Polar [3 + 2] cycloaddition of ketones with electrophilically activated carbonyl ylides. Synthesis of spirocyclic dioxolane indolinones

The [3 + 2] cycloaddition reaction between carbonyl ylides generated from epoxides and ketones (ethyl pyruvate, ethyl phenylglyoxylate, isatin, N-methylisatin and 5-chloroisatin) to give substituted dioxolanes and spirocyclic dioxolane indolinones was investigated. The effect of microwave irradiation on the outcome of the reaction was studied. The thermal reaction between 2,2-dicyano-3-phenyloxirane and N-methylisatin was theoretically studied using DFT methods. This reaction is a domino process that comprises two steps. The first is the thermal ring opening of the epoxide to yield a carbonyl ylide intermediate, whereas the second step is a polar [3 + 2] cycloaddition to yield the final spiro cycloadducts. The cycloaddition presents a low stereoselectivity and a large regio- and chemoselectivity. Analysis of the electrophilicity values and the Fukui functions of the reagents involved in the cycloaddition step allowed the chemical outcome to be explained.     

Gold‐Catalyzed [2+2+1] Cycloaddition of 1,6‐Diyne Carbonates and Esters with Aldehydes to 4‐(Cyclohexa‐1,3‐dienyl)‐1,3‐dioxolanes

A synthetic method to stereoselectively prepare 4‐(cyclohexa‐1,3‐dienyl)‐1,3‐dioxolanes in good to excellent yields by gold(I)‐catalyzed [2+2+1] cycloaddition of 1,6‐diyne carbonates and esters with aldehydes is described. The cascade process involves 1,2‐acyloxy migration followed by cyclopropenation and cycloreversion. This leads to an unprecedented [2+2+1] cycloaddition of the resulting alkenylgold carbenoid species, examples of which are extremely rare, with two aldehyde molecules at catalyst loadings as low as 1 mol %. The usefulness of this cycloisomerization chemistry was further demonstrated by the transformation of one example to the corresponding phenol.     

Palladium‐Catalyzed Decarboxylative Cycloaddition of Vinylethylene Carbonates with Formaldehyde: Enantioselective Construction of Tertiary Vinylglycols

An efficient method for the enantioselective construction of tertiary vinylglycols through a palladium‐catalyzed asymmetric decarboxylative cycloaddition of vinylethylene carbonates with formaldehyde was developed. By using a palladium complex generated in situ from [Pd₂(dba)₃]?CHCl₃ and a phosphoramidite ligand as a catalyst under mild reaction conditions, the process allows conversion of racemic 4‐substituted 4‐vinyl‐1,3‐dioxolan‐2‐ones into the corresponding 1,3‐dioxolanes, as methylene acetal protected tertiary vinylglycols, in high yields with good to excellent enantioselectivities.     

Chiral Brønsted acid-catalyzed enantioselective ionic [2+4] cycloadditions

The first asymmetric chiral N-triflylphosphoramide-catalyzed ionic [2+4] cycloaddition reaction of unsaturated acetals is described. This reaction proceeds through the intermediacy of a vinyl oxocarbenium/chiral anion pair, and the chiral N-triflylphosphoramide anion controls the stereoselectivity of the cycloaddition step. Moderate enantioselectivities (up to 80:20 e.r.) have been obtained when α,β-unsaturated dioxolanes were employed as the dienophiles. These reactions demonstrate strong dependence on the counterion coordinating properties and solvent polarity, a behavior characteristic of oxocarbenium ions.     

1H NMR spectra,configuration, and conformations of 2-mono- and 2,4-disubstituted 1,3-dioxolanes

The stereochemistry of 2-furyl-substituted 1,3-dioxolanes was studied. The ethane fragment of 2-monosubstituted dioxolanes displays the spectrum that is typical for an AA'BB' spin system, while the spectra of the 2,4-disubstituted compounds are typical for an ABC system. The contribution of the various conformational forms to the pseudorotation cycle of the dioxolanes is discussed on the basis of an analysis of the spectra by means of an iteration program.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No, 12, pp. 1613–1617, December, 1980     

Investigations of polyfunctional oxides

The reaction of esters of 4,5-epoxy-2-hexenoic acid with ketones in the presence of acid catalysts gives 2,2,4-trialkyl-5-(2-carboalkoxyvinyl)-1,3-dioxolanes, the hydrogenation of which gives the corresponding saturated dioxolanes. The conformations and configurations of the dioxolanes obtained were studied by means of their PMR spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 447–451, April, 1972See [1] for communication IV.     

Synthesis of New Chiral and Racemic 1,3‐Dioxolanes

A series of chiral 1,3‐dioxolanes, 3 – 12 , with >99% ee values, have been synthesized. This is the first study of chiral ketalization reaction starting from ketones with aryl, monosubstituted aryl, and long alkyl chains (C₁₁—AC₁₃). Their ee values were determined by chiral high‐performance liquid chromatography (HPLC) on Chiralcel OD column, using their racemic 1,3‐dioxolanes rac‐ 3 – 12 , which were also synthesized for the first time. These chiral and racemic 1,3‐dioxolanes were characterizated by infrared, NMR (¹H, ¹³C), mass spectrometry, elemental analysis, optical rotation, and chiral HPLC.     

Direct Barbier-type allylation of aromatic acetals and dioxolanes in the presence of β-cyclodextrin in water

A new and convenient procedure for the synthesis of homoallylic alcohols directly from aromatic acetals and dioxolanes has been developed with very good yields under biomimetic conditions using a Zn-mediated Barbier-type allylation in the presence of β-cyclodextrin in water.     

Conjugated elimination versus [1,2]-Wittig rearrangement of unsaturated diox(ol)anes

A set of unsaturated dioxanes and dioxolanes has been prepared in three steps from acetoxy-1-isoprene. When reacted with two equivalents of t-BuLi in THF, these compounds provided, under various conditions, a mixture of two types of 1,3-dienes. The first one, derived from a conjugated elimination reaction resulting in the heterocycles opening, is relatively unstable but could be trapped as an acrylate. The second one resulted probably from a [1,2]-Wittig rearrangement. The competition between these two reactions has been observed for both dioxanes and dioxolanes (but not for acyclic ketals) and is the object of a strong temperature effect, the Wittig rearrangement being favored over the elimination at room temperature. A difference between kinetic and thermodynamic deprotonation sites is proposed to be at the origin of this competition on the base of both experimental and theoretical results.     

Halogenocycloprop anation des dioxolannes ethyleniques et des enones correspondantes par les monohalogenocarbenoides

The monohalocyclopropanation of conjugated enones and their dioxolanes has been achieved by monohalocarbenoîds generated from methylene chloride and gem-dichloroethane. In both cases, besides expected chloro-adducts, corresponding bromo-adducts are obtained. Formation of these adducts involves halogen exchange by the primary chlorocarbenoid with lithium bromide associated with methyllithium. Conjugated enones give trans α-halocyclopropanic alcohols stereospecifically while unsaturated dioxolanes lead to cis and trans α-halocyclopropyl ketones with, generally, trans prédominating. The determination of configuration has been achieved by spectroscopic methods specially the LIS effect in NMR. Stereoselectivity effect of temperature and nature of the methyllithium reagent, are studied and discussed.     

exo- and enantioselective cycloaddition of azomethine ylides generated from N-alkylidene glycine esters using chiral phosphine-copper complexes

High diastereo- and enantioselectivities were obtained for the asymmetric 1,3-dipolar cycloaddition of azomethine ylides generated from N-alkylideneglycine esters with dipolarophiles using chiral phosphine-copper complexes as catalysts. Whereas the cycloaddition of azomethine ylides catalyzed by metal salts generally afforded endo-adducts as the predominant product, the present method is the first example of an exo-selective cycloaddition. [reaction: see text]     

Reaction of 2-methyl-6-p-bromophenyl-3,5-hexadiyn-2-ol with alcohols and ketones

Conclusions The nucleophilic addition of alcohols and ketones to a p-bromophenyldiacetylenic alcohol leads respectively to p-bromophenylenyne ethers and dioxolanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2827–2829, December, 1974.     

4-氧-3-氮杂-三环[5.3.1.02,5]十一烷-9-甲酸甲酯的合成及晶体结构

以2-金刚烷酮为起始原料,通过烯烃与氯磺酰异氰酸酯的[2+2]环加成等5步反应合成了新型双环β-内酰胺类化合物5.采用1H NMR,IR和MS等手段对所得化合物的结构进行了表征.此外,还通过将化合物5酰化并采用X射线单晶衍射分析方法进一步测定了化合物5的空间立体结构.结果表明,烯烃3与氯磺酰异氰酸酯的[2+2]环加成反...     

Preparation of 5-Alkylthio and 5-Arylthiotetrazoles from Thiocyanates Using Phase Transfer Catalysis

A very efficient method of preparation for 5-alkyl and 5-arylthiotetrazoles from the corresponding alkyl or aryl halides is described. The halides are first transformed into thiocyanates which further react with azide, yielding the corresponding tetrazoles with [2+3] polar cycloaddition. All synthetic transformations are performed under phase transfer catalytic conditions. The yields vary from good to excellent except for the preparation of 5-benzylthiotetrazole, where the reaction between benzyl thiocyanate and azide [2+3] cycloaddition is in competition with nucleophilic substitution, with benzyl azide as product.     

Highly Diastereoselective Synthesis of Syn‐1,3‐Dihydroxyketone Motifs from Propargylic Alcohols via Spiroepoxide Intermediates

Syn dihydroxyketone motifs are embedded in a wide range of biologically active natural products, however the development of stereoselective synthetic methods to assemble these structures has proven a challenging task. We report a highly diastereoselective method for the synthesis of syn dihydroxyketones from propargylic alcohols, with wide scope for application in natural product synthesis. The reaction sequence involves regioselective cyclisation of propargylic alcohols with incorporation of a triketone to give enol dioxolanes that are then diastereoselectively epoxidised to form unusual spiroepoxide intermediates. Hydrolysis affords syn dihydroxyketones as essentially single diastereisomers. The reaction sequence is operationally simple, of wide substrate scope, and remarkably can be efficiently carried out as a one‐pot process with no loss of overall yield or diastereoselectivity.     

Resolution and determination of the absolute configuration of 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxaldehyde

Racemic 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxaldehyde 1 was resolved via the formation of diastereomeric dioxolanes with (S)-(+)-1-phenyl-1,2-ethanediol. Four stereoisomers were separated by column chromatography. The absolute configuration of one of them (2′′R, 4′′S,1R) was established by X-ray diffraction. Acid hydrolysis of the dioxolanes afforded quantitatively (R)- and (S)-enantiomers of 1. Optical rotatory dispersion (ORD) spectra of both enantiomers are also reported.     

Solid-phase synthesis of oxazolidinones by cycloaddition of resin-bound epoxides with isocyanates

The first solid-phase synthesis of oxazolidinones by cycloaddition of resin-bound epoxides with isocyanates is described. Synthesis of the title compounds was achieved by alkylation of resin-bound carbamates with glycidyl tosylate, followed by cycloaddition of the resulting epoxides with isocyanates at elevated temperature in high yields and purity. Because N-aryloxazolidinones have been known to possess various biological activities, this method is useful from the viewpoint of drug discovery.     

Synthesis and Enantiomeric Selectivity of Chiral Crown Ethers

Condensation of (4S,5S)-4,5-dihydroxymethyl-2-substituted dioxolanes with polyethylene glycols ditosylates yielded new chiral crown ethers. By potentiometry the enantioselectivity of complexing between the compounds obtained and L- and D-valine methyl ester hydrochlorides was evaluated.     

Two carbon homologated alpha,beta-unsaturated aldehydes from alcohols using the in situ oxidation-Wittig reaction

The in situ oxidation-Wittig reaction, followed by subsequent hydrolysis, has been applied to the conversion of primary alcohols into alpha,beta-unsaturated aldehydes. This conversion, which proceeds via the intermediacy of the homologated unsaturated dioxolanes, gives good to excellent yields with a range of benzylic alcohols and heterocyclic methanols.     

[4+3] Cycloadditions of some allylic dioxolanes

Four allylic dioxolanes were prepared and reacted with several dienes in the presence of Lewis acids, affording [4+3] cycloadducts. The reaction could be conducted with catalytic amounts of Lewis acid. The use of a chiral Lewis acid gave a cycloadduct with only a low enantiomeric excess.