Intramolecular carbozincations alkynes

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). 

Intramolecular carbozincations of alkynes appeared relatively restricted in scope, at least under the conditions that were used to generate the open-chain organozinc species. 

Compared to carboalumination, carbozincation is used less often in organic synthesis4,571. Analogous to carboalumination, stereoselective cis carbozincation of terminal alkynes can be achieved with dialkylzinc reagents or with allylzinc halides in the presence of zirconocene diiodide34-56. Palladium-catalyzed intramolecular carbozincation has been used in the stereoselective synthesis of cyclopentanes72. 

Nickel-catalyzed carbozincation can also proceed smoothly vith alkynes for the synthesis of substituted alkenes regio- and stereoselectively. The reaction may proceed via an intramolecular version leading to tri- or tetrasubstituted alkenes. Thus, treatment of ry-iodoalkyne with RjZn in the presence of 7.5 mol% Ni(acac)2 in THF and NMP yield the cyclopentane derivative in 62% yield [102,112]. Presumably, a reductive elimination step from the corresponding organonickel intermediate may occur. It is noteworthy that no cydization is observed when internal alkyne is used. 

---