Propargylic metalation

For a review of directive effects in allylic and benzylic metalation, see Klein, J. Tetrahedron, 1983, 39, 2733-2759. For a review of propargylic metalation, see Klein, J. in Patai The Chemistry of the Carbon-Carbon Triple Bond, pt. 1 Wiley NY, 1978, p. 343. 

Ma et al. demonstrated that the palladium-catalyzed coupling of vinyl halides 60 and allenyl/propargyl metal species 59 can deliver vinyl allenes 61 [40],... 

J. Klein, "Propargylic Metallation" D.A. Ben Efraim, "The Preparation of Acetylenes and their Protection" P.F. Huldrik, A.M. Huldiik, "Applications of Acetylenes in Organic Synthesis" F. Thdron, M. Verney, R. Vessiete, "Rearrangements Involving Acetylenes" W.D. Huntsman, "Synthetic Acyclic... 

Attempts to extend the chemistry described in the previous section to group VIII propargyl metal complexes afforded considerably different products, and in some cases no allenyl-containing carbonyl complexes could be isolated. 

Allylic or propargylic metal compounds are often intermediates in isomerization reactions of unsaturated systems (see Section 4.5.5) the product distribution on protonation depends very much on the substitution and the conditions of hydrolysis and most often mixtures of isomers are obtained. In contrast double bond shift generally occurs on protodesilylation of allylic silanes by acids, a reaction which takes place stereospecifically anti. Only when intramolecular delivery of the proton in a chair-like transition state is possible may a different kind of stereoselectivity be effective and good 1,3- or 1,4-induction in hydrogen transfer be observed (Scheme 83). ° ... 

Cyclodimerization of disubstituted alkynes R C=CR" mediated by this type of precatalyst (Ln = La, Ce Y is unreactive) seems to be limited to alkynes bearing at least one a-methyl group (R ) and a small second alkyl group (eq. (6)) [97]. Already use of R" = Et, n-Pr results in formation of two isomers. For example, formation of l,2-dimethyl-3-ethylidenecyclobutene from excess 1- butyne is complete in ca. 10 h at 80 °C, giving a TOF of 2 h. Unprecedented propargylic metalation/alkyne insertion are the key steps of the proposed mechanistic cycle. 

Alkylation ofa-thio- and a-seleno-alkyllithiums Alkylation ofa-thio- and a-seleno-benzylmetals Alkylation ofa-thio- and a-seleno-allylmetals Alkylation ofa-thio- and a-seleno-propargylic metal derivatives Alkylation of a-metallovinyl sulfides and selenides... 

Alkylations of 1,1 -(Dithiolallyl- and 1,1 -(Dithio)propargyl-metals and their Synthetic Uses... 

Alkylations of l,l (Dithio)allyl- and l,l-(D>thio)propargyl-metals and their Synthetic... 

Klein, J. Propargylic metalation, in The Chemistry of the Carbon—Carbon Triple Bond, (Patai, S., Ed.), p. 343, Wiley, New York 1978... 

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