Rearrangement of 4-Alkynylcyclobutenones. A New Synthesis of 1,4-Benzoquinones

Article abstract of DOI:10.1021/ja00185a030

A new convergent synthesis of 1,4-benzoquinones from 4-alkynyl-4-alkoxy(or hydroxy or trimethylsilyloxy)cyclobutenones is described.The required cyclobutenones are prepared from squaric acid and converted to the quinones upon mild thermolysis.The reaction proceeds via electrocyclic ring opening of the required cyclobutenones to (2-alkynylethenyl)ketenes, which then ring close to unique diradical intermediates.These then give the quinone products.The scope and mechanism of this unusual rearrangement are discussed.