In 1963, Hekmat Bechir Fathallah Antaki reported the first synthesis of ethyl 4-aryl-1,4,5,6,7,8-hexahydro-2-methyl-5-oxoquinoline-3-carboxylates via three-component condensation of cyclohexane-1,3-dione, aromatic aldehydes, and ethyl β-aminocrotonate in ethanol and glacial acetic acid under reflux for one hour.
The synthesis requires no transition metal catalysts, no inert atmosphere, and no specialised equipment. The three starting materials are commercially available and inexpensive. The product crystallises directly from the reaction mixture. Antaki reported a full series of aryl substituents at the 4-position — p-nitrophenyl, p-methoxyphenyl, 3,4-dimethoxyphenyl, p-dimethylaminophenyl, p-chlorophenyl, and o-nitrophenyl derivatives — with melting points and elemental analyses fully documented.
The hexahydroquinoline intermediates were further subjected to oxidative dehydrogenation by chromium trioxide in dilute acetic acid to yield the corresponding 5,6,7,8-tetrahydroquinolines, demonstrating controlled manipulation of scaffold oxidation state.
This synthesis has been formally classified as the Antaki synthesis — alongside the Hantzsch and Stankevich reactions — as one of three foundational multicomponent methods for hexahydroquinoline formation:
"These approaches established the mechanistic foundation for multicomponent HHQ formation and provided a framework for structural diversification in modern synthesis." — Oduselu et al., Frontiers in Chemistry, 2026
The 1963 paper is cited as reference 324 in Acheson, R.M. (ed.), Chemistry of Heterocyclic Compounds, Vol. 9 (Wiley, 1973) — the canonical Wiley heterocyclic chemistry reference series.
Independent patent families citing Antaki's 1963 synthesis as prior art include filings by ICI/AstraZeneca (1991), Gilead Sciences (2014), and Shin Nippon Biomedical Laboratories (2013), spanning cardiovascular, urological, and transporter pharmacology across more than two decades.
The hexahydroquinoline scaffold has attracted renewed pharmaceutical interest in antimalarial drug discovery as resistance to artemisinin-based therapies grows. Antaki directed his programme explicitly toward antiparasitic applications:
"In continuation of previous work on the schistosomicidal activity in the pyrido[1,2-a]pyrimidine series, the synthesis of some basic derivatives was considered." — H. Antaki, J. Org. Chem., 1962
He was working on diseases of the poor, with tools accessible to resource-limited laboratories, six decades before the current antimalarial interest in this scaffold.
Antaki, H. The Synthesis of Ethyl 4-Aryl-5,6,7,8-tetrahydro-5-oxoquinoline-3-carboxylates and their Derivatives. J. Org. Chem. 1963, 28, 2360–2362. DOI: 10.1021/jo01044a508
A Perspective consolidating the synthesis, its spectroscopic framework, and its antimalarial relevance is available as a preprint on ChemRxiv:
View Preprint on ChemRxiv →