Intramolecular carbozincations alkenes

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). 

Carbozincation of alkenes is a very facile method for the formation of new C—C bonds. A smooth intramolecular reaction occurs when functionalized 5-hexenyl iodides are treated with diethylzinc in ether, followed by acid work-up (equation 106)416. 

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. 

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