Alkyl radicals iodides

The hydrogen of the imino-group may be replaced lay acid and alkyl radicals. In the latter case the sodium compound is tieated with an alkyl iodide. 

A completely different method of synthesis of azo compounds from diazonium salts involving radical intermediates was found by Citterio et al. (1980, 1982 c), Cit-terio and Minisci (1982), and Fontana et al. (1988). It is a new general synthesis of arylazoalkanes based on the addition of an alkyl radical to an arenediazonium ion followed by reduction of the intermediate azo radical cation adduct by a metal salt (Scheme 12-80). The preferred source for the alkyl radical R in this reaction is an alkyl iodide, which gives rise to alkyl radicals cleanly in the presence of an arenediazonium salt and a Ti3+ or Fe2+ salt as in Scheme 12-81. The overall stoichiometric equation is therefore as given in Scheme 12-82. The yields vary between 36% and 79% (with respect to alkyl iodide). 

N-Alkoxylamines 88 are a class of initiators in "living" radical polymerization (Scheme 14). A new methodology for their synthesis mediated by (TMSlsSiH has been developed. The method consists of the trapping of alkyl radicals generated in situ by stable nitroxide radicals. To accomplish this simple reaction sequence, an alkyl bromide or iodide 87 was treated with (TMSlsSiH in the presence of thermally generated f-BuO radicals. The reaction is not a radical chain process and stoichiometric quantities of the radical initiator are required. This method allows the generation of a variety of carbon-centered radicals such as primary, secondary, tertiary, benzylic, allylic, and a-carbonyl, which can be trapped with various nitroxides. 

A hydroxymethyl group can be introduced (ArH —> ArCH20H) by several variations of this method. Alkylation of these substrates can also be accomplished by generating the alkyl radicals in other ways from hydroperoxides and FeS04, from alkyl iodides and H2O2—Fe V from carboxylic acids and lead tetraacetate, or from the photochemically induced decarboxylation of carboxylic acids by iodoso-benzene diacetate. 

Cr(II) has been used to bring about dehalogenation of alkyl halides involving the production of alkyl radicals, and details have been provided in a substantive review (Castro 1998). The ease of reduction is generally iodides > bromides > chlorides, while tertiary halides are the most reactive and primary halides the least (Castro and Kray 1963, 1966). 

The radicals generated in this way can initiate a variety of chain processes. Alkyl radicals can be generated from alkyl iodides.298 For example, addition of alkyl radicals to alkynes can be accomplished under these conditions. 

The addition of a vinyl radical to a double bond is usually favorable thermodynamically because a more stable alkyl radical is formed. The vinyl radical can be generated by dehalogenation of vinyl bromides or iodides. An early study provided examples of both five-and six-membered rings being formed.329 The six-membered ring is favored when a branching substituent is introduced. 

Clerici and Porta reported that phenyl, acetyl and methyl radicals add to the Ca atom of the iminium ion, PhN+Me=CHMe, formed in situ by the titanium-catalyzed condensation of /V-methylanilinc with acetaldehyde to give PhNMeCHMePh, PhNMeCHMeAc, and PhNMeCHMe2 in 80% overall yield.83 Recently, Miyabe and co-workers studied the addition of various alkyl radicals to imine derivatives. Alkyl radicals generated from alkyl iodide and triethylborane were added to imine derivatives such as oxime ethers, hydrazones, and nitrones in an aqueous medium.84 The reaction also proceeds on solid support.85 A-sulfonylimines are also effective under such reaction conditions.86 Indium is also effective as the mediator (Eq. 11.49).87 A tandem radical addition-cyclization reaction of oxime ether and hydrazone was also developed (Eq. 11.50).88 Li and co-workers reported the synthesis of a-amino acid derivatives and amines via the addition of simple alkyl halides to imines and enamides mediated by zinc in water (Eq. 11.51).89 The zinc-mediated radical reaction of the hydrazone bearing a chiral camphorsultam provided the corresponding alkylated products with good diastereoselectivities that can be converted into enantiomerically pure a-amino acids (Eq. 11.52).90... 

The use of Et3B as a radical initiator makes it possible to carry out the addition of other alkyl radicals to nitrone (286) using alkyl iodides. Good yields have been obtained of products (288b-d) when an excess of the appropriate alkyl iodide was used (Scheme 2.110). It has been established that the yield of alkyl by-products (288a) tends to decrease with the increase of the reaction temperature. The stereochemical features of this reaction are explained by the alkyl radical addition taking place predominantly from the less hindered re-face of (286) to avoid steric interaction with the phenyl group (525). 

Sunlamp irradiation of butynyl iodide (6) in the presence of hexabutylditin generates an alkyl radical that reacts with an electron-deficient alkene (7) to form an (iodomethylene)cyclopentene (8) in moderate yield. This product can be reduced by Bu3SnH (AIBN) to the methylenecyclopentane (9).2... 

Radical addition to an Af-acyliminium ion is also an interesting feature of the cation pool chemistry. We found that an alkyl iodide reacted with an N-acyliminium ion pool in the presence of hexabutyldistannane to give coupling product 19.24 A chain mechanism shown in Scheme 10, which involves the addition of the alkyl radical to the N-acyliminium ion to form the corresponding radical cation, seems to be reasonable. The present reaction opens a new possibility for radical-cation crossover mediated carbon-carbon bond formation. 

Intramolecular hydrogen abstraction by primary alkyl radicals from the Si-H moiety has been reported as a key step in several unimolecular chain transfer reactions.59,60 In particular, the 1,5-hydrogen transfer of radicals 14-17 [Eq. (5)], generated from the corresponding iodides, was studied in... 

Primary [21] and secondary [22] alkyl iodides are reduced in a stepwise fashion at mercury cathodes to form alkyl radicals and alkyl carbanions the alkyl radicals undergo coupling and disproportionation as well as interaction with the electrode to yield diorganomercury compounds, and... 

Alkyl radicals can be generated from alkyl iodides in a chain process initiated by a trialkylborane and oxygen.204 The alkyl radicals are generated by breakdown of a borane-oxygen adduct. 

The transfer constant for f-butylbenzene is low, since there are no benzylic C—H bonds present. Primary halides such as n-butyl chloride and bromide behave similar to aliphatics with low transfer constants, corresponding to a combination of either aliphatic C—H bond breakage or the low stability of a primary alkyl radical on abstraction of Cl or Br. The iodide,... 

Additions of perfluoroalkyl groups generated from perfluoroalkyl iodides (Rpl) and perfluoroacyl peroxides [RpC(0)00(0)CRp] have also been carried out [50]. Another usable source of CEj radicals is the stable [(CF3)2CF]2 CCF2CE3 radical (Scheme 6.8) [51]. As with alkyl radical additions, ESR spectroscopic investigations... 

Benzoxazinones 141 and 143 have been reacted in a reductive radical alkylation using triethylborane as the alkyl radical source <2004SL2597>. Triethylborane could also be used in catalytic amount with isopropyl, tert-h xVj, or cyclohexyl iodide as the alkylating agent. Zinc with copper iodide could also he used as initiator (Scheme 8). 

The rate constants for reactions of alkyl radicals with various organic halides demonstrate a clear dependence on the thermodynamics of the reactions. Iodides react faster than bromides, which react faster than chlorides, and the rate constants for reactions for a series of bromides or iodides correlate with the stability of the radical product. The reactions of a primary alkyl radical with an iodomalonate and with a bromomalonate are quite fast (k = 2x 10 M s and k=lx 10 M s, respectively, at 50 °C). To a good approximation, the rate constants for reactions of RSePh are the same as those for reactions of RBr, and the rate constants for reactions of RTePh are about the same as those for reactions of RI. Dichalcogenides are useful for radical functionalization reactions they react with primary alkyl radicals at ambient temperature with the following rate constants MeSSMe, 6 x 10 M s PhSSPh, 2 x lO M s PhSeSePh, 2.6 x 10 M s PhTeTePh, 1.1 x 10 M s... 

The gas phase photodecomposition of higher alkyl iodides has received relatively little attention and the contribution made by hot alkyl radicals is uncertain. Schindler and Wijnen6 have compared the rate of production of ethane during the photolysis of pure ethyl iodide, with that in the presence of HI and I2. They assume that in the presence of HI, all the ethyl radicals produced in the primary process form ethane, whereas in the presence of I2 ethane is produced only through reaction of hot ethyl radicals with the parent molecule. Since the rate of production of ethane in the presence of HI is approximately fifty times greater than in the presence of I2, they estimate that <2% of the ethyl radicals produced in the primary process react as hot radicals. 

Linkers that enable the preparation of y-lactones by cleavage of hydroxy esters from insoluble supports are discussed in Section 3.5.2. Resin-bound y-lactones have been prepared by Baeyer-Villiger oxidation of cyclobutanones [39], by intramolecular addition of alkyl radicals to oximes [48], by electrophilic addition of resin-bound sele-nenyl cyanide or bromide to 3,y-unsaturated acids (Figure 9.2 [100]), and by palladium-mediated coupling of resin-bound aryl iodides with allenyl carboxylic acids (Entry 10, Table 5.7 [101]). 

The method has been applied to the preparation of paraffin hydrocarbons as high in the senes as hexacontane Q0H122. The alkyl radicals may be the same or different in the iodide or iodides taken. 

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