4516-69-2Relevant academic research and scientific papers
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.
EVIDENCE FOR SINGLE ELECTRON TRANSFER IN THE REACTION OF A LITHIUM ENOLATE WITH A PRIMARY ALKYL IODIDE
Ashby, E.C.,Argyropoulos, J.N.
, p. 7 - 10 (1984)
Evidence for a radical process in the reaction of the lithium enolate of propiophenone with a primary alkyl iodide was obtained by the observation of cyclization of an appropriate radical probe, by the trapping of the radical intermediate and by the comparison of the relative rates of reactions of the probe alkyl iodide with the corresponding bromide and tosylate.
Electron Transfer in the Reactions of Geminal Dihalides with Ph2P(-). Evidence for the Formation of a Carbene Intermediate from a Radical Precursor
Ashby, E. C.,Deshpande, Abhay K.
, p. 7117 - 7124 (2007/10/03)
The reactions of two sterically hindered geminal dihalides, 6,6-dichloro-5,5-dimethyl-1-hexene (5a) and 6,6-diiodo-5,5-dimethyl-1-hexene (5b), with Ph2P(-) have been found to involve a single electron transfer (SET) pathway.Since the corresponding monochl
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*.
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.
Investigation of the Purity of Alkali Metal Diphenylphosphides and Their Reactions with Organic Halides. Evidence for Single Electron Transfer
Ashby, E. C.,Gurumurthy, R.,Ridlehuber, R. W.
, p. 5832 - 5837 (2007/10/02)
For the first time the purity of lithium, sodium, and potassium diphenylphosphide, prepared by various methods, has been evaluated using (31)P NMR spectroscopy.A method was developed to prepare each of the phosphides in a high state of purity.Highly pure potassium diphenylphosphide was then allowed to react with p-iodotoluene in order to determine the effect of purity on the SRN1 nature of this reaction.The results were then compared with literature reports which used less pure KPPh2.The mechanism of reaction of alkyl halides with pure alkali metal diphenylphosphides, using the radical probes 6-halo-5,5-dimethyl-1-hexenes and 1-halo-2,2-dimethylhexanes, was investigated.The results provide the first evidence to support single electron transfer (SET) in the reaction of an alkali metal diphenylphosphide with an alkyl halide.SET was found to be the major reaction pathway in the reaction of hindered alkyl iodides (neopentyl type).On the other hand, SET was found to be a minor pathway in the reaction of the corresponding alkyl bromides and chlorides with PPh2(1-).There was no evidence found for SET in the reactions of unhindered alkyl halides with PPh2(1-) although SET participation cannot be rigorously excluded.
Competing Radical, Carbanion, and Carbene Pathways in the Reactions of Hindered Primary Alkyl Halides with Lithium Dialkylamides
Ashby, E. C.,Park, B.,Patil, G. S.,Gadru, K.,Gurumurthy, R.
, p. 424 - 437 (2007/10/02)
A variety of methods were utilized to study the mechanism of reaction of 6-iodo-5,5-dimethyl-1-hexene and its bromo, chloro, and tosylate derivatives with LDA and several other lithium dialkylamides.In the reaction of 6-iodo-5,5-dimethyl-1-hexene with LDA in THF, radical, carbanion, and carbene pathways occured simultaneously.However, when the corresponding bromide was allowed to react with LDA, the radical pathway was minor and when the corresponding chloride or tosylate was allowed to react with LDA, no evidence for radical products was observed.This is the first time that competing radical, carbanion, and carbene pathways have been detected in the reaction of a primary alkyl halide with any nucleophile.
Reactions of 1,1,3,3-Tetramethylcyclobutane on Evaporated Metal Films
Clarke, John K. A.,Hegarty, Bernard F.,Rooney, John J.
, p. 2511 - 2518 (2007/10/02)
Reactions of 1,1,3,3-tetramethylcyclobutane (TMCB)-hydrogen mixtures on evaporated metal films have shown that both ring scission to 2,2,4-trimethylpentane (TMP) and ring enlargement to 1,1,3-trimethylcyclopentane (TMCP) are dominant on sintered platinum films, while ring scission to TMP predominates on sintered palladium and on unsintered molybdenum films.Unsintered tantalum and molybdenum films gave a large production of iC4 hydrocarbon, particularly above ca. 500 K: ring enlargement was a minor reaction found particularly with tantalum.The homogeneous reaction of TMCB giving a large iC4 production sets in at 600 K.The possibility, suggested by the product distribution, that the reaction of TMCB on Mo and Ta is a metal-assisted free-radical reaction is examined.While it may not be completely excluded that the catalysed ring enlargement on Pt and Pd is a free-radical reaction it is argued that only the previously proposed Rooney-Samman bond-shift mechanism accommodates without added qualifications published facts on bond shifts, including those at quaternary carbon atoms, and also ring enlargements.
Single Electron Transfer in the Reaction of Enolates with Alkyl Halides
Ashby, E. C.,Argyropoulos, J. N.
, p. 3274 - 3283 (2007/10/02)
Single electron transfer (SET) in the reaction of a model system consisting of lithiopropiophenone with primary neopentyl type alkyl halides and tosylate was investigated by (1) the use of an appropriate cyclizable alkyl radical probe, (2) observing the effect of varying the leaving group on reaction rate and product distribution, (3) studying the effect of light, di-tert-butyl nitroxyl radical, and p-dinitrobenzene on the rate of reaction, (4) observing the consequence of varying solvent composition on both the reaction rate and product distribution, and (5) studying the effects of the radical traps, dicyclohexylphosphine and 1,4-cyclohexadiene, on product composition.The results of these studies indicate that single electron transfer is the major reaction pathway involved in the reaction of the enolate with the alkyl iodide in HMPA and that the corresponding bromide and tosylate react by an SN2 process.
