Visible-Light-Induced Regioselective C–H Sulfenylation of Pyrazolo[1,5-a]pyrimidines via Cross-Dehydrogenative Coupling

Abstract

A visible-light-induced cross-dehydrogenative methodology has been developed for the regioselective sulfenylation of pyrazolo[1,5-a]pyrimidine derivatives. Rose bengal, blue LEDs, KI, K 2 S 2 O 8 , and DMSO are all essential for this photocatalytic transformation. The protocol is applicable for the synthesis of a library of 3-(aryl/heteroaryl thio)pyrazolo[1,5-a]pyrimidine derivatives with broad functionalities. The selectivity and scalability of the methodology have been also demonstrated. Moreover, the efficiency of this strategy for sulfenylation of pyrazoles, indole, imidazoheterocycles, and 4-hydroxy coumarin has been proven. The mechanistic investigation revealed the radical-based mechanism and formation of diaryl disulfide as a key intermediate for this cross-dehydrogenative coupling reaction.

Rose‐Bengal‐Photocatalyzed Cross‐Dehydrogenative Coupling Reactions under Visible Light

“…Pual et al in 2023, developed a visible light induced crossdehydrogenative coupling procedure for the regioselective sulphenylation of pyrazolo[1,5-a]pyrimidines using thiophenols as sulphenylating agents (Scheme 33). [119] This photocatalytic transformation requires the use of rose bengal, blue LEDs, KI, K 2 S 2 O 8 , and DMSO. A wide range of functionalized 3-(aryl/heteroaryl thio)pyrazolo[1,5-a]pyrimidine derivatives have been synthesized with excellent yields using this protocol.…”

“…in 2023, developed a visible light induced cross‐dehydrogenative coupling procedure for the regioselective sulphenylation of pyrazolo[1,5‐ a ]pyrimidines using thiophenols as sulphenylating agents (Scheme 33). [119] …”

Oxone® Mediated Regioselective C(sp2)−H Selenylation and Thiocyanation of Pyrazolo[1,5‐a]pyrimidines at Room Temperature

“…[14] Recently, Bagdi et al reported a blue lightinduced, KI-mediated chalcogenation of pyrazolo[1,5-a]pyrimidines using Rose Bengal as a photocatalyst in presence of potassium peroxodisulfate (K 2 S 2 O 8 ) (Scheme 1a). [15] They also achieved white light-mediated selenylation of pyrazolo[1, 5a]pyrimidines employing erythrosine-B as photocatalyst in presence of molecular oxygen (Scheme 1b). [16] Further this group also demonstrated a photocatalyst-free white-light driven protocol for selenylation of pyrazolo[1,5-a]pyrimidines using potassium peroxodisulfate (K 2 S 2 O 8 ) (Scheme 1c).…”

“…Recently, Bagdi et al . reported a blue light‐induced, KI‐mediated chalcogenation of pyrazolo[1,5‐ a ]pyrimidines using Rose Bengal as a photocatalyst in presence of potassium peroxodisulfate (K 2 S 2 O 8 ) (Scheme 1a) [15] . They also achieved white light‐mediated selenylation of pyrazolo[1,5‐ a ]pyrimidines employing erythrosine‐B as photocatalyst in presence of molecular oxygen (Scheme 1b) [16] .…”