Chiral ytterbium complex-catalyzed direct asymmetric aldol-Tishchenko reaction: synthesis of anti-1,3-diols

The asymmetric aldol-Tishchenko reaction of aromatic aldehydes with aliphatic and aromatic ketones has been developed as an efficient strategy for the synthesis of anti-1,3-diols in good yield with high diastereocontrol and good levels of enantioselectivity. This domino-type reaction is catalyzed by a chiral ytterbium complex that promotes both the aldol reaction through enolization of the carbonyl compound and the Evans-Tishchenko reduction of the aldol intermediate. The stereochemistry of the resulting diols is also investigated and finally proved by using CD techniques.     

氨水介质中金属锌促进醛的呐偶联反应

传统的呐偶合反应必须在无水有机溶剂条件下, 由金属或金属化合物促进羰基化合物进行呐偶合反应. 曾经报道过金属锌在强碱介质或弱酸介质中, 促进羰基化合物进行水相呐偶合反应. 本文报道一种简便、有效的水相呐偶合反应, 它是在含有少量冠醚的稀氨水溶液中, 使用锌粉促进醛基化合物进行水相呐偶合反应, 其中加入少量的冠醚有助于提高反应的产率, 呐醇产率由63%提高到84%. 然而, 呐偶合反应的产率受到羰基周围环境的立体位阻影响较大, 在此条件下, 锌粉能有效地促进芳香族醛类化合物进行水相呐偶合反应, 得到的呐醇产率高, 但非对映异构体选择性差, 而脂肪族醛类化合物得到的呐醇产率较低, 在同样的条件下, 酮类化合物不能顺利进行呐偶合反应.     

Chloracylierung und Bromacylierung von Carbonylverbindungen: Eine in Vergessenheit geratene Carbonylreaktion. I. Präparative Anwendungsbreite

Chloroacylation and bromoacylation of carbonyl compounds: A forgotten carbonyl reaction. I. Scope of the reaction Aliphatic, α,β-unsaturated and aromatic aldehydes as well as aliphatic ketones react with acyl halides to (α-haloalkyl)esters. These bifunctional derivates contain two leaving groups of different reactivity. The scope of this scarcely of this scarcely known carbonyl reaction is discussed.     

氨水介质中金属锌促进醛的(口片)呐偶联反应

传统的(口片)呐偶合反应必须在无水有机溶剂条件下,由金属或金属化合物促进羰基化合物进行(口片)呐偶合反应.曾经报道过金属锌在强碱介质或弱酸介质中,促进羰基化合物进行水相(口片)呐偶合反应.本文报道一种简便、有效的水相(口片)呐偶合反应,它是在含有少量冠醚的稀氨水溶液中,使用锌粉促进醛基化合物进行水相(口片)呐偶合反应,其中加入少量的冠醚有助于提高反应的产率,(口片)呐醇产率由63%提高到84%.然而,(口片)呐偶合反应的产率受到羰基周围环境的立体位阻影响较大,在此条件下,锌粉能有效地促进芳香族醛类化合物进行水相(口片)呐偶合反应,得到的(口片)呐醇产率高,但非对映异构体选择性差,而脂肪族醛类化合物得到的(口片)呐醇产率较低,在同样的条件下,酮类化合物不能顺利进行(口片)呐偶合反应.     

水介质中无催化剂下醛酮与活泼亚甲基化合物的缩合反应

报道了水相中无催化剂下各种羰基化合物与活泼亚甲基化合物的Knoevenagel缩合反应. 芳香醛与活泼亚甲基化合物如丙二腈、氰基乙酸乙酯、氰基乙酰胺的缩合在室温下即能顺利进行, 获得了很高的收率; 而对于杂环芳醛、α,β-不饱和的醛以及脂肪醛与活泼亚甲基化合物的缩合, 需在50～65 ℃下进行, 也取得了很高的收率; 对于脂肪酮、芳香酮以及二元醛与丙二腈的缩合在75～85 ℃下也能顺利地进行, 获得中等以上的收率. 反应简单、高效而且对环境友好.     

Metal‐Free σ‐Bond Metathesis in 1,3,2‐Diazaphospholene‐Catalyzed Hydroboration of Carbonyl Compounds

The first metal‐free catalytic hydroboration of carbonyl derivatives has been developed in which a catalytic amount of 1,3,2‐diazaphospholene effectively promotes a hydroboration reaction of aliphatic and aromatic aldehydes and ketones. The reaction mechanism involves the cleavage of both the P? O bond of the alkoxyphosphine intermediate and the B? H bond of pinacolborane as well as the formation of P? H and B? O bonds. Thus, the reaction proceeds through a non‐metal σ‐bond metathesis. Kinetic and computational studies suggest that the σ‐bond metathesis occurred in a stepwise but nearly concerted manner.     

Mass spectrometry in structural and stereochemical problems—CLXIV. Electron impact promoted fragmentation of some thiosemicarbazones

The mass spectral fragmentation of thiosemicarbazone derivatives of some typical aliphatic, alicyclic and aromatic aldehydes and ketones has been rationalized using high resolution mass spectrometry supplemented by deuterium labeling. Thiosemicarbazone derivatives of carbonyl compounds yield mass spectra which have little in common with those generated by their semicarbazone analogs.     

Chemoselective thioacetalisation and transthioacetalisation of carbonyl compounds catalysed by tetrabutylammonium tribromide (TBATB)

Thioacetals and thioketals of various aldehydes and ketones were obtained directly from carbonyl compounds or by a transthioacetalisation process from cyclic O,O-acetals in the presence of dithiols and a catalytic amount of tetrabutylammonium tribromide (TBATB). Chemoselective thioacetalisation of aromatic aldehydes containing an electron-donating group in the presence of an aldehyde containing an electron-withdrawing group, aldehydes in the presence of ketones, aliphatic cyclic ketones in the presence of aromatic ketones and less hindered ketones in the presence of more hindered ketones have been achieved. A cyclic acetal containing an electron-donating group has been chemoselectively transthioacetalised in the presence of an acetal having an electron-withdrawing substituent. These selectivities are due to the intrinsic reactivity of the substrate themselves and are independent of the catalyst and reaction conditions. Shorter reaction times, mild reaction conditions, stability of acid sensitive protecting groups, high efficiencies, facile isolation of the desired products and the catalytic nature of the reagent are the attractive features of the present method.     

Hafnium trifluoromethanesulfonate (hafnium triflate) as a highly efficient catalyst for chemoselective thioacetalization and transthioacetalization of carbonyl compounds

A range of carbonyl compounds including aliphatic and aromatic aldehydes and ketones were converted to the corresponding thioacetals in high yields in the presence of a catalytic amount of hafnium trifluoromethanesulfonate (0.1 mol %, room temperature). The mild conditions tolerated various sensitive functional and protecting groups and were racemization-free when applied to alpha-aminoaldehydes. Transacetalization and chemoselective thioacetalization of aromatic aldehydes in the presence of aliphatic aldehydes and ketones were also documented.     

A new convenient synthesis of trisubstituted 1,3-dioxole-4-carboxylates from methyl 2-diazo-3-oxobutyrate and aldehydes

The interaction between methyl 2-diazo-3-oxobutyrate and the carbonyl group of aliphatic, aromatic, and α,β-unsaturated aldehydes under bis(hexafluoroacetoacetonato)copper(II) catalysis furnishes 1,3-dioxole-4-carboxylates in preparatively useful yields. The apparent 1,3-dipolar cycloaddition reaction of the metal carbene complex is remarkably free of competing processes.     

Kinetics of catalytic Meerwein-Ponndorf-Verley reduction of aldehydes and ketones using boron triethoxide

Catalytic Meerwein-Ponndorf-Verley (MPV) reduction of various aliphatic, aromatic, and unsaturated aldehydes and ketones to corresponding alcohols (analyzed by GC-MS) in the presence of boron triethoxide (B(OEt)₃) were studied. Kinetics of this reduction reaction was also studied and the respective rate constants were determined. It was found that B(OEt)₃ catalyzes the reduction of aliphatic aldehydes and ketones to alcohols at room temperature while aromatic aldehydes and ketones were not reduced under the same conditions. In addition, MPV reduction using B(OEt)₃ was found to be chemoselective as unsaturated aldehydes and ketones afforded the corresponding alcohols without affecting unsaturated groups. The mechanism proposed involves a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same boron centre of a boron alkoxide catalyst.     

Activation and synthetic applications of thiostannanes. Conversion of aldehydes and acetals into 1,3-dithianes with high chemodifferentiation

Novel method for transforming aldehydes and acetals into 1,3-dithianes has been achieved with the aid of organotin thioalkoxides and organotin triflates. Under these reaction conditions, various acid-sensitive groups are tolerated. Differentiation between aromatic or aliphatic aldehydes and acetals has been realized.     

An efficient synthetic approach to optically active β-carboline derivatives via Pictet–Spengler reaction promoted by trimethylchlorosilane

A highly diastereoselective Pictet–Spengler reaction using chiral tryptamine carbamates has been developed. The reaction proceeds using aromatic and aliphatic aldehydes in the presence of trimethylchlorosilane.     

Chemistry of ethyleneimine

The mechanism of the reaction of N-aminoethyleneimine with some aliphatic aldehydes and with acrolein have been studied. It has been shown that the reaction takes place at the carbonyl bond C=O with the formation of hydrazones.For part II, see [1].     

Coupling Reaction of Carbonyl Compounds Mediated by Gallium Metal in Aqueous Media

A simple and effective pinacol coupling of various aromatic aldehydes mediated by gallium in good yields has been carried out. The reaction is highly effective in water in the prurience of KOH or HCl and was strongly affected by the steric environ-ment surrounding the carbonyl group. Aliphaflc aldehydes, ke-tones and aromatic ketones appear inert under the same reac-tion conditions.     

Stereoselective aldol condensations via enolboronates.

Enolboronates, new enolates directly accessible from carbonyl compounds, exhibit extraordinary high erythro diastereoselection both with aliphatic and aromatic aldehydes.     

Allylation of Carbonyl Compounds Mediated by Aluminum/Fluoride Salts in Water

A novel mediator (Al/KF) has been developed and employed in the Barbier‐type alkylations of various aldehydes and ketones with alkyl halide in water. The carbonyl compounds could be effectively converted into corresponding homoallylic alcohol in good yields only when allyl bromides or substituted allyl bromides were used as halides. Aromatic aldehydes could afford homoallylic alcohols in high yields, unfortunately, the allylation of aromatic aldehyde substituted by nitro‐ or amino‐group could not proceed smoothly, and the allylation yields of ketones and aliphatic carbonyl compounds were lower under the same condition. The diastereoselectivity and regioseletivity of the reaction have also been studied, the predominant products preferred the erythro‐ or anti‐isomer in dominant γ‐adduct by using Al/KF mediated allylation of benzaldehydes with cinnamyl bromide and ethyl 4‐bromo‐2‐butenoate in water.     

An indium-TMSCl promoted reaction of diphenyl diselenide and diorganyl disulfides with aldehydes: novel routes to selenoacetals, thioacetals and alkyl phenyl selenides

The reactions of diphenyl diselenide and dialkyl disulfides with aldehydes in the presence of In-TMSCl have been investigated. Aliphatic aldehydes provide the corresponding selenoacetals and aromatic aldehydes lead predominantly to benzyl phenyl selenides on reaction with diphenyl diselenide. However, the reaction of dimethyl disulfide and diphenyl disulfide with both aromatic and aliphatic aldehydes produce dithioacetals. This provides a novel route to the synthesis of selenoacetals, thioacetals and selenides from aldehydes.     

Scope of the asymmetric intramolecular stetter reaction catalyzed by chiral nucleophilic triazolinylidene carbenes

A highly enantioselective intramolecular Stetter reaction of aromatic and aliphatic aldehydes tethered to different Michael acceptors has been developed. Two triazolium scaffolds have been identified that catalyze the intramolecular Stetter reaction with good reactivity and enantioselectivity. The substrate scope has been examined and found to be broad; both electron-rich and -poor aromatic aldehydes undergo cyclization in high yield and enantioselectivity. The tether can include oxygen, sulfur, nitrogen, and carbon linkers with no detrimental effects. In addition, the incorporation of various tethered Michael acceptors includes amides, esters, thioesters, ketones, aldehydes, and nitriles. The catalyst loading may be reduced to 3 mol % without significantly affecting the reactivity or selectivity of the reaction.     

Bismuth(III) chloride-catalyzed one-pot Mannich reaction: three-component synthesis of β-amino carbonyl compounds

A simple and efficient method has been developed for the one-pot Mannich reaction of β-amino carbonyl compounds from aromatic aldehydes, aromatic ketones and aromatic amines in the presence of a catalytic amount of bismuth trichloride.