Photoexcited Palladium-Initiated Remote Desaturation of N-Alkoxypyridinium Salts

Abstract

1,5-Hydrogen atom transfer (HAT) is an effective strategy to achieve remote desaturation of nonfunctionalized alkanes. Herein, we report a photoinduced remote desaturation reaction of N-alkoxypyridinium salts, which serve as alkoxyl radical precursors. Mechanistic studies show that a single electron transfer between the excited palladium complex and a N-alkoxypyridinium salt initiates a radical chain process leading to desaturation of N-alkoxypyridinium salts. This chain mechanism is supported by the measurement of the quantum yield of this reaction (Φ = 82). This reaction is applicable to a range of N-alkoxypyridinium salts, including some complex molecule-derived ones.

Pd-Catalyzed Homologation of Arylboronic Acids as a Platform for the Diversity-Oriented Synthesis of Benzylic C–X Bonds

“…1 H NMR (500 MHz, 1 H NMR (500 MHz, CDCl3) d 7.54 (dd, J = 7.4, 1.8 Hz, 1 H), 7.37 (dd, J = 7.2, 1.8 Hz, 1 H), 7.32 (dd, J = 7.4, 1.8 Hz, 2 H), 7.06 (dd, J = 17.4, 11.0 Hz, 1 H), 5.71 (dd, J = 17.4, 1.4 Hz, 1 H), 5.37 (dd, J = 11.0, 1.3 Hz, 1 H), 4.77 (d, J = 5.1 Hz, 2 H), 1.56 (t, J = 6.1 Hz, 1 OH). 13 C NMR (126 MHz, CDCl3) d 137.7, 136.8, 133.9, 128.5, 128.4, 128.1, 126.1, 116.7, 63.6.The spectral data were consistent with the literature 20. …”

“…18,19 While historically utilized in C(sp 2 )-C(sp 2 ) cross-coupling reactions, contemporary work has employed C(sp 3 )-B organoboron reagents as a method to prepare more C(sp 3 )-rich scaffolds for improved biological characteristics in medicinal chemistry. 20 As such, both the preparation and utilization of C(sp 3 )-B bonds remains a strategic focal point within academic and industrial research settings. Several benzyl boronic acids are known; however, very few are commercially available likely due to their propensity to degrade (protodeboronation).…”

Recent Advances in Visible Light Induced Palladium Catalysis

“…Later, the same group employed N ‐alkoxypyridinium salts 5.1 for the synthesis of alkenols 5.2 (Scheme 5). [27] In contrast to the previous reports, a radical chain mechanism was proposed for this transformation, as supported by a measured quantum yield of 82. Thus, the Pd catalyst only serves to initiate the radical chain through the initial formation of alkoxy radical A .…”

Visible-Light-Induced Alkoxypyridylation of Alkenes Using N-Alkoxypyridinium Salts as Bifunctional Reagents

“…Compared to pyridine, electron-deficient pyridinium salts exhibit higher reactivity, thereby enhancing the reactivity and selectivity for various chemical transformations under photoredox catalysis. Pyridinium salts have been demonstrated as readily accessible, efficient, and bench-stable precursors that may offer N -, O -, and C -center radicals . In recent decades, remarkable progress has been achieved by Studer’s, Zhu’s, and Hong’s groups.…”