Rearrangements of (chloromethyl)organylsilanes induced by Lewis acids or by Lewis bases: Regioselective methylenation of allylic systems

Eisch, John J.; Chiu, Chingchen S.

doi:10.1002/hc.520050312

Cited by 13 publications

(3 citation statements)

References 14 publications

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“…Ph 3 SiCH 2 PCl 2 (2): A 250-mL Schlenk flask equipped with a stir bar was charged with freshly ground Mg turnings (10 g, 0.411 mol) and THF (50 mL). Meanwhile, Ph 3 SiCH 2 Cl [24] (13.0 g, 0.042 mol) was dissolved in THF (50 mL) in a separate Schlenk flask. The alkyl chloride was slowly added to the Mg turnings in 10 mL portions over 1 h, at which time the Grignard reaction was initiated.…”

Section: Methodsmentioning

confidence: 99%

Making the True “CP” Ligand

et al. 2006

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The quest for cyaphide, the phosphorus equivalent of cyanide, has been a continuous struggle for many years. Potential applications arising from the use of C P as a bridging ligand between two metals, the incorporation of CP into coordination polymers and new materials, and the basic synthetic challenges of making C P have provided inspiration for decades. While phosphaalkynes (R À C P) have been known for some time, [1][2][3] the terminal MÀCP has only been reported as a transient species. [4,5] Other C-functionalized XÀCP compounds (X = R 3 Si, [6] R 2 N, [7,8] RO, [8] F, [9] Cl, [10] ), anionic species [XÀCP] À (X = R 3 B, [11] RN, [8] O, [12] S [13] ), and the cationic phosphonio phosphaalkyne [R 3 P À C P] + , [14] have been synthesized, but the vast majority of reports deal with tert-butyl, [15] adamantyl, [16] 2,4,6-trimethylphenyl [17] and 2,4,6-tri-tert-butylphenyl [18] phosphaalkynes. Recently, we devised a very simple method for accessing the kinetically stable crystalline triphenylmethyl (trityl)-substituted phosphaalkyne, Ph 3 CC P (1), which allowed for the economical metal-promoted synthesis of phosphorus heterocycles. However, our ultimate goal and incentive for synthesizing the trityl-substituted phosphaalkyne was to find an adequate leaving group that would lead us to cyaphide. [19] Treatment of 1 or its complexes [MH(dppe) 2 (Ph 3 C-CP)]OTf (M = Fe or Ru; dppe = bis(1,2-diphenylphosphinoethane); OTf = trifluoromethanesulfonate) with nucleophiles (Nu) did not furnish the desired cyaphide, C P À , or its complexes [Eq. (1); electrophile (E) = C].Therefore, we reasoned that silicon would be more susceptible to nucleophilic attack (E = Si) and applied an analogous synthetic procedure to access the higher homologue Ph 3 SiCP (3).Conversion of Ph 3 SiCH 2 Cl into the Grignard reagent followed by treatment with PCl 3 produced the silyl-substituted alkyl phosphonous dichloride, Ph 3 SiCH 2 PCl 2 (2), in over 87 % yield (Scheme 1). Employing 2.2 equiv of DABCO (1,8-diazabicyclo[2.2.2]octane) effected the dehydrohalogenation reaction, and 2 was fully transformed into the triphenylsilyl-substituted phosphaalkyne 3. The reaction occurred at ambient temperature and in multiple solvents in less than one hour. (In contrast, the reaction of DABCO with Ph 3 CCH 2 PCl 2 to furnish Ph 3 CC P required a 10-fold excess of base, elevated temperatures, and proceeded best in acetonitrile.[19] ) While DABCO alone was effective for the conversion of 2 into 3, we saw rapid decomposition of this new phosphaalkyne, which was dependent on the solvent. Qualitatively, the rate of decomposition of 3 followed the order Et 2 O % toluene < THF ! CH 3 CN. Suspecting that DABCO-HCl was acting as a soluble source of chloride anion in the more polar solvents that then attacked silicon to produce Ph 3 SiCl and the CP anion, which is seemingly unstable under the reaction conditions, we added AgOTf to the reaction mixture. When a solution of 2 in toluene was pretreated with 2.2 equiv of AgOTf for 5 min followed by addition of 2.2 equ...

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Section: Methodsmentioning

confidence: 99%

Making the True “CP” Ligand

et al. 2006

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“…The reaction of (2-methyl-2-propenyl)dimethyl(chloromethyl)silane ( 1g ) containing a methallyl group under the same reaction conditions as above was complete within 10 min to give (3-methyl-3-butenyl)dimethylchlorosilane ( 2g ) in 65% yield, as shown in eq 3. The reaction of 1g is faster than that of 1a , suggesting that an electron-donating methyl substituent on the second carbon of the allyl group of the reactant facilitates the allyl rearrangement reaction.…”

Section: Resultsmentioning

confidence: 95%

Aluminum Chloride-Catalyzed Intramolecular Allyl-Migration Reaction of Allyl(chloromethyl)silanes and Trapping of the Intermediate with Allyltrimethylsilane

et al. 2004

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Allyl(chloromethyl)diorganosilanes [CH2CHCH2SiR1R2(CH2Cl), R1 = Me, Ph; R2 = Me, Ph, p-ClC6H4] in the presence of aluminum chloride undergo an allyl rearrangement reaction with allylic inversion to afford (3-butenyl)diorganochlorosilanes at room temperature. When allyltrimethylsilane was added to the reactions, the intermediate was trapped to give 1,1-dimethyl-3-(2-trimethylsilylmethyl-4-pentenyl)silacyclopentane (4) along with 3-(butenyl)dimethylchlorosilane in 40% and 18% yields, respectively. The formation of 4 can be explained by the addition reaction of allyltrimethylsilane to 1-silacyclopent-3-yl cation produced by the intramolecular cyclization of (allyl)silylmethyl cation intermediate derived from the interaction of the chloromethyl group with aluminum chloride catalyst, followed by desilylation reaction.

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“…Commercial (chloromethyl)dimethylchlorosilane (2) was distilled in the presence of Bu 3 N directly before use. N-[(chloromethyl)dimethylsilyl]amines 4a and 4b were synthesized according to [33,34]. N-(chloromethyl)dimethylsilyl-Nmethylamide of diisopropylphosphoric acid (5) was prepared by the earlier described procedure [35].…”

Section: Resultsmentioning

confidence: 99%