Preparation of tri- and tetrasubstituted allenes via regioselective lateral metalation of benzylic (trimethylsilyl)alkynes using TMPZnCl·LiCl.

The zincation of various 1-(trimethylsilyl)-3-aryl-1-propynes with TMPZnCl·LiCl followed by a Pd-catalyzed coupling with aryl halides provides arylated allenes in 52-92% yield. Subsequent metalation with TMPZnCl·LiCl and cross-coupling with a second different aryl halide provides regioselectively tetrasubstituted allenes in 42-70% yield. This sequence can be performed in a one-pot procedure. DFT calculations and NMR studies support the formation of allenylzinc and propargyllithium intermediates starting from 1-(trimethylsilyl)-3-phenyl-1-propyne.