The lanthanide alkyls Cp 2 *LnCH(SiMe 3 ) 2 (Ln = La, Ce) are efficient catalysts for the cyclodimerization of 2-alkynes MeC≡CR (R = Me, Et, n-Pr) to 1,2-disubstituted 3-alkylidenecyclobutenes. The first step in the reaction is a propargylic metalation of the α-methyl group, giving Cp* 2 LnCH 2 C≡CR compounds and free CH 2 (SiMe 3 ) 2 . © 1990, American Chemical Society. All rights reserved.
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