Highly Efficient Synthesis of Di-Substituted Allenes Via Copper-Catalyzed SN2′- Substitution Reaction of Organotitanium Reagents with Propargyl Bromides

A simple and mild catalytic SN2 '-type displacement of propargyl halides with organotitanium reagents is reported. The SN2 '-type displacement of propargyl bromides with organotitanium reagents mediated by CuI (2 mol %)/MePPh2(4 mol%) in dichloro methane afforded multi-substituted allenes in good yields (up to 95 %) at 40 degrees C for 5 h. The aryls bearing electron-donating or electron-withdrawing groups in aryltitanium reagents gave multisubstituted allenes in good yields. In addition, the di-substituted allenes bearing a naphthyl group was obtained in 54-99 % selectivities with isolated yields of 43-83 %. The process was simple and easily performed, and it provides an efficient method for the synthesis of di-substituted allene derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed.