Catalyst-Free Regioselective Nazarov Cyclization of Aryl Allenyl Ketones

The catalyst-free Nazarov cyclization of aryl allenyl ketones under thermal condition is developed. Various densely functionalized 2,3-dihydroindanones or indenones are readily produced in moderate to excellent yields. Significantly, this procedure features high functional group tolerance and exclusive regioselectivity. The resulting substituted 2,3-dihydroindanones can be conveniently converted into valuable conjugated benzofulvene building blocks.