required feature of name reactions. And, at any rate, Professors Ciamician and Paternò had arrived at the same conclusions with the same compounds much earlier, except for the measurement of quantum yields. Things are too long away now for introducing any change, but one should remember that using Norrish name here is a mistake, while it would be appropriate to add the name of Ciamician for a different name reaction, the 2 + 2 cycloaddition of alkenes and conjugated carbonyls. In 1968, such an attribution was proposed by Professor Schömberg, but this had no effect and the present assignment has become a habit. The most important thing, however, is that the 2 + 2 reaction has become one of the most popular reactions in synthetic photochemistry.

Enhanced thermal and photo-stability of a para-substituted dicumyl ketone intercalated in a layered double hydroxide

“…Hence, an alternative photoreaction sequence must be considered. One likelihood is the Norrish type II pathway (Oelgemöller and Hoffmann, 2016;Albini, 2021), which starts with the intramolecular abstraction of a γ-hydrogen to produce a 1,4-biradical (Scheme 2). In the case of 3, the final products could include the dimethylbenzocyclobutenol derivative D (via Norrish-Yang cyclization) and the keto-enol system E (via a methyl migration Frontiers in Chemistry frontiersin.org reaction) (Scheme 2), which could both explain the new singlet observed in the aromatic region of the 1 H NMR spectra.…”

Applications of Norrish type I and II reactions in the total synthesis of natural products: a review

“…Paquette et al disclosed the first enantiospecific total synthesis of antibiotic (−)-punctatin A (19) applying Norrish type I1 photochemistry as a central step from (+)-diketone (15), commercially available in an enantiomeric purity of 99.6% [54]. The crystalline levorotatory substance punctatin A (19), originally called antibiotic M95464, was isolated from the dung fungus Poronia punctata [55][56][57].…”

“…Photochemical transformations proceed differently compare to thermal protocols because paths of photochemical transformations access high energy intermediates that cannot be achieved by the conventional thermal transformations usually. Hence, photochemical reactions can overcome higher activation barriers in a short time, and permitting transformations that are not accessible by thermal protocols [15][16][17][18][19][20]. Since one of the most significant photo-induced transformations of carbonyl molecules, Norrish reaction is a vital issue of photochemistry, which could provide chemists with both challenges and opportunities to access versatile and influential toolboxes for organic synthesis.…”

“…Norrish type reactions like other photochemical transformations provide transient reactive intermediates and significantly change the reactivity of a chemical substance. The input of energy furnished by light thus offers a means to generate strained and unique desired molecules that cannot be assembled by the conventional thermal transformations [15][16][17][18][19][20]. Synthetic studies of natural products with complex structures using Norrish photoreactions are very beneficial environmentally as classical thermal protocols require toxic, explosive materials, tedious, and long procedures frequently.…”

“…Currently, the uses of photochemistry in organic synthesis are expanding to avoid toxic reagents and photochemical transformation is induced by light absorption, which promotes one of the reagents to its excited state. A key feature of all light-promoted reactions is the participation of electronically excited states which leads to the formation of transient reactive intermediates [15][16][17][18][19][20]. Hence the reactivity of a chemical compound is altered remarkably, a process that can be controlled to give the desired product in high yield and with excellent selectivity [21,22].…”