The diastereomers of ketones 2 and 3 are shown to exhibit distinct photochemical reactivities due to conformational preferences; while the anti isomers of 2 and 3 undergo efficient Yang cyclization in 75-90% yields with a remarkable diastereoselectivity (> 90%), the syn isomers predominantly undergo Norrish Type II elimination. The differences in the product profiles of the diastereomers are consistent with a mechanistic picture involving the formation of precursor diastereomeric triplet 1,4-biradicals in which the substituents at alpha and beta-positions stabilize the cisoid (cyclization) or transoid (elimination) geometry. The fact that such a diastereomeric relationship does indeed ensue at the triplet-excited-state itself is demonstrated via the nanosecond laser-flash photolysis of model ketones 1. The diastereomeric discrimination in the product profiles observed for ketones 2 and 3 as well as in the triplet lifetimes observed for ketones 1 can both be mechanistically traced back to different conformational preferences of the ground-state diastereomeric ketones and the intermediary 1,4-biradicals. Additionally, it emerges from the present study that the syn and anti diastereomers of ketones 2 and 3 represent two extremes of a broad range of widely examined butyrophenones, which lead to varying degrees of Yang photocyclization depending on the alkyl substitution pattern.
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http://dx.doi.org/10.1021/ja0523643 | DOI Listing |
J Org Chem
January 2025
Department of Pharmacy, College of Pharmacy, Kyung Hee University, 26 Kyungheedae-ro, Dongdaemun-gu, Seoul 02447, Republic of Korea.
In this study, we developed palladium-catalyzed dehydrogenative cyclization to transform 1-(2-aminoaryl)-3-arylpropan-1-ones into 2-arylquinolin-4(1)-ones, also known as aza-flavones which are the bioisosteres of flavones, in an atom-economic manner. This method exhibited excellent chemical compatibility with a broad substrate scope, accommodating up to 25 derivatives. Additionally, kinetic studies were performed to elucidate the reaction mechanism.
View Article and Find Full Text PDFJ Org Chem
January 2025
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000 Gansu, P. R. China.
The asymmetric total syntheses of sarglamides A, C, and E in concise and protecting group free fashion is disclosed. Key steps involve an -selective Diels-Alder reaction to construct the bicyclo[2.2.
View Article and Find Full Text PDFOrg Lett
January 2025
Key Laboratory of Combinatorial Biosynthesis and Drug Discovery, Ministry of Education and School of Pharmaceutical Sciences, Wuhan University, Wuhan 430071, China.
The cyclic structure of non-ribosomal peptides (NRPs) is critical for enhancing their stability and bioactivity, which highlights the importance of exploring NRP cyclization enzymes for natural product discovery. Thioesterases (TEs) are crucial enzymes that catalyze the formation of various lactams, including macrolactams, β-lactams, and γ-lactams; however, their potential to produce other lactam types remains largely unexplored. In this study, we identified spinactin A () and novel derivatives, spinactin B-E (-), from NRRL 18395 and characterized the biosynthetic enzymes involved, particularly a unique TE SncF, responsible for δ-lactam formation.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
January 2025
Chinese Academy of Sciences Fujian Institute of Research on the Structure of Matter, State Key Laboratory of Structural Chemistry, 350108, Fuzhou, CHINA.
Here, we report the facile synthesis of imidazole-linked porous organic cages (IPOCs) via an in-situ cyclization reaction protocol. Specifically, three IPOCs with [2+4] lantern-like structures and one with a [3+6] triangular prism structure were successfully prepared through condensation reactions between tetraformyl-functionalized calix[4]arene and bis(o-phenylenediamine) monomers in a single pot. Notably, these IPOCs exhibit high porosity, with Brunauer-Emmett-Teller (BET) specific surface areas reaching up to 1162 m2 g-1.
View Article and Find Full Text PDFOrg Biomol Chem
January 2025
School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China.
A visible-light-induced deoxygenative alkylation/cyclization of acrylamides with alcohols activated by CS has been developed by using xanthate salts as alkyl radical precursors in the presence of tricyclohexylphosphine. It proceeds through a tandem radical addition/cyclization process, and this protocol provides a reliable and practical approach to building the skeleton of 3,3-disubstituted oxindoles in moderate to good yields. Notable features of this reaction include readily available starting reagents, broad substrate scope and mild reaction conditions.
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