Unexpected Formation of A 4,6-O-Propylidene Derivative from Galactose and Allyl Alcohol in the Presence of AmberlystR15

Abstract

Allyl ethers are convenient and widely used protecting groups in synthetic carbohydrate chemistry.² One of the attractive reactions of the allyl ether group is its ready isomerization into a prop-1-enyl ether function under basic or metal-mediated conditions.^2-4 In our research projects to extend galactosyltransferase reactions to the enzymic syntheses of βGal 1,1-linked sugars,⁵ 1-O-allyl galactopyranoside was needed as a key synthetic intermediate. Anhydrous cation exchange resin (Amberlyst^R15:Rohm & Haas Co.) was chosen as the acidic catalyst owing to its ease of handling and removal. In this paper we report an unexpected result of this reaction which gave allyl 4,6-O-propylidene galactopyranoside from galactose and Amberlyst in refluxing allyl alcohol.

On treatment of galactose (200 mg) and Amberlyst (100 mg) in allyl alcohol (5 mL) at 100–110 °C, TLC analysis (silica gel, acetonitrile:water, 10:1) indicated that the allyl glycosylation was completed within 15 min, affording allyl D-galactopyranoside.     

Reactions of Elemental Phosphorus and Phosphine with Electrophiles in Superbasic Systems: XV. Phosphorylation of Allyl Halides with Elemental Phosphorus

Elemental phosphorus (red or white) reacts with allyl chloride and allyl bromide in a two-phase system aqueous KOH-organic solvent to form tertiary symmetrical and mixed phosphine oxides among which tris(prop-2-enyl)-, bis(prop-2-enyl)[(E)-prop-1-enyl]-, bis(prop-2-enyl)[(Z)-prop-1-enyl]-, (prop-2-enyl)[(E)-prop-1-enyl][(Z)-prop-1-enyl]-, bis[(E)-prop-1-enyl](prop-2-enyl)-, bis[(Z)-prop-1-enyl](prop-2-enyl)-, tris-[(E)-prop-1-enyl]-, and bis[(E)-prop-1-enyl][(Z)-prop-1-enyl]phosphine oxides were identified. The conditions (room temperature, 60% aqueous KOH-dioxane) allowing preparation from white phosphorus and allyl bromide of tris(prop-2-enyl)- and bis(prop-2-enyl)[(E)-prop-1-enyl]phosphine oxides as major products in the total yield of up to 96% were found.     

Catecholborane Reductive Cleavage of Allyl and Propargyl Acetals and Ketals: A Simple Route to Allyl and Prop-2-ynyl Ethers

the chemoselective conversion of allyl and prop-2-ynyl acetals as well as ketals by reductive cleavage with catecholborane into the corresponding allyl and prop-2-ynyl ethers is described.     

Ruthenium-catalyzed chemoselective N-allyl cleavage: novel Grubbs carbene mediated deprotection of allylic amines

A novel application of the Grubbs carbene complex has been discovered. The first examples of the catalytic deprotection of allylic amines with reagents other than palladium catalysts have been achieved through Grubbs carbene mediated reaction. Significantly, the catalytic system directs the reaction toward the selective deprotection of allylic amines (secondary as well as tertiary) in the presence of allylic ethers. A variety of substrates, including enantiomerically pure multifunctional piperidines, are also usable. The new method is more convenient, chemoselective, and operationally simple than the palladium-catalyzed method. The current mechanistic hypothesis invokes a nitrogen-assisted ruthenium-catalyzed isomerization, followed by hydrolysis of the enamine intermediate. We believe that the reactive species involved in the reaction may be an Rubond;H species rather than the Grubbs carbene itself. Thus, the isomerization may occur according to the hydride mechanism. The synthetic utility of this ruthenium-catalyzed allyl cleavage is illustrated by the preparation of indolizidine-type alkaloids.     

Tautomerization of α,β-and β,γ-unsaturated phosphonium salts resulting from the reaction of triphenylphosphine with β-bromomethacrylic acid. Nucleophilic addition at the γ position of the allyl group in phosphonium salt

Temperature factor was found to be determining in the isomerization of 2-carboxyprop-1-en-1-yl-and 2-carboxyprop-2-en-1-yl(triphenyl)phosphonium bromides. Elevated temperature favors formation of isomer with the double bond in the β,γ position with respect to the phosphonium group. Alkaline hydrolysis at room temperature promotes the reverse isomerization. The isomerization of 2-carboxyprop-1-en-1-yl(triphenyl)phosphonium bromide is hampered by addition of hydrobromic acid, as well as by carrying out its synthesis in the presence of aqueous HBr. Alkaline hydrolysis of 2-carboxyprop-1-enyl(triphenyl)phosphonium bromide and (E)-(2-carboxyvinyl)triphenylphosphonium chloride is accompanied by phenyl group migration to the α-position with formation of 2-methyl-3-(diphenylphosphoryl)-3-phenylpropionic acid and 3-(diphenyl-phosphoryl)-3-phenylpropionic acid, respectively. The possibility for nucleophilic addition at the γ position of the allyl group in 2-carboxyprop-2-enyl(triphenyl)phosphonium bromide was demonstrated using the reaction with triphenylphosphine as an example.     

Catalyzed olefin isomerization leading to highly stereoselective Claisen rearrangements of aliphatic allyl vinyl ethers

Iridium(I)-catalyzed olefin isomerization in bis(allyl) ethers is integrated into a generally applicable strategy for affecting highly stereoselective Claisen rearrangements. Catalyzed alkene isomerization affords allyl vinyl ethers from easily prepared di(allyl) ethers; direct thermolysis of these reaction mixtures leads to highly diastereoselective [3,3] sigmatropic rearrangements affording syn-2,3-dialkyl-4-pentenal derivatives. An easily executed strategy for realizing asymmetric variants of the isomerization-Claisen rearrangement (ICR) reactions is also described.     

A facile cleavage of allyl ethers on solid phase

A simple and efficient protocol for the cleavage of allyl ethers on solid phase using a palladium(0)-catalyzed allyl transfer reaction is reported.     

Kinetics and mechanism of palladium (II) chloride catalyzed oxidation of allyl alcohol by potassium hexacyanoferrate (III)

A kinetic study of the oxidation of allyl alcohol by potassium hexacyanoferrate (III) in the presence of palladium (II) chloride is reported. The reaction was observed by measuring the disappearance of the potassium hexacyanoferrate (III) spectrophotometrically. The reaction is first order with respect to allyl alcohol and palladium (II) chloride, inverse second order with respect to [Cl^?], and zero order with respect to potassium hexacyanoferrate (III). The rate is found to increase linearly with hydroxyl ion concentration.     

Allyl, methallyl, prenyl, and methylprenyl ethers as protected alcohols: their selective cleavage with diphenyldisulfone under neutral conditions

Diphenyldisulfone is a mild and efficient reagent for selective cleavage of methylprenyl (2,3-dimethylbut-2-en-1-yl), prenyl (3-methylbut-2-en1-yl), and methallyl (2-methylallyl) ethers. These reaction conditions are compatible with the presence of other protecting groups such as acetals, acetates, and allyl, benzyl, and TBDMS ethers. Exposure of 2,3-dimethylbut-2-en-1-yl and 3-methylbut-2-en1-yl ethers to diphenyldisulfone led to the formation of 2,3-dimethylbuta-1,3-diene and isoprene, respectively. 2-Methylallyl ethers undergo isomerization to 2-methylpropenyl ethers, which are easily hydrolyzed into the corresponding free alcohols and isobutyraldehyde. [reaction: see text]     

Preparation and antiviral properties of new acyclic, achiral nucleoside analogues: 1- or 9-[3-hydroxy-2-(hydroxymethyl)prop-1-enyl]nucleobases and 1- or 9-[2,3-dihydroxy-2-(hydroxymethyl)propyl]nucleobases

Acyclic, achiral nucleoside derivatives 1b-e of adenine, cytosine, 5-methylcytosine, and guanine, containing a 3-hydroxy-2-(hydroxymethyl)prop-1-enyl group on N-1 or N-9, have been prepared analogously to the previously described thymine derivative 1a. In contrast to the adenine and guanine derivatives, the cytosine derivative 9 was unstable, and was obtained in a low yield due to side reactions. These include cleavage of the propenyl group from the base, and the formation of a bicyclic compound. The thymine derivative, although stable under neutral conditions, likewise underwent a reversible cyclization reaction (Michael addition) in the presence of acids or bases. The 5-methylcytosine derivative was stable under neutral and basic conditions. Four other nucleoside derivatives 26a-d containing a 2,3-dihydroxy-2-(hydroxymethyl)propyl group on N-1 or N-9, three of which are new, have likewise been prepared. All compounds were evaluated as antiviral agents against HIV-1 and HSV-1 but were devoid of antiviral activity.     

Palladium- or ruthenium-catalyzed synthesis of 2-phenylindoles

Allyl α-phenyl-2-aminophenethyl carbonates undergo a smooth decarboxylation-dehydrogenation reaction to afford 2-phenylindole derivatives in acetonitrile at 80° in the presence of palladium complex as catalyst. In the reaction, the ruthenium hydride complex showed more effective catalytic activities. 2-Phenylindoles were also prepared from the corresponding α-phenyl-2-aminophenethylalcohols and allyl methyl carbonate by ruthenium-catalyzed cyclization.     

Isomerization of Functionalized Olefins by Using the Dinuclear Catalyst [PdI(μ-Br)(PtBu3)]2: A Mechanistic Study

In a combined experimental and computational study, the isomerization activity of the dinuclear palladium(I) complex [Pd^I(μ-Br)(P^tBu₃)]₂ towards allyl arenes, esters, amides, ethers, and alcohols has been investigated. The calculated energy profiles for catalyst activation for two alternative dinuclear and mononuclear catalytic cycles, and for catalyst deactivation are in good agreement with the experimental results. Comparison of experimentally observed E/Z ratios at incomplete conversion with calculated kinetic selectivities revealed that a substantial amount of product must form via the dinuclear pathway, in which the isomerization is promoted cooperatively by two palladium centers. The dissociation barrier towards mononuclear Pd species is relatively high, and once the catalyst enters the energetically more favorable mononuclear pathway, only a low barrier has to be overcome towards irreversible deactivation.     

An Allyl Uranium(IV) Sandwich Complex: Are ϕ Bonding Interactions Possible?

A method to explore head-to-head ϕ back-bonding from uranium f-orbitals into allyl π* orbitals has been pursued. Anionic allyl groups were coordinated to uranium with tethered anilide ligands, then the products were investigated by using NMR spectroscopy, single-crystal XRD, and theoretical methods. The (allyl)silylanilide ligand, N-((dimethyl)prop-2-enylsilyl)-2,6-diisopropylaniline (LH), was used as either the fully protonated, singly deprotonated, or doubly deprotonated form, thereby highlighting the stability and versatility of the silylanilide motif. A free, neutral allyl group was observed in UI₂(L1)₂ ( 1 ), which was synthesized by using the mono-deprotonated ligand [K][N-((dimethyl)prop-2-enyl)silyl)-2,6-diisopropylanilide] (L1). The desired homoleptic sandwich complex U[L2]₂ ( 2 ) was prepared from all three ligand precursors, but the most consistent results came from using the dipotassium salt of the doubly deprotonated ligand [K]₂[N-((dimethyl)propenidesilyl)-2,6-diisopropylanilide] (L2). This allyl-based sandwich complex was studied by using theoretical techniques with supporting experimental spectroscopy to investigate the potential for phi (ϕ) back-bonding. The bonding between U^IV and the allyl fragments is best described as ligand-to-metal electron donation from a two carbon fragment-localized electron density into empty f-orbitals.     

SYNTHESIS OF ALKYL AND ARYL 1-PROPENYL ETHER MONOMERS: A NEW APPROACH

A new, convenient synthesis of alkyl and aryl 1-propenyl ether monomers in good to excellent yields has been developed. Alkyl and aryl allyl ethers can be smoothly isomerized to the desired 1-propenyl ethers by refluxing in a basic ethanolic solution containing pentacarbonyliron as a catalyst. A simplified two-step, one-pot procedure has also been developed which consists of combining an alcohol with allyl bromide in the presence of base and then adding pentacarbonyliron to isomerize the in-situ generated allyl ether to directly give the 1-propenyl ether. Good yields of alkyl 1-propenyl ethers were obtained using this process. Factors affecting the isomerization reaction were investigated and a mechanism was proposed.     

Palladium-Catalyzed Fluorinative Bifunctionalization of Aziridines and Azetidines with gem-Difluorocyclopropanes

An unprecedented Pd-catalyzed fluorinative bifunctionalization of aziridines and azetidines was successfully developed via regioselective C−C and C−F bond cleavage of gem-difluorocyclopropanes, leading to various β,β′-bisfluorinated amines and β,γ-bisfluorinated amines. This reaction was achieved by incorporating a 2-fluorinated allyl group and a fluorine atom scissored from gem-difluorocyclopropane in 100 % atom economy for the first time. The mechanistic investigations indicated that the reaction underwent amine attacking 2-fluorinated allyl palladium complex to generate η²-coordinated N-allyl aziridine followed by fluoride ligand transfer affording the final β- and γ-fluorinated amines.     

Synthesis of [2-(methoxyaryl)-1-methylethyl]phosphinic acids from red phosphorus and (allyl)(methoxy)benzenes

(Allyl)(methoxy)benzenes react with red phosphorus in the superbasic system KOH-DMSO in the presence of small amounts of water and hydroquinone (3 h, 130 °C) to regio- and chemoselectively give [2-(methoxyaryl)-1-methylethyl]phosphinic acids in preparative yields up to 52%. The reactions involve isomerization of allylbenzenes into (prop-1-enyl)benzenes.     

Syntheses on the basis of 2H-chromen-2-one and 2H-chromene-2-thione

4-Hydroxy-2H-chromen-2-one and 4-hydroxy-2H-chromene-2-thione reacted with allyl bromide, 1,1,3-trichloroprop-1-ene, and 1,3-dichlorobut-2-ene to give the corresponding ethers, which were oxidized to (2-oxo-2H-chromen-4-yloxy)acetic acid with potassium permanganate, and various derivatives of that acid were obtained. 3-(3,3-Dichloroprop-2-enyl)-7-hydroxy-4-methyl-2H-chromen-2-one and 3-(3,3-dichloroprop-2-enyl)-7-hydroxy-4-methyl-2H-chromene-2-thione were synthesized, and some their transformations were studied.     

Novel methodology for the synthesis of the benz[a]anthracene skeleton of the angucyclines using a Suzuki-Miyaura/isomerization/ring closing metathesis strategy

The synthesis of the benz[a]anthracene skeleton of the angucyclines is described. Key steps involve the Suzuki-Miyaura reaction, isomerization of an aromatic allyl substituent to the corresponding styrene, and the use of the ring closing metathesis reaction to construct a benzene ring. For example, exposure of 3-allyl-2-bromo-1,4,5-trimethoxynaphthalene to (2-formyl-4-methoxyphenyl)boronic acid under palladium catalysis conditions resulted in the formation of 2-(3-allyl-1,4,5-trimethoxynaphthalen-2-yl)-5-methoxybenzaldehyde. This 2-naphthyl benzaldehyde then underwent a Wittig reaction to furnish 3-allyl-1,4,5-trimethoxy-2-(4-methoxy-2-vinylphenyl)naphthalene. Isomerization of the allyl group of this compound afforded the diene, (E)-1,4,5-trimethoxy-2-(4-methoxy-2-vinylphenyl)-3-(prop-1-en-1yl)naphthalene. Exposure of the formed diene to the Grubbs II catalyst resulted in the formation of the benzanthracene, 3,7,8,12-tetramethoxytetraphene, which was easily oxidized to the corresponding quinone.     

The relative stability of allyl ether,allyloxycarbonyl ester and prop-2 enylidene acetal,protective groups toward Iridium,Rhodium and Palladium catalysts.

The deprotection of allyloxycarbonyl derivatives of sugars was realized in the presence of allylether or prop-2-enylidene acetal with Pd(PPh₃)₄ or RhCl (PPh₃)₃ as catalyst while [Ir (COD) [PMePh₂)₂]PF₆ isomerized selectively the allyl ethers.     

25,26-Dialkoxycalix[4]arenes. Part 1: 25-Alkoxy-26,27-diacetoxy route

Acetylation of calix[4]arene 1,3-dialkyl ethers yielded the corresponding monoacetates. The ¹H NMR spectral analysis indicated that the products’ alkoxy moieties were ‘rotation restricted’. Acylation of calix[4]arene monoalkyl ethers with acetyl chloride yielded monoacetates and/or 2,3-diacetates in different reaction conditions. A simple recrystallization process was able to isolate 2,3-diacetates in good yield. The ¹H NMR spectra of the diacetylated products indicated that those compounds also possessed the ‘rotation restricted’ alkoxy moieties. In the presence of K₂CO₃ as reaction base, alkylation of 2,3-diacetates produced the acetyl-migrated 1,3-dialkyloxy derivatives. Basic hydrolysis of the acetyl-migrated compounds yielded the known 1,3-dialkoxycalix[4]arenes. In the presence of NaH as reaction base, 2,3-diacetates were alkylated with and without the acetyl-migration. For the highly reactive benzyl bromide and allyl bromide, the majority of alkylation proceeded without acetyl-migration. In the other alkyl halides, the products were the acetyl-migrated 1,3-dialkoxy derivatives along with less than one-fourth the amount of non-migrated 1,2-dialkoxy derivatives.