New methodology for the synthesis of benzoazacrown ethers by transformation of the macrocycle of benzocrown ethers

The review summarizes the results of studies aimed at constructing new promising macrocyclic ligands that bind metal and ammonium ions. A new approach to the synthesis of formyl and nitro derivatives of 1-aza-2,3-benzocrown ethers possessing considerable synthetic potential is described. The review presents a radically new methodology for the synthesis of such benzoazacrown ethers based on stepwise transformations of the macrocycle of readily accessible benzocrown ethers. The main structural factors and necessary conditions enabling stepwise transformations of the macrocycle of crown ethers into azacrown ethers were revealed. For the first time, the ability of N-methylbenzoazacrown ethers to form complexes was found, which is much superior to that of widely used N-phenylazacrown ethers and benzocrown ethers with the same size of the macrocycle.     

First synthesis of a alpha-trifluoromethyl allenol ether via the Julia-Lythgoe process

Alpha-trifluoromethyl allenol ethers 9a-e were prepared in moderate to good yields by the Julia-Lythgoe process using beta-ethoxy-beta-trifluoromethyl vinylic sulfone 3. Several reactions of 9c were examined to give alpha,beta-unsaturated trifluoromethyl ketone derivatives 11 and 12.     

Solvent-free synthesis of dihydroxy dithiacrown ethers

The solvent-free reaction of oligoethylene glycol diglycidyl ethers with dimercaptoethane in the presence of benzyltrimethylammonium hydroxide (Triton B) gave, via regiospecific epoxide opening reactions, dihydroxy dithiacrown ethers in excellent yields and in short reaction times.     

Microwave-assisted fast and efficient synthesis of some crown ethers

13-Crown-4,16-crown-5,dibenzo-12-crown-4 and dibenzo-14-crown-4 were synthesized by a one-pot microwave-assisted procedure in good yields.Irradiation of diols and dichlorides in the presence of sodium hydroxide in DMSO gave title crown ethers presumably within a template effect.     

Efficient synthesis of naphthodiazacrown ethers

A benign and efficient synthesis of naphthodiazacrown ethers has been described. Reaction of simple dialdehyde precursor with α,ω-diamines followed by sodium borohydride reduction leads to 16-27 membered naphthodiazacrown ethers in 80-90% yields.     

端烯丙基冠醚的合成

本文合成了六个不同结构的端烯丙基冠醚,除冠醚1、2外,其它均为新化合物,其结构均经IR、^1HNMR、MS和元素分析的数据所证实。     

Efficient synthesis of N-aryl-aza-crown ethers via palladium-catalyzed amination

N-Aryl-aza-crown ethers were efficiently prepared by reaction of an aza-crown ether with an aryl bromide via a palladium-catalyzed amination. The combination of Pd(2)(dba)(3) and a biphenyl-based electron-rich bulky monophosphine is effective for catalyzing the coupling of 1-aza-15-crown-5 with both electron-deficient and electron-rich aryl bromides under mild conditions. N-Aryl-aza-crown ethers were produced in 75-91% yields. N-Aryl-aza-crown ethers with o-aryl substituents can also be synthesized using this catalyst system, albeit in lower yields ( approximately 40%).     

A novel B(C(6)F(5))(3)-catalyzed reduction of alcohols and cleavage of aryl and alkyl ethers with hydrosilanes

The primary alcohols 1a-e and ethers 4a-d were effectively reduced to the corresponding hydrocarbons 2 by HSiEt(3) in the presence of catalytic amounts of B(C(6)F(5))(3). To the best of our knowledge, this is the first example of catalytic use of Lewis acid in the reduction of alcohols and ethers with hydrosilanes. The secondary alkyl ethers 4j,k enabled cleavage and/or reduction under similar reaction conditions to produce either the silyl ethers 3m-n or the corresponding alcohol 5a upon subsequent deprotection with TBAF. It was found that the secondary alcohols 1g-i and tertiary alcohol 1j, as well as the tertiary alkyl ether 4l, did not react with HSiEt(3)/(B(C(6)F(5))(3) reducing reagent at all. The following relative reactivity order of substrates was found: primary > secondary > tertiary. A plausible mechanism for this nontraditional Lewis acid catalyzed reaction is proposed.     

Convergent synthesis of polycyclic ethers via the intramolecular allylation of alpha-acetoxy ethers and subsequent ring-closing metathesis

The Lewis acid mediated reaction of alpha-acetoxy ethers 15-22 gave the corresponding cyclized products 23, 25, 27, 29, 31, 32, 34, and 36 in good yields with high stereoselectivities. Those cyclized products were subjected to ring-closing metathesis to afford the polycyclic ethers 38-42, 44, and 45 in good yields. The usefulness of the present methodology was demonstrated by the convergent synthesis of the CDEF ring system of brevetoxin B (1) and the CDEFG ring system of gambierol (2).     

Efficient method for the deprotection of tert-butyldimethylsilyl ethers with TiCl4-Lewis base complexes: application to the synthesis of 1beta-methylcarbapenems

TiCl4-Lewis base (AcOEt, CH3NO2) complexes smoothly deprotected tert-butyldimethylsilyl (TBDMS) ethers. The reaction velocity with these complexes, which seemed less reactive due to the influence of Lewis bases, was considerably greater than that with TiCl4 alone. Selective desilylations between aliphatic and aromatic TBDMS ethers (1 and 5), between 1 and benzyl, allyl, tosyl, methoxyphenyl, and chloroacetyl ethers (13, 14, 15, 16, and 17), and between TBDMS and TBDPS ethers (18 and 19) were successfully performed. Desilylation of TBDMS-aldol, acyloin, and beta-lactam analogues 9-12 proceeded smoothly due to anchimeric assistance by the neighboring carbonyl groups. The present method was successfully applied to the practical synthesis of 1beta-methylcarbapenems 20a'-f'.     

Phosphonyl radical addition to enol ethers. The stereoselective synthesis of cyclic ethers

Addition of diethyl phosphite or diethyl thiophosphite to enol ethers, in the presence of a radical initiator, results in the regioselective synthesis of organophosphonate or phosphonothioate derivatives, respectively, under mild conditions. This method can be applied to the stereoselective formation of substituted tetrahydrofurans and tetrahydropyrans, on cyclisation of vinyl ethers bearing unsaturated side chains.     

Efficient and stereoselective synthesis of allylic ethers and alcohols

[Structure: see text] A short and efficient synthesis of allylic TBS ethers and allylic alcohols has been developed, based upon a unique Kocienski-Julia olefination reaction. Allylic alcohols and allylic ethers are obtained in good to excellent yields and with high (E)-selectivity. The conditions are mild and the procedure is broadly applicable.     

无溶剂微波辅助合成醚类化合物的工艺探讨

与传统加热方法相比,通过体系内部分子运动摩擦产热的微波辐射方法可催化化学反应,缩短反应时间,提高转化率和收率.传统的加热方法需要数十小时,甚至几天的反应.     

The synthesis of unique structures of tetra-crown ethers through Michael addition

Unique structures of tetra-crown ethers were successfully synthesized by the reaction of tetramethylolmethane tetraacrylate (TMMT) reacted with crown ethers containing primary amine functional group such as 2-aminomethyl crown ethers and 4-aminobenzo crown ethers; containing secondary amine group like 1-aza crown ethers through Michael reaction. The newly synthesized tetra-crown ethers were characterized by ¹H NMR, ¹³C NMR, FAB mass spectrum, elemental analyses, IR, respectively.     

Functionalized chloroenamines in aminocyclopropane synthesis - VI. Chlorotetrahydropyridines as a basis for the synthesis of 3-azabicyclo[3.1.0.]hexane derivatives

Enamines 8a-e could be chlorinated by equimolar amounts of N-chlorosuccinimide (9) generating monochloroenamines 10a-e; 10a and 10d were isolated as pure substances. Two equivalents of 9 afforded the dichloroenamines 12a,c from 8a,c. Interaction of the chlorinated enamines 10a-e and 12a,c with cyanide gave morpholino-azabicyclohexane derivatives. 10a-d, thereby, led to exo-cyano-isomers lla-c; 12a,c generated endo-cyano compounds 13a,c. In the case of the ethoxycarbonylated chloroenamine 10e a mixture of diastereomeric products 11e and 14e resulted from the analogous reaction. Reduction of 11a and 14e with lithium aluminum hydride produced a pair of diastereomeric triamines 15 and 16. A tricyclic diazasystem 19 was formed from the reaction of cyanide with the carbamoylated chloroenamine 18. Monochloroenamine 10a and dichloroenamine 12a showed a significant mutagenic behaviour in the Ames test.     

Efficient synthesis of substituted vinyl ethers using the Julia olefination

Julia olefination between alpha-alkoxy sulfones 2a-c and a wide variety of ketones or aldehydes afforded substituted vinyl ethers in 46-90% yields. Sulfones 2a-c were readily prepared in two steps from commercially available reagents in 68-80% yields. Optimization revealed that the nature of the base, the solvent, and the temperature were crucial to obtaining the desired vinyl ethers. [reaction: see text]     

Dibenzotetraaza crown ethers: a new family of crown ethers based on o-phenylenediamine

Dibenzotetraaza (DBTA) crown ethers possess two o-phenylenediamine moieties. They are homologues of dibenzo crown ether phase-transfer catalysts and were prepared from the condensation of benzimidazoles with oligo(ethyleneglycol) dichlorides and oligo(ethyleneglycol) ditosylates. Compounds with ring sizes ranging from 18-crown-6 to 42-crown-14 were prepared. In addition, various altered benzimidizoles were used to produce DBTA crown ethers with modified substituents and ether bridges, as well as benzimidazolidine crown ethers. The synthetic approach presented here proved to be a convenient route to a new family of crown ethers with overall yields of up to 48% based on the benzimidazole. Yields for the ring-closing step were generally high, ranging from 51% to 94%, without the need for high-dilution conditions. Reaction of the DBTA crown ethers with alkyl and benzyl halides was found to be a facile way to obtain the corresponding tetra(N-organyl) compounds. Picrate extraction studies were carried out to determine phase-transfer catalytic capabilities. Extraction efficiencies for alkali-metal ions were lower than those for dibenzo-18-crown-6. Efficiencies were higher for other metal ions, with some selectivity for Pb(2+). Tetra(N-methyl) DBTA-18-crown-6 generally exhibited higher extraction efficiencies than its N-H analogue, but the selectivity was lower.     

A general and mild Ullmann-type synthesis of diaryl ethers

[reaction: see text] An efficient method for the synthesis of diaryl ethers under particularly mild conditions is described. Inexpensive ligands were found to greatly accelerate the Ullmann-type coupling of aryl bromides or iodides with phenols. A series of diaryl ethers were obtained with excellent yields in acetonitrile in the presence of Cs(2)CO(3) and catalytic copper(I) oxide. The reaction tolerates substrates with unfavorable substitution patterns, such as sterically hindered coupling partners or electron-rich aryl halides.     

Water as an efficient medium for the synthesis of functionalized enol ethers

Herein we report an efficient method for synthesis of β-alkylated and β,β-dialkylated α-iodo enol ethers in water. Radical addition in aqueous medium of ethyl iodoacetate, iodoacetonitrile, and iodoacetamide to ynol ethers leads to α-iodo enol ethers with moderate to excellent yields and high stereoselectivities.     

Evaluation of C-trialkylsilyl enol and thioenol ethers as intermediates in the synthesis of acylsilanes

C-silyl enol ethers or thioenol ethers have been prepared by a Peterson reaction, as intermediates for acylsilane synthesis. Bis(trialkylsilyl)(methoxy)- or -(methylsulfanyl)methanes bearing identical or different trialkylsilyl groups were used as starting materials in order to assess the selectivity of the Peterson elimination step. A good selectivity was observed only with ethers bearing the TMS and TBDMS groups. However, there is no practical interest to use such reagents owing to the difficulty to obtain them in correct yields. Bis(trimethylsilyl)(methylsulfanyl)methane proved to be a good reagent for the preparation of C-silyl thioenol ethers, which are hydrolyzed under classical acid conditions to give acylsilanes in fair overall yields. This convenient procedure was extended to the synthesis of bis(acylsilanes).