Ring Expansion of 4-Alkynylcyclobutenones. Synthesis of Enantiomerically Pure Pyranoquinones from 4-(4-Oxo-1,6-enynyl)-4-hydroxycyclobutenones and 4-(4-Oxo-1,6-dialkynyl)-4-hydroxycyclobutenones

Article abstract of DOI:10.1021/jo00125a037

Thermolysis of 4-(4-oxo-1,6-enynyl)-4-hydroxycyclobutenones 23 in refluxing toluene provides an enantiospecific synthesis of pyranoquinones 27.The 4-methoxy analog 32 was shown to give a quinone methide 35 and ultimately the trimer 36.