Divergent reactivity of sulfinates with pyridinium salts based on one-versustwo-electron pathways

Abstract

One of the main goals for modern synthesis is to develop distinct reaction pathways from identical starting materials for the efficient synthesis of diverse compounds. Herein, we disclose the unique...

Recent advances in difunctionalization of alkenes using pyridinium salts as radical precursors

“…Hong and co-workers reported the aminopyridylation of alkenes with N-aminopyridinium salts as bifunctional reagents (Scheme 29). 45 Consistent with previous reports that sterically bulky N-substituents on pyridinium salts would benefit the C4 pyridylation, 39 the reaction showed broad substrate scope, good functional group compatibility and excellent C4 regioselectivity. The activated terminal alkenes, vinyl ethers (36a-36f) and amides (36g-36h), were good substrates for this transformation.…”

“…Later, Hong and co-workers achieved the photoinduced sulfonative pyridylation of alkenes with N-amidopyridinium salts (Scheme 23). 39 This reaction showed good C4 selectivity as the sterically bulky N-substituents on the pyridinium substrates provided good regiochemical induction, allowing alkylation at the C4 position over C2 of pyridines. This strategy showed good compatibility with substituted Namidopyridinium salts (Scheme 23, 31a-31b), and aryl and alkyl sulfonates (31b-31d), as well as activated and unactivated alkenes (31e-31h).…”

Enantioselective functionalization at the C4 position of pyridinium salts through NHC catalysis

“…We propose that Breslow intermediate anion ( E o = −1.7–−1.8 V vs. SCE) 39 has a sufficient reduction potential for a pyridinium salt ( E o = −0.75 to −0.82 V vs. SCE) 16 . At this juncture, we reasoned that Breslow intermediates would serve as efficient SET reductants for electron-deficient pyridinium salts to generate the corresponding homoenolate radicals.…”

“…Consequently, great effort has been devoted to functionalizing pyridine-containing compounds 3 – 9 . Recently, the photoinduced heteroarene modification has proven to be a powerful strategy for dealing with elusive radical transformations under mild conditions 10 – 16 . Despite the remarkable achievements of the Minisci-type radical-addition reaction, precise control over the regiochemical outcome of such a reaction has proven to be challenging owing to the presence of multiple reactive sites, which limits the site-selective applicability of this approach.…”

Nucleophilic C–H Etherification of Heteroarenes Enabled by Base-Catalyzed Halogen Transfer

“…Thus, existing routes for N -heteroaryl C–H etherification require independent synthesis of a functionalized arene followed by an alcohol substitution reaction. A common strategy in this regard involves heteroaryl N -oxide or N -triflyl formation en route to nitro-, cyano-, or phosphonium-substituted azines. − Alternatively, a two-step metalation/halogenation sequence provides heteroaryl halides; however, this often requires irreversible metalation and a directing group for good selectivity. − Thus, a new activation strategy is likely required if N -heteroaryl C–H etherification is to be achieved in a single operation. In addition to increased synthetic efficiency, a new oxidative coupling method could complement the scope, selectivity, and practicality of existing routes to aromatic ethers.…”