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4. (l) See for review of cyclotrimerization; e.g. E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.) Comprehensive Organometallic Chemistry II, Vol. 12, 1995; L.S. Hegedus (Ed.) Transition metal Organometallics in Organic Syntheses: 7.3; D.B. Grotjahn, Transition metal alkyne complexes: Transition metal catalyzed cyclo- rimerization, Pergamon, Oxford.
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