An efficient synthesis of α,β-unsaturated aldehydes by a four-carbon unit extension of Grignard reagents

Copper-catalyzed addition of organomagnesium halides to 2-(2,2-diethoxyethyl)oxirane ( 1 ) affords aldol acetals 2 which upon acid treatment undergo hydrolysis and dehydration to give α,β-unsaturated aldehydes 7 with high yields.     

Relative activities of tetrahydrofurfural acetals in the detachment of a hydrogen atom by tert-butoxyl radicals

The reactivities of linear and cyclic acetals of tetrahydrofurfural in the reaction with tert-butoxyl radicals were studied. The k_a/k_d parameters, which are the ratios of the rate constants for the accumulation of tert-butyl alcohol to the rate constants for the formation of acetone, are close to the parameters for 2-alkyl-substituted acetals. Linear acetals are less active than cyclic acetals, the activities of which increase on passing from 2-tetrahydrofuryl-1,3-dioxolane to its sulfur- and nitrogen-containing analogs.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1597–1599, December, 1981.     

[4+2] Annulation of 3-(2,2-diethoxyethyl)-1,3-dicarbonyl compounds with indoles catalyzed by Brønsted acid ionic liquid for the synthesis of carbazoles

Various carbazoles were synthesized via [4+2] annulation of 3-(2,2-diethoxyethyl)-1,3-dicarbonyl compounds with indoles. A Brønsted acid ionic liquid, [BPy]HSO₄, was proven to be effective catalyst for this reaction. The ionic liquid catalyst can be recycled three times without significant loss of its catalytic activity.     

The first synthesis of cyclopropanone acetals from the reaction of Fischer carbene complexes with ketene acetals

The reaction of iso-propoxy stabilized Fischer carbene complexes with ketene acetals gives moderate to excellent yields of cyclopropanone acetals when carried out under a carbon monoxide atmosphere. This is in contrast to the known reaction of methoxy substituted complexes which give cyclic ortho esters under the same conditions. A mechanism is proposed which involves a branch point between the two products as the zwitterionic intermediate resulting from nucleophilic addition of the ketene acetal to the carbene carbon. A 1,3-migration of the methoxyl group to the cationic center leads to the ortho ester and a ring closure by backside attack leads to the cyclopropanone acetal. A double-labeling experiment shows that the 1,3-migration occurs by an intramolecular process that is proposed to involve a bridging oxonium ion. The effect of the isopropoxy group is thus interpreted to be to sterically hinder the formation of a bridged oxonium ion.     

Transformations of Cyclic Acetals under the Action of Some Organic and Inorganic Oxidants

Liquid-phase oxidation of cyclic acetals and 2,2-disubstituted 1,3-dioxacyclanes with dimethyldioxirane, Caro salt, potassium persulfate, and complex of potassium chlorodiperoxochromate with 15-crown-5 was studied.     

The correlation of the intensities of the M+˙ and [M − H]+ ions in electron impact mass spectra of cyclic acetals and thioacetals containing a phenylalkoxyester group

The correlation between the intensities of the M^+˙ and [M ? H]⁺ ions of 47 cyclic acetals and thioacetals of alkyl formylphenoxyacetates and propionates as well as the fragmentation patterns in the vicinity of the molecular ion are discussed. The characteristic differences between the spectra of 1,3-dioxolanes, 1,3-oxathiolanes, 1,3-dithiolanes and 1,3-dioxanes are presented.     

13C NMR study of the structures of some acyclic and cyclic ketene acetals

A ¹³C NMR study of the spatial structures of some acyclic and cyclic ketene acetals (for example, ketene dimethyl acetal and 2-methylene-1,3-dioxolane) has been carried out. The conclusions obtained are based on observation of the effect of structural changes on the ¹³C NMR chemical shift of the β carbon on the ketene moity. Since the extent of p-π conjugation and hence the ¹³C chemical shift of this carbon depend on the spatial orientation of the alkoxy groups about the O-C(sp²) bonds, the shift concerned may be used as a measure of the planarity of the system. The most stable retamers of ketene dimethyl acetal are s-cis,s-cis (planar) and s-cis,gauche (slightly nonplanar), in the order of decreasing stability. For ketene dialkyl acetals, the relative stability of the planar s-cis,s-cis form decreases with increasing bulkiness of the alkyl groups, but at least for primary and secondary alkyl groups, the s-cis,s-cis rotamer appears to be the most favored species. The conformations of 5- to 8-membered cyclic ketene acetals are discussed and compared with those of the corresponding cyclic vinyl ethers and hydrocarbons.     

Three-component condensation of Meldrum’s acid with 2-naphthylamine and esters derived from vanillin

Three-component condensation of Meldrum’s acid (2,2-dimethyl-1,3-dioxane-4,6-dione) with 2-naphthylamine and esters derived from vanillin involves intermediate formation of N-arylmethylidene-2-naphthylamines which are cleaved with Meldrum’s acid to give 5-arylmethylidene-2,2-dimethyl-1,3-dioxane-4,6-diones and arylmethylideneketenes. Reaction of the latter with 2-naphthylamine leads to formation of 2-methoxy-4-(3-oxo-1,2,3,4-tetrahydrobenzo[f]quinolin-1-yl)phenyl carboxylates.     

Synthesis of chiral 3-substituted gamma-lactones and 9-furanosyladenine from (R)-2-(2,2-diethoxyethyl)-1,3-propanediol monoacetate prepared by lipase-catalyzed reaction

A chiral building block, (R)-2-(2,2-diethoxyethyl)-1,3-propanediol monoacetate was synthesized in high optical and chemical yields by lipase-catalyzed transesterification. From this compound, we synthesized chiral 3-substituted gamma-lactones and a new nucleoside with antiviral activity.     

Co2(CO)8-catalyzed carbonylation of acetals using N-silylamines

Formaldehyde dialkyl acetals and cyclic acetal, 1,3-dioxolane, are smoothly carbonylated using N-silylamines at 140–160 °C under 70–88 kg cm⁻² CO pressure in the presence of a catalytic amount of Co₂(CO)₈ to give the corresponding 2-alkoxyamides in moderate to good yields. In the carbonylation of formaldehyde dialkyl acetals using N-silylamines, addition of pyridine drastically enhances the catalytic activity.     

Regioselective Synthesis of Partially Protected Trehalose Analogues and Assignment of Ring Size in Isopropylidene Acetal Derivatives by 13 C Nmr Spectroscopy

ABSTRACT

The ¹³C NMR spectra of a range of di-O-isopropylidene acetals of α,α-trehalose and its analogues 1, 2, 4-7 have been studied Attention has been focussed on the chemical shifts of the acetal carbon and methyl groups of the acetals. These parameters are characteristic of ring-size (1,3-dioxolane and 1,3-dioxane). Di-n-butylstannylene and cyclic orthoester intermediates 9 and 12 of 2,6-di-O-benzoyl-α-D-galactopyranosyl 2,6-di-O-benzoyl-α-D-galactopyranoside (8) were used to synthesize the partially protected trehalose analogue having chain extension at positions 4,4′ and 3,3′ (10 and 13) respectively. Acetonation of the synthetic trehalose type disaccharide yielded mainly 3,4:3′,4′-di-O-isopropylidene derivative 4. The benzoylation of 4 followed by acid hydrolysis gave 8 in 85% yield, which was the key intermediate for the synthesis of 10 and 13     

Synthesis and characterization of acrylated phosphonates and their polymers having 1,3-dioxolane and 1,3-dioxane moieties derived from brominated cyclic acetals of polyols through the Arbuzov reaction. II

Glycerol, D -mannitol, and D -sorbitol were converted into their mono- and di-O-1,3-dioxolane and 1,3-dioxane bromoethylidene derivatives through a transacetalation reaction with bormoacetaldehyde diethyl acetal under controlled conditions. These brominated dioxolane or dioxane derivatives were subsequently phosphonylated through the Arbuzov reaction. The phosphonylated cyclic acetals were used as precursors for the synthesis of acrylated phosphonate monomers. All these compounds have been characterized by elemental analysis and spectroscopic (IR, ¹H-,¹³C-, ³¹P-NMR and mass) methods. A mixture of 1,3-dioxane and 1,3-dioxolane derivatives was obtained with D -sorbitol, whereas the reaction products with glycerol and D -mannitol yielded primarily the 1,3-dioxolane derivatives. The acrylated phosphonates of glycerol and mannitol have been polymerized and studied on the basis of gel permeation chromatography and their spectral and thermal properties. The acrylated phosphonates, monomers, and polymers, were shown to have a large capacity to solvate and dissolve heavy metal salts. This results in a dramatic increase (> 100°C) of the glass transition temperature of these polymers.     

Exploring the Border between Concerted and Two‐Step Pathways of 1,3‐Dipolar Cycloadditions of Organic Azides to Cyclic Ketene N,X‐Acetals. – Synthesis and 15N‐NMR Spectra of Zwitterions and Spirocyclic Cycloadducts

Cyclic ketene N,X‐acetals 1 are electron‐rich dipolarophiles that undergo 1,3‐dipolar cycloaddition reactions with organic azides 2 ranging from alkyl to strongly electron‐deficient azides, e.g., picryl azide ( 2L ; R¹=2,4,6‐(NO₂)₃C₆H₂) and sulfonyl azides 2M – O (R¹=XSO₂; cf. Scheme 1). Reactions of the latter with the most‐nucleophilic ketene N,N‐acetals 1A provided the first examples for two‐step HOMO(dipolarophile)–LUMO(1,3‐dipole)‐controlled 1,3‐dipolar cycloadditions via intermediate zwitterions 3 . To set the stage for an exploration of the frontier between concerted and two‐step 1,3‐dipolar cycloadditions of this type, we first describe the scope and limitations of concerted cycloadditions of 2 to 1 and delineate a number of zwitterions 3 . Alkyl azides 2A – C add exclusively to ketene N,N‐acetals that are derived from 1H‐tetrazole (see 1A ) and 1H‐imidazole (see 1B , C ), while almost all aryl azides yield cycloadducts 4 with the ketene N,X‐acetals (X=NR, O, S) employed, except for the case of extreme steric hindrance of the 1,3‐dipole (see 2E ; R¹=2,4,6‐(^tBu)₃C₆H₂). The most electron‐deficient paradigm, 2L , affords zwitterions 16D , E in the reactions with 1A , while ketene N,O‐ and N,S‐acetals furnish products of unstable intermediate cycloadducts. By tuning the electronic and steric demands of aryl azides to those of ketene N,N‐acetals 1A , we discovered new borderlines between concerted and two‐step 1,3‐dipolar cycloadditions that involve similar pairs of dipoles and dipolarophiles: 4‐Nitrophenyl azide ( 2G ) and the 2,2‐dimethylpropylidene dipolarophile 1A (R, R=H, ^tBu) gave a cycloadduct 13 H , while 2‐nitrophenyl azide ( 2 H ) and the same dipolarophile afforded a zwitterion 16A . Isopropylidene dipolarophile 1A (R=Me) reacted with both 2G and 2 H to afford cycloadducts 13G , J ) but furnished a zwitterion 16B with 2,4‐dinitrophenyl azide ( 2I) . Likewise, 1A (R=Me) reacted with the isomeric encumbered nitrophenyl azides 2J and 2K to yield a cycloadduct 13L and a zwitterion 16C , respectively. These examples suggest that, in principle, a host of such borderlines exist which can be crossed by means of small structural variations of the reactants. Eventually, we use ¹⁵N‐NMR spectroscopy for the first time to characterize spirocyclic cycloadducts 10 – 14 and 17 (Table 6), and zwitterions 16 (Table 7).     

Interaction of 1-acylamino-2,2-dichloroethenyl(triphenyl)phosphonium chlorides with alkanolamines

Abstract

It is shown that the interaction of 1-acylamino-2,2-dichloroethenyl(triphenyl)-phosphonium chlorides with alkanolamines having a primary amino group results in the formation of 4-oxazolylphosphonium salts containing hydroxyalkylamine substituents at position 5 of the oxazole cycle. Under similar conditions the reaction of N-substituted alkanolamines with 1-acylamino-2,2-dichloroethenyl-(triphenyl)phosphonium chlorides leads to the formation of 1,3-oxazolidin-2-ylidene derivatives, in which the triphenylphosphonium group is located in the side chain. The structure of the new synthesized compounds has been reliably proven by elemental analysis, IR, ¹Н, ¹³С, ³¹Р NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction.     

17O, 13C, and 1H NMR Studies of p–π Conjugation in 2-Substituted 4-Methylene-1,3-dioxolanes and 4-Methyl-1,3-dioxoles

The ¹⁷O NMR spectra of a number of unsaturated 5-membered cyclic acetals, 2-substituted 4-methylene-1,3-dioxolanes and their endocyclic isomers, 4-methyl-1,3-dioxoles, have been recorded. The ¹⁷O NMR chemical shifts, in comparison with those of similarly 2-substituted 1,3-dioxolanes, were used to explore the variation of the strength of p– conjugation in the unsaturated acetals as a function of the nature of substitution at C2. The ¹⁷O NMR shift data reveal that alkoxy substituents have a significantly more favorable effect on the strength of p– conjugation in 4-methyl-1,3-dioxoles than in 4-methylene-1,3-dioxolanes. This fact appears to be responsible for the previously observed unexpectedly large effect of alkoxy substitution on the relative thermodynamic stabilities of these two classes of isomeric compounds. Additional information of the unexpected charge distribution in 4-methyl-1,3-dioxoles is provided by their ¹H and ¹³C NMR spectra.     

Reaction of 2-Alkoxypropenals with α-Hydroxyamino Oximes and 1,2-Bis(hydroxyamino)cyclohexane

Reactions of 2-alkoxypropenals with α-hydroxyamino oximes in neutral medium involve the aldehyde group of the former to afford both acyclic and cyclic azomethine oxides: N-(2-hydroxyiminoalkyl)-N-(2-alkoxy-2-propenylidene)amine oxides and 1-hydroxy-2,5-dihydroimidazole 3-oxides. The state of tautomeric equilibrium between the cyclic and acyclic products depends on the solvent nature and temperature. The reaction in acidic aqueous medium is accompanied by hydrolysis of the vinyl ether moiety in 2-alkoxy-propenals with formation of 2-oxopropionaldehyde which reacts with α-hydroxyamino oxime at the hydroxy-amino group to give substituted pyrazine 1,4-dioxides. The reaction of 2-alkoxypropenals with 1,2-bis-(hydroxyamino)cyclohexane leads to formation of 2-(1-alkoxyvinyl)-1,3-dihydroxyperhydrobenzimidazoles. The structure of the products was proved by IR, UV, and ¹H and ¹³C NMR spectroscopy and X-ray analysis.     

Reactions SRN1 en serie heterocyclique: IV: Reactivite des sels du dimethyl-2,2 nitro-5 dioxanne-1,3

2-Alkyl 2-nitro 1,3-propanediol, 2-alkylidene 1,3-propanediol and 2-dialkylidene 1,3-propanediol are prepared via S_RN1 reactions with salts of 2,2-dimethyl 5-nitro 1,3-dioxane and acid-catalyzed cleavage of the resulting acetals.     

Cationic copolymerization of 2-methylene-5,5-dimethyl-1,3-dioxane with 2-methylene-1,3-dioxolane and 2-methylene-1,3-dioxane

Copolymers of the cyclic ketene acetals, 2-methylene-5,5-dimethyl-1,3-dioxane, 3 , (M₁) with 2-methylene-1,3-dioxolane, 4 , (M₂) or 2-methylene-1,3-dioxane, 5 , (M₂), were synthesized by cationic copolymerization. An experimental method was designed to study the reactivity of these very reactive and extremely acid sensitive cyclic ketene acetal monomers. The reactivity ratios, calculated using a computer program based on a nonlinear minimization algorithm, were r₁ = 6.36 and r₂ = 1.25 for the copolymerization of 3 with 4 , and r₁ = 1.56 and r₂ = 1.42 for the copolymerization of 3 with 5. FTIR and ¹H-NMR spectra when combined with the values of r₁ and r₂ showed that these copolymers were formed by a cationic 1,2-polymerization (ring-retained) route. Furthermore the tendency existed to form very short blocks of M₁ or M₂ within the copolymers. Cationic copolymerization of cyclic ketene acetals have the potential to be used for synthesis of novel polymers. © 1996 John Wiley & Sons, Inc.     

Ring-expansion polycondensation of 2-stanna-1,3-dioxepane (or 1,3-dioxepene) with dicarboxylic acid chlorides

2,2-Dibutyl-2-stanna-1,3-dioxepane 1 (or 1,3-dioxepene 2) were prepared from 1,4-butane (or 1,4-butene) diol and dibutyltin dimethoxide. They were polycondensed at 80°C in n-heptane with adipoyl-, suberoyl, sabacoyl chloride and with decane-1,10-dicarbonyl chloride. In the case of suberoyl chloride and 2,2-dibutyl-2-stanna-1,3-dioxepane reaction time, temperature and stoichiometry were varied to optimize both the molecular weight and the fraction of cyclic polyesters. With a slight excess of the dicarboxylic acid chlorides, only macrocyclic polyesters were obtained in all cases. The resulting cyclic polyesters were characterized by viscosity measurements, by ¹H and ¹³C NMR and by MALDI-TOF mass spectrometry.