Hitherto unknown diamino-substituted bisketenes with both free (14) and tethered (16) amino substituents have been generated by using laser flash photolysis for ring opening of the corresponding cyclobutenediones. The time-resolved kinetics of ring closure of the amino bisketenes back to the cyclobutenediones were measured by IR or UV spectroscopy, and give first-order rate constants which vary by a factor of 7.5x10(4), and the bis(Me2N) bisketene 14 is the most reactive in ring closure that has been reported. Rate constants for ring closure of these and previously observed bisketenes vary by a factor of 10(13). The dialkylamino bisketenes 16 (R=Me, n-Bu) with tethered substituents and restricted geometries are less reactive than the bis(Me2N) bisketene 14 by factors of 1700 and 540, respectively. Computational results obtained with DFT methods suggest angle strain in the tethered cyclobutenediones 15 inhibits facile cyclization of bisketenes 16.
Download full-text PDF |
Source |
|---|---|
| http://dx.doi.org/10.1021/jo062090h | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Synthesis of 2,7-Dihydrooxepine-spirodithiophene Derivatives via an Intramolecular Ring Closure Reaction.
ACS Omega
December 2024
Department of Chemistry and Materials Science, Xi'an Jiaotong-Liverpool University, Suzhou, Jiangsu 215000, P. R. China.
Spiro architectures with π-conjugation have improved thermal stability and stronger photosensitivity, making them potentially useful for organic optoelectronic devices. Our recent work has demonstrated the synthetic chemistry of a novel thiophene oligomer combining 2,7-dihydrooxepine and dispiro structure and derived it into A-D-A-type compounds. The optical spectroscopy and electrochemical characteristics were investigated.
View Article and Find Full Text PDFOn the Role of Hydrogen Migrations in the Taxadiene System.
Angew Chem Int Ed Engl
January 2025
University of Bonn: Rheinische Friedrich-Wilhelms-Universitat Bonn, Kekulé Institute for Organic Chemistry and Biochemistry, Gerhard-Domagk-Straße 1, 53121, Bonn, GERMANY.
Taxa-4,11-diene is made by the taxa-4,11-diene synthase (TxS) from Taxus brevifolia. The unique reactivity of the taxane system is characterised by long distance hydrogen migrations in the biosynthesis. This study demonstrates that selective long range hydrogen migrations also play a role in the high energy process of the EI-MS fragmentation of taxa-4,11-diene.
View Article and Find Full Text PDFSimple reaction time to visual and auditory stimulation in glaucoma.
Eur J Ophthalmol
January 2025
University of Lille, Inserm, CHU Lille, UMR-S 1172 - Lille Neurosciences and Cognition, CNRS, 59000 Lille, France.
Background/objectives: Glaucoma can impact the ability to perform daily life activities such as driving. In such tasks, reaction time is critical to detect hazards. Understanding the modalities that affect response times is thus essential for clinical care.
View Article and Find Full Text PDFMCM2-7 ring closure involves the Mcm5 C-terminus and triggers Mcm4 ATP hydrolysis.
Nat Commun
January 2025
DNA Replication Group, Institute of Clinical Science, Imperial College London, London, UK.
The eukaryotic helicase MCM2-7, is loaded by ORC, Cdc6 and Cdt1 as a double-hexamer onto replication origins. The insertion of DNA into the helicase leads to partial MCM2-7 ring closure, while ATP hydrolysis is essential for consecutive steps in pre-replicative complex (pre-RC) assembly. Currently it is unknown how MCM2-7 ring closure and ATP-hydrolysis are controlled.
View Article and Find Full Text PDFInterrogation of Enantioselectivity in the Photomediated Ring Contractions of Saturated Heterocycles.
J Am Chem Soc
January 2025
Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, United States.
We recently reported a chiral phosphoric acid (CPA) catalyzed enantioselective photomediated ring contraction of piperidines and other saturated heterocycles. By extruding a single heteroatom from a ring, this transformation builds desirable C(sp)-C(sp) bonds in the ring contracted products; however, the origins of enantioselectivity remain poorly understood. In this work, enantioselectivity of the ring contraction has been explored across an expanded structurally diverse substrate scope, revealing a wide range of enantioselectivities (0-99%) using two distinct CPA catalysts.
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!