Acyclic Ketene Research Articles

Copper(II)‐catalyzed Domino Reaction of the Acyclic Ketene‐(S,S)‐Acetals with Diazo Compounds: Convenient Synthesis of Poly‐substituted Thiophenes

AbstractCopper(II)‐catalyzed domino reaction between the acyclic ketene‐(S,S)‐acetals and diazo compounds has been successfully developed. This reaction proceeds through a sequential formation of electrophilic copper carbenoid, sulfur ylide and subsequent C−S bond coupling and cleavage. Notably, the domino reaction features broad the readily available acyclic ketene‐(S,S)‐acetals scope and provides a new strategy for the synthesis of poly‐substituted thiophenes.magnified image

ChemInform Abstract: α‐Trifluoromethyl‐(indol‐3‐yl)methanols as Trifluoromethylated C3 1,3‐Dipoles: [3 + 2] Cycloaddition for the Synthesis of 1‐(Tifluoromethyl)‐cyclopenta[b]indole Alkaloids.

AbstractThis first formal [3+2] cycloaddition of α‐trifluoromethyl‐3‐indolylmethanol silyl ethers and acyclic ketene dithioacetals furnishes trifluoromethylated cyclopenta[b]indoles.

ChemInform Abstract: syn-Selective Aldol Reaction of Propynal-Hexacarbonylcobalt Complexes with Ketene Silyl Acetals.

3-Phenylpropynal–hexacarbonylcobalt complex, prepared from 3-phenylpropynal with octacarbonyl-cobalt, afforded on treatment with the seven-membered ketene trimethylsilyl acetal the syn-aldol product in a highly stereoselective manner. Similar exposure of the above complex to the six- and five-membered ketene trimethylsilyl acetal gave the corresponding syn-aldol products predominantly. The aldol reaction of the cobalt complexes derived from 3-trimethylsilyl- and 3-butyl-propynal with those cyclic ketene silyl acetals proceeded syn-selectively to provide the syn-aldol products. The preferential formation of the syn- over the anti-isomers was also achieved in the reaction of the cobalt complexed 3-trimethylsilylpropynal with acyclic ketene trimethylsilyl acetals, derived from methyl or tert-butyl propionate. In contrast, uncomplexed 3-phenyl-, 3-trimethylsilyl- and 3-butylpropynal furnished the corresponding aldol products nonselectively or anti-isomers predominantly depending on the structure of the starting ketene trimethylsilyl acetal.

Carbon Acid Induced Mukaiyama Aldol Type Reaction of Sterically Hindered Ketones

1,1,3,3-Tetrakis(trifluoromethanesulfonyl)propane (Tf(2)CHCH(2)CHTf(2)) is one of the most effective Brønsted acid precatalysts for the Mukaiyama aldol type reactions of sterically hindered ketones. By using Tf(2)CHCH(2)CHTf(2) in a range from 0.5 to 2.0 mol %, the vinylogous Mukaiyama aldol reaction of alpha-substituted cyclohexanones with 2-silyloxyfurans smoothly proceeded to give the aldol products in excellent yield without the loss of diastereoselectivity. Under similar conditions, acyclic ketene silyl acetals also performed as nice nucleophiles toward sterically hindered ketones. These findings suggest that Tf(2)CHCH(2)CHTf(2) induced Mukaiyama aldol type reactions can overcome the steric hindrance between reaction sites.

ChemInform Abstract: Acyclic Ketene Aminal Phosphates Derived from N,N‐Diprotected Acetamides: Stability and Cross‐Couplings.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Acyclic ketene aminal phosphates derived from N, N-diprotected acetamides: stability and cross-couplings

The synthesis of a stable ketene aminal phosphate (α-phosphoryloxy enecarbamate) derived from N, N-diprotected acetamide, bearing two different removable protecting groups, is disclosed. This synthetic intermediate underwent successful palladium-catalyzed cross-coupling reactions to afford functionalized enynes and dienes.

Efficient Regioselective Synthesis of 6-Amino-5-benzoyl-1-Substituted 2(1H)-Pyridinones

[Reaction: see text]. A regioselective and efficient approach toward 6-amino-5-benzoyl-1-substituted 2(1H)-pyridinones by reaction of acyclic ketene aminals with propiolic acid ester was developed. The effect of the solvent and temperature on the regioselectivity of the reaction and the compatibility of the target compounds to functional group manipulations was examined. Substrates with an ortho substituent build atropisomers due to the restricted rotation around the C-N bond. The enantiomers were separated, and the barrier of rotation was determined experimentally. Quantum chemical calculations allowed a ranking of the barrier heights, and a new mechanism of rotation by deformation of the central pyridinone moiety is proposed.

Cycloadditions of Ketene Diethyl Acetal and 2‐Methylene‐1,3‐ Dioxepane to Electrophilic Alkenes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Cycloadditions of Ketene Diethyl Acetal and 2-Methylene-1,3-dioxepane to Electrophilic Alkenes

Reactions of strong electron-rich donor alkenes with strong electron-poor acceptor alkenes give a variety of products, including cyclobutanes, cyclohexanes composed of two alkenes of one kind and one of the other, open chain adducts, and homopolymers of the alkenes. We examined cycloadditions of ketene diethyl acetal and 2-methylene-1,3-dioxepane to alkenes containing from one to four acceptor groups. The products and rates, in particular the structure of the cyclohexane adducts produced, are correlated with the ionic homopolymerizability of the alkenes, zwitterion stabilization, and gem-dialkyl cyclization effects. These concepts are extended to enamines and enolate anions as other electron-rich alkenes. 2-Methylene-1,3-dioxepane is the ketene acetal of choice for the preparation of many cyclobutanes, presumably due to the instability of the cationic end of the initial zwitterion from this cyclic ketene acetal relative to those from acyclic ketene acetals.

Ketene acetal monomers: Cationic photopolymerization

A study of the photoinduced cationic polymerization of a novel series of cyclic and acyclic ketene acetal monomers was carried out. It was observed that the cyclic monomers underwent facile cationic polymerization to give high molecular weight polymers while the acyclic ketene acetals did not. Thermally induced polymerization was also observed on standing catalyzed by glass surfaces. Photoinduced cationic polymerizations employing both diaryliodonium and triarylsulfonium salt photoinitiators were studied. It was observed that the position and type of substitutents in the cyclic ketene acetals was the major factor in determining the proportion of vinyl and ring-opening polymerizations that take place. © 1996 John Wiley & Sons, Inc.

Syn-Selective aldol reaction of propynal–hexacarbonylcobalt complexes with ketene silyl acetals

3-Phenylpropynal–hexacarbonylcobalt complex, prepared from 3-phenylpropynal with octacarbonyl-cobalt, afforded on treatment with the seven-membered ketene trimethylsilyl acetal the syn-aldol product in a highly stereoselective manner. Similar exposure of the above complex to the six- and five-membered ketene trimethylsilyl acetal gave the corresponding syn-aldol products predominantly. The aldol reaction of the cobalt complexes derived from 3-trimethylsilyl- and 3-butyl-propynal with those cyclic ketene silyl acetals proceeded syn-selectively to provide the syn-aldol products. The preferential formation of the syn- over the anti-isomers was also achieved in the reaction of the cobalt complexed 3-trimethylsilylpropynal with acyclic ketene trimethylsilyl acetals, derived from methyl or tert-butyl propionate. In contrast, uncomplexed 3-phenyl-, 3-trimethylsilyl- and 3-butylpropynal furnished the corresponding aldol products nonselectively or anti-isomers predominantly depending on the structure of the starting ketene trimethylsilyl acetal.

Thionation reactions of diacylketene thioacetals with the Lawesson reagent and analogues

Attempted thionation of diacylketene thioacetals derived from dimedone with dithiadiphosphetane disulphides (the Lawesson reagent and analogues) led to the expected monothioacylketene thioacetals only when the thioacetal sulphur atoms formed part of a dithiolane or dithiane ring. Acyclic analogues readily underwent dealkylation and further reactions, giving a 1,2-dithiole-3-thione derivative as the main isolated product. Reaction of an acyclic ketene thioacetal with P4S10–Et3N in acetonitrile at –30 °C permitted the isolation of the primary dealkylation product, a dimedonedithiocarboxylate, in 44% yield. A phenoxaphosphorine derivative was isolated as a by-product in the synthesis of bis(phenoxyphenyl)dithiaphosphetane disulphide.

The remarkable reactivity of 2-alkylidene-imidazolidines in inverse diels-alder reactions

The reactivity of 2-alkylidene-imidazolidines 2 in inverse Diels-Alder syntheses with several pyridazines and 1,2,4-triazines is compared with that of acyclic ketene acetals 1 . The 2-cyclopropylidene-imidazolidine 2c is particularly suited for less reactive dienes.