Visible-Light Driven Selective C–N Bond Scission in anti-Bimane-Like Derivatives

Abstract

In the present study, we report the photochemical transformation of pyrazolo­[1,2-a]­pyrazolone substrates that reach an excited state upon irradiation with visible light to initiate the homolytic C–N bond cleavage process that yields the corresponding N1-substituted pyrazoles. Moreover, chemoselective heterolytic C–N bond cleavage is possible in the pyrazolo­[1,2-a]­pyrazole core in the presence of bromomalonate.

Photoinduced Ring Opening of Methyl 1-Aryl-5-oxo-6,7-dihydro-1H,5H-pyrazolo[1,2-a]pyrazole-2-carboxylates in the Presence of Diaryl Disulfides

“…As one of the most commonly catalysts, we selected thiophenols and diaryl disulfides. The irradiation of com in DCM at 450 nm resulted in the formation of 2a as reported previously [9]. A irradiation, a 24% NMR yield of 2a was determined (Table 1, entry 1).…”

“…In this study, we focused on the C7-N8 homolytic bond cleavage of pyrazolo [1,2-a]pyrazolones, which occurs upon the irradiation of the substrates with a 400 nm light source. This process involves intramolecular hydrogen atom transfer (HAT), leading to the formation of an aldehyde functionality (Scheme 1, highlighted in red), which we confirmed through deuterium labeling [9].…”

“…The a Scheme 1. Irradiation of pyrazolo [1,2-a]pyrazolones can lead to ring opening, which either produces an unsaturated amide (highlighted in purple), an amide, an ester or carboxylic acid (highlighted in blue), or an aldehyde (highlighted in red) [9]. Scheme 1.…”

“…Numerous methodologies for the synthesis and derivatization of pyrazoles have been reported and they continue to be developed [7]. For instance, we recently disclosed a photoredox-catalyzed oxidation of N1-substituted pyrazolidin-3-ones to azomethine imines [8], as well as the photoinduced selective preparation of highly functionalized pyrazoles from pyrazolo[1,2-a]pyrazolones (Scheme 1) [9]. In this study, we focused on the C7-N8 homolytic bond cleavage of pyrazolo [1,2-a]pyrazolones, which occurs upon the irradiation of the substrates with a 400 nm light source.…”

Visible photons as ideal reagents for the activation of coloured organic compounds

“…, alcohols and amines), induced the photochemical C 5 –N 4 photocleavage, resulting in the formation of functionalized pyrazoles 112.5 (Scheme 112b). 349…”