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Preparation of Tri- and Tetrasubstituted Allenes via Regioselective Lateral Metalation of Benzylic (Trimethylsilyl)alkynes Using TMPZnCl·LiCl

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journal contribution
posted on 20.02.2015, 00:00 by Pauline Quinio, Cyril François, Ana Escribano Cuesta, Andreas K. Steib, Florian Achrainer, Hendrik Zipse, Konstantin Karaghiosoff, Paul Knochel
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.