Arene-catalysed lithiation of phenyl- and 1,1-diphenylcyclopropane: synthetic applications

The reaction of phenylcyclopropane (1) with an excess of lithium and a catalytic amount of DTBB (2.5% molar) in THF at room temperature, followed by treatment with an electrophile [Me₃SiCl, PhMe₂SiCl, t-BuCHO, PhCHO, Me₂CO, Et₂CO, (CH₂)₅CO, adamantan-2-one, i-Pr₂CO, di(cyclopropyl)ketone] and final hydrolysis with water leads to allylic products 10 or 11 depending on the structure of the electrophile: whereas for chlorosilanes or crowded ketones γ-products 11 are isolated, for aldehydes and non-congested ketones α-products 10 are formed. The application of the same protocol to 1,1-diphenylcyclopropane (7) leads to a mixture of products 13-15 resulting from the introduction of one or two electrophilic fragments to the open-chain mono- or dilithiated intermediate: also in this case the regiochemistry of the reaction is governed by steric reasons.