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Palladium-catalyzed [2 + 2 + 2] cocyclotrimerization of benzynes with bicyclic alkenes: an efficient route to anellated 9,10-dihydrophenanthrene derivatives and polyaromatic compounds.
MedLine Citation:
PMID:  15549819     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Abstract/OtherAbstract:
An efficient method for the cocyclotrimerization of bicyclic alkenes and benzynes catalyzed by palladium phosphine complexes to give the corresponding norbornane anellated 9,10-dihydrophenanthrene derivatives is described. Bicyclic alkenes 1a-i undergo [2 + 2 + 2] cocyclotrimerization with benzynes generated from precursors 2a-d [2-(trimethylsilyl)phenyl triflate (2a), 4,5-dimethyl-2-(trimethylsilyl)phenyl triflate (2b), 6-(trimethylsilyl)-2,3-dihydro-1H-5-indenyl triflate (2c), 4-methyl-2-(trimethylsilyl)phenyl triflate (2d)] in the presence of PdCl(2)(PPh(3))(2) in acetonitrile at ambient temperature to yield anellated 9,10-dihydrophenanthrene products 3a-r in moderate to excellent yields. The [2 + 2 + 2] cocyclotrimerization products from oxa- and azabicyclic alkenes can be applied for the synthesis of polyaromatics, substituted benzo[b]triphenylenes (8a-f), via a simple Lewis acid mediated deoxyaromatization in good yields. In addition the [2 + 2 + 2] products undergo retro Diels-Alder reaction readily, providing a new method for the synthesis of substituted phenanthrenes and for generating isobenzofurans. A plausible mechanism is proposed to account for the catalytic [2 + 2 + 2] cycloaddition reaction.
Authors:
Thiruvellore Thatai Jayanth; Masilamani Jeganmohan; Chien-Hong Cheng
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  The Journal of organic chemistry     Volume:  69     ISSN:  0022-3263     ISO Abbreviation:  J. Org. Chem.     Publication Date:  2004 Nov 
Date Detail:
Created Date:  2004-11-19     Completed Date:  2005-01-13     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  2985193R     Medline TA:  J Org Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  8445-50     Citation Subset:  -    
Affiliation:
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30013, ROC.
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