Photodecarbonylation of 2,5,5-Trimethyl-2-(1-propynyl)cyclopentanone. 1,5- vs. 1,4-ring Closure of a Propargyl-Alkyl Biradical

Propargyl-alkyl biradical 12 generated by photodecarbonylation of title ketone 3 undergoes ring closure to cyclobutane 7 and to vinyl carbene 13 , this latter intermediate rearranging to the 5-ethylidenecyclopentenes 8a and 8b .