4516-69-2Relevant articles and documents
A Photochemical Probe for Single Electron Transfer in Nucleophilic Aliphatic Substitution: Evidence for Geminate Radical Coupling in the Solvent Cage
Tolbert, Laren M.,Sun, Xiao-Jing,Ashby, E.C.
, p. 2681 - 2685 (1995)
A major effort to establish single electron transfer (SET) as an important pathway in nucleophilic aliphatic substitution reactions has involved the use of cyclizable probes, e.g., 6-iodo-5,5-dimethyl-1-hexene.In order to examine the partition between cyclization and direct radical-radical recombination, we have investigated the ground-state and excited-state chemistry of the 9-phenylfluorenyl anion (9PF-) with neopentyl-type iodides.It has been shown that 9PF- does not react with Me3CCH2I, but it does undergo efficient reaction upon irradiation (Φ=1.0) to yield nucleophilic aliphatic substitution products.With the sterically analogous cyclizable probe 6-iodo-5,5-dimethyl-1-hexene, no ground-state reaction is observed.However, both cyclized and uncyclized products of substitution, 9PFRc and 9PFRu, are produced upon irradiation.Thus photoproducts clearly involving electron-transfer-induced radical intermediates can result without acommpanying free-radical cyclization.These results suggest that, although the observation of cyclized products in the reaction of a cyclizable radical probe with a nucleophile is evidence of a radical intermediate, the absence of such cyclized products does not require the absence of radical intermediates.
Mechanism of Reaction of Geminal Dihalides with Lithium Naphthalenide (LiNp(.-)): Evidence for an Electron Transfer Mechanism. Similarities to the Mechanism of Reaction of Geminal Dihalides with Certain Nucleophiles and Other One-Electron Donors
Ashby, E. C.,Desphande, Abhay K.
, p. 4530 - 4535 (2007/10/02)
The reactions of the sterically hindered geminal dihalides 6,6-dichloro-5,5-dimethyl-1-hexene (1a) and 6,6-diiodo-5,5-dimethyl-1-hexene (1b) with lithium naphthalenide (LiNp(.-)) in THF were investigated in an attempt to compare the results of reactions involving a known one-electron donor (LiNp(.-)) with those involving nucleophiles believed to be one-electron donors.On the basis of radical-trapping studies, deuterium tracer studies, and product studies using cyclizable radical probes, it can be concluded that the reactions studied are very similar to those reported by us earlier involving magnesium metal, LiAlH4, and other nucleophiles.In addition to radical-derived products, the reaction of 1a with LiNp(.-) afforded hydrocarbons, in high yields, that were derived from a carbene intermediate.On the other hand, 1b, on reaction with LiNp(.-), did not yield any carbene-derived hydrocarbons.These results show that the formation of a carbene intermediate, derived from a radical, depends on the nature of the halogen present.It was also found that naphthalene can behave as a hydrogen atom donor toward a radical in the presence of known hydrogen atom donors, such as THF.
Mechanism of Reaction of Geminal Dihalides with Lithium Aluminum Hydride. Evidence for Single Electron Transfer as the Major Reaction Pathway
Ashby, E. C.,Deshpande, Abhay K.
, p. 3798 - 3805 (2007/10/02)
The reactions of a sterically hindered geminal dichloride 4a and the corresponding diiodide 4b with LiAlH4 (LAH) were found to involve an electron-transfer mechanism.Whereas the monochloro analog of 4a (8) is inert toward LAH, 4a was more reactive.Observation of radical-derived products in the reaction of 4a with LAH indicates that the presence of two chlorine atoms on the same carbon atom results in a favorable reduction potential for 4a, as compared to 8.These results show that LAH can function as a one-electron donor toward geminal dichlorides.It was found that the diiodo analog 4b is more reactive toward LAH than 4a due to the inherent favorable reduction potentials of alkyl iodides compared to chlorides.The reactivity of 4b toward LAH was also found to be greater than that of the monoiodo analog (1b) in keeping with the more favorable reduction potential of the diiodide (4b) compared to the monoiodide (1b).The rates of cyclization of the corresponding haloalkyl radicals generated from 4a and 4b were also determined and were found to be 7.4E5/s for the chloroalkyl and 5.5E5/s for the iodoalkyl radical at 25 deg C.The formation of small amounts of the carbene-derived product, 5, in the reactions of both 4a and 4b with LAH appeared to be preceded by a radical intermediate.
