Highly Stereoselective Gold‐Catalyzed Coupling of Diazo Reagents and Fluorinated Enol Silyl Ethers to Tetrasubstituted Alkenes

We report a highly stereoselective synthesis of all‐carbon or fluorinated tetrasubstituted alkenes from diazo reagents and fluorinated enol silyl ethers, using C−F bond as a synthetic handle. Cationic Au^I catalysis plays a key role in this reaction. Remarkable fluorine effects on the reactivity and selectivity was also observed.     

黄烷酮烯醇硅醚氧化重排成异黄酮

3,3″-偶联的双黄烷酮类化合物自1979年首次从瑞香狼毒中分离得到以来,对于它们的合成一直受到重视。我们试图应用Moriarty等人发现的用氧化碘苯氧化酮的烯醇硅醚合成1,4-二芳基-1,4-二酮的方法。     

An Efficient Regio and Stereoselective Synthesis of Silyl Enol Ethers

Ketones and aldehydes on treatment with NaBr-Me₃SiCl-Et₃N in DMF at ambient temperature yield silyl enol ethers with high regio- and stereoselecti-vity.     

FLP‐Catalyzed Transfer Hydrogenation of Silyl Enol Ethers

Herein we report the first catalytic transfer hydrogenation of silyl enol ethers. This metal free approach employs tris(pentafluorophenyl)borane and 2,2,6,6‐tetramethylpiperidine (TMP) as a commercially available FLP catalyst system and naturally occurring γ‐terpinene as a dihydrogen surrogate. A variety of silyl enol ethers undergo efficient hydrogenation, with the reduced products isolated in excellent yields (29 examples, 82 % average yield).     

Rhodium‐Catalyzed Dehydrogenative Silylation of Acetophenone Derivatives: Formation of Silyl Enol Ethers versus Silyl Ethers

A series of rhodium–NSiN complexes (NSiN=bis (pyridine‐2‐yloxy)methylsilyl fac‐coordinated) is reported, including the solid‐state structures of [Rh(H)(Cl)(NSiN)(PCy₃)] (Cy=cyclohexane) and [Rh(H)(CF₃SO₃)(NSiN)(coe)] (coe=cis‐cyclooctene). The [Rh(H)(CF₃SO₃)(NSiN)(coe)]‐catalyzed reaction of acetophenone with silanes performed in an open system was studied. Interestingly, in most of the cases the formation of the corresponding silyl enol ether as major reaction product was observed. However, when the catalytic reactions were performed in closed systems, formation of the corresponding silyl ether was favored. Moreover, theoretical calculations on the reaction of [Rh(H)(CF₃SO₃)(NSiN)(coe)] with HSiMe₃ and acetophenone showed that formation of the silyl enol ether is kinetically favored, while the silyl ether is the thermodynamic product. The dehydrogenative silylation entails heterolytic cleavage of the Si?H bond by a metal–ligand cooperative mechanism as the rate‐determining step. Silyl transfer from a coordinated trimethylsilyltriflate molecule to the acetophenone followed by proton transfer from the activated acetophenone to the hydride ligand results in the formation of H₂ and the corresponding silyl enol ether.     

Rhodium‐Catalyzed Remote C(sp3)−H Borylation of Silyl Enol Ethers

A rhodium‐catalyzed remote C(sp³)?H borylation of silyl enol ethers (SEEs, E/Z mixtures) by alkene isomerization and hydroboration is reported. The reaction exhibits mild reaction conditions and excellent functional‐group tolerance. This method is compatible with an array of SEEs, including linear and branched SEEs derived from aldehydes and ketones, and provides direct access to a broad range of structurally diverse 1,n‐borylethers in excellent regioselectivities and good yields. These compounds are precursors to various valuable chemicals, such as 1,n‐diols and aminoalcohols.     

The Use of Silyl Ketene Acetals and Enol Ethers in the Catalytic Enantioselective Alkylative Ring Opening of Oxa/Aza Bicyclic Alkenes

Silyl ketene acetals and enol ethers are employed as reactive and functional group tolerant nucleophiles in the enantioselective rhodium‐catalyzed alkylative ring opening of a diverse class of oxa/azabicyclic alkenes. This method provides access to enantioenriched dihydronaphthalene and cyclohexene scaffolds, which have the potential to be derivatized toward core motifs of naphthoquinone and sesquiterpene natural products.     

N—乙酰乙酰基吡咯及其烯醇硅醚的合成和结构研究

N-乙酰乙酰基吡咯为有机合成上有用的起始原料和中间体。例如,可能作为合成Carbapenam类β-内酰胺化合物的原料。1977年,Wang Nam-Chiang和And-     

Chiral Organosiucon Compounds. Part 1. Synthesis of Chiral Silyl Enol Ethers

A convenient synthesis of menthol- and borneol-derived chiral silyl enol ethers is described.     

Enantioselective Addition of Cyclic Enol Silyl Ethers to 2-Alkenoyl-Pyridine-N-Oxides Catalysed by Cu(II) -Bis(oxazoline) Complexes

Asymmetric reactions involving (E)-3-aryl-1-(pyridin-2-yl-N-oxide)prop-2-en-1-ones and cyclic enol silyl ethers show good yields and excellent enantioselectivities (up to 99.9?% ee) when catalysed by bis(oxazoline)-Cu(II) complexes. Different reaction pathways can be followed by different enol silyl ethers: with 2-(trimethylsilyloxy)furan, a Mukaiyama-Michael adduct is obtained, whereas a hetero Diels-Alder cycloadduct was formed by using (1,2-dihydronaphthalen-4-yloxy)trimethylsilane. In the latter reaction, the absolute configuration of the product is consistent with a reagent approach to the less hindered Re face of the coordinated substrate in the reactive complex.     

Bench-Stable Electrophilic Fluorinating Reagents for Highly Selective Mono- and Difluorination of Silyl Enol Ethers

Efficient methods for the synthesis of fluorinated compounds have been intensively studied, recently. Development of practical fluorinating reagents is indispensable for this purpose. Herein, bench-stable electrophilic fluorinating reagents were synthesized as N-fluorobenzenesulfonimide (NFSI) substitutes. Reagents obtained by replacing one of the NFSI sulfonyl groups with an acyl group led to the highly selective monofluorination of silyl enol ethers with suppression of undesired overreaction, that is, difluorination. On the other hand, reagents bearing electron-withdrawing substituents at NFSI benzenesulfonyl groups efficiently facilitated the difluorination of silyl enol ethers under base-free conditions. Thus, both mono- and difluorinated target materials were prepared from the same substrate.     

Stereoselective Access to Fully Substituted Aldehyde-Derived Silyl Enol Ethers by Iridium-Catalyzed Alkene Isomerization

An in situ generated cationic Ir-catalyst isomerizes simple allylic silyl ethers into valuable, fully substituted aldehyde-derived silyl enol ethers. Importantly, by judicious choice of substrate, either of the two possible stereoisomers of a given enolate derivative is accessible with complete stereoselectivity. One-pot isomerization-aldol and isomerization-allylation processes illustrate the synthetic utility of this method.     

A Mild and Highly Efficient Method for the Preparation of Silyl Ethers using Fe(HSO4)3/Et3N by Chlorosilanes

A very efficient and mild procedure for preparation of silyl ethers from benzylic, allylic, propargilic alcohols, phenols, naphtoles and some of phenolic drugs with trimethylsilylchloride (TMSCl), triethylsilylchloride (TESCl) and t‐buthyldimethylsilyl chloride (TDSCl) ethers in the presence of Fe(HSO₄)₃/Et₃N in room temperature in excellent yields is reported. This procedure also allows the excellent selectivity for silylation of alcohols and phenols.