Iron-Catalyzed Aerobic α,β-Dehydrogenation

Abstract

An iron-catalyzed direct aerobic α,β-dehydrogenation of carbonyls has been reported. The combination of tert-butyl nitrite and N-hydroxyphthalimide worked as the organo cocatalyst system; thus, no extra transition metal reagents are required. A large variety of lactams and flavanones as well as lactone and thiochromen-4-one could be produced via this method in high yields.

Transition‐Metal‐Catalyzed α,β‐Dehydrogenation of Carbonyl Compounds

“…Recently, a FeCl 3 -catalyzed aerobic α,β-dehydrogenation with organo cocatalyst tert-butyl nitrite and N-hydroxyphthalimide (NHPI) have been reported by Kang and Qu. [34] The α,βunsaturated lactones and lactams could be obtained in moderate to high yield under the optimal conditions (Scheme 15), which included steroid-derived substrate and flavanones with heterocyclic substituents. To investigate the reaction mechanism, a series of control experiments were performed.…”

“…Lactams are a kind of important structure because they are usually found in biological molecules, which may exist in natural products, agrochemicals and pharmaceuticals. [34,37] Dong and co-workers developed a direct catalytic method to synthesize α,β-unsaturated lactams under mildly acidic conditions (Scheme 19). [37b] This approach is effective for a big range of substrate scope, such as lactams with various functional groups at different position, lactams with different ring size and so on.…”

Recent Developments on the Earth-Abundant-Metal-Catalyzed α,β-Dehydrogenation of Carbonyl Compounds

“…Following our work on the Fe-Cl 3 -catalyzed ,-dehydrogenation of carbonyl compounds, in 2023, we reported a FeCl 3 -catalyzed aerobic ,-dehydrogenation with an organo-cocatalyst, tert-butyl nitrite and N-hydroxyphthalimide (NHPI), which effectively solved the problem of the low yields encountered with the ,-unsaturated lactones and lactams in our previous work (Scheme 3). 23 A variety of ,-saturated lactones, lactams and flavanones, including steroid-derived substrates and flavanones with heterocyclic substituents, could be dehydrogenated under the optimized conditions, generating the corresponding products in moderate to good yields. Control experiments indicated that a radical process may be involved, and FeCl 3 as a Lewis acid may activate 23.…”

Iron-catalyzed selective construction of indole derivatives via oxidative C(sp3)–H functionalization of indolin-2-ones

“…For constructing carbon–carbon and carbon–heteroatom bonds in modern organic synthesis, iron, as the most abundant transition metal in the Earth's crust, has found extensive application as an eco-friendly and readily available catalyst. 1–11 Inspired by iron-containing enzyme catalysis, 12,13 the iron-catalyzed C(sp 3 )–H bond oxidation, coupled with the utilization of molecular oxygen, has emerged as a highly promising reaction over the past decade. 14–24 In 2015, Li's group pioneered the utilization of cross-dehydrogenative coupling (CDC) to develop an iron salt-catalyzed cross-dehydrogenative arylation between 3-substituted indolin-2-ones generating a series of 3,3′-disubstituted oxindole compounds.…”