Ring-closing metathesis in flavonoid synthesis, part 2: neoflav-3-enes.

A series of neoflav-3-enes with a variety of natural substitution patterns was prepared from 1-(allyloxy)-2-[1-(aryl)vinyl]benzenes by Grubbs second generation (GII) catalyst-promoted ring-closing metathesis (67 - 99% yield). The 1-(allyloxy)-2-[1-(phenyl)vinyl]benzene substrates were accessible in yields of 52 - 94% from the corresponding 2-(allyloxy)acetophenones via a Grignard reaction and Lewis acid-promoted dehydration, either in a one pot process in the presence of Al(OTf)3 or in consecutive steps with CuSO4 as dehydrating agent. [ABSTRACT FROM AUTHOR]