Microwave-Assisted Branching Cascades: A Route to Diverse 3,4-Dihydroquinazolinone-Embedded Polyheterocyclic Scaffolds

Quinazolines annelated at the N(3)-C(4) bond: Synthesis and biological activity

This review covers article and patent data obtained mostly within the period 2013-2023 on the synthesis and biological activity of quinazolines [c]-annelated by five- and six-membered heterocycles. Pyrazolo-, benzimidazo-, triazolo- and pyrimido- [c]quinazoline systems have shown multiple potential activities against numerous targets. We highlight that most research efforts are directed to design of anticancer and antibacterial agents of azolo[c]quinazoline nature. This review emphases both on the medicinal chemistry aspects of pyrrolo[c]-, azolo[c]- and azino[c]quinazolines and comprehensive synthetic strategies of quinazolines annelated at N(3)-C(4) bond in the perspective of drug development and discovery.

Synthesis of pyrimido[2,1-a]isoindolone and isoindolo[2,1-a]quinazolinone via intramolecular aza-Prins type reaction

A novel aza-Prins type cyclization reaction involving N-acyliminium ions and amides is reported for the synthesis of tetrahydropyrimido[2,1-a]isoindole-2,6-dione and 6,6a-dihydroisoindolo[2,1-a]quinazoline-5,11-dione derivatives in excellent yields. The strategy features inexpensive reagents, mild reaction conditions, and metal-free synthesis of N-heterocyclic frameworks. Further, post-synthetic modification results in the unprecedented formation of its triazole, tetracyclic diazacyclopenta[def]phenanthrene-1,4(9a1H)-dione and carbonyl derivatives.

Benzylidene succinimides as 3C synthons for the asymmetric tandem Mannich reaction/transamidation of cyclic trifluoromethyl ketimines to obtain F3C-containing polycyclic dihydroquinazolinones

By taking advantage of benzylidene succinimides as a new class of 3C synthons, a highly diastereo- and enantioselective tandem Mannich reaction/transamidation has been established by reacting them with cyclic trifluoromethyl N-acyl ketimines. Using a Cinchona alkaloid-derived squaramide as the catalyst, the tandem reaction proceeded smoothly under mild conditions and afforded a range of F3C-containing chiral polycyclic dihydroquinazolinones with excellent results (up to 99% yield, all cases >20 : 1 dr, up to 99% ee).

Synthesis of substituted 3,4-dihydroquinazolinones via a metal free Leuckart-Wallach type reaction

The 3,4-dihydroquinazolinone (DHQ) moiety is a highly valued scaffold in medicinal chemistry due to the vast number of biologically-active compounds based on this core structure. Current synthetic methods to access these compounds are limited in terms of diversity and flexibility and often require the use of toxic reagents or expensive transition-metal catalysts. Herein, we describe the discovery and development of a novel cascade cyclization/Leuckart-Wallach type strategy to prepare substituted DHQs in a modular and efficient process using readily-available starting materials. Notably, the reaction requires only the addition of formic acid or acetic acid/formic acid and produces H₂O, CO₂ and methanol as the sole reaction byproducts. Overall, the reaction provides an attractive entry point into this important class of compounds and could even be extended to isotopic labelling via the site-selective incorporation of a deuterium atom.

Catalytic C3 aza-alkylation of indoles

The aza-alkylation reaction at position 3 of the indole scaffold allows the introduction of a differently substituted aminomethyl group, with the formation of a stereogenic centre. Critical summary of 2000–2019 meaningful papers.

Synthesis of Cyclopropanoids via Substrate-Based Cyclization Pathways

A series of unexpected reactions triggered by the dimethyloxosulfonium methylide led to the discovery of unconventional approaches for the synthesis of cyclopropa-fused tetralones and indeno-spirocyclopropanes. These highly functionalized structures were further elaborated in one step to privileged scaffolds such as tetralones, indenones, and fluorenones. As a whole, the results presented herein establish new diversity-oriented folding pathways.

Microwave-Assisted aza-Friedel-Crafts Arylation of N-Acyliminium Ions: Expedient Access to 4-Aryl 3,4-Dihydroquinazolinones

A one-pot microwave-assisted aza-Friedel-Crafts arylation of N-acyliminium ions, generated in situ from o-formyl carbamates and different amines, is reported. This metal-free protocol provides rapid access to diverse 4-aryl 3,4-dihydroquinazolinones in excellent yield without any aqueous workup. A solvent-directed process for the selective aza-Friedel-Crafts arylation of electron-rich aryl/heteroaryl/butenyl-tethered N-acyliminium ions is also described.

Synthesis of pyrimido[1,6-a]quinoxalines via intermolecular trapping of thermally generated acyl(quinoxalin-2-yl)ketenes by Schiff bases

Acyl(quinoxalin-2-yl)ketenes generated by thermal decarbonylation of 3-acylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones react regioselectively with Schiff bases under solvent-free conditions to form pyrimido[1,6-a]quinoxaline derivatives in good yields.

Acetic acid-promoted cascade N-acyliminium ion/aza-Prins cyclization: stereoselective synthesis of functionalized fused tricyclic piperidines

A novel acetic acid-promoted metal-free cascade N-acyliminium ion/aza-Prins cyclization of o-formyl carbamates and homoallylamines is reported. This one-pot protocol provides efficient and rapid access to masked cis-hydroxyhexahydropyrido[1,2-c]quinazolin-6-ones with concomitant generation of two stereogenic centers, four C-C/C-O/C-N bonds and two new rings in good yield and excellent diastereoselectivity.