Annelation of Aromatic Compounds via 1-Aminoisobenzofurans
Chen, Chin-Wen
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https://hdl.handle.net/2142/70307
Description
Title
Annelation of Aromatic Compounds via 1-Aminoisobenzofurans
Author(s)
Chen, Chin-Wen
Issue Date
1985
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Abstract
The annelation of aromatic amides via 1-aminoisobenzofurans as transient reaction intermediates are reported. Three different methodologies are developed for generation of the aminoisobenzofurans in the presence of dienophiles. These involve: (1) the decomposition of an N,N-diisopropyl-o-((alpha)-diazomethyl) aromatic amide in the presence of a catalyst, (2) cesium fluoride induced (alpha)-elimination of an N,N-diisopropyl-o-((alpha),(alpha)'-bromotrimethylsilylmethyl)benzamide and (3) 2,2',6,6'-tetramethyl-piperidine induced 1,4-elimination of the cyclic imidate salt. In all cases, precursors can be synthesized by o-lithiation methodology.
The intermediate 1-aminoisobenzofurans are suggested to undergo Diels-Alder reactions with dienophiles from the endo side to give an oxabicyclic compound. This compound is unstable under the reaction condition and undergoes ring-opening and hydrogen migration to give an N,N-dialkyl-2-carboxy-4-hydroxy-3,4-dihydro benzene ring annelated onto the original system. The reactions of the aminoisobenzofuran and dienophiles are regio- and stereoselective consistent with Frontier Molecular Orbital theory. The aromatic systems annelated by this approach included benzene, naphthalene and pyridine.
A comparison between ortho and benzylic metalation of secondary and tertiary benzamide has been made. When there is intramolecular competition between a primary or secondary benzylic hydrogen adjacent to the amide and an ortho hydrogen, the lithiation goes exclusively to the benzylic site. On the other hand, the metalation goes exclusively to the ortho site if the adjacent benzylic hydrogen is tertiary. A steric hindrance rationalization is provided.
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