Metal-Mediated [6 + 3] Cycloaddition Reactions of Fulvenes. A Novel Approach to Indan Systems
摘要:
The [6 + 3] cycloaddition of 2-oxyallyl cations to the electron rich fulvene ketene acetal provides an efficient route to the indan skeleton. The structures of these indan adducts were assigned by extensive 2D NMR experiments. Direct hydrolysis of these ketal adducts affords the corresponding diketones or indens. Reaction of the fulvene ketene thioacetal as well as the tandem [6 + 3]-[4 + 3] cycloadditions were also studied. A mechanism is proposed which may account for the origin of stereo-and regioselectivity in this cycloaddition.
Pentafulvenes with alkyl and/or aryl substituents at the exocyclic position are formed rapidly in high yields through reaction of crystalline sodium cyclopentadienide directly with the appropriate ketones.
Facile synthesis of azulenols: [6 + 4] cycloadditions of fulveneketene acetal
作者:Bor-Cherng Hong、Si-Shoung Sun
DOI:10.1039/cc9960000937
日期:——
In contrast to the Diels–Alder reaction of fulvenes and pyrones, fulveneketene acetal reacts with α-pyrone to give the [6 + 4] cycloaddition adduct, an efficient and novel route to the azulenols.
A novel [6+3] cycloaddition of 2-oxyallyl cation and fulveneketene acetal is described which provides a conceptually novel methodology for the synthesis of indan ring systems.
A microwave-enhanced [6 + 4]-cycloaddition reaction between 6-aminofulvene and pyrones followed by CO2 extrusion provides azulene-indoles which display interesting antineoplastic activity. (C) 2001 Elsevier Science Ltd. All rights reserved.