Synthesis of some novel annulated pyrido[2,3-d]pyrimidines via stereoselective intramolecular hetero Diels-Alder reactions of 1-oxa-1,3-butadienes

Indole as a Versatile Building Block in Cycloaddition Reactions: Synthesis of Diverse Heterocyclic Frameworks

Indole, a ubiquitous and structurally versatile aromatic compound, has emerged as a key player in the synthesis of diverse heterocyclic frameworks via cycloaddition reactions. These reactions are completely atom-economical and, hence, are considered as green reactions. This review article provides a comprehensive overview of the pivotal role played by indole in the construction of complex and biologically relevant heterocyclic compounds. Here we explore the chemistry of indole-based cycloadditions, highlighting their synthetic utility in accessing a wide array of heterocyclic architectures, including cyclohepta[b]indoles, tetrahydrocarbazoles, tetrahydroindolo[3,2-c]quinoline, and indolines, among others. Additionally, we discuss the mechanistic insights that underpin these transformations, emphasizing the strategic importance of indole as a building block. The content of this article will certainly encourage the readers to explore more work in this area.

Catalyst-free and additive-free reactions enabling C-C bond formation: a journey towards a sustainable future

This review focuses on the catalyst- and additive-free C-C bond forming reactions reported mostly from the year 2005 to date. C-C bond forming reactions are highly important as large and complex organic molecules can be derived from simpler ones via these reactions. On the other hand, catalyst- and additive-free reactions are economical, environmentally friendly and less sensitive to air/moisture, allow easy separation of products and are operationally simple. Hence, a large number of research articles have been published in this area. Though a few reviews are available on the catalyst-free organic reactions, most of them were published a few years ago. The current review excludes catalysts as well as additives and is specific to only C-C bond formation. Besides many organic name reactions, catalyst/additive-free C-H functionalizations, coupling reactions and UV-visible-light-promoted reactions are also discussed. Undoubtedly, the contents of this review will motivate readers to do more novel work in this area which will accelerate the journey towards a sustainable future.

A facile and concise route to (hydroxybenzoyl)pyrido[2,3-d]pyrimidine heterocycle derivatives: synthesis, and structural, spectral and computational exploration

In this work, we report the efficient synthesis of novel (hydroxybenzoyl)pyrido[2,3-d]pyrimidine heterocycle derivatives: 6-(2-hydroxy-5-methylbenzoyl)-1-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (6a), 6-(5-fluoro-2-hydroxybenzoyl)-1-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (6b), 6-(5-ethyl-2-hydroxybenzoyl)-1-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (6c) and 6-(2-hydroxy-5-isopropylbenzoyl)-1-methylpyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (6d). The chemical structures of the title compounds were ascertained by spectral techniques including 1H, 13C NMR, UV-visible and FT-IR spectroscopy as well as single-crystal X-ray diffraction analysis. Additionally, density functional theory (DFT) and time-dependent (TD-DFT) computation were adopted to analyze the electronic structures of 6a-d. Compounds 6a-d were computed in the ground state for FT-IR spectroscopic and natural bond orbital (NBO) analysis by DFT/B3LYP with the 6-311+G(d,p) basis set. UV-vis spectroscopic and HOMO and LUMO energy values for 6a-d were determined via TD-DFT/B3LYP with the 6-311+G(d,p) basis set. The optimized geometric parameters, UV-vis findings, and vibrational frequencies indicate good consistency with the experimental data. NBO analysis was conducted to explore the interactions and charge transfer among different orbitals in the title compounds. The HOMO and LUMO band gap (ΔE) values for 6a-d were found to be 3.93, 3.91, 4.10 and 3.91 eV, respectively. Molecular electrostatic potential (MEP) analysis explored the reactivity of the title compounds by predicting their nucleophilic as well as electrophilic sites.