Oxidative Radical Cyclization of N‐methyl‐N‐arylpropiolamide to Isatins via Cleavage of the Carbon‐carbon Triple Bond

Abstract

A radical cyclization of N-methyl-Narylpropiolamide to isatins via an oxidative cleavage of a carbon-carbon triple bond has been developed. In the presence of oxone and NaNO 2 , a variety of N-methyl-N-arylpropiolamides were smoothly transformed into isatins. A nitration reaction proceeded along with the oxidative cyclization; both nitrated and non-nitrated isatins were obtained in a one-pot reaction with moderate to good total yields. This is the first example for the synthesis of isatins via the oxidative radical cleavage of a carbon-carbon triple bond.

Applications of Sodium Nitrite in Organic Synthesis

“…Zheng and Tang et al disclosed the first radical cyclization of N ‐protected‐ N ‐arylpropiolamide 63 to isatin 64 and nitro‐isatin ( 65 and 66 ) via oxidative cleavage of C≡C bond in the presence of oxone and NaNO 2 (Scheme ) . The developed protocol afforded both nitrated and non‐nitrated isatins in a one‐pot reaction with moderate to good yields.…”

Dichalcogenides/Oxone®‐Mediated Cyclization of (Z)‐Chalcogenoenynes under Ultrasound Irradiation

“…Oxone ® (2KHSO 5 ⋅KHSO 4 ⋅K 2 SO 4 ) acts as oxidant in many selective oxidation reactions [16] and it has been used to synthesize several heterocyclic compounds by intra- [17][18][19][20][21][22][23][24] and intermolecu-lar reactions, [25][26][27][28][29] including oxidative cyclization ones. [30][31][32][33][34][35][36] Recently, our group has explored the application of this oxidant in the synthesis of organoselenium and organotellurium compounds, [37][38][39][40][41][42] such as 2,3-bis-organochalcogenyl-benzo [b] chalcogenophenes, via the electrophilic cyclization of 2functionalized selanyl-and sulfanylalkynes (Scheme 1a). [43] In parallel, cyclization of enynes represents a versatile strategy for accessing cyclic compounds, specially due to the high atom-economy and excellent functional group tolerance.…”

Copper-Catalyzed Aerobic Oxidation Strategy: A Concise Route to Isatin

“…In view of this, new synthetic methods to overcome these drawbacks are still highly required. Inspiringly, some efficient methods have been found, such as aryne-based methods, [6] transition-metal catalyzed oxidation, [7] oxidative cleavage of carbon-carbon triple bond, [8] sulfur ylide-mediated carbonyl homologation, [9] iodine-mediated oxidation, [10] and C-H amination (Scheme 1). [11] Although these methods showed some im-provements, there are still many problems like the requirement of heavy metal catalysts and excess amount of bases or strong oxidants and relatively low yields of products.…”