Despite the ubiquity of reports describing titanium (Ti)-catalyzed [2 + 2 + 2] cyclotrimerization of alkynes, the incorporation of arynes into this potent manifold has never been reported. The in situ generation of arynes often requires fluoride, which instead will react with the highly fluorophilic Ti center, suppressing productive catalysis. Herein, we describe the use of group 4 diarylmetallocenes, CpR 2MAr2 (CpR = C5H5, C5Me5; M = Ti, Zr), as aryne precursors for the Ti-catalyzed synthesis of substituted naphthalenes via coupling with 2 equiv of an alkyne. Fair-to-good yields of the desired naphthalene products could be obtained with 1% catalyst loadings, which is roughly an order of magnitude lower than similar reactions catalyzed by palladium or nickel. Additionally, naphthalenes find broad applications in the electronics, photovoltaics, and pharmaceutical industries, urging the discovery of more economic syntheses. These results indicate that aryne transfer from a CpR 2M(?2-aryne) complex to another metal is a viable route for the introduction of aryne fragments into organometallic catalytic processes.
Bibliographical noteFunding Information:
Financial support was provided by the National Institutes of Health (Grant 1R35GM119457) and the Alfred P. Sloan Foundation (I.A.T. is a 2017 Sloan Fellow). Equipment for the Chemistry Department NMR facility was supported through a grant from the National Institutes of Health (Grant S10OD011952) with matching funds from the University of Minnesota.
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