Chemoselective deprotection of silyl ethers by DIBALH

The first examples of highly selective deprotection of silyl ethers by DIBALH are reported. Its selectivity enabled us to remove a primary TBS group and a primary TBDPS group in the presence of a secondary TES group.     

Selective deprotection of alcoholic and phenolic silyl ethers

Hydrofluoric acid and tetrabutylammonium fluoride will selectively deprotect alcoholic and phenolic silyl ethers respectively.     

Solvent-modulated Pd/C-catalyzed deprotection of silyl ethers and chemoselective hydrogenation

Recently we have reported undesirable and frequent deprotection of the TBDMS protective group of a variety of hydroxyl functions occurred under neutral and mild hydrogenation conditions using 10% Pd/C in MeOH. The deprotection of silyl ethers is susceptible to significant solvent effect. TBDMS and TES protecting groups were selectively cleaved in the presence of acid-sensitive functional groups such as TIPS ether, TBDPS ether and dimethyl acetal under hydrogenation condition using 10% Pd/C in MeOH. In contrast, chemoselective hydrogenation of reducible functional groups such as acetylene, olefin and benzyl ether, proceeds in the presence of TBDMS or TES ethers in AcOEt or MeCN.     

The chemoselective and efficient deprotection of silyl ethers using trimethylsilyl bromide

An efficient and chemoselective cleavage of silyl ethers (primary, secondary and aromatic) by using catalytic quantities of trimethylsilyl bromide (TMSBr) in methanol is reported. A wide range of alkyl silyl ethers such as TBS, TIPS, and TBDPS can be chemoselectively cleaved in high yield in the presence of aryl silyl ethers. The deprotection of silyl esters was also achieved employing catalytic quantities of TMSBr.     

Inept-29Si NMR study of a TiCl4-mediated reaction of an enol silyl ether

Condensation of 1,3-bis(trimethylsiloxy)-1-methoxybutadiene ($\text{1}$) and 2-phenyl-2,2-dimethoxyethanal ($\text{2}$) under TiCl₄ condition gave the γ-hydroxycyclopentenone product $\text{3}$. The reaction was followed by INEPT²⁹Si NMR. Implication to the mechanism of the reaction was discussed.     

Efficient chemoselective deprotection of silyl ethers using catalytic 1-chloroethyl chloroformate in methanol

Fast and chemoselective desilylation of silyl-protected alcohols was achieved using a catalytic amount of 1-chloroethyl chloroformate in methanol. With a minimal amount of 1-chloroethyl chloroformate as the source for anhydrous HCl, extremely efficient cleavage of silyl ethers of primary and secondary alcohols was accomplished, and chemoselective deprotection of one silyl ether in the presence of another silyl or other acid-labile group was possible through controlling the amount of the chloroformate and reaction time.     

Phenylthiomethylstannylation of silyl enol ethers and silyl dienol ethers

Silyl enol ethers (2) react with tributyl [(phenylthio) chloromethyl] stannane (1) in the presence of Zinc bromide to give β-phenylthiomethylstannyl ketones (3) in good yields. Silyl dienol ethers (4) mainly give products (5) due to γ-attack, under these conditions.     

An atom-efficient and powerful method for direct esterification of silyl ethers catalyzed by HClO4-SiO2

An efficient and convenient procedure for direct esterification of alkyl and aryl silyl ethers with Ac₂O and a catalyst system of perchloric acid immobilized on a silica gel (HClO₄-SiO₂) has been developed. The silyl protecting groups are directly replaced by acetyls and the protecting groups themselves are transformed into acetates as the sole byproducts, which can be readily recovered and converted back to silylchlorides, the original protecting agents, thus minimizing wastes.     

BF3-OEt2-mediated rearrangement of 4-substituted-5,5-diphenylazepan-4-ols

Synthesis of 2-(2-substituted-ethylidene)-3,3-diphenylpyrrolidines has been established starting from different 4-substituted-4-aryl-5,5-diphenylazepan-4-ols via boron trifluoride etherate-mediated rearrangement.     

Ruthenium-catalyzed oxidation of silyl ethers to silyl esters

Direct oxidation of silyl ethers to silyl esters, using RuO₄ formed in situ, is reported. The reaction was optimized to minimize formation of the corresponding carboxylic acid product whose formation pathway appears to be solvent dependent. The reaction is tolerant of halides, nitriles, nitro groups, esters, epoxides, and ketones.     

Synthesis of the C5-C30 fragment of cyclodidemniserinol trisulfate via I2-mediated deprotection and ring closure tandem reaction

The marine natural product cyclodidemniserinol trisulfate displayed moderate HIV-1 integrase inhibitory activity. Its novel structure triggered our interest to synthesize it. In our total synthesis effort, the natural product was dissected into four fragments based on the rational retrosynthetic analysis. All four fragments were successfully prepared with orthogonal protection. And the assembly of fragment A and B furnished the C₅-C₃₀ key subunit by employing the I₂-mediated deprotection and intramolecular ketal formation tandem reaction in the presence of NaHCO₃ in MeCN. Our work provided flexible and practical approaches to synthesize and derive the 3,5,7-trisubstituted 6,8-dioxabicyclo [3.2.1] octane based analogs to search for new structure HIV-1 integrase inhibitors.     

Deracemization of silyl enol ethers

The deracemization by enantioselective protonation of silyl enol ethers was tested using 2,2-dimethyl 5-phenyl 1,3-dioxolan 4-one 1. The results obtained, especially with pantolactone as a chiral proton donor, are better than when the deracemization is carried out with the lithium enolate of 1.     

TiCl3/PhN2-mediated radical addition of ethers to aldimines generated in situ under aqueous conditions

Ti(III)-mediated one-electron reduction of phenyldiazonium cation, followed by phenyl radical α-H atom abstraction from ethers, leads to one-pot radical addition of ethers to the C-atom of imines generated in situ from the corresponding aldehydes and imines under aqueous conditions. The reaction is not limited to aromatic aldehydes and may be applied to imines generated in situ from formaldehyde and enolizable aldehydes.     

Diallylation of 2,2-dialkylbenzodioxoles from TiCl4-mediated allylsilane reaction

Reaction of aliphatic ketones with catechol afforded 2,2-dialkylbenzodioxoles. Treatment of these benzodioxoles with allyltrimethylsilane in the presence of titanium tetrachloride led to 4,4-dialkylhepta-1,6-dienes resulting from a diallylation process. Ring-closing metathesis gave rise to 4,4-dialkylcyclopentenes.     

Catalytic isomerization of acetylenic silyl ethers to dienol silyl ethers by ruthenium hydride complexes

Acetylenic silyl ethers are converted catalytically to the corresponding conjugated dienol silyl ethers by ruthenium hydride complexes.     

Lewis acid-catalyzed nucleophilic substitutions of propargylic and allylic silyl ethers with enol silyl ethers

Nucleophilic reactions of various enol silyl ethers with carbocation species generated from propargyl silyl ethers by the action of a Lewis acid have been developed. The present method is highly useful for the introduction of allenic or enyne functionalities into the alpha-position of substituted ketones. [reaction--see text]     

Trimethylsilyl derivatives of N-Boc-cytosine and their effect on I2-mediated nucleosidation of O-MTM ethers

Mono- and bis(trimethylsilyl) derivatives of N⁴-Boc-cytosine were synthesized and characterized by ¹H NMR. Only the mono(trimethylsilyl)-N⁴-Boc-cytosine participates in the iodine-mediated nucleosidation of N-Fmoc-O-methylthiomethyl serine benzyl ester to produce the cytosine nucleoamino acid, while the bis(trimethylsilyl) derivative failed to give any product. A tentative mechanistic explanation is proposed.     

Synthesis of tetrahydroisoquinolines through TiCl4-mediated cyclization and Et3SiH reduction

A versatile and efficient telescoped reaction sequence for the synthesis of tetrahydroisoquinolines(THIQs)is reported that uses TiCl4 to promote cyclization of a benzylaminoacetal derivative and Et3SiH for reduction of the intermediate 4-hydroxy-THIQ.This method is complimentary to the classical Pomeranz-Fritsch and related reactions since it tolerates electron-withdrawing substituents and allows access to 8-substituted THIQs.     

K2HPO4-mediated Photocatalytic H2 Production over NiCoP/RP Heterojunction

In this work, bimetallic NiCoP nanoparticles（NPs） were firstly prepared by a solvothermal method using red phosphorus（RP） as P source, and it was combined with RP nanosheets via a physical grinding process. Investigation indicates that NiCoP has better charge transfer ability and faster H₂ releasing kinetics than the corresponding single metal phosphides alone. 6 wt% NiCoP/RP exhibits an excellent H2 evolution activity in 20 vol.% triethanol-amine/water solution under a 300W Xe-lamp i...