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Cycloaddition of Arynes and Cyclic Enol Ethers as a Platform for Access to Stereochemically Defined 1,2‐Disubstituted Benzocyclobutenes
Author(s) -
Yedulla Vijayendar R.,
Pradhan Padmanava,
Yang Lijia,
Lakshman Mahesh K.
Publication year - 2015
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201403250
Subject(s) - cycloaddition , chemistry , aryne , enol , ring (chemistry) , enol ether , ketene , olefin fiber , bond cleavage , computational chemistry , stereochemistry , medicinal chemistry , organic chemistry , catalysis , polymer
Benzocyclobutenes (BCBs) are important entities in a multitude of areas, such as complex organic synthesis, materials and polymer chemistry, and electronics. Whereas reactions between arynes and ketene acetals have been well studied, reactions with cyclic enol ethers are unknown. A cis olefin geometry in cyclic enol ethers makes them well suited for formal [2+2] cycloaddition with arynes than for competing ene reactions, making them effective reactants. Reactions of 2,3‐dihydrofuran, 2,3‐dihydro‐3 H ‐pyran, 5‐butyl‐2,3‐dihydrofuran, ( S )‐2‐[(benzyloxy)methyl]‐2,3‐dihydrofuran, and 1,4‐dioxene with various arynes were successful. An advantage of the use of cyclic enol ethers is that despite the plausible intermediacy of zwitterionic intermediates, the products are limited to a cis ring junction. This can be exploited for potential access to stereochemically defined 1,2‐disubstituted BCBs. As a demonstration, ether ring cleavage with BBr 3 provided trans ‐functionalized BCBs, and displacement with azide then provided cis derivatives. DFT computations have been utilized to understand the structures of three arynes in relation to the cycloadditions and for a predictive evaluation of product ratios in two cases. A comparative evaluation of the HOMO energies of a related series of cyclic olefins has also been performed by DFT computations.