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Synthesis of dihydroquinazolines from 2-aminobenzylamine: N ³ -aryl derivatives with electron-withdrawing groups.

ABSTRACT: The sequential N-functionalization of 2-aminobenzylamine (2-ABA) followed by cyclodehydration allowed for a straightforward and efficient synthesis of 3,4-dihydroquinazolines with N-aryl substituents bearing electron-withdrawing groups. The sequence involves an initial S_NAr displacement, N-acylation and MW-assisted ring closure. Remarkably, the uncatalyzed N-arylation of 2-ABA led to the monosubstitution product using equimolar amounts of both reagents. The individual steps were optimized achieving good to excellent overall yields of the desired heterocycles, avoiding additional protection and deprotection steps. A mechanistic interpretation for the cyclodehydration reaction promoted by trimethylsilyl polyphosphate (PPSE) is also proposed on the basis of literature data and our experimental observations.

SUBMITTER: Gruber N

PROVIDER: S-EPMC6178284 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Synthesis of dihydroquinazolines from 2-aminobenzylamine: N 3 -aryl derivatives with electron-withdrawing groups.

Gruber Nadia N Díaz Jimena E JE Orelli Liliana R LR

Beilstein journal of organic chemistry 20180926

The sequential N-functionalization of 2-aminobenzylamine (2-ABA) followed by cyclodehydration allowed for a straightforward and efficient synthesis of 3,4-dihydroquinazolines with N-aryl substituents bearing electron-withdrawing groups. The sequence involves an initial SNAr displacement, N-acylation and MW-assisted ring closure. Remarkably, the uncatalyzed N-arylation of 2-ABA led to the monosubstitution product using equimolar amounts of both reagents. The ...[more]

PMID: 30344774

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Project description:The central role of Coulombic interactions in enzyme catalysis has inspired multiple approaches to sculpting electrostatic potential fields (EPFs) for controlling chemical reactivity, including ion gradients in water microdroplets, the tips of STMs, and precisely engineered crystals. These are powerful tools because EPFs can affect all reactions, even those whose mechanisms do not involve formal charges. For some time now, supramolecular chemists have become increasingly proficient in using encapsulation to control stoichiometric and catalytic reactions. However, the field has not taken advantage of the broad range of nanocontainers available to systematically explore how EPFs can affect reactions within their inner-spaces. With that idea in mind, previously, we reported on how positively and negatively charged supramolecular capsules can modulate the acidity and reactivity of thiol guests bound within their inner, yoctoliter spaces (Cai, X.; Kataria, R.; Gibb, B. C. J. Am. Chem. Soc. 2020, 142, 8291-8298; Wang, K.; Cai, X.; Yao, W.; Tang, D.; Kataria, R.; Ashbaugh, H. S.; Byers, L. D.; Gibb, B. C. J. Am. Chem. Soc. 2019, 141, 6740-6747). Building on this, we report here on the cyclization of 14-bromotetradecan-1-amine inside these yoctoliter containers. We examine the rate and activation thermodynamics of cyclization (Eyring analysis), both in the absence and presence of exogenous salts whose complementary ion can bind to the outside of the capsule and hence attenuate its EPF. We find the cyclization rates and activation thermodynamics in the two capsules to be similar, but that for either capsule attenuation of the EPF slows the reaction down considerably. We conclude the capsules behave in a manner akin to covalently attached electron donating/withdrawing groups in a substrate, with each capsule enforcing their own deviations from the idealized SN2 mechanism by moving electron density and charge in the activated complex and TS, and that the idealized SN2 mechanism inside the theoretical neutral host is relatively difficult because of the lack of solvation of the TS.

Project description:The structure-property relationship study of a series of cationic Ir(III) complexes in the form of [Ir(C^N)2(dtBubpy)]PF6 [where dtBubpy = 4,4'-di-tert-butyl-2,2'-bipyridine and C^N = cyclometallating ligand bearing an electron-withdrawing group (EWG) at C4 of the phenyl substituent, i.e., -CF3 (1), -OCF3 (2), -SCF3 (3), -SO2CF3 (4)] has been investigated. The physical and optoelectronic properties of the four complexes were comprehensively characterized, including by X-ray diffraction analysis. All the complexes exhibit quasireversible dtBubpy-based reductions from -1.29 to -1.34 V (vs SCE). The oxidation processes are likewise quasireversible (metal + C^N ligand) and are between 1.54 and 1.72 V (vs SCE). The relative oxidation potentials follow a general trend associated with the Hammett parameter (σ) of the EWGs. Surprisingly, complex 4 bearing the strongest EWG does not adhere to the expected Hammett behavior and was found to exhibit red-shifted absorption and emission maxima. Nevertheless, the concept of introducing EWGs was found to be generally useful in blue-shifting the emission maxima of the complexes (λem = 484-545 nm) compared to that of the prototype complex [Ir(ppy)2(dtBubpy)]PF6 (where ppy = 2-phenylpyridinato) (λem = 591 nm). The complexes were found to be bright emitters in solution at room temperature (ΦPL = 45-66%) with microsecond excited-state lifetimes (τe = 1.14-4.28 μs). The photophysical properties along with density functional theory (DFT) calculations suggest that the emission of these complexes originates from mixed contributions from ligand-centered (LC) transitions and mixed metal-to-ligand and ligand-to-ligand charge transfer (LLCT/MLCT) transitions, depending on the EWG. In complexes 1, 3, and 4 the 3LC character is prominent over the mixed 3CT character, while in complex 2, the mixed 3CT character is much more pronounced, as demonstrated by DFT calculations and the observed positive solvatochromism effect. Due to the quasireversible nature of the oxidation and reduction waves, fabrication of light-emitting electrochemical cells (LEECs) using these complexes as emitters was possible with the LEECs showing moderate efficiencies.

Dataset Information

Synthesis of dihydroquinazolines from 2-aminobenzylamine: N ³ -aryl derivatives with electron-withdrawing groups.

Publications

Synthesis of dihydroquinazolines from 2-aminobenzylamine: <i>N</i> <sup>3</sup> <i>-</i>aryl derivatives with electron-withdrawing groups.

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