5-Hexenyl iodides

One experimental test for the involvement of radical intermediates is to study 5-hexenyl systems and look for the characteristic cyclization to cyclopentane derivatives (see Part A, Section 11.2.3). When 5-hexenyl bromide or iodide reacts with LiAlH4, no cyclization products are observed. However, the more hindered 2,2-dimethyl-5-hexenyl iodide gives mainly cyclic product.164... 

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. 

Wunderlich and Knochel recently published the alkylation of diaryliron compounds by alkyl iodides or benzyl chloride 1 (entry 33) [77]. The reaction works well with 98% pure FeCl2 2LiCl but not with 99.998% pure metal salt. Addition of other transition metal salts showed that nickel contained in the FeCl2 of 98% purity is the likely catalyst. Alkylarenes 3 were obtained in 65-88% yield. The method tolerates ester, nitrile, fluoride, or chloride substituents. Although the use of 5-hexenyl iodide did not provide a cyclized product, the initial formation of radicals cannot be excluded safely. 

S-Allyloxy tellurides also underwent similar radical 5-exo cyclizations catalyzed by 7 mol% of Ni(acac)2 and 2 equiv. of Et2Zn [113]. The reaction proceeded with high r/.v-selectivity in 56% yield. In contrast to the reactions of 5-hexenyl iodides shown above, 5-exo cyclization reactions of 5-hexynyl iodides were proposed to proceed by a two-electron pathway consisting of alkyne coordination/oxidative addition/intramolecular carbonickelation and reductive elimination, resulting in alkylidenecyclopentanes [114]. 

The cyclization of 4-substituted 5-hexenyl iodides proceeds well, leading to cyclopentylz-inc iodides that can be trapped with various electrophiles such as 3-iodo-2-cyclohexenone, iodine, acid chlorides, allylic halides, and ethyl propiolate (carbocupration) (Scheme 1) Various substitution patterns allow a successful cyclization. Also, a range of functional groups like esters or nitriles are tolerated in the ring closure (Scheme 8). 

Z)-1-Hexenyl iodide was prepared by treating acetylene with lithium... 

Z)-1-Hexenyl iodide 1-Hexene, 1-iodo-, (Z)- (8,9) (16538-47-9) (E)-l-Hexenyl iodide 1-Hexene, l-1odo-, (E)- (8,9) (16644-98-7) Tetrakis(triphenylphosphine)palladium Palladium,... 

Radical rearrangement products from, for example, 6-hexenyl iodide and vinyl iodide are minimal, although the cyclopropylcarbinyl example (Scheme 49) shows the nearly complete rearrangement typical of a cyclopropylcarbinyl radical. 

So, both methods (using the activated zinc of Rieke, and Et2Zn) allow the carbocyclization of hexenyl iodides with a sensitive function, thanks to the less reactive... 

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