petasis reagent: (cp)2Ti(cyclopropane)2

Cp2Ti(cyclopropane)2 is used to convert a ketone into cyclopropane-alkene.

1. making of this reagent.
Li,Et2O, 0 C, add cyclopropanebromide dropwise into the solution.( very exothermic).
low sodium Li can be used. 1hr at rt, then the solution was transfered into a Et2O solution of Cp2TiCl2 at 0 C. stirred for 90 min, quenched by ice water. washed, dried over MgSO4, concentrated. red solid. dissolved in toluene (0.5-0.8 mol/l). The solubility is poor in toluene, so can't make more concentrated). stored in freezer. Solid will be precipitated from the solution in the freezer, so warm it up before use.

2. reaction.
usually, 3-5 eq. of the reagent, toluene as solvent, 50-55C. overnight.
the product is very easy to isomerize to other alkene-isomers. So during the reaction, some NaHCO3 solid can bee added to prevent isomerization.