Heads or tails? Chemo-, regio-, and stereoselective access to cross- and linear conjugated poly-ynene scaffolds from alkynyl-derived group six metal carbenes is reported. The metal carbenes shown (M=Cr, W; TIPS=triisopropylsilyl) readily undergo low-temperature, tail-to-tail dimerization in the presence of potassium tert-butoxide by reaction at either of the Cβ atoms to provide E-polyalkynylethenes.
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