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 Magnesium. Evidence for the Formation of Carbenes from Radical Precursors. The Similarity in Reactions of Geminal Dihalides with Magnesium and LiAlH4
Ashby, E. C.,Deshpande, Abhay K.,Doctorovich, Fabio
, p. 6223 - 6232 (2007/10/02)
The geminal dihalides, 6,6-dichloro-5,5-dimethyl-1-hexene (2a) and 6,6-diiodo-5,5-dimethyl-1-hexene (2b) were allowed to react with Rieke activated magnesium (Mg*) in THF at 25 deg C.Both radical and carbene intermediates were identified by product analyses, by radical trapping experiments using DCPH and THF-d8, and by selective experiments in which isolated intermediates were shown to form the predicted products.Although carbene products predominated over radical products when the dichloride was allowed to react with Mg*, radical products predominated when the diiodide was allowed to react with Mg*.Evidence is presented that indicates that the carbene intermediate arises from a radical precursor.A mechanistic scheme (Scheme 5) is presented that is consistent with all of the observed data.A comparison of the reactions of 2b with Mg* and 2b with LiAlH4 shows that most of the products are common in both reactions thereby providing further evidence for LiAlH4 as a one-electron donor, as is known behavior of Mg*.
