Green synthesis of new lawsone enaminones and theirZ/E(CC)-isomerization induced by organic solvent

Abstract

The synthesis of a new class of lawsone enaminone derivatives by using lawsone, triethyl orthoformate and aromatic amines in the presence of guanidinium chloride under solvent-free conditions has been developed.

Divergent Pd-catalyzed Functionalization of 4-Oxazolin-2-ones and 4-Methylene-2-oxazolidinones and Synthesis of Heterocyclic-Fused Indoles

“…The E / Z isomerization of β-enaminones is a feasible process because of the push–pull effect. Their energetic barriers have been calculated and experimentally determined by NMR . Considering the protonated species VI and VII , the s-trans isomers have greater stability than the s-cis isomers for 24a / 25a and 27a / 28a (Figure and Table ).…”

“…The selectivity observed is likely controlled by the push–pull effect of the nitrogen lone electron pair of the enamide moiety, which is involved in modifying the tautomeric E / Z -isomerization of the conjugate enaminone system. ,, The Pd­(II)-catalyzed cyclization of the 24a–24c / 25a–25c mixtures in the presence of pivalic acid gave the corresponding tricyclic 9-formyloxazolo­[3,4- a ]­indol-3-ones 26a–26c , albeit in low yields (27–34%). In the absence of pivalic acid, the yields increased modestly (38–46%) (Scheme , in parenthesis).…”

“…The reaction is apparently carried out through an oxidative addition of Pd(0) to the C–Br bond. The E isomer is probably isomerized into the Z isomer, being promoted by the nitrogen lone pair resonance of the enaminone moiety, which would not occur for simple bromo olefins . The cyclization is noteworthy, considering that the direct intramolecular Pd-catalyzed alkenyl halide arylation of N -allyl or N -vinyl anilines is an uncommon and usually inefficient process …”

Design of Anti-infectious Agents from Lawsone in a Three-Component Reaction with Aldehydes and Isocyanides

“…The 13 C NMR analyses of their compounds exhibited chemical shifts for the 1,4-naphthoquinone ring at 181–183 ppm, while the chemical shift of the carbon atom bearing the hydroxyl group of the enol function was close to 160 ppm. In 2021, Olyaei et al 42 reported the synthesis of lawsone enaminone derivatives. They identified two forms and attributed the alkene proton ( 1 H NMR in DMSO) of the enaminone at 9.2 and 9.3 ppm in DMSO.…”

An Efficient One‐Pot Pseudo Five‐Component Synthesis of Bis‐heteroarylaminomethylnaphthoquinone Mannich Bases from Lawsone

“…In 2016, Mohammadpoor‐Baltork and his co‐workers have published synthesis of symmetric and unsymmetric bis‐aminonaphthoquinones from dialdehyde (terephthaladehyde and isophthalaldehyde) and/or diamines (benzene‐1,4‐diamine and 1,2‐ethylenediamine) in the presence of Fe 3 O 4 @TDSN−Bi(III) in EtOH at room temperature [26] . In continuation of our previous works, reported on synthesis of a new series of lawsone derivatives via one‐pot multi‐component reactions, [27–30] herein we reported the synthesis of a new series of bis‐heteroarylaminomethylnaphthoquinones through one‐pot, multi‐component reactions of lawsone, heteroaryl amines and terephthaldehyde in the presence of a catalytic amount of p ‐TSA in CH 3 CN under reflux conditions.…”