Ionene supported peroxodisulfates: Polymeric reagents for the oxidative deprotection of <Emphasis Type="Italic">TMS</Emphasis> and <Emphasis Type="Italic">THP</Emphasis> ethers and oxidative cleavage of the C=N bond in water

Oxidative deprotection of trimethylsilyl and tetrahydropyranyl ethers, and deprotection of phenylhydrazones, semicarbazones, and oximes to their corresponding carbonyl compounds carried out in water at reflux condition using ionene supported peroxodisulfates is reported. The reagents are recyclable and products are obtained in excellent yield under environmentally benign conditions without overoxidation to carboxylic acid. Correspondence: Moslem Mansour Lakouraj, Department of Chemistry, Mazandaran University, Babolsar, Iran.     

N-[(S)-脯氨酰]羟胺的合成及催化直接不对称羟醛反应研究

(S)-脯氨酸用苯甲氧羰酰氯保护氨基后用混合酸酐法与羟胺偶合, 给出N-[N-苯甲氧羰酰-(S)-脯氨酰]羟胺, 催化氢解脱去保护基得标题化合物. 该化合物对映选择性催化直接羟醛反应, 产率最高达到90.0%, 对映体过量最高达89.5%.     

BiOClO4-mediated deprotection of silyl ethers

TES- and TBS-protected alcohols undergo deprotection in good to excellent yield upon heating with 1 equiv of BiOClO₄-xH₂O in CH₂Cl₂. TBDPS- and TIPS-protected 2° alcohols are more resistant to deprotection. The use of this method in selective desilylation is, however, limited to the deprotection of alkyl silyl ethers in the presence of TBDPS-protected phenols.     

Highly efficient and chemoselective cleavage of prenyl ethers using ZrCl4/NaBH4

An efficient and chemoselective deprotection of prenyl ethers of phenols and alcohols with ZrCl₄/NaBH₄ in DCM was achieved in high yields. The selectivity of prenyl ether deprotection is well demonstrated by carrying out the reaction in the presence of several other ether and ester functionalities.     

Ionic addition of t-butyl N,N-dibromocarbamate (BBC) to alkenes and cycloalkenes

The addition of t-butyl N,N-dibromocarbamate (BBC) to alkenes and cycloalkenes in the presence of BF₃·Et₂O proceeds smoothly at −20°C in CH₂Cl₂ affording upon reduction with aqueous Na₂SO₃ the corresponding β-bromo-N-Boc-amines. Immediate deprotection of these adducts with gaseous HCl yields β-bromoamine hydrochlorides in moderate yields. The regioselectivity typical for Markovnikov addition was observed for styrene. Stereospecific anti-addition of BBC to cyclohexene and (E)-hex-3-ene, as proven by ¹H NMR evidence, is compatible with an ionic addition pathway and can be rationalized by assuming the intermediate complex formation between BBC and BF₃.     

Synthesis of aryl benzyl NH-sulfoximines

Efficient synthesis and characterisation of a series of aryl benzyl NH-sulfoximines are described. While N-protected versions of aryl benzyl sulfoximines have been previously described, reports of their deprotection are very limited, presumably due to lability under the typically harsh deprotection conditions which can be employed with the less reactive aryl alkyl derivatives. Use of N-cyanosulfoximines as key intermediates overcomes these difficulties leading to an effective synthetic route to these compounds.     

Base-labile tert-butoxycarbonyl (Boc) group on phenols

Phenols are deprotected with weak bases from their tert-butoxycarbonyl (Boc) derivatives. Boc deprotection with bases can avoid side reactions during the deprotection with acids. We note the lability of the Boc to bases and are able to utilize it as a new cleavage condition for synthetic studies.     

A new route to the formation of biomimetic phosphate assemblies on gold: synthesis and characterization

A biomimetic model system based on long-chain alkanethiols tailored with serine, threonine and tyrosine side-chain groups is created as a platform for the study of phosphorylated amino acids. The phosphorylated analogues are synthesized with protective tert-butyl groups that after assembly on thin polycrystalline gold films are removed in an acidic deprotection solution to form the corresponding phosphate self-assembled monolayers (SAMs). The SAMs are thoroughly characterized with null ellipsometry, contact angle goniometry, infrared reflection-absorption spectroscopy and X-ray photoelectron spectroscopy. The assembly and the subsequent deprotection process are optimized with respect to molecular orientation and chain conformation by varying the incubation time and the exposure time to the deprotection solution. The high quality of the generated SAMs suggests that the present assembly/deprotection approach is an attractive alternative when traditional synthetic routes become demanding because of solubility problems.     

Mild and efficient method for the cleavage of benzylidene acetals using HClO4-SiO2 and direct conversion of acetals to acetates

HClO₄-SiO₂ has been used successfully for the deprotection of benzylidene acetals and the direct conversion of benzylidene acetals to the corresponding di-O-acetates. The reactions are very fast and yields are excellent.     

A remarkable cyclization of TADDOL-bisthioacetate under oxidative conditions

Abstract  

Attempted oxidation of a TADDOL-derived bisthioacetate resulted in a rather unexpected and remarkable cyclization and deprotection reaction, giving a thiolane-1,1-dioxide as the main product. Systematic in situ ESI-HRMS studies revealed a bicyclic, highly acid labile key intermediate of this reaction. Supported by force field calculations, the high sensitivity of this intermediate was judged to be due to the formation of a highly strained trans-configured bicyclo[3.3.0]skeleton.     

Partial syntheses of avermectin Bla and ivermectin from avermectin B2a

4″,5-Bis-O-($\text{tert}$-butyldimethylsilyloxyacetyl)-23-O-(4-methylphenyloxythiocarbonyl)avermectin B_2a gave on pyrolysis and deprotection avermectin B_la, while reduction with tri-n-butyltin hydride followed by deprotection afforded 22,23-dihydroavermectin B_la (ivermectin).     

Poly(4-vinylpyridinium tribromide) as metal-free and recoverable oxidizing agent for the selective oxidation of alcohols, and oxidative deprotection of trimethylsily ethers

Poly(4-vinylpyridinium tribromide) was found to be an efficient oxidizing polymer for the chemoselective oxidation of a wide range of alcohols into aldehydes and ketones. In addition it was used for the oxidative deprotection of trimethylsilyl ethers into alcohols or carbonyl compounds depending on the structure of trimethylsilyl ether.     

Selective deprotection of the Cbz amine protecting group for the facile synthesis of kanamycin A dimers linked at N-3″ position

The optimal conditions for the regioselective deprotection of per-N-Cbz-kanamycin A and the reaction mechanism was investigated. We found that the Cbz group at N-3″ position was selectively deprotected under milder basic conditions and the cyclic carbamate is an intermediate of the deprotection reaction. The selective deprotection of the amine protecting group enable us to synthesize several kanamycin A dimers linked at N-3″ position in a straightforward way.     

Convergent synthesis of the tetrasaccharide repeating unit related to the O-antigenic polysaccharide of Escherichia coli 78

A convergent synthesis of the tetrasaccharide repeating unit of the O-antigenic cell wall polysaccharide of Escherichia coli 78, as the corresponding methyl glycoside (I), is being reported. It involved stereoselective glycosidation of a β-linked mannodisaccharide acceptor with a β-linked glucosamine based disaccharide thioglycoside donor, which were prepared from the corresponding functionalised monosaccharide based glycosyl donors and acceptors. The resulting tetrasaccharide derivative was finally converted to (I) by selective deprotection and also by global protection and deprotection techniques.     

3-位环庚烷(酰)基取代的焦脱镁叶绿酸-a甲酯的合成

以焦脱镁叶绿酸-a甲酯(MPP-a)为起始原料, 在对其E-环羰基进行保护的前提下, 经焦脱镁叶绿酸-d甲酯与环庚基溴化镁进行Grignard反应; 所生成新的卟吩仲醇再经脱保护、脱水和氧化等诸多反应, 将3-位仲羟基转化成碳碳双键和羰基, 其碳氧双键再行Grignard反应并脱水成烯, 完成一系列未见报道的3-位环庚基取代的焦脱镁叶绿酸-a甲酯衍生物的合成. 其化学结构均经UV, IR, ¹H NMR及元素分析予以证实.     

Rapid, simple, and efficient deprotection of benzyl/benzylidene protected carbohydrates by utilization of flow chemistry

A rapid, simple, and efficient deprotection procedure for the deprotection of benzyl- and/or benzylidene protected carbohydrates is described utilizing a continuous flow hydrogenation reactor. The method tolerates both acid- and base sensitive functional groups. The high efficiency, simple work-up, and short reaction time should make this method appealing to researchers working in the fields of carbohydrate chemistry and total synthesis.     

Useful methods for the synthesis of isopropylidenes and their chemoselective cleavage

A catalytic amount of phosphotungstic acid (PTA) has been found to be a very effective catalyst for isopropylidenation of 1,2-diols and their deprotection at room temperature. The ease of handling, cost and activity of the catalyst, good to excellent yields and chemoselectivity for deprotection are some of the highlights of the reported method.     

A novel in situ deprotection/coupling and iterative divergent/convergent strategy for the synthesis of oligo(1,4-phenyleneethynylene)s

A novel in situ deprotection/coupling and iterative divergent/convergent strategy for the synthesis of oligo(1,4-phenyleneethynylene)s is described.     

A simple and selective method for the O-AcCl removal using sodium borohydride

A deprotection of chloroacetylated alcohols using NaBH₄ is reported. The free alcohols are obtained in excellent yields. The reaction was performed on primary, secondary, alkyl, allyl, benzylic alcohols and phenols. The compatibility of the method with other sensitive or protective groups is demonstrated.     

A mild, efficient and selective deprotection of t-butyldimethylsilyl-protected phenols using cesium carbonate

A mild and efficient method for the deprotection of aryl t-butyldimethysilyl (TBS) ethers is described. The protecting group TBS could be cleaved from aryl silyl ethers using cesium carbonate in DMF-H₂O at room temperature to give the corresponding phenols in excellent yields. The reaction conditions allowed selective deprotection of aryl TBS-protected phenols in the presence of TBS, phenyloxycarbonyl or tetrahydropyranyl-protected alcohols.