Preparation of Tri- and Tetrasubstituted Allenes via Regioselective Lateral Metalation of Benzylic (Trimethylsilyl)alkynes Using TMPZnCl·LiCl
journal contributionposted on 20.02.2015 by Pauline Quinio, Cyril François, Ana Escribano Cuesta, Andreas K. Steib, Florian Achrainer, Hendrik Zipse, Konstantin Karaghiosoff, Paul Knochel
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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.