An Efficient Flow-Photochemical Synthesis of 5H-Furanones Leads to an Understanding of Torquoselectivity in Cyclobutenone Rearrangements

摘要

Thermal rearrangements of cyclobutenones give access to numerous ring systems and have proven especially valuable for the de novo synthesis of quinones, benzoquinones, and related heteroaromatics with dense substitution. A classic example is the rearrangement of arylcyclobutenone 1a→ 3a, where the emergence of a protocol to realize this transformation in near quantitative yield means it achieves many of the ideals for a green-chemical reaction.4' In principle, such criteria could also be met by the related photochemical rearrangement of 1a to 5H-furanone 4a, yet this reaction has lain almost dormant since its introduction by Moore et al. in 1988 because of the low yields attained in each of the published examples (27-51 %, Scheme 2).