Intermolecular carbozincations alkynes

Arylzinc reagents are completely inert towards alkenes and alkynes in the absence of any added catalyst, whereas the reported examples of uncatalyzed intermolecular carbozincations involving alkylzincs appear to be restricted to the more nucleophilic di(tert-butyl)zinc. 

Thus, whereas intermolecular carbozincations of alkenes and alkynes appear restricted in scope and limited to the more reactive di(terf-butyl)zinc, the zinc-induced cyclization of... 

Cyclizations of iodoalkynes have also been demonstrated to proceed with C-C bond formation (Scheme 3-89). Little mechanistic information is available for this process, but a net syn addition across the alkyne was noted. Additionally, intermolecular carbozincations of alkynes were demonstrated under similar... 

Also promising are both intermolecular and intramolecular carbozincation of alkynes catalyzed by №( ) in THF-NMP. The intramolecular cyclic carbozincation has also been observed with -iodo-l-alkenes (Scheme 20). 

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