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Published on: November 11, 2008
Cycloaddition reactions of dihapto-coordinated furans
Lee A Friedman1, Michal Sabat, W Dean Harman
1Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901, USA.
Rhenium complexes with furan ligands undergo cycloaddition reactions with TCNE and DMAD, forming novel oxabicycloheptene and oxabicyclo[3.2.0]heptadiene structures. These reactions yield valuable intermediates for oxepin synthesis.
Area of Science:
- Organometallic Chemistry
- Organic Synthesis
- Coordination Chemistry
Background:
- Rhenium complexes featuring hydridotris(pyrazolyl)borate (Tp) ligands are versatile in organometallic transformations.
- Furan and its derivatives serve as key substrates in cycloaddition reactions.
Purpose of the Study:
- To investigate the cycloaddition reactivity of [TpRe(CO)(L)(eta(2)-furan)] complexes with various electrophiles.
- To explore the synthesis of novel oxabicycloheptene and oxabicyclo[3.2.0]heptadiene derivatives.
- To evaluate the potential of these products as precursors for oxepin synthesis.
Main Methods:
- Synthesis of rhenium-furan complexes with varying ancillary ligands (L).
- Dipolar cycloaddition reactions with tetracyanoethylene (TCNE) and dimethyl acetylenedicarboxylate (DMAD).
- Structural characterization of products, including X-ray crystallography.
- Oxidative decomplexation and thermal conversion to target molecules.
Main Results:
- Dipolar cycloadditions with TCNE yielded 7-oxabicycloheptene complexes.
- Reactions with DMAD produced carbonyl ylide cycloaddition products and [2+2] cycloaddition products with the furan double bond.
- Stereoselective formation of [2+2] adducts was observed with substituted furans.
- Oxidative decomplexation and thermal rearrangement afforded oxepins in good yield.
Conclusions:
- Rhenium-furan complexes effectively participate in cycloaddition reactions with electron-deficient alkenes and alkynes.
- The reaction pathway (dipolar vs. [2+2] cycloaddition) is influenced by the electrophile and the furan substitution pattern.
- The synthesized oxabicycloheptadiene derivatives are valuable precursors for oxepin synthesis.
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