Comparison of TEMPO and its derivatives as mediators in laccase catalysed oxidation of alcohols

A series of TEMPO (2,2′,6,6′-tetramethylpiperidinyl-1-oxy) derivatives were studied as mediators of laccase (from Trametes versicolor) in the oxidation of benzyl alcohol and 1-phenylethyl alcohol. TEMPO (1), 4-hydroxy-TEMPO (2) and 4-acetylamino-TEMPO (4) turned out to be the most active mediators for laccase. In addition, 4-acetylamino-TEMPO and 4-hydroxy-TEMPO were more active in the oxidation of 1-phenylethanol compared to TEMPO. For these mediators kinetic isotope effects in the range of 2.1-3.2 were observed for α-monodeutero-p-methylbenzyl alcohol oxidation. These values are consistent with a mechanism involving oxoammonium intermediacy. Competition experiments between benzyl alcohol and 1-phenylethanol showed that TEMPO and its derivatives react faster with primary alcohols than with secondary alcohols, also in line with the proposed mechanism.     

Synthesis of heteroaryl 1,2-diketones

Reactions of lithiated heteroaryl- (or aryl-) methylbenzotriazoles 4a-e with heteroaryl (or aryl) esters 5a-f give alpha-benzotriazolyl ketones 6a-n in average yields of 90-95%. Oxidation of ketones 6a-l in aqueous DMSO in the presence of oxygen and sodium bicarbonate gave heteroaryl- (aryl-) 1,2-ethanediones 7a-l in average yields of 60-80%.     

Synthesis of trans-perhydroisoquinolines by 6-endo-trig radical cyclization of amino-tethered vinyl bromides and cyclohexenes

Bu₃SnH-promoted cyclization of several N-(2-bromoprop-2-enyl)-N-[(4-oxocyclohex-1-enyl)methyl]alkylamines is reported. It has been found that the generated vinyl radicals evolve through a 6-endo-cyclization pathway giving rise to the corresponding 4,6-functionalized perhydroisoquinolines in a prevalent trans-relative configuration.     

Iodine as a versatile catalyst for the hydroalkylation of vinyl arenes with 1,3-diketones

The vinyl arenes undergo smooth hydroalkylation with 1,3-diketones in the presence of 10 mol % of iodine to afford phenethyl diketones and ketoesters in good yields in short reaction times. The use of inexpensive and readily available molecular iodine makes this method quite simple, more convenient and practical.     

自由基修饰共轭微孔聚合物应用于5-羟甲基糠醛选择性氧化

采用有机单体侧链嫁接2,2,6,6-四甲基哌啶氧自由基（2,2,6,6-tetramethylpiperidineoxyl,TEMPO）的策略将TEMPO嫁接到2,5-二溴苯甲酸侧链,并与四（4-乙炔基苯）甲烷通过Sonogashira偶联反应,构筑TEMPO自由基功能化共轭微孔聚合物CMP-4-TEMPO.利用核磁共振谱（NMR）、扫描电子显微镜（SEM）、粉末X-射线衍射（XRD）红外吸收光谱（FT-IR）和电子顺磁共振谱（EPR）等技术研究了所合成单体及CMP形貌和结构.催化性能测试结果表明CMP-4-TEMPO可将5-羟甲基糠醛（5-HMF）高效、高选择性氧化成高附加值2,5-二甲酰基呋喃（2,5-DFF）.CMP-4-TEMPO催化剂循环利用10次仍保持较高的转化率.提出了CMP-4-TEMPO中形成TEMPO氧正离子是实现5-HMF转化为2,5-DEF的催化氧化机理.CMP-4-TEMPO有望成为各种醇高效、高选择性氧化以及可循环利用的异相催化剂.     

Nitroxide-mediated oxidation of cellulose using TEMPO derivatives: HPSEC and NMR analyses of the oxidized products

Regenerated cellulose (viscose rayon) was oxidized using NaBr, NaClO and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) or one of ten related nitroxyl radicals in water at pH 10–11. The C6 primary hydroxyl groups in rayon were oxidized to carboxyl groups in most cases, thus giving water-soluble products. However, the oxidation times required for complete dissolution of the products varied substantially, depending on the nitroxyl radical used. Weight average degrees of polymerization (DPw) of the oxidized products were determined by means of high performance size exclusion chromatography (HPSEC) using pullulan standards. All the products had bimodal HPSEC distribution patterns, probably reflected by the solid-state structure of viscose rayon. When 4-acetamido-TEMPO and 4-carboxy-TEMPO were used, cellouronic acids having almost homogeneous chemical structures with higher DPw than for TEMPO were obtained quantitatively within 30 min. The oxidations using 4-amino-TEMPO, 4-carboxy-PROXYL and 4-carbamoyl-PROXYL gave cellouronic acids having the highest DPw, although reaction times of more than 4 h were required, and some side reactions occurred on the products.     

A practical synthetic method for vinyl chlorides and vinyl bromides from ketones via the corresponding vinyl phosphate intermediates

A new synthetic method for the preparation of vinyl chlorides and vinyl bromides from acyclic and cyclic ketones is described. Vinyl halides are practically obtained from the corresponding vinyl phosphate intermediates with triphenylphosphine dihalide.     

A novel method of synthesis of 1,2-diketones from 1,2-diols using N-bromosuccinimide

A simple and convenient procedure is reported for the synthesis of benzils and aliphatic 1,2-diketones of cyclic and open chain compounds from corresponding hydrobenzoins and 1,2-diols by refluxing with N-bromosuccinimide in carbon tetrachloride in presence or absence of pyridine.     

Synthesis of vinyl fluorides by ring-closing metathesis

The first ring-closing olefin metatheses of alkenyl α-fluoroacrylamides or acrylates incorporating a fluorinated double bond are reported. Several N-benzyl-N-alkenyl-α-fluoroacrylamides were cyclized in the presence of 2 mol % of Grubbs II catalyst at room temperature to form an unsaturated γ-lactam, and at 80 °C to form the corresponding δ-lactams bearing a fluoro vinyl moiety. At elevated temperature, cyclization of an N-methallyl 2-fluoroacrylamide to form a fluorinated, tetrasubstituted double bond was achieved. Similarly, 3-fluorocoumarin was prepared from (2-vinylphenyl)-α-fluoroacrylate.     

Synthesis of tri-substituted vinyl boronates via ruthenium-catalyzed olefin cross-metathesis

Tri-substituted vinyl pinacol boronates, which are key reactive intermediates in a variety of transformations, are synthesized using ruthenium-catalyzed olefin cross-metathesis of α-substituted vinyl boronates and various alkenes. Cross-metathesis of 2-isopropenyl pinacol boronate proceeds with moderate yield and high Z-selectivity when sterically unhindered cross partners are used. Cross-metathesis of vinyl boronates that possess α-substitution larger than a methyl group is also achieved. Yield and Z-selectivity are lower in these cases, and the success of a cross-metathesis reaction is highly dependent on the steric bulk surrounding the double bond of the α-substituted vinyl boronate.     

Regioselective Michael-induced cyclisation of γ- and δ-hydroxy vinyl sulfides and vinyl dithiocarbamates

We herein describe the unprecedented use of heteroaryl vinyl sulfides and vinyl dithiocarbamates as hetero-Michael addition acceptors. Combined chelating and electron-withdrawing effects are postulated to stabilise the transient anionic species and allow smooth Michael-induced ring closure to produce diversely functionalised C-glycosides.     

TBHP/TEMPO-Mediated Oxidative Synthesis of Imides from Amides

A new protocol for the synthesis of imides has been developed. In the presence of copper catalyst, N‐benzylamides were oxidized to the corresponding imides by TBHP/TEMPO system in moderate to good yields.     

Palladium-catalyzed coupling of vinyl tosylates with arylsulfinate salts

The first palladium-catalyzed coupling of vinyl tosylates with arylsulfinate salts is described. A variety of cyclic and acyclic vinyl tosylates were coupled with aryl sulfinate salts using 2.5 mol % Pd₂(dba)₃/5.0 mol % XantPhos to give vinyl aryl sulfone products in good yields. The coupling was extended to the preparation of a cyclopropyl vinyl sulfone.     

B2pin2-mediated copper-catalyzed oxidation of alkynes into 1,2-diketones using molecular oxygen

An intriguing aerobic oxidation of alkynes through copper catalysis is described, in which bis(pinacolato)diboron (B₂pin₂) played a dominant intermediary role in the formation 1,2-diketones. This novel protocol, which can be performed at room temperature, is versatile for various substituted alkynes, including diarylalkynes and arylalkylalkynes. The mechanism of this reaction was preliminarily investigated by control experiments.     

Photocyclisation of α-bromomethyl-1,2-diketones

Appropriately substituted α-bramamethyl-1,2-diektones undergo photocyclisation in solution to hydroxycyclobutanone and hydroxycyclopentenone derivatives without loss of bromine.     

Synthesis of 1,2,3-trisubstituted cyclopropanes by MIRC reactions of dithianyllithiums with monocarboxylic vinyl epoxide analogues

A variety of cyclopropane derivatives bearing stereochemistry at all three positions on the ring were readily obtained in a high yield of 76-92% and high stereoselectivity (trans:cis > 95:5) when the monocarboxylic vinyl epoxide analogues reacted with dithianyllithiums in the presence of HMPA. This reaction was supposed to be a tandem conjugation addition-opening epoxide ring sequence.     

Fragmentation of carbohydrate anomeric alkoxyl radicals. Synthesis of highly functionalized chiral vinyl sulfones

The reaction of derivatives of 3-acetyl-d-glucal, 3-acetyl-l-rhamnal, 3-acetyl-d-galactal, and 3-acetyl-d-lactal with sodium benzenesulfinate in acid medium catalyzed by HgSO₄ afforded diastereoisomeric mixtures of the corresponding 2,3-dideoxy-3-(phenylsulfonyl)-hexopyranoses through a Ferrier rearrangement. The anomeric alkoxyl radical fragmentation of these γ-hydroxy sulfones using the system (diacetoxyiodo)benzene and iodine gave vinyl sulfones with structures of 1,2-dideoxy-4-O-formyl-2-(phenylsulfonyl)-pent-1-enitol and configurations d-erythro, l-erythro, and d-threo at the two stereogenic centers.     

Synthesis of bis-and tetrakis-(ω-dimethylamino)-substituted cross-conjugated polyene α-diketones of the thiophene series

Bis-and tetrakis(ω-dimethylamino)-substituted cross-conjugated polyene α-diketones, containing two thiophene rings, were synthesized from α-diketones of the thiophene series and β-dimethylaminoacrolein aminals and also 2-aza-3-dimethylaminoacrolein acetal. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 841–847, June, 2006.