4‐π‐Photocyclization: Scope and Synthetic Applications

Abstract

This minireview highlights the scope of 4‐π‐photocyclizations (photoinduced electrocyclizations that involve 4 pi electrons and generate bicyclic cyclobutenes from 1,3‐dienes), including an overview of the historical progressions as well as recent developments. A range of 1,3‐diene substrates is covered, including cycloheptatrienes, tropones, tropolones, cyclic 1,3‐dienes, 2‐pyrones, 2‐pyridones, pyrimidines, 1,2‐dihydropyridines, and 1,2‐dihydro‐pyridazines. The bicyclic cyclobutene products formed through the photocyclizations are highly versatile synthetic intermediates, and examples of the application of these building blocks in the context of synthetic methodology development, natural product synthesis, medicinal chemistry and materials chemistry are featured throughout.

Excited‐State Distortions Promote the Photochemical 4π‐Electrocyclizations of Fluorobenzenes via Machine Learning Accelerated Photodynamics Simulations

“…Their reactivity and selectivity can depend simply on light absorption wavelength and are free of typically expensive organometallic catalysts. Photochemical reactions such as 4π-electrocyclization [1] and [2 + 2]cycloaddition [2][3] feature shortened synthetic routes with high atom economy. Recent innovations in chemical biology [4] and material science have made significant progress on novel lightharnessing materials.…”

Oxetanes and Oxetenes: Fused-Ring Derivatives

“…61 <Scheme 13 near here> 4-p-Photocyclization of 2-pyrone, a process reported for the first time in 1964, leads to a valuable bicyclic b-lactone 62 whose chemistry has been reviewed early 2020 by Coote. 63 Selected examples over the 2008-2020 period demonstrate the versatility of this building block for the straightforward synthesis of relevant cyclobutenes or cyclobutanes. [64][65][66][67][68][69][70][71][72]…”

Photochemical rearrangements in organic synthesis and the concept of the photon as a traceless reagent

“…Numerous heterocyclic compounds undergo photochemically induced electrocyclic reactions leading to constrained bicyclic moieties which are hardly accessible by conventional methods of chemical synthesis. 109,110 Pyridones such as 144 (Scheme 26) undergo photochemical [π2s + σ2s] electrocyclization. 111 According to the Woodward-Hoffmann rules 112 , this disrotatory cyclization is symmetry allowed at the excited state (Figure 4).…”