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The lanthanide alkyls Cp2*LnCH(SiMe3)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*2LnCH2C≡CR compounds and free CH2(SiMe3)2.
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Heeres et al. (1990) studied this question.
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