Photoinduced electron transfer / Cyclization f Ring opening / Enones Photolysis of the unsaturated enones 1 yields [2 + 21 cycloaddition products 2 and 3 with varying regioselectivity. Under electron-transfer conditions (PET) spirocyclic products 4 are formed. The straight [2 + 2 1 cycloaddition products 2b.c.f are converted to the spirocyclic products 4b,c,f under the same reaction conditions. The cyclobutane 5 and the cyclopropane 11 also undergo this new reductive ring opening reaction, l b 0 2 4b 50 % l c 0 3 4c 53 % If CH2 2 4f 40% [2+2] Cycloadduct Yield [b] Enone X n la 0 1 l b 0 2 l c 0 3 Id 0 4 l e CH2 1 lg[gl CH2 3 If CH2 2 3a (crossed) 46 % cc] 2c (straight) 65 % 2d (straight) 25 % mixture 2f (straight) 90 % [fl mixture 60 %, 15 %, 15 % (dl 2b (straight) 82 % 55 %, 22 %, 20 % [d.e]
A 0.5 mM solution of the starting material in CH3CN containing triethylamine (0.5 mM) and n-decane (internal standard) sealed in Duran glass tubes under argon was irradiated in a Rayonet reactor fitted with a merry-go-round inset. -Ibl Yields were determined by GLC with an internal standard.