Presence Of Me3SiCl Research Articles

A free boratriptycene-type Lewis superacid.

Bicyclic pyrazabole-bridged ferrocenes with BH groups at their bridgehead positions were prepared from [Li(thf)]2[1,1′-fc(BH3)2] and pyrazole or 3,5-dimethylpyrazole in the presence of Me3SiCl (1 or 1Me, respectively; 1,1′-fc = 1,1′-ferrocenylene); Me3SiH and H2 are released as byproducts. Treatment of 1 or 1Me with 1 eq. of the hydride scavenger [Ph3C][B(C6F5)4] afforded the borenium salts [2][B(C6F5)4] (72%) and [2Me][B(C6F5)4] (77%). According to X-ray crystallography, [2Me]+ contains one trigonal-planar borenium cation, the cyclopentadienyl (Cp) rings of the 1,1′-fc fragment remain parallel to each other, but the Cp–B bond vector is bent out of the Cp plane by an unprecedentedly large dip angle α* of 40.6°. The Fe⋯B(sp2) distance is very short (2.365(4) Å) and the 11B NMR signal of the cationic B(sp2) center is remarkably upfield shifted (23.4 ppm), suggesting a direct Fe(3d) → B(2p) donor–acceptor interaction. Although this interpretation is confirmed by quantum-chemical calculations, the coupling between the associated orbitals corresponds to an energy of only 12 kJ mol−1. Accordingly, both the experimental (e.g., Gutmann–Beckett acceptor number AN = 111) and theoretical assessment (e.g., Et3PO and F−-ion affinities) of the Lewis acidity proves that [2]+ is among the strongest boron-based Lewis acids available to date.

Alkyne [2 + 2 + 2] Cyclotrimerization Catalyzed by a Low-Valent Titanium Reagent Derived from CpTiX3 (X = Cl, O-i-Pr), Me3SiCl, and Mg or Zn

Inter-, partially intra-, and intramolecular [2 + 2 + 2] cycloadditions of alkynes were catalyzed by a low-valent titanium species generated in situ from the reduction of CpTi(O-i-Pr)3, CpTiCl3, or Cp*TiCl3 with Mg or Zn powder in the presence of Me3SiCl. The role of Me3SiCl as an additive in the reaction mechanism is discussed.

Low-valent titanium-catalyzed deprotection of allyl- and propargyl-carbamates to amines

In the presence of Me3SiCl, Ti(O-i-Pr)4/Mg and CpTiCl3/Mg reagents effectively catalyzed the deprotection of allyloxycarbonyl (alloc)- and propargyloxycarbonyl (poc)-protected amines in THF at around room temperature to produce parent amines in good yields. Alloc- and poc-protected secondary amines were smoothly deprotected to parent amines by a reaction catalyzed by a Ti(O-i-Pr)4/Me3SiCl/Mg reagent. The deprotection of alloc- and poc-protected primary amines was successfully catalyzed by a CpTiCl3/Me3SiCl/Mg reagent.

Synthetic Reactions Using Low-valent Titanium Reagents Derived from Ti(OR)4 or CpTiX3 (X = O-i-Pr or Cl) in the Presence of Me3SiCl and Mg.

In the presence of Me3SiCl, Ti(OR)4 or CpTiX3 (X = O-i-Pr or Cl) is reduced by Mg powder in THF to gradually generate a specific low-valent titanium (LVT) species that mediates several synthetic reactions. The LVT-catalyzed C-O bond-cleaving reactions of allyl and propargyl ethers and esters generate parent alcohols and carboxylic acids, respectively. O-allyl and propargyl carbamates are also readily deprotected by the LVT to afford parent amines. In addition, the respective reductive N-S or O-S bond cleavage of sulfonamides or sulfonyl esters mediated by the LVT was developed as a novel facile deprotection method. The reagent catalyzes intra- and intermolecular alkyne or alkyne/nitrile cycloaddition to produce substituted benzenes and pyridines, while epoxides and oxetanes are reduced to alcohols via an LVT-mediated homolytic ring opening. The McMurry coupling of aryl aldehydes and ketones proceeds with the LVT under homogeneous and mild reaction conditions and is effective for the polymerization of aromatic dialdehydes, generating conjugated polymers. Finally, imino-pinacol coupling of imines is mediated by the LVT to provide 1,2-diamines.

Reduction of CO2 to free CO by a Pd(I)-Pd(I) dimer.

Reaction of CO2 with a Pd(I)-Pd(I) dimer supported by amido/bis(phosphine) pincer PNP ligands produces free CO in the presence of Me3SiCl and Me3SiOTf.

Electrochemical and Chemical Reduction of Phosphine Oxides to the Corresponding Phosphines

Phosphines (R3P) have been used as reductants in Wittig, Staudinger, Appel, and Mitsunobu reactions as well as ligands in various transition metal catalysts. Though phosphines can be synthesized by reduction of the corresponding phosphine oxides (R3P=O) with hydrosilanes, P=O bond is so strong that the reduction proceeds only under harsh conditions, and C-P bonds would be cleaved. We reported that Ph3P was obtained from Ph3P=O via Ph3PCl2.1 Since Ph3PCl2 is moisture-sensitive, Ph3PCl2 is hard to be stored and should be prepared just before the reduction. We investigated direct reduction of R3P=O to R3P under mild conditions. In this paper, we describe that the reduction proceeds electrochemically and chemically under 45 ºC in the presence of an efficient oxophile, Me3SiCl (Fig. 1).Fig. 1. Reduction of Phosphine Oxides 1 A typical procedure for electrochemical reduction (ECR) is as follows. In an undivided cell fitted with Zn anode (1.0 x 1.5 cm2) and Cu cathode (1.0 x 1.5 cm2) was placed an acetonitrile (5 mL) solution of 1 (2 mmol), Me3SiCl (6 mmol),2 and Bu4NBr (2 mmol). The electroreduction was carried out under constant current conditions (100 mA, 4 F/mol-1) at 45 ºC. Usual work-up and purification by silica gel column chromatography gave 2(Table 1, ECR). Table 1. Me3SiCl-Assisted Electrochemical (ECR) and Chemical Reduction (CR) of Phosphine Oxides 1 The reduction of triarylphosphine oxides 1a and 1c-1e proceeded smoothly to give the corresponding triarylphosphines 2a and 2c-2e in 80-96% yields (Table 1, Runs 1, 3-5, ECR), whereas tris(o-tolyl)phosphine oxide 1b was reduced less effectively to give 2b in 22% yield, presumably due to steric hindrance of the o-substituents (Run 2). Electroreduction of alkyl-diarylphosphine oxides 1f and 1g was performed in a similar manner to give the corresponding phosphine 2f and 2g in 82% and 46% yields, respectively (Runs 6, 7). It is worthy to note that no appreciable peaks except for 1 and 2 were observed in 31P NMR of the crude products. Electroreduction of triphenyl phosphate 1hwas not successful (Run 8). .Similar reduction of 1 was performed chemically (CR) by using Mg as an electron source. A typical procedure is as follows: A mixture of 1 (2 mmol), magnesium powder (8 mmol),3 and Me3SiCl (6.0 mmol)2 in 1,3-dimethylimidazolidinone (8 mL) was stirred for 2 hours at room temperature under Ar atmosphere. Usual work-up followed by silica gel column chromatography gave 2 (Table 1, CR).4 Proper choice of the solvent is essential: the reduction of 1 proceeded smoothly only in DMI, and 2was obtained in less than 10% yields in MeCN and DMF, and no reduction occurred in THF. Chemical shift of Ph3P=O (1a, 31P NMR: d 27.3 ppm) did not shift by the addition of Me3SiCl. CV curve of 1a showed a single, irreversible wave at -3.0 V versus Ag/Ag+, whereas Me3SiCl did not show any reduction wave at range of 0 - -3.5 V. Addition of Me3SiCl caused significant increase of the reduction current without change of the reduction potential of 1a. From these facts, we propose a plausible mechanism of the reduction of phosphine oxide 1 (Fig. 2). In the initial stage of the reduction of 1, one-electron reduction would occur to form an anion radical [R3P·-O]- 3, which would be trapped with Me3SiCl to give radical [R3P·-OSiMe3] 4. Further one-electron reduction of 4, leading to anion 5, and subsequent P-O bond cleavage followed by silylation with Me3SiCl would give 2 together with (Me3Si)2O. Fig. 2. A Plausible MechanismIn conclusion, R3P=O is reduced to the corresponding R3P electrochemically and chemically in the presence of Me3SiCl under mild conditions. 1Yano, T.; Hoshino, M.; Kuroboshi, M.; Tanaka, H. Synlett 2010, 801-803. 2Though the reduction proceeded with t BuMe2SiCl and i Pr3SiCl similarly, no 2 was obtained with MgCl2 and SiCl4, probably because 2 is easily adsorbed on MgCl2 and SiO2 derived from SiCl4, to prevent electron transfer from Mg. 3Mg turnings gave 2in lower yield, whereas zinc powder and aluminum chips did not proceed the reduction at all. 4Though CuCl activated Mg to give 2 quantitatively, 2 formed complex with Cu species.

Synthesis of Heterodinuclear Hemisalen Complexes on a Hexaarylbenzene Scaffold and their Application for the Cross‐Pinacol Coupling Reaction

Intermolecular cross-pinacol coupling reaction between aliphatic and aromatic aldehydes by using heterodinuclear hemisalen complexes 1cis with vanadium(V) and titanium(IV) on a hexaarylbenzene scaffold is reported. Our ligand design is based on the individual activation of two aldehydes by vanadium and titanium, which are positioned with a suitable space on the rigid scaffold. Ligands such as 1cis were synthesized by Diels-Alder addition and decarbonylation reaction, followed by condensation of dialdehyde 3cis with various aminophenols. The influence of the substituents on the ligands on the pinacol coupling reaction was investigated. As a result, the reductive coupling reaction between aliphatic and aromatic aldehydes by using a catalytic amount of 1cis in the presence of Me3 SiCl and Zn provided the corresponding cross-coupled 1,2-diol in good yields with high cross-selectivity.

Condensed isoquinolines. 37.* Heterocyclization using 3-(arylamino)- and 3-(hetarylamino)isoquinolin-1(2H)-ones

The reaction of 3-NHR-isoquinolin-1(2H)-ones (R = Ar) with aromatic aldehydes in the presence of Me3SiCl or in acetic acid leads to the formation of derivatives of dibenzo[b,f][1, 8]naphthyridin-5(6H)- one and benzo[f]isoquino[3,4-b][1, 8]naphthyridine-5,9(6H,7H)-dione. The reaction for R = Het in the presence of Me3SiCl gives derivatives of 5H-pyrido[1',2':1,2]pyrimido[4,5-c]isoquinolin-5-one, benzo[f]isoquinoline[3,4-b][1,8]naphthyridine-5,9[6H,7H]-dione, and derivatives of new heterocyclic systems, 5H-pyrazino[1',2':1,2]pyrimido[4,5-c]isoquinolin-5-one, 5H-[1,3]thiazolo[3',2':1,2]pyrimido- [4,5-c]isoquinolin-5-one, 5-H-benzo[f]pyrazolo[3,4-b][1,8]naphthyridin-5-one, and isoquino[3,4-b]- [1,5]naphthyridin-5(6H)-one. The effect of the structure of substituent R and nature of the substituent in the benzaldehydes on the structure of the reaction products was studied.

ChemInform Abstract: Application of Homochiral Lithium Amide Base Chemistry to a Thiane Oxide System.

Treatment of the thiane oxide 6 with a homochiral lithium amide (HCLA) base 7, followed by electrophilic quench of the so-formed sulfoxide carbanion with Me3SiCl, Mel or ButCO2Et, gives the optically active products (+)-8, (+)-11 and (+)-12, respectively, in 55–60% enantiomeric excess (ee). The reaction of 6 with the HCLA base 9 can be carried out in the presence of Me3SiCl (in situ quench conditions), in which case a silylation–in situ kinetic resolution process occurs, furnishing (–)-8 in low chemical yield, in up to 69% ee. Further transformations of thiane oxides (+)-8 and (+)-11 involving reduction or removal of the ring sulfur atom were conducted, in order to establish the absolute configuration of the products. Highly stereoselective reduction of the keto sulfoxide (+)-12 was also carried out, leading ultimately to an epoxide product 20via opening of the thiane ring.

Reactions of N,N′-thiobisamines with norbornene in the presence of Me3SiCl

Reactions of N,N′-thiobisamines with norbornene in the presence of Me3SiCl

The structural transformations of silicon phthalocyanine in reaction with magnesium and trimethylchlorosilane

The reaction of PcSi(OSiMe3)2 with Mg in the presence of Me3SiCl at 20–100°C was shown to cause the phthalocyamine macrocycle contraction and give the silicon α,β,γ-triazatetrabenzocorrole macrocycle. The reaction proceeds in the polar donor solvents (THF, pyridine), but does not occur in aromatic hydrocarbons. The electronic and EPR spectra indicate that the silicon phthalocyanine mono- and dianions are active intermediate reaction products.

Three-component condensation of diethyl isophthaloyldiacetate, aromatic aldehyde, and urea as a new method for the synthesis of 1,3-bis(2-oxo-1,2,3,4-tetrahydropyrimidin-6-yl)benzenes

Condensation of diethyl isophthaloyldiacetate, aromatic aldehyde, and urea in the presence of Me3SiCl proceeds efficiently and faster than in the absence of the latter to form 1,3-bis(2-oxo-1,2,3,4-tetrahydropyrimidin-6-yl)benzene derivatives capable to give inclusion complexes with DMF.

Photoreactivity and Photopolymerization of Silicon‐Bridged [1]Ferrocenophanes in the Presence of Terpyridine Initiators: Unprecedented Cleavage of Both Iron–Cyclopentadienyl Bonds in the Presence of Chlorosilanes

The photopolymerisation of sila[1]ferrocenophane [Fe(eta-C5H4)2SiMe2] (3) with 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine (tBu3terpy) as initiator has been explored. High-molecular-weight polyferrocenylsilane (PFS) [{Fe(eta-C5H4)2SiMe2}n] (5) was formed in high yield when a stoichiometric amount of tBu3terpy was used at 5 degrees C. Photopolymerisation of ferrocenophane 3 at higher temperatures gave PFS 5 in lower yield and with a reduced molecular weight as a result of a slower propagation rate. Remarkably, when Me3SiCl was added as a capping agent before photopolymerisation, subsequent photolysis of the reaction mixture resulted in the unprecedented cleavage of both iron-Cp bonds in ferrocenophane 3: iron(II) complex [Fe(tBu3terpy)2Cl2] (7Cl) was formed and the silane fragment (C5H4SiMe3)2SiMe2 (8) was released. The iron-Cp bond cleavage reaction also proceeded in ambient light, although longer reaction times were required. In addition, the unexpected cleavage chemistry in the presence of Me3SiCl was found to be applicable to other photoactive ferrocenes such as benzoylferrocene. For benzoylferrocene and ferrocenophane 3, the presence of metal-to-ligand charge transfer (MLCT) character in their low-energy transitions in the visible region probably facilitates photolytic iron-Cp bond cleavage, but this reactivity is suppressed when the strength of the iron-Cp bond is increased by the presence of electron-donating substituents on the cyclopentadienyl rings.

A One-Pot Fusion of Nitrogen-Containing Heterocycles

Aromatic and heteroaromatic dialkylaminoaldehydes react with various active methylene compounds in the presence of Me3SiCl to give functionally and structurally diverse pyrrolo[1,2-a]quinolines, pyrido[1,2-a]quinolines, pyrazolo[3,4-e]indolizines, pyrazolo[4,3-c]quinolizines, benzo[g]pyrrolo[1,2-a]-1,8-naphthyridines, and benzo[g]pyrido[1,2-a]-1,8-naphthyridines in high yield and excellent purity.

Transformation of Aldehydes into (E)-1-Alkenylsilanes and (E)-1-Alkenylboronic Esters with a Catalytic Amount of a Chromium Salt

Abstract (Diiodomethyl)trimethylsilane (Me3SiCHI2, 1) is produced by treatment of iodoform with manganese in the presence of Me3SiCl. Aldehydes are converted to (E)-1-trimethylsilyl-1-alkenes in a stereoselective manner with a geminal dichromium reagent generated from 1, manganese, Me3SiCl, and a catalytic amount of CrCl3[thf]3 in THF. Similarly, (E)-1-alkenylboronic esters are prepared stereoselectively in good to excellent yields by treatment of aldehydes with a geminal dichromium reagent derived from Cl2CHB(OR)2 [(OR)2 = OCMe2CMe2O] and LiI instead of 1.

Synthesis and structure of a novel Pd(0)–Pd(IV)–Pd(IV)–Pd(0) mixed-valence complex

The interaction of PdCl2(PhCN)2 with 1,2-[PhP(H)CH2CH2CH2P(Ph)CH2]2C6H4, generated in situ from the reduction of the corresponding phosphine oxide with LiAlH4 in the presence of Me3SiCl, gave a complex mixture, from which a di- and a tetra-nuclear palladium complex 1 and 2 whose solid state structures were ascertained by X-ray crystallography, were isolated. A novel Pd(0)–Pd(IV)–Pd(IV)–Pd(0) mixed-valence structure was observed in complex 2.

Exchange of boryl ligand substituents in Os[B(OEt) 2]Cl(CO)(PPh 3) 2

Reaction between Os[B(OEt) 2]Cl(CO)(PPh 3) 2 and 1,2-ethanediol in the presence of Me 3SiCl (1 equivalent) leads to the tethered boryl complex, ▪Cl(CO)(PPh 3) 2 ( 1), in which one ethoxy substituent on the boryl ligand is exchanged with one hydroxy group of the 1,2-ethanediol leaving the other OH group available to coordinate to osmium, so giving a six coordinate complex. This formulation is confirmed by crystal structure determination. The same reactants, but with 2 equivalents of Me 3SiCl, lead to the yellow, coordinatively unsaturated complex, Os ▪Cl(CO)(PPh 3) 2 ( 2). Complex ( 2) adds CO to give Os ▪Cl(CO) 2 (PPh 3) 2 ( 3). Crystal structure determinations of 2 and 3 reveal a very marked difference in the Os–B distances found in the five coordinate complex 2 (2.043(4) Å) and the six coordinate complex 3 (2.179(7) Å). In a reaction similar to that used for forming 2 but with 1,3-propanediol replacing 1,2-ethanediol, the product is Os ▪Cl(CO)(PPh 3) 2 ( 4). The crystal structure for 4 is also reported.

An Efficient and Inexpensive Catalyst System for the Aza‐Michael Reactions of Enones with Carbamates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

TMSCl-Promoted Transition Metal-Catalyzed Aza-Michael Reactions of Chalcones with Carbamates

An improved strategy, which uses transition metals as effective catalyst in the presence of Me3SiCl, has been developed for the conjugate addition of chalcones with unactivated weakly nucleophilic carbamates.

Palladium-catalyzed alkylation of unactivated olefins

Abstract The reaction of a 3-butenyl β-diketone with a catalytic amount of PdCl2(CH3CN)2 in dioxane at room temperature led to olefin hydroalkylation and formation of the corresponding 2-acylcyclohexanone in good yield as a single regioisomer. Deuterium-labeling experiments for the hydroalkylation of 7-octene-2,4-dione were in accord with a mechanism involving outer-sphere attack of the pendant enol on a palladium-complexed olefin to form a palladium cyclohexyl species, followed by palladium migration via iterative β-hydride elimination/addition and protonolysis from a palladium enolate complex. In comparison to a 3-butenyl β-diketone, reaction of a 4-pentenyl β-diketone with a catalytic amount of PdCl2(CH3CN)2 in the presence of CuCl2 led to oxidative alkylation and formation of the corresponding 2-acyl-3-methyl-2-cyclohexenone in good yield as a single isomer. Unactivated olefins tethered to less reactive carbon nucleophiles such as β-keto esters, α-aryl ketones, and even dialkyl ketones underwent palladium-catalyzed hydroalkylation in the presence of Me3SiCl or HCl to form the corresponding cyclohexanones in moderate-to-good yield with high regioselectivity.