Unusual cerium(III) chloride-promoted reactions of alkenyl grignard reagents or alkenyl-lithiums with 1,3-diphenyl-2-propanone: Formation and trapping of diorganometallic species

Treatment of vinylmagnesium chloride with anhydrous cerium(III) chloride in tetrahydrofuran at −20°C, followed by reaction with 1,3‐diphenyl‐2‐propanone, afforded (Z)‐2,7‐dibenzyl 1,8‐diphenyl‐4‐octene‐2,7‐diol and (Z)‐2,7‐dibenzyl‐1,8‐diphenyl‐4,6‐octadien‐2‐ol in 19% and 9% yield, respectively. Isopropenyl‐magnesium bromide underwent trimerization on treatment with cerium chloride at 20°C, and the subsequent reaction with the same ketone provided (Z,Z)‐2,9‐dibenzyl‐4,5,7‐trimethyl‐1,10‐diphenyl‐4,6‐decadiene‐2, 9‐diol in 22% yield. Under similar conditions, the reaction of 2‐methyl‐1‐propenylmagnesium bromide provided (Z)‐2,6‐dibenzyl‐4‐methyl‐1,7‐diphenyl‐3,5‐heptadien‐2‐ol in 7% yield. Vinyl‐lithium and isopropenyl‐lithium were also subjected to dimerization by the action of cerium chloride, and the generated diorganometallic species were trapped by 1,3‐diphenyl‐2‐propanone.