Cyclopentyl iodide, reaction

Naito has also described analogous tandem radical addition-cyclization processes under iodine atom-transfer reaction conditions [16,32], Treatment of 186 with z-PrI (30 eq.) and triethylborane (3x3 eq.) in toluene at 100 °C gave, after cleavage from the resin, the desired lactam product 190 in 69% yield (Scheme 46). Similar reactions involving cyclohexyl iodide, cyclopentyl iodide, and butyl iodide were also reported as well as the reaction with ethyl radical from triethylborane [16,32], The relative stereochemistry of the products was not discussed. 

Secondary alkyl bromides (e.g., isopropyl bromide) react less readily and higher temperatures are required. To avoid any decomposition of the lithiated thioacetal or its reaction with THF, the alkylations are usually carried out with the iodides [1]. Cyclopentyl bromide (reaction carried out at + 10°C) and LiCH(SCH3)2 gave the expected product in a moderate yield [3]. With cyclohexyl bromide the predominant reaction is dehydrobromination [1]. 

Iodide ion is both a better nucleophile than cyanide and a better leaving group than bromide. The two reactions shown are therefore faster than the reaction of cyclopentyl bromide with sodium cyanide alone. 

Palladium complexes, e.g. Cl2Pd(dppf), have been shown to catalyse not only Zn-I exchange between alkyl iodides and dialkylzincs but also intramolecular carbozincation to produce cyclopentylmethylzincs.60 Once cyclopentyl-methylzincs are formed, they may be utilized in cross-coupling, conjugate addition, and other synthetically useful transformation reactions (Scheme 11.17). 

Bicyclic pentenes are used as trapping agents in addition reactions of 3-butynyl radicals81. Addition occurs exclusively trans to the annulated cyclopentyl ring, while the regioselectivity is low when polar substituents are not present. Under thermal conditions, the reaction finishes after iodine atom abstraction to yield the overall trans-addition product. With photochemical initiation and in the presence of hexabutylditin, further cyclization and iodine atom abstraction occurs to form exocyclic vinyl iodides. 

Most of the useful iodine transfer radical reactions arise from the addition of alkyl iodides, which have been activated by one or more adjacent carbonyl or nitrile substituents, to unactivated olefins. This both labilizes the initial iodide, facilitating chain initiation, and helps ensure that the atom transfer step is exothermic. The requisite iodides are typically synthesized by deprotonation with EDA or NaH, followed by iodination with I2 or A-iodosuccinimide. Cyclization of an iodoester yields primarily lactone product, proceeding through the intermediacy of the I-transfer products as shown in Scheme 5 [19]. Reactions in which a-iodoesters cyclized with alkynes also proved efficient. Similar ketones yielded less synthetically useful mixtures of cyclopentyl and cyclohexyl (arising from 6-endo transition states) products. 

Similarly, fused and spiro cyclopropane systems 31 and 33 can also be synthesized by the reaction of appropriate cycloalkenyl cobaloximes 30 and 32 with free radical precursors such as toluenesulfonyl iodide (Scheme 11). The thermal and photochemical reactions of hexenyl cobaloximes 34 with a large excess of CCI4 gives mainly the pentachloroheptane 35 (path A). On the other hand, the photochemical reactions in the presence of low concentration of CCI4 gives mainly the cyclopentyl methyl chloride 36a through homolysis of the C-Co bond followed by cyclization of the hexenyl radical and chlorine atom abstraction (path B). However,... 

Cyclohexyl and cyclopentyl bromides underwent rapid reaction with SbCl, in CCl to give vicinal trans- bromochlorides in high yield. The insertion compound of SbClj in graphite, Cj SbClj, was also employed with the above substrates, where the major products were cyclohexyl and cyclopentyl chlorides ca. 60 %) and smaller amounts (18—35%) of vicinal trans-bromochlorides. Cyclohexyl chloride was obtained in 86% and 22% yield from the iodide and tosylate. 

Li and coworkers reported the conjugate addition of alkyl groups to enamides mediated by zinc in aq. NH4CI to generate a -amino acid derivatives (Eq. 4.73). No reaction was observed in the absence of water. Both secondary and tertiary alkyl groups such as linear (2-butyl, 2-propyl, 2-pentyl), cyclic (cyclohexyl, cyclopentyl, cycloheptyl), and bulky ones (tert-butyl) were all transferred to the substrate successfully. Even simple primary iodides and methyl iodide provided the desired products in good yields. Miyabe et al. as well as Jang and Cho reported the addition of alkyl radicals from alkyl iodide to a,p unsaturated ketones, esters, and nitriles mediated by indium in aqueous media. Indium-mediated Michael addition of allyl bromide to l,l-dicyano-2-arylethenes also proceeded well in aqueous medium. ... 

Cyclization of a-sulfonyl-or a-cyano-e-acetylenic esters to al-lylic cyclopentyl sulfones or nitriles is promoted by copper iodide. The reaction has been shown to go through a vinylic copper species. A catalytic version has heen developed using r-BuOK (15 mol %) as ahase and Cul (10 mol %) in THF (eq 19). Other cyclizations reported include the copper iodide-catalyzed cyclization of IV-aUylhalodtfluoroacetamides, which allows the synthesis of a,a-dtfluorinated-)/-lactams, and the copper iodide-assisted synthesis of new Se—N heterocycles. ... 

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