Competitive demethylation and substitution in N,N,N-trimethylanilinium fluorides

Fluorination of aromatic compounds by nucleophilic displacement of trimethylanilinium salts by fluoride is a commonly used reaction for radiotracer synthesis. Though the liberated trimethylamine is thought to be an excellent leaving group for this type of S_NAr reaction, scattered reports show that amine demethylation (reverse Menschutkin reaction) sometimes dominates over substitution, particularly when relatively electron rich fluoroarenes are the desired targets. Here we provide systematic experimental and theoretical studies of trimethylanilinium demethylation and substitution. Results from these studies highlight the limits of this leaving group in fluoroarene synthesis and have important ramifications for the design of nucleophilic fluorinating agents featuring ammonium cations.     

Enhancement of Acid‐Catalyzed Esterification by the Addition of Base

General acid‐catalyzed reaction can be enhanced by the addition of base. Self‐catalyzed esterification of benzoic acid and octan‐1‐ol was enhanced by the addition of certain base such as imidazole. The rate of the esterification was accelerated as the concentration of imidazole increased. Trans‐esterification of 4‐nitrophenyl acetate was promoted in chloroform by the mixture of benzoic acid and imidazole, but not by benzoic acid or imidazole alone.     

Mild Approach to the Deprotection of Troc from Protected Amines Using Mischmetal and TMSCl

The 2,2,2-trichloroethoxycarbonyl (Troc) protecting group was efficiently removed from Troc-protected aliphatic and aromatic amines and also some Troc, Tos- and Troc, Ac-protected amines using activated mischmetal (MM). All reactions were performed by refluxing in dry tetrahydrofuran under an argon atmosphere and gave moderate to excellent yields. Several new compounds were synthesized, and new data about reactivity of Troc group were obtained.     

Deprotection of durable benzenesulfonyl protection for phenols — efficient synthesis of polyphenols

A robust protection method for phenol was demonstrated by the use of durable benzenesulfonyl group, which survives various harsh reaction conditions using Grignard reagent, organolithium reagent, metal alkoxide, phosgene, mineral, and Lewis acids. A facile deprotection condition utilizing pulverized KOH (5 equiv) and t-BuOH (10 equiv) in hot toluene makes this protocol as a practical method, which can be applied to the multistep synthesis of biologically and medicinally important polyphenol compounds.     

Efficient Chemoselective Mild Deprotection of S,Sand S,O-Acetals and Ketals with Electrophilic Halogens

A novel and simple method for the chemoselective deprotection of S,S- and S,O-acetals and ketals in the presence of their O,O-analogs with electrophilic halogens to their corresponding carbonyl compounds is described using N-bromosuccinimide, N-chlorosuccinimide, 2,4,4,6-tetrabromo-2,5-cyclohexen-1-one, trichlorocyanuric acid, or molecular bromine in aqueous acetonitrile. The use of these reagents in the presence of hydrated silica gel provide efficient, novel, and mild procedures for the deprotection of cyclic and acyclic O,O-, S,S-, and S,O-acetals and ketals in excellent yields in short reaction times.     

Heterogeneous Thiocyanation of Benzylic Alcohols and Silyl and THP Ethers,and Deprotection of Silyl and THP-Ethers by [PCl3-n(SiO2)n] (Silphos)

Silicaphosphite (silphos), [PCl_3-n(SiO₂)_n], as a heterogeneous phosphorous compound, catalyzes the thiocyanation of benzylic alcohols and silyl and THP ethers in the presence of I₂ and NH₄SCN in refluxing CH₃CN. The produced silphos oxide byproduct can be easily separated by a simple filtration. Silphos is also used for the efficient and selective deprotection of silyl and THP-ethers to their corresponding alcohols.     

FACILE AND EFFICIENT METHOD FOR DEPROTECTION OF 1,3-OXATHIOLANES WITH N,N′-DIBROMO-N,N′-1,2-ETHANEDIYLBIS(p-TOLUENESULPHONAMIDE)

Aliphatic and aromatic 1,3-oxathiolanes[3pc] are readily oxidized to aldehydes and ketones in good yields under mild conditions by N,N′-dibromo-N,N′-1,2-ethanediylbis(p-toluenesulphonamide) [BNBTS].     

ZEOLITE-SUPPORTED CHROMIUM(VI) OXIDE: A MILD,EFFICIENT, AND INEXPENSIVE REAGENT FOR OXIDATIVE DEPROTECTION OF TRIMETHYLSILYL ETHERS UNDER MICROWAVE IRRADIATION

Primary and secondary trimethylsilyl ethers are effeciently converted to the corresponding carbonyl compounds using HZSM-5 zeolite-supported CrO ₃ under microwave irradiation in solventless system.     

Na_3PO_4·12H_2O选择性催化脱去芳香性叔丁基二甲基硅醚

报道了以磷酸盐为催化剂选择性脱去芳香性叔丁基二甲基硅醚的方法.以DMF为溶剂,室温下在0.5质量分数的Na3PO4.12H2O催化下,能顺利地脱去芳香性叔丁基二甲基硅醚得到相应的酚类化合物,而不影响其他的保护基和官能团.     

Highly Efficient and Selective Deprotection Method for Prenyl,Geranyl, and Phytyl Ethers and Esters Using Borontrifluoride–Etherate

An efficient, simple, and practical method has been developed for the deprotection of prenyl, geranyl, and phytyl ethers and esters of aromatic and aliphatic compounds using borontrifluoride–etherate (BF₃ · OEt₂) at room temperature in good to excellent yields for the first time.

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