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Nickel-catalyzed
Huang1, Rayabarapu, Li
1Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan. chcheng@mx.nthu.edu.tw
Chemistry (Weinheim an Der Bergstrasse, Germany)
|November 10, 2000
Summary
Oxabenzonorbornadienes and azabenzonorbornadiene undergo catalytic [2+2] cycloaddition with alkynes. These cyclobutene derivatives then expand their rings to form eight-membered dienes, with one derivative yielding a cyclooctatetraene.
Area of Science:
- Organic Chemistry
- Cycloaddition Reactions
- Heterocyclic Chemistry
Background:
- Benzonorbornadiene derivatives are versatile building blocks in organic synthesis.
- Catalytic cycloaddition reactions offer efficient routes to complex cyclic structures.
- Ring expansion reactions provide access to larger ring systems.
Purpose of the Study:
- To investigate the [2+2] cycloaddition of oxa- and azabenzonorbornadienes with various alkynes.
- To explore the ring expansion of the resulting cyclobutene derivatives.
- To synthesize novel eight-membered carbocyclic dienes and cyclooctatetraenes.
Main Methods:
- Catalytic [2+2] cycloaddition using [Ni(PPh3)2Cl2], PPh3, and Zn powder.
- Flash vacuum pyrolysis for high-temperature ring expansion.
- Deoxygenation of cyclobutene derivatives using TiCl4 and Zn.
Main Results:
- Successful synthesis of exo-cyclobutene derivatives (4a-e, 5a-e, 6) in good yields.
- Isolation of cycloadduct 4f in 83% yield using acetonitrile as solvent.
- Generation of eight-membered dienes (13a-d, 15) in 70-96% yields via pyrolysis.
- Synthesis of cyclooctatetraene derivative 16 in 89% yield.
Conclusions:
- The study demonstrates a novel synthetic pathway to eight-membered carbocyclic dienes and cyclooctatetraenes.
- Catalytic [2+2] cycloaddition followed by thermal ring expansion is an effective strategy.
- The reaction conditions can be tuned for efficient cycloaddition, even with less reactive alkynes.