Cyclopentadienones Oxapentafulvene

Tetracyclone 17 with moderate reactivity as a diene has been well known as a versatile synthetic building block for perphenyl-substituted aromatic compounds. 

The chemistry has a long history [8], Recent developments in carbon-rich compounds have renewed the interest in CPDNs, because HBC 22 [10, 11] as a representative carbon-rich compound, can be prepared from 17 and related compounds. Moreover, in the past two decades, CPDN and its benzannulated derivatives (indenone 18 and fluorenone 19) have received much attention as synthetic targets for five-membered ring-construction reactions using transition-metal catalysts. A variety of new synthetic methods and applications have been published to date. This section mainly describes the chemistry of CPDNs from the viewpoints of synthesis and reactivity. 

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