Temperature Dependent Addition Reactions During Photolysis of Aryl Vinyl Sulfides and Aryl Vinyl Ethers. Design and Construction of a Variable Temperature Photoreactor
“…The attention of researchers to these issues is not weakened. Temperature effects upon photolysis of aryl vinyl sulfides in comparison with aryl vinyl ethers are studied [79]. The behavior of aryl vinyl sulfides in reactions of tandem photocyclization and intramolecular addition is investigated [80].…”
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“…The attention of researchers to these issues is not weakened. Temperature effects upon photolysis of aryl vinyl sulfides in comparison with aryl vinyl ethers are studied [79]. The behavior of aryl vinyl sulfides in reactions of tandem photocyclization and intramolecular addition is investigated [80].…”
recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
“…The photoinitiated intramolecular ylide−alkene cycloaddition reaction provides a method for construction of up to three rings and six chiral centers in a single experimental operation from relatively simple starting materials. − This one-step process involves photocyclization of aryl vinyl ether, aryl vinyl sulfide, or aryl vinyl amine systems 1 to generate ylide intermediates 2 that can undergo addition to a pendant alkene to provide 3 or 4 . The current study details the use of laser flash photolysis techniques to characterize these ylides and to probe the reactivities of excited state intermediates.…”
Aryl vinyl thioethers 5a and 9a and aryl vinyl ethers 5b and 9b form ylide intermediates following laser irradiation at 308 nm. In benzene, the ylides possess long-lived absorption bands in the 600-800 nm region with a second weaker band at approximately 460 nm. In methanol, a known quencher of zwitterionic species, the lifetimes are reduced significantly. The decay kinetics measured within the long wavelength absorption envelope vary with wavelength, indicating the presence of more than one ylide species. Formation of the ylides occurs via a naphthalene-like triplet state in the case of aryl vinyl ethers, while for the thioethers the multiplicity of the ylide precursor could be either singlet or triplet. Product formation in benzene for 5a and 5b involves ring closure of the ylide to produce dihydrothiophene and dihydrofuran products, respectively. For short periods of irradiation (either lamps or laser) a mixture of cis- and trans-fused products is observed, while for prolonged irradiation only the cis-fused compound is detected, suggesting a photoenolization mechanism for conversion of trans to cis. In addition to products derived from ring closure, 9a provides intramolecular addition product 12. Conversely, the ylide derived from 9b gives rise to the [3 + 2] cycloaddition product 13.
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