论文 Cyclobutenone Ethylenedithioacetals and their Ready Electrocyclic Ring opening a Synthesi and 随后开环 Cyclobutenone Ethylen d Regenhardt, Wilko ithioacetals Ernst Schaumann,* a Harold W. Moore* ba Institut fur Organische Chemie, Technische Universitat Clausthal, Leibnizstrase 6, 38678 Clausthal- Zellerfeld,德国传真 +49(5323)722858;电子邮件:ernst.schaumann@tu-clausthal.de b 加州大学欧文分校化学系,欧文,CA 92697–2025,美国 传真
A potentially general regiospecific synthesis of substituted quinones from dimethyl squarate
摘要:
A potentially general regiospecific synthesis of benzo- and naphthoquinones is described. This method starts with dimethyl squarate (1), which is converted to the cyclobutenone ketal 3 upon sequential treatment with an organolithium reagent and then BF3 etherate or TFAA in THF/methanol. Treatment of these with a second lithium reagent followed by hydrolysis gives the cyclobutenones 5. Addition of an alkynyl-, alkenyl- or aryllithium agent to 5 followed by hydrolysis of the ketal linkage gives the corresponding 4-alkynyl- 4-alkenyl- or 4-aryl-4-hydroxycyclobutenones 7-9, and these readily rearrange to the respective quinones or hydroquinones upon thermolysis in refluxing benzene. In a similar fashion, 15 was employed as a reagent to prepare mono- and disubstituted hydroquinones and quinones.