Migration Of Trimethylsilyl Group Research Articles

Migration of trimethylsilyl group in the reaction of sodium bis(trimethylsilyl)amide with bromobenzene

The reaction of sodium bis(trimethylsilyl)amide with bromobenzene gave a mixture of N,N-bis-(trimethylsilyl)aniline and N,2-bis(trimethylsilyl)aniline, the latter being a rearrangement product formed via 1,3-migration of trimethylsilyl group from the nitrogen atom to the ortho-carbon atom in the benzene ring.

Catalytic and Thermal 1,2-Rearrangement of (α-Mercaptobenzyl)trimethylsilane

The mechanisms of catalytic and thermal 1,2-rearrangement of (alpha-mercaptobenzyl)trimethylsilane were studied by using density functional theory (DFT) at the MP2/6-31+G(d,p)//B3LYP/6-31G(d) levels. The results show that (alpha-mercaptobenzyl)trimethylsilane rearranges to (benzylthio)trimethylsilane through a trimethylsilyl group migration from C to S atom via a transition state of pentacoordinate Si atom with or without radical initiators. The low reaction activation energy (15.1 kcal/mol) is responsible for the fast rearrangement in the presence of radical initiators. Both radical and nonradical thermal rearrangement mechanisms were suggested, and the radical mechanism dominates through its self-catalyzing. These results are consistent with the experiment results. The activation energy (DeltaH(act) = 15.1 kcal/mol) for the rate-determining step within the self-catalytic cycle is low enough to make (trimethylsilylbenzyl)thiyl radical be a reasonable catalyst for the thermal rearrangement. The catalytic and thermal 1,2-rearrangement mechanisms of (alpha-mercaptobenzyl)trimethylsilane, especially the self-catalytic radical mechanism, were revealed for the first time. The comparison of the rearrangement mechanisms between (alpha-mercaptobenzyl)trimethylsilane and silylmethanethiol discloses the factors in determining the reaction mechanism of such kinds of mercaptoalkyl-functionalized organosilanes. The phenyl group is found to be favorable for the radical rearrangement, thus making (alpha-mercaptobenzyl)trimethylsilane instable.

Synthesis, Structure, and Reactivity of an Unusual Platinum Olefin Carbene Complex, [(η4-cod)Pt{C(Ph2PNSiMe3)2-κC,κN}

The organolithium dimer [Li2C(Ph2PNSiMe3)2]2 ([Li2-1]2) reacts with 2 equiv of [PtCl2(cod)] (cod = 1,5-cyclooctadiene) in Et2O solution to give the novel Pt−carbene complex [(η4-cod)Pt{C(Ph2PNSiMe3)2-κC,κN}] (2), which is characterized by a relatively long Pt−C(carbene) bond and relatively short Pt−C(olefin) interactions indicative of an electron-rich Pt center. Under oxygen- and moisture-free conditions, 2 is remarkably inert; the cod ligand is not displaced by either monodentate or bidentate phosphines, phosphine sulfide, phosphite, or pyridine at room temperature, nor is the four-membered C,N-chelate ring opened by these reagents. However, 2 reacts with the electrophiles MeOTf (OTf = trifluoromethanesulfonate) and CO2. In the former case, the uncoordinated N atom of 2 is methylated to form [(η4-cod)Pt{C(Ph2PNSiMe3)(Ph2PN(Me)SiMe3-κC,κN}][OTf] (3). In the latter, initial nucleophilic attack by the uncoordinated N atom on CO2, followed by trimethylsilyl group migration from N to O, gives [(η4-cod)Pt{C(Ph2PNSiMe3)(Ph2PNC(O)OSiMe3-κC,κN}] (4). Heating a benzene solution of 2 to 100 °C in a sealed tube for several hours, or to 60 °C for 10 min in the presence of H2O, yields the ortho-metalated complex [(η4-cod)Pt{CH(Ph(C6H4)PNSiMe3)(Ph2PNSiMe3)-κC,κC‘}] (5), which is characterized by Pt−C distances that are in the typical range for Pt−C(alkyl) and Pt−C(arene) interactions. The diastereoselectivity of the ortho metalation is consistent with an oxidative addition (nucleophilic) reaction mechanism for the ortho metalation. In contrast to 2, 5 displays typical cod substitution reactivity with chelating phosphines. The reaction between [Li2-1]2 and [PtCl2(cod)] in C6H6 solution proceeds only very slowly and gives [Li][Pt{CH(Ph(C6H4)PNSiMe3)(Ph2PNSiMe3)-κC,κC‘}{CH(Ph2PNSiMe3)2-κC,κN}] (7) in low yield.

Trimethylsilyl group migration in the Criegee intermediate of gas-phase ozonolysis of trimethylsilylethenes

GC, GC/MS and GC/FTIR analyses of the final products of ozonolysis of trimethylsilylethene and trans-1,3-bis(trimethylsilyl)ethene reveal that the ester channel of decomposition of the Criegee intermediate takes place exclusively via migration of Me 3Si group.

Migration of trimethylsilyl groups in enolates of silyl esters

The lithium enolate of trimethylsilyl acetate ( 1) undergoes a 1,3-O → C migration of the trimethylsilyl group.

Trimethylsilyl group migration in the mass spectra of trimethylsilyl ethers of cholesterol oxidation products. Product ion characterization by linked-scan tandem mass spectrometry

Loss of the A ring in the electron-impact mass spectra of the trimethylsilyl (TMS) derivatives of several cholesterol oxidation products is accompanied by intramolecular migration of the 3- O-TMS group to the charge-retaining portion of the molecule. Linked-scan techniques (B/E and B 2/E) were used to establish the fragmentation processes leading to the formation of the rearrangement ion. The TMS group appears to migrate to heteroatomic sites in the 5-, 6-, or 7-positions of the B ring. This structural assignment is supported by isotopic labeling studies and collision-induced dissociation of the resulting product ion.

Studies on Silyl Furans IV. A Novel Trimethylsilyl Group Migration: Formation of Ethyl 5-Chloro-4-trimethylsilyl-2-furoate with Sulfuryl Chloride in Dichloromethane.

The reaction of ethyl 5-trimethylsilyl-2-furoate (1) with sulfuryl chloride in dichloromethane afforded an unexpected product, ethyl 5-chloro-4-trimethylsilyl-2-furoate (2a), through a novel trimethylsilyl group migration.

Synthesis of new metallacycles of rhenium(VII) oxides: migration of trimethylsilyl group to form the cis-dioxo cyclometallaphosphoranimino phosphane NPPh2CH2PPh2Re(O)2(OSiMe3)2 and arsane NPPh2(CH2)2AsPh2Re(O)2(OSiMe3)2

The new bifunctional phosphoranimino phosphane ligand Me 3 SiN=PPh 2 CH 2 PPh 2 and its arsane analogue Me 3 SiN=PPh 2 CH 2 CH 2 AsPh 2 react with Me 3 SiOReO 3 to form metallacycles

ChemInform Abstract: Base‐Assisted Migration of Trimethylsilyl Group from Carbon to Oxygen in γ‐Trimethylsilyl‐γ,δ‐unsaturated Alcohols, γ‐Trimethylsilyl‐γ,δ‐epoxy Alcohols, and β‐Trimethylsilyl‐β,γ‐epoxy Alcohols to the Corresponding Silyl Ethers.

AbstractProtodesilylation of the silanes (I) and (V), yielding the compounds (II) and (VI), is achieved either by basic treatment followed by acidic hyrolysis or in a one‐step procedure by addition of fluoride.

ChemInform Abstract: Photolysis of 1‐Aryl‐1,2,3‐triazoles; Rearrangement via 1H‐Azirines.

AbstractThe preparation of various naphthyltriazoles such as (I), (III), (VII) or (IX) is described.

Base-assisted Migration of Trimethylsilyl Group from Carbon to Oxygen in g-Trimethylsilyl-g,d-unsaturated Alcohols, g-Trimethylsilyl-g,d-epoxy Alcohols, and b-Trimethylsilyl-b,g-epoxy Alcohols to the Corresponding Silyl Ethers

Base-assisted Migration of Trimethylsilyl Group from Carbon to Oxygen in g-Trimethylsilyl-g,d-unsaturated Alcohols, g-Trimethylsilyl-g,d-epoxy Alcohols, and b-Trimethylsilyl-b,g-epoxy Alcohols to the Corresponding Silyl Ethers

Photolysis of 1-aryl -1,2,3-triazoles; rearrangement via 1H-azirines

The preparation and photolysis of a seriesof 1-(1-naphthyl)-1,2,3-triazoles, (2)–(5), and of 1-(2-methyl-1 -naphthyl)-1,2,3-triazoles, (6)–(9), with and without electron-withdrawing groups (CO2R, CONH2, CN, CHO, COPh) in the triazole ring, are described. In the first series, triazoles (3) with two electron-withdrawing groups, and triazoles (4) with one such group at C-4, mostly give good yields of the expected benz[g] indoles (10) and (11) respectively. Triazoles (5) with the electron-withdrawing group at C-5 also give benz[g]indoles but these are now mixtures of the expected (12) and rearranged indoles (11). Photolysis of the 1-phenyltriazoles (21) and (22) follows the same pattern, those [(22)] with the electron-withdrawing group at C-5 rearranging to give mixtures of indoles (23) and (24). This is explained by a mechanism (Scheme 3) in which the less stable carbene intermediate (13) rearranges to the more stable carbene (15)via the 1H-azirine (14), in competition with its direct cyclisation. This provides the first evidence for antiaromatic 1H-azirines as intermediates in a photochemical reaction. Photolysis of the 2-methylnaphthyl′compounds follows a different path: diester (7b) and dinitrile (7d) give high yields of the deeply coloured 9-methyl-1H-benzo[de]quinoline derivatives (25a) and (25b) respectively, the first stable examples of this ring system to be isolated. Photolysis of the nitrile (8c) gives 9b- methyl-9bH-benz[g] indole-3-carbonitrile (28), a rare example of a stable indole with a ring junction substituent. 1,2-Shifts in the carbenes are only observed with the bis(trimethylsilyl)triazoles (2d) and (6f), in keeping with the known rapid migration of trimethylsilyl groups to carbene centres.

PHOTOLYSIS AND PYROLYSIS OF POLYSILYLATED DIAZOMETHANES. EFFECTIVE MIGRATING TENDENCY OF TRIMETHYLSILYL GROUP TO A CARBENE CENTER

Abstract Photolysis and pyrolysis of polysilylated diazomethanes were investigated, and a selective migration of trimethylsilyl group to a carbene center was observed.

A trimethylsilyl group migration in the chemistry of η 5-C 5H 5Fe(CO) 2SiMe 3

Reaction of η 5-C 5H 5Fe(CO) 2SiMe 3 with either n-BuLi or lithium diisopropylamide (LDA) results in a migration of the trimethylsilyl group from iron to the complexed Cp ligand. The resulting η 5-C 5H 4SiMe 3Fe(CO) 2 anion is readily alkylated to give σ-bonded derivatives. The unique reactivity of the trimethylsilyl systems is underscored by comparison with the behavior of η 5-C 5H 5Fe(CO) 2Me under identical conditions. Some chemical transformations of η 5-C 5H 4SiMe 3Fe(CO) 2R derivatives involving migratory insertion and β-hydride abstraction are also reported.

Trimethylsilyl group migration during electron impact and chemical ionization mass spectrometry of the trimethylsilyl ethers of 20-hydroxy-5alpha-pregnan-3-ones and 20-hydroxy-4-pregnen-3-ones.

The electron impact and chemical ionization (isobutane) mass spectra of the TMS derivatives of 20-hydroxy-5alpha-pregnan-3-ones and 20-hydroxy-4-pregnen-3-ones include ions [M--44]+-attributable to loss of a CH3CHO fragment from C-17 with migration of the TMS group to the charge-retaining fragment. Mass spectra of isotopically labelled ([3-18O], [20-18O] and [2H9-TMS]) analogues are consistent with this mechanism; [2H9-TMS] labelling further indicates that subsequent loss of a methyl group from [M--44]+-ions does not involve the TMS group. Corresponding ions are not observed at significant abundance in the spectra of 20beta-trimethylsilyloxy-5alpha-pregnane and 20beta-trimethylsilyloxy-4-pregnen-3-one 3-O-methyloxime. In the electron impact mass spectrum of the t-butyldimethylsilyl ether of 20beta-hydroxy-4-pregnen-3-one, an ion is observed corresponding to loss of 44 atomic mass units from the intense [M--C4H9]+ ion.

Gas chromatography mass spectrometry of trimethylsilyl ethers of sidechain hydroxylated Δ4-3-ketosteroids. Long range trimethylsilyl group migration under electron impact

The electron impact mass spectrum (70 eV) of 26-trimethylsilyloxy-4-cholesten-3-one shows a base peak at m/e 196, attributable to combination of the trimethylsilyl group with a fragment of m/e 123 produced by cleavage across ring B. 18O labelling confirms that the fragment of m/e 196 contains the 3-oxygen atom, and 2H labelling indicates retention of the trimethylsilyl moiety. Similar ions are observed from other Δ4-3-ketones with sidechain trimethylsilyloxy groups: abundances depend on the site of substitution. The corresponding enol trimethylsilyl ethers are readily separable from the keto forms by gas-liquid chromatography, and afford mass spectra in which the molecular ions are abundant, while ions of m/e 196 are of only moderate intensity.

The study and characterization of nucleosides by mass spectrometry—I: The mass spectra of pyrimidine 2,2′‐anhydronucleosides and their derivatives

AbstractThe mass spectra of 2,2′‐anhydrouridine, 2,2′‐anhydrothymidine and 2,2′‐anhydro‐4‐thiouridine are reported. The acetyl, trifluoroacetyl, trityl, pivaloyl and trimethylsilyl ether derivatives were also studied. Deuterium labeling in acetyl and trimethylsilyl groups aided characterization of many ions in the spectra, as well as helping to clarify hydrogen migration processes. The anhydronucleosides and their derivatives are readily distinguished from natural nucleosides by the presence of an ion containing the base moiety plus the anhydro‐ring plus one hydrogen atom from the rest of the molecule. As for natural nucleosides the [base + H]+ and [base + 2H]+ ions are usually prominent, but in contrast to natural nucleosides, ions characteristic of the sugar moiety do not retain the 2′‐oxygen atom (i.e. the oxygen atom of the anhydro‐ring). The mass spectra of deuterium labeled derivatives suggest a test for the presence of a 3′‐O‐acetyl function (the O‐acetyl group is lost from the molecular ion much more readily from the 3′‐ than from the 5′‐carbon atom). The trimethylsilyl derivatives showed evidence in their mass spectra for migration of trimethylsilyl groups in addition to hydrogen atoms.

Reactions of group IV organometallic compounds: XVII. Addition reactions of heptamethyldisilazane with benzoyl iso(thio)cyanate and subsequent eliminations

Benzoyl isocyanate and isothiocyanate react with heptamethyldisilazane to give 1 1 adducts, which exist as mixtures of the isomers involving 1,3-transfer of trimethylsilyl groups. The adducts from benzoyl isothiocyanate decompose thermally by two βB-elimination processes; one, at temperatures below 100°, givesmethyl isothiocyanate, and the other, at 150°, gives trimethylsilyl isothiocyanate. Migration of trimethylsilyl groups was confirmed by means of NMR measurements at various temperatures. This migration is important in determining the course of subsequent βB-elimination reactions.