Oxidation of enamines to α-hydroxy ketones and α-amino ketones using N-sulfonyloxaziridines

Tri-substituted enamines are oxidized to α-hydroxy ketones by N-sulfonyloxaziridines while di-substituted enamines are oxidized to α-amino ketones. A unified mechanism for the formation of both α-hydroxy ketones and α-amino ketones is proposed.     

二氧杂环丙烷参与的烯烃环氧化反应

酮是催化烯烃环氧化反应的一类重要催化剂, 酮与氧化剂KHSO₅ (Oxone)可原位产生二氧杂环丙烷中间体, 然后二氧杂环丙烷中间体将氧原子传递给烯烃使之成为环氧化物, 而自身又生成原来的酮. 酮的催化效能大小与酮产生二氧杂环丙烷的能力、二氧杂环丙烷将氧原子传给烯烃的能力以及反应条件下酮的稳定性有关. 本工作对各种脂肪酮、脂环酮、杂环酮对烯烃环氧化催化能力的大小及其影响因素进行了评述.     

New synthetic routes towards various α-fluorinated aryl ketones and their enantioselective reductions using baker's yeast

Highly electrophilic dichlorofluoromethyl aryl ketones were obtained by oxidation of dichlorofluoromethyl aryl alcohols. Subsequent dechlorination of these ketones using sodium formaldehyde sulfoxylate (Rongalite) and reductive dehalogenating system SnCl₂/Al led to various fluoromethyl aryl ketones and chlorofluoromethyl aryl ketones, respectively. Asymmetric reductions of these fluorinated ketones using the inexpensive baker's yeast produced the corresponding fluoromethyl aryl alcohols with different enantioselectivities.     

Reduction of Aromatic α-Halo Ketones with Metallic Bismuth

Aromatic α-bromo ketones and α-iodio ketones can be reduced by bismuth prepared from NaBH₄ and BiCl₃ in water to their parent ketones in high yields, but aromatic α-chloro ketones should be added to sodium iodide first.     

玉米秸秆纤维素在亚/超临界乙醇中液化生成酮类化合物的机理探讨

利用间歇式高压反应釜,在反应温度320℃、反应时间60 min条件下,研究乙醇用量对玉米秸秆纤维素液化生成酮类化合物的作用。当乙醇添加量为0时,酮类化合物的产率仅为1.25%。随着乙醇用量由0增加到160 mL,生物油产率不断的升高,酮类化合物产率增加至18.38%,乙醇促进了纤维素液化生成酮类化合物。利用GC/MS和FT-IR对生物油进行了定性分析,结果表明,在亚/超临界乙醇中,酮类化合物主要通过三条路径形成,纤维素脱水形成了含-C=O的活性纤维素,活性纤维素按逆Diels-Alder机理进行开环、脱水、异构化形成了4-羟基-4-甲基-2-戊酮等脂肪族酮类化合物;在乙醇自由基作用下,活性纤维素中C-O-C、C-C等键断裂、开环,形成环戊烯酮等脂环族酮类化合物,环戊烯酮与多种中间产物发生缩合、酯化形成2-甲酸基-1-苯基乙酮等芳香族酮类化合物;在高浓度乙醇自由基作用下,芳香族酮类化合物进一步发生裂解形成酸类、酮类等化合物。根据对酮类化合物生成机理的分析,建立了纤维素在亚/超临界乙醇中液化生成酮类化合物的反应网络。     

1,2-联烯基酮的合成与反应

1,2-联烯基酮可以通过2-丙炔基酮异构化反应,相应有机金属试剂中间体与酯、酰氯或酰胺的反应,[2,3]或[3,3]迁移反应,Wittig反应,消除反应,2,3-联烯醇氧化等方法合成。由于联烯酮上含有吸电子基团羰基,它可发生亲核加成、环加成、环化反应。     

Catalytic ketone olefination with methyltrioxorhenium

Methyltrioxorhenium (MTO) catalyses the olefination of ketones with ethyl diazoacetate in the presence of triphenylphosphane. Unactivated ketones require the addition of 0.5 equiv of benzoic acid to achieve good yields, while trifluoromethyl ketones require no co-catalyst. The optimised system allows the olefination of aromatic, aliphatic, unsaturated, cyclic and trifluoromethyl ketones.     

Synthesis of cyclopentenyl and cyclohexenyl ketones via [3 + 2] and [4 + 2] annulations of 1,2-allenic ketones简

In this paper, an efficient synthesis of cyclopentenyl ketones and cyclohexenyl ketones through tertiary phosphine catalyzed [3 ＋ 2] and [4 ＋ 2] annulations of 1,2-allenic ketones with activated alkenes has been developed. Compared with published synthetic methods on cyclopentenyl ketones and cyclohexenyl ketones, the protocols developed in this paper have the advantages such as readily available starting materials, mild reaction conditions and high efficiency.     

Reactions of β-heteroatom substituted α,β-unsaturated ketones with dimethylsulfonium methylide

β-Alkoxy- and β-alkylthio α,β-unsaturated ketones react with dimethylsulfonium methylide (DMSM) to give a furan, while β-anilino α,β-unsaturated ketones give the pyrrole. β,β-Bis(alkylthio) α,β-unsaturated ketones react with DMSM to afford the methylene inserted products, λ,λ-bis(alkylthio) β,λ-unsaturated ketones.     

Direct organocatalytic asymmetric α-oxidation of ketones with iodosobenzene and N-sulfonyloxaziridines

The novel, direct amino acid-catalyzed α-oxidation of ketones with iodosobenzene and N-sulfonyloxaziridines is presented. A screen of several synthetically common oxidants revealed that iodosobenzene and N-sulfonyloxaziridines act as electrophiles in the direct organocatalytic asymmetric α-hydroxylation of ketones. The direct proline-catalyzed asymmetric α-oxidation of ketones with iodosobenzene yielded the corresponding α-hydroxylated ketones with up to 77% ee. Furthermore, several amino acid derivatives catalyze the stereoselective α-oxidation of ketones with N-sulfonyloxaziridines. For example, the direct diamine-catalyzed enantioselective α-hydroxylation of ketones with N-sulfonyloxaziridines furnished the corresponding α-hydroxylated products in moderate yield with up to 63% ee.     

A novel pyrrolidine imide catalyzed direct formation of alpha,beta-unsaturated ketones from unmodified ketones and aldehydes

A method for direct, stereoselective preparation of (E)-alpha,beta-unsaturated ketones from ketones and aldehydes, promoted by a novel pyrrolidine imide organocatalyst, has been developed in moderate to high yields. Unlike the Claisen-Schmidt condensation and Lewis acid catalyzed tandem aldol-dehydration processes, this method provides mild reaction conditions to access alpha,beta-unsaturated ketones from simple, unmodified ketones. [reaction: see text]     

A convenient and efficient one-pot way to synthesize α,β-epoxy ketones directly from acetophenones and arylaldehydes

A convenient and efficient one-pot way to synthesize α,β-epoxy ketones directly from ketones and aldehydes has been described. Reactions were carried out at room temperature and the corresponding α,β-epoxy ketones were isolated in moderate to excellent yields.     

Trimethylsilylethynyl ketones as surrogates for ethynyl ketones in the double Michael reaction

Trimethylsilylethynyl ketones can be desilylated in the presence of a tethered carbon diacid and induced to undergo a double Michael reaction in situ. The trimethylsilylethynyl ketones can serve as surrogates of ethynyl ketones that are difficult to prepare or isolate.     

The remarkable role of water during the chemoselective reduction of ketones mediated by metallic aluminium

Diaryl ketones are reduced selectively to the corresponding benzhydrols in good yield by aluminium powder in the presence of sodium hydroxide in the solvent system MeOH:H₂O=2:1 whereas dialkyl ketones, α-tetralone, aryl alkyl ketones and cycloalkanones remain mostly unaffected. Interestingly, diaryl ketones remain totally unchanged by the present reagent combination in the absence of water, that is in anhydrous methanol.     

α-Methoxymethyl ketones via aldol reaction

Paraformaldehyde in a methanolic solution of KOH converts ketones into α-methoxymethylated and α- hydroxymethylated products. The method was tested on nine steroidal ketones. On prolonged treatment the ketones formed are reduced to alcohols.     

Photopolymerization of methyl methacrylate sensitized by aliphatic ketones

The polymerization of methyl methacrylate photosensitized by several alkyl ketones has been investigated. It was found that alkyl ketones can induce the free radical polymerization of the monomer with an efficiency that increases when the triplet lifetime decreases. For ketones of similar triplet lifetime those decomposing predominantly by a type I photocleavage show greater initiation efficiencies than those that react by a type II mechanism. The results obtained show that quenching of the excited ketones by the monomer does not induce polymerization. For ketones bearing γ-hydrogens the initiation is due to the 1,4-biradical produced by intramolecular hydrogen abstraction.     

Studies on K2CO3-catalyzed 1,4-addition of 1,2-allenic ketones with diethyl malonate: controlled selective synthesis of beta,gamma-unsaturated enones and alpha-pyrones

The K2CO3 (10 mol %)-catalyzed 1,4-addition reaction of diethyl malonate with various substituted 1,2-allenic ketones leading to polyfunctionalized beta,gamma-unsaturated enones 3 or 4 was studied. With 3-unsubstituted 1-substituted-1,2-allenyl ketones, the highly selective formation of beta,gamma-unsaturated enones 4 was observed; with 1,2-allenyl ketones bearing one or two 3-substituents in the allenyl group, only beta,gamma-unsaturated enones 3 with an unmigrated carbon-carbon double bond were produced; with 3-monosubstituted-1,2-allenyl ketones Z-beta,gamma-unsaturated enones 3 were formed with excellent stereoselectivity (E:Z > 96:4); with propadienyl ketones, mixtures of beta,gamma-unsaturated enones 3 and 4 were formed. alpha-Pyrone derivatives were synthesized via the K(2)CO(3)-catalyzed or -promoted reaction of 1,2-allenic ketones with diethyl malonate via a sequential Michael addition-carbon-carbon double bond migration-lactonization process.     

Two classes of enzymes of opposite stereochemistry in an organism: one for fluorinated and another for nonfluorinated substrates

Reduction of methyl ketones by dried cells of Geotrichum candidum (APG4) afforded (S)-alcohols in excellent enantiomeric excess (ee), whereas the reduction of trifluoromethyl ketones gave the corresponding alcohols of the opposite configuration also in excellent ee. The replacement of the methyl moiety with a trifluoromethyl group alters both the bulkiness and the electronic properties, the effect of which on the stereoselectivity was examined. No inversion in stereochemistry was observed in the reduction of hindered ketones such as isopropyl ketone, while the stereoselectivity was inverted in the reduction of ketones with electron-withdrawing atoms such as chlorine. The mechanism for the inversion in stereochemistry was investigated by enzymatic studies. Several enzymes with different stereoselectivities were isolated; one of them catalyzed the reduction of methyl ketones, and another with the opposite stereoselectivity catalyzed the reduction of trifluoromethyl ketones. Furthermore, both APG4 and the isolated enzyme were applied to the reduction of fluorinated ketones on a preparative scale, which resulted in the synthesis of chiral fluorinated alcohols with excellent ee.     

Synthesis of Cyclohexyl and Isopropyl Ketones from Benzimidazole Methiodide Salt and Grignard Reagents

The reaction of 2-alkyl-l, 3-dimethylbenzimidazolinm salts with Grignard reagents gave addition products which were hy-drelyzed to give ketones. A new method for the preparation of cyclohexyl ketones and isopropyl ketones is provided.     

Metal-assisted reactions—12 : Unusual selectivity in the reduction of ketones with zinc or cadmium bis-tetrahydroborate/dimethylformamide complex

Zinc bis-tetrahydroborate forms a solid complex with dimethylformamide (DMF) of composition, Zn(BH₄)₂ 1.5DMF. Unlike zinc bis-tetrahydroborate itself, the complex with DMF can be stored as a solid at room temperature. Ketones and aldehydes are reduced to the corresponding alcohols by the complex but the mechanism of reduction appears to be different from that using zinc bis-tetrahydroborate itself and from other tetrahydroborates in that only one hydride equivalent from each BH₄⁻ unit is utilized and not four. Further, although saturated aliphatic ketones are reduced rapidly to alcohols, aromatic ketones react much more slowly and ,β-unsaturated ketones react very slowly so that the complex appears to have selective reducing potential with regard to different classes of ketones. It is also apparent that the zinc bis-tetrahydroborate/DMF complex reduces sterically hindered saturated ketones much more slowly than it does unhindered ketones. An analogous cadmium bis-tetrahydroborate/DMF complex can be prepared in solution and reacts with ketones similarly to the zinc complex.