Synthesis of Hindered 1-Arylnaphthalene Derivatives via Ring Expansion of Benzocyclobutenones
摘要:
[GRAPHICS]Various 1-aryinaphthalenes, including highly substituted derivatives, are accessible via a simple two-step process. Treatment of alkenylbenzocyclobutenones with aryllithium provides two-carbon expanded dihydronaphthalenes, which are readily dehydrated by MsCl-Et3N or PPTS in MeOH.
The first total synthesis and absolute structure assignment of PD-116740 (2) was achieved by exploiting two key steps: 1) a thermal ring expansion of a benzocyclobutene derivative, and 2) pinacol cyclization of biaryl dialdehyde.
Two optional routes to β-phenylnaphthalene structure are developed by introducing α- and β-styryl groups onto different positions in the benzocyclobutene ring followed by ring enlargement.
Dienylbenzocyclobutenes, readily available by the cycloaddition of benzyne and ketene silyl actetal followed by addition of dienyllithium, underwent thermal four-carbon ring expansion to give benzocyclooctenone derivatives in high yields. In some cases, acid treatment of the thermal product gave tricyclic ketones via transannular bondformation.