Recent Advances in Reactions Using Enaminone in Water or Aqueous Medium

Abstract

Enaminones have in the past decade received renewed interest in organic synthesis by acting as highly versatile building blocks. Particularly, the featured amino and carbonyl group in the enaminone structure endow them with the ability of tolerating water via hydrogen bonding effect. Thus, designing synthetic methods in aqueous medium with enaminones as the main building blocks has received extensive attention and notable success. Based on our longstanding efforts and interests in enaminone chemistry, we review herein the research advances in enaminone participated organic synthesis in aqueous medium.

Thiazole-5-carbaldehyde Synthesis by Cascade Annulation of Enaminones and KSCN with Dess–Martin Periodinane Reagent

“…Eluent: V PET /V EA = 5:1; white solid (25.8 mg, 43% yield); mp 92−94 °C; 1 H NMR (400 MHz, DMSO-d 6 ) δ 9.60 (s, 1 H), 8.09−8.04 (m, 2 H), 7.88 (s, 1 H), 7.75 (t, 1 H), 3.22 (s, 6 H); 13 C{ 1 H} NMR (100 MHz, DMSO-d 6 ) δ 181. 5,173.0,161.5,134.8,134.0,130.4,126.9,126.2,124.4;19 F NMR (376 MHz, ) δ −61.17, −77.74; HRMS (ESI-TOF) m/z [M + H] + calcd for C 13 H 12 F 3 N 2 OS 301.0617, found 301.0636.…”

“…Over the past decade, designing novel synthetic methods on enaminones has won important advances. 5 Particularly, employing enaminones as the main building blocks for the construction of aromatic ring systems has gained significant success. In the presence of proper reaction partners and/or with proper conditions, enaminones have been employed for the construction of phenyl, 6 pyridine, 7 pyrrole, 8 pyrazole, 9 quinoline, 10 indole, 11 pyrimidines, 12 thiazoles, 13 1,2,3-triazoles 14 azirines, 15 and diverse other heteroaromatic ring systems.…”

Electrochemical Synthesis of Polysubstituted Sulfonated Pyrazoles via Cascade Intermolecular Condensation, Radical–Radical Cross Coupling Sulfonylation, and Pyrazole Annulation

“…In 2014, Wan and co-workers described the pioneering TBAI/TBHP catalyzed cascade reaction for the synthesis of fully substituted sulfonated pyrazoles from aryl sulfonyl hydrazides and 1,3-diketones using pyridine and Co­(OAc) 2 ·4H 2 O as additives, in which sulfonyl hydrazides function both as the ring component and sulfonyl precursor . As easily accessible and versatile building blocks, enaminones have been widely applied in the synthesis of various carbocyclic and heterocyclic compounds . In particular, utilizing the dual-role-sulfonyl-hydrazide strategy with the iodine as catalyst and TBHP as oxidant, elegant works from the group of Wan and Sheng revealed the cascade reactions of NH 2 -functionalized enaminones and N , N -disubstituted enaminones with aryl sulfonyl hydrazides to afford fully substituted sulfonated pyrazoles and 1,4,5-trisubstituted sulfonated pyrazoles, respectively (Scheme a).…”

Photocatalytic C–H Thiocyanation of NH2-Enaminones and the Tunable Synthetic Routes to 2-Aminothiazoles and 2-Thiazolinones

“…5 The more recent tendency in the thiocyanation reaction, however, focuses on energy-economical catalysis, including visible light photocatalytic reactions and electrochemical reactions, which has shed light on the designation of thiocyanate synthesis with enhanced eco-friendliness. 6 Benefiting from the recent advances in novel enaminonebased organic synthesis, 7,8 thiocyano functionalization on enaminones has been proven to be a useful tool for the synthesis of different thiocyanates or derived heterocyclic compounds. In 2019, our group reported the first enaminone C−H thiocyanation reaction using N,N-disubstituted tertiary enaminones and ammonium thiocyanate as starting materials via transition-metal-free photocatalysis (Scheme 1A).…”