Synthetic methods enabling late-stage modification of heterocycles hold tremendous importance in the pharmaceutical and agrochemical industry and drug discovery. Accordingly, efficient, functional group tolerant and selective late-stage alkylation of valuable molecular entities is of enormous significance and well-acknowledged in medicinal chemistry. Radical alkylation of heteroarenes employing carboxylic acids as the alkyl radical precursor represents one of the most direct ways of CÀ H functionalizations of heterocycles. Recently, the field has undergone a revolutionary development especially with regard to the generation of alkyl radicals under much milder conditions. In this regard N-(acyloxy)phthalimides (NHPI esters) have emerged as a suitable precursor of a diverse set of alkyl radicals allowing formal CÀ H alkylation of not only N-heteroarenes but a diverse set of non-aromatic heterocycles under visible light photocatalysis or electrochemical conditions. This review delineates all these discoveries and provides readers a comprehensive overview of this rapidly expanding field.
A chemo- and regioselective intermolecular sp C-H and sp C-H coupling reaction for C-C bond formation is described to access unsymmetrical diaryl acetamides under TM-free conditions from sec- and tert-arylacetamides and nitroarenes using tert-butoxide base in DMSO at room temperature. The coupling partners with sensitive functionalities such as chloro, bromo, hydroxy, and cyano were also amenable to the developed reaction. Synthesized α-(2/4-nitroaryl) phenylacetamides have been transformed into biologically important benzofurans, xanthenes, diaryl indoles, and unsymmetrical benzophenones by novel routes without applying a transition metal. Overall, an economical, yet efficient, strategy has been devised to access unsymmetrical diarylacetamides with the possibility of their further elaboration into a variety of biologically important heterocycles. Mechanistic understanding suggests that the reaction proceeds by a nucleophilic addition of a phenylacetamide carbanion, which is generated in the presence of tert-butoxide base, to the para or ortho (if para is substituted) position of nitrobenzene. The formed α-(4-nitrocyclohexa-2,4-dien-1-yl) phenylacetamide anion intermediate oxidized by a basic solution of DMSO or atmospheric oxygen led to the desired sp C-H and sp C-H coupled α-(2/4-nitroaryl) phenylacetamides.
Substituted 2‐arylquinoxalines have been synthesized by an unprecedented CuI‐catalyzed ring‐opening/cyclization reaction followed by detosylation/aromatization of activated aziridines with 2‐bromoanilines. The transformation efficiently accommodates a wide range of aziridines and 2‐bromoanilines to afford the desired quinoxaline frameworks in excellent yields (up to 86 %) as single regioisomers. The methodology has also been conveniently applied to the synthesis of tyrphostin AG 1296, a PDGF‐receptor tyrosine kinase inhibitor.
The incessantly increasing demand for highly dense storage medium in this era of big-data has led to the development of 3D NAND Flash memories. 3D NAND Flash based SSDs have revolutionized edge storage and become an integral part of the data warehouses and the cloud storage systems. The conventional 3D NAND flash memory with greater than hundred stacked word-line (WL) layers suffer from channel tapering and non-uniformity in the threshold voltage of cells in different WL layers which necessitates the use of different programming voltages for different WL layers and a complex error-correction circuitry. A non-uniform vertical (Gaussian) channel doping profile alleviates the threshold voltage non-uniformity and leads to a significant reduction in the complexity of the error-correction circuitry and a simple (uniform) programming scheme for all WLs. Although behavioral models have been proposed to utilize 3D NAND flash memory for circuit and system-level applications, an analytical model is important to understand the intricate details of the device physics and propose design guidelines for efficient cell design. To this end, in this paper, for the first time, we have proposed an analytical model for the characteristic length, surface potential and inner potential of the Macaroni-body 3D NAND flash cell with vertical Gaussian doping profile. A strong agreement between the analytical model and the TCAD simulations for different gate lengths (down to 25 nm), inner and outer radius, channel and oxide thickness of the 3D NAND flash cell validates the efficacy of the developed model.INDEX TERMS 3D NAND flash memory, Macaroni body, Vertical Gaussian doping, Analytical model.
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