Mn-Catalyzed Electrooxidative Radical Cascade Cyclization for the Synthesis of 6-Phosphorylated Quinoxalino[2,1-b]quinazolin-12-ones

Due to their important potential medicinal value, chemists are pursuing mild and efficient methods to synthesize structurally diverse quinazolinone derivatives. In this paper, a series of isocyano-tethered N-aryl quinazolinones were designed and synthesized to conduct electrocatalytic radical cascade cyclization reactions with phosphine oxides by utilizing inexpensive MnII salt as the catalyst. The desired 6-phosphorylated quinoxalino[2,1-b]quinazolin-12-ones were obtained in moderate to good yields.

Photoredox/HAT-Catalyzed Intramolecular Hydrocyclization of Alkenes toward 2,3-Fused Quinazolinones and Dihydroquinazolinones

New photochemical approaches to 2,3-fused quinazolinones and dihydroquinazolinones are disclosed. The intramolecular hydrocyclization proceeds in moderate to excellent yields across diverse alkenes with high regioselectivity and diastereocontrol. Mechanistic studies indicated that the radical cascade processes involve thiophenol acting as single-electron transfer and hydrogen atom transfer reagents. The success of the gram-scale synthesis proves the strategy can be used for practical applications.

Synthesis of Pyrimido[1,2-a]indolediones and Pyrimidinediones via [4+2] Annulation of 2H-Azirine-2-carbaldehydes

NHC-catalyzed [4+2] annulation of 2H-azirine-2-carbaldehydes with ketimines and isocyanates has been developed, providing straightforward synthetic protocols for constructing structurally intriguing pyrimido[1,2-a]indolediones and pyrimidinediones under mild conditions with excellent yields. This protocol can be used to synthesize the core skeleton of pharmaceutically important drugs and pyrimido[1,2-a]indoledione-containing natural products, making it potentially valuable for creating biologically active derivatives.

Cyclizations of Alkenyl(Alkynyl)-Functionalized Quinazolinones and their Heteroanalogues: A Powerful Strategy for the Construction of Polyheterocyclic Structures

Quinazolin-4-one, its heteroanalogues, and derivatives represent an outstandingly important class of compounds in modern organic, medicinal, and pharmaceutical chemistry, as these molecular structures are noted for their wide synthetic and pharmacological potential. In the last years, ever-increasing research attention has been paid to quinazolinone derivatives bearing alkenyl and alkynyl substituents on the pyrimidinone nucleus. The original structural combination of synthetically powerful endocyclic amidine (or amidine-related) and exocyclic unsaturated moieties provides a driving force for cyclizations, which offer an efficient toolkit to construct a variety of fused pyrimidine systems with saturated N- and N,S-heterocycles. In this connection, the present review article is mainly aimed at systematic coverage of the progress in using alkenyl(alkynyl)quinazolinones and their heteroanalogues as convenient bifunctional substrates for regioselective annulation of small- and medium-sized heterocyclic nuclei. Much attention is paid to elucidating the structural and electronic effects of reagents on the regio- and stereoselectivity of the cyclizations as well as to clarifying the relevant reaction mechanisms.

Cyanomethylative cyclization of unactivated alkenes with nitriles for the synthesis of cyano-containing ring-fused quinazolin-4(3H)-ones

The synthesis of cyano-containing pyrrolo- and piperidino-quinazolinones was developed using alkyl nitriles through radical cascade addition/cyclization under metal-free conditions.

Photoinduced homolytic decarboxylative acylation/cyclization of unactivated alkenes with α-keto acid under external oxidant and photocatalyst free conditions: access to quinazolinone derivatives

A novel and green strategy for the synthesis of acylated quinazolinone derivatives via photo-induced decarboxylative cascade radical acylation/cyclization of quinazolinone bearing unactivated alkenes has been developed. The protocol provides a novel route to access acyl radicals from α-keto acids through a self-catalyzed energy transfer process. Most importantly, the reaction proceeded smoothly without any external photocatalyst, additive or oxidant, and could be easily scaled-up in flow conditions with sunlight irradiation.

Peroxide-Mediated Oxidative Radical Cyclization to the Quinazolinone System: Efficient Syntheses of Deoxyvasicinone, Mackinazolinone and (±)-Leucomidine C

An efficient protocol for obtaining fused quinazolinones through an oxidative free-radical cyclization under metal- and tin-free conditions is described. The oxidative cyclization of various N-3-ω-iodoalkyl derivatives to provide tricyclic systems using dicumyl peroxide as the sole reagent is studied. The method then is employed for the syntheses of 5-, 6-, and 7-membered fused quinazolinone analogues, including the natural products deoxyvasicinone and mackinazolinone. A xanthate-based oxidative radical cascade addition/cyclization process that allows the production of new menthol- and testosterone-quinazolinone conjugates, as well as the first total synthesis of leucomidine C, are also reported.