Chemo-, site-selective reduction of nitroarenes under blue-light, catalyst-free conditions

A switchable redox annulation of 2-nitroarylethanols affording N-heterocycles: photoexcited nitro as a multifunctional handle

“…To gain more solid data concerning the reaction mechanism, the intermolecular kinetic isotope effect (KIE) experiments were performed by using the reactions of equivalent molar 1a and the deuterium-labeled substrate of N-hydroxyl oxindoles may be related to dual homolysis of a-C-H bonds. 33 Based on the above mechanistic experiments and previous reports, 19,20,34 the plausible mechanisms were proposed (Scheme 7). If ground-state nitroarene (1a) is exposed to appropriate irradiation, it could be photoexcited to the longlived triplet state (T), which has a biradical character.…”

“…Herein, we disclose a redox annulation of 2-nitroarylethanols via a photoexcited nitro-triggered d -HAA process under blue-light irradiation, which delivers diboron-switched indoles, N -hydroxyl oxindoles or N –H oxindoles (Scheme 1D) in good to excellent yields. This reaction does not need any metal catalyst or photocatalyst, and three characteristics stand out as given below: (1) nitro serves as a masked nitrogen precursor, as well as an internal photosensitive and oxidative functionality; (2) the branched hydroxyalkyl serves as an internal carbon precursor and a double hydrogen donor (α-C–H and O–H); (3) the in situ generated nitrosoarene and N -hydroxylaniline intermediates may undergo diboron-based deoxygenation, 20,21 thus avoiding the addition of extra activators. 22 The different usages of a diboron reagent could lead to different products (Scheme 1D).…”

Photoinduced Oxygen Transfer using Nitroarenes for the Anaerobic Cleavage of Alkenes

“…33,34 Hence, the diradical nature of the photoexcited nitroarene likely engages in a radical cyclization event with the alkene. 35 To garner support for this, we subjected trans-radical cyclopropane clock 5 to the reaction conditions (Figure 1C). The expected radical trapped/ring-opened product resulting from IV was not detected and instead a 2.7:1 trans/cis isomeric mixture of alkene 6 was isolated.…”

Photoinduced Oxygen Transfer using Nitroarenes for the Anaerobic Cleavage of Alkenes

“…33 Hence, the biradical nature of the photoexcited nitroarene likely engages in a radical cyclization event with the alkene. 34 To probe this pathway, we subjected trans-radical cyclopropane clock 5 to the reaction conditions (Figure 1C). The expected radical trapped/ring-opened product resulting from IV was not detected, and instead a 2.7:1 trans/cis isomeric mixture of 6 was isolated.…”