Notiz über einen Zugang zu β, γ-ungesättigten Carbonsäurederivaten mit Hilfe der Amidacetal-Claisenumlagerung. Über synthetische methoden, 17. Mitteilung

Note on a preparation of β, γ-unsaturated carboxylic acid derivatives using the amide acetal Claisen rearrangement 3-(Trimethylsilyl)allyl alcohols smoothly undergo the amide acetal Claisen rearrangement furnishing allyl silanes. Subsequent protolysis with HF at ?20° provides a convenient, stereoselective method for the preparation of β, γ-unsaturated carboxylic acid derivatives. Three model examples illustrate the procedure.     

Photocycloadditions of tetrachloro-1,4-benzoquinone (chloranil) onto cyclobutene and cyclopropene. Expected and unexpected products

Solutions of chloranil (CA) in chlorobenzene were irradiated in the presence of cyclobutene and cyclopropene. Cyclobutene gave rise to two conventional 1 : 2 cycloadducts onto the dichloroethene subunits of CA and an α,β-unsaturated α,γ-dichloro-γ-lactone. Heating of the crude product in methanol converted the lactone into an α,β-unsaturated methyl γ-oxocarboxylate (25% yield) and a large amount of the major 1 : 2 cycloadduct, which contains chlorocyclobutane entities, into a cyclopropylcarbinyl chloride derivative (24% yield). An entirely new product type was the result in the case of cyclopropene. After treatment of the crude product with methanol a tetracyclic acetal containing a cyclopentanone and a dihydropyran subunit was isolated in 36% yield. Apparently, CA had taken up two molecules of cyclopropene. One of the resulting cyclopropane entities must have undergone a rearrangement en route to the final product.     

Calix[4]resorcinols bearing γ-aminoacetal groups on the upper rim. Synthesis and properties

Synthesis of new calix[4]resorcinol molecules with acetal groups on the upper rim associated with calixarene skeleton through γ-aminoalkyl spacers was performed. The condensation of the compounds studied with 2-methylresorcinol was studied.     

Lithiated anions derived from (alkenyl)pentamethyl phosphoric triamides: Useful synthons for the stereoselective synthesis of 9-oxo- and 10-hydroxy-2(E)-decenoic acids, important components of queen substance and royal jelly of honeybee Apis mellifera

Lithiated anions derived from (alkenyl)pentamethyl phosphoric triamides as homoenolate equivalents are used in the reaction with halogenated acetal and ketal giving regioselectively the γ-alkylation adducts. Chemoselective acidic hydrolysis of the enephosphoramide moiety in the presence of acetal or ketal groups leads to expected carbonyl products, key intermediates in the synthesis of natural compounds. The synthetic potential of the presented strategy is illustrated by stereoselective synthesis of two pheromones namely, 9-oxo-2(E)-decenoic acid 1 from queen substance and 10-hydroxy-2(E)-decenoic acid 2 from royal jelly of honeybee Apis mellifera.     

18O assisted analysis of a γ,δ-epoxyketone cyclization: synthesis of the C16-C28 fragment of ammocidin D

The C16-C28 fragment common to the cytotoxic macrolide ammocidin D has been prepared by a stereospecific 5-exo closure of a γ,δ-epoxyketone followed by a rearrangement to a pyran acetal. The reaction pathway was traced by (18)O labeling of the keto carbonyl and observation of (18)O induced (13)C shifts in the pyran acetal product. NMR data of the synthetic C16-C28 fragment compared favorably to the natural product providing support of the assigned stereochemistry.     

An unexpected synthesis of an α,β,γ,δ-unsaturated ketone due to an abnormal opening of benzylidene acetal by bromide anion

An unexpected synthesis of an α, β, γ,δ-unsaturated ketone, which embodies a new type of oxy-carbon cyclic structure, was achieved, while we tried to construct the taxane CB-ring system. Also, a series of abnormal reaction phenomena was found to be related to the formation and reaction of seven membered cyclic benzylidene acetal.     

Alpha-Acylation and -allylation of β,β,β-trifluoropropionic esters via the ketene silyl acetals

α-Acylation of the ketene silyl acetal of methyl β,β,β-trifluoropropionate and α-allylation via the ester enolate Claisen rearrangement of the 2-alkenyl trifluoropropionates are described which provide the corresponding α-CF₃ β-ketoesters and α-CF₃ γ,δ-unsaturated acids, respectively.     

Synthesis and Chemical Behaviour of 4, 5-Dideoxy-4, 5-Epithio-2, 3-DI-0-Methanesulfonyl-L-Xylose Dimethyl Acetal

ABSTRACT

Selective substitution of the primary sulfonate group in 2, 3, 4, 5-tetra-0-methanesulfonyl-D-arabinose dimethyl acetal (1) gives 5-S-acetyl-2, 3, 4-tri-0-methanesulfonyl--5-thio-D-arabinose dimethyl acetal (2) which is further converted into the title compound (3). Reductive desul-furization of 3 afforded deoxy dimethyl acetal derivatives 5 and 6 in a low yield. Unsaturated monosaccharide derivative 7 was obtained as the only reaction product from 3 with triphenylphosphine. Catalytic hydrogenation of 7 gave dideoxy-sugar 6 in a satisfactory yield. Finally, epi-sulfide 3 with acetyl chloride afforded 4-chloro-4-deoxy derivative 4, which can be recycled into the starting 3.     

Monodispersed polystyrene latex particles functionalized by the macromonomer technique. II. Application in immunodiagnosis

Monodispersed polymer colloids with aldehyde and acetal functionalities, introduced by the macromonomer technique, were synthesized by a two‐step emulsion polymerization process. The latex samples so formed were chosen as the polymeric support to carry out covalent coupling with the antibody IgG anti‐C reactive protein, to test the utility of the latex–protein complexes formed in immunoassays. More than the 45% of the initially linked protein was covalently coupled in the acetal latex samples. Copyright © 2001 John Wiley & Sons, Ltd.     

Study of photocrosslinkable polysiloxanes bearing gem di-styrenyl groups: Synthesis and thermal properties

The synthesis of photocrosslinkable polysiloxanes containing gem di-oxaalkylene styrenyl groups and gem di-urethane-α-methyl styrenyl groups has been performed by copolycondensation of α,ω-dihydroxy polydimethyl siloxanes and dichlorosilanes bearing either cyclic acetal groups or Si-H groups (onto which the cyclic acetal groups are further added) and dichlorosilanes bearing alkyl groups. The introduction of styrenyl groups was then achieved by hydrolysis of the acetal groups into the corresponding alcohols followed by reaction with chloromethyl styrene or with 3-isopropenyl-α,α- dimethylbenzyl isocyanate.The structure of the different products synthesized was determined by IR, ¹H, ¹³C and ²⁹Si NMR spectroscopies. The thermal properties of the polysiloxanes bearing gem di-styrenyl groups have been studied at low and high temperatures.These products have been crosslinked under UV, in the presence of a cationic photoinitiator, and showed very good release paper properties.     

Two-carbon homologation of aldehydes via silyl ketene acetals. 2. Study of the stereochemical control in the formation of (E)-alkenoic acids.

The condensation of C,O,O-tris(trimethylsilyl)ketene acetal 1 with aldehydes 2 in the presence of catalytic amounts of mercuric iodide at room temperature affords syn and anti beta-trimethylsiloxy alpha-trimethylsilyl alkanoic acid silyl esters 3 in good yields. These new compounds gave, under acidic or basic conditions, E and (or) Z enoic acids 4. The paths for the formation of these alkenoic acids are discussed.     

Simplified synthesis of carbohydrate‐functional siloxanes via transacetalation. I. Glucose‐functional siloxanes

Carbohydrate‐functional siloxanes (CHFSs) that exhibit high intermolecular interactions and good environmental friendliness have successfully been synthesized by acid‐catalyzed transacetalation between an acetal‐functional siloxane and glucose in dimethylformamide/dioxane mixed solvents. Activated clay has proven to be a good catalyst because of its high activity and its easy removal from the product. Acetal‐functional siloxanes as starting materials can be easily synthesized in good yields by hydrosilylation between Si? H‐functional siloxanes and acrolein diethyl acetal. This method has the following advantages: (1) the inexpensive materials used, (2) the simplified process employed, and (3) the high yield achieved. Because the carbohydrate moieties in these materials have the nature of strong intermolecular interactions and are highly hydrophilic, CHFSs exhibit very high bulk viscosities in comparison with the corresponding acetal‐functional siloxanes and good solubilities in polar solvents such as dimethylformamide and dimethyl sulfoxide. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3336–3345, 2003     

Photolysis of 3-oxo-δ5(10)-steroids in alcoholic solvents and in the solid phase

Irradiation of the β, γ-unsaturated ketone 1a in alcoholic solvents afforded the 1,2 and 1,3-acyl shift products 2a and 3 respectively. The cyclobutanone 3 underwent further photochemistry incorporating a molecule of solvent and affording the ring expanded cyclic acetal 6. Solid phase irradiation of 1a yielded 2a and 3 but 1b was photostable.     

Synthesis and evaluation of 1-arylsulfonyl-3-piperazinone derivatives as factor Xa inhibitors(1-6) VI. A series of new derivatives containing N,S- and N,SO2-spiro acetal scaffolds

In the course of development of factor Xa (FXa) inhibitors, we have found unique compounds containing an N,O- and an N,N-spiro acetal structure. It appeared that the difference in overall conformation due to the N,X-spiro acetal structure might be important for FXa inhibitory activity. Therefore, other N,X-spiro acetal structures, an N,S- and an N,SO2-spiro acetal, were developed as analogues of the N,X-spiro acetal structure. Compound 7b (N,S-spiro acetal structure) was found to have the strongest activity in these series of N,X-spiro acetal compounds, which had ever been synthesized.(4,5)).     

Identification of ω-oxocarboxylic acids as acetal esters in aerosols using capillary gas chromatography-mass spectrometry

An homologous series of ω,ω-dimethoxycarboxylic acid methyl esters (acetal esters) has been identified in the most polar methyl ester fraction separated from remote aerosol samples by liquid chromatography. These compounds were separated by silica gel column chromatography and their structures determined by capillary gas chromatography (GC) and GC—mass spectrometry with a synthesized standard. The acetal esters are originally present in the samples as ω-oxocarboxylic acids, which are derivatized to acetal esters during treatment with boron trifluoride in methanol. This method enables the determination of ω-oxocarboxylic acids in environmental samples as their acetal esters.     

Formal syntheses of naturally occurring welwitindolinones

The formal syntheses of N-methylwelwitindolinone C isothiocyanate, N-methylwelwitindolinone C isonitrile, N-methylwelwitindolinone D isonitrile, 3-hydroxy-N-methylwelwitindolinone C isothiocyanate, and 3-hydroxy-N-methylwelwitindolinone C isonitrile are reported. The synthesis features several novel processes, including a Lewis acid mediated coupling between a benzylic-type heteroaromatic alcohol and a highly functionalized silyl ketene acetal, an intramolecular enolate arylation, and a regioselective, Pd(0)-catalyzed π-allylic cyclization of a γ-benzoyloxy enone moiety that is revealed by unmasking a furan ring.     

Synthesis of heparin saccharides III. Synthesis of derivatives of D-glucosamine as starting materials for disaccharides.

Derivatives of benzyl 2-[1-(benzyloxy)formamido]-2-deoxy-α-D-glucopyranoside with various protecting groups at C(3) (benzoyl, benzyl and N-phenylcarbamoyl) and C(6) (benzoyl, benzylsulfonyl, N-phenylcarbamoyl and tosyl) have been synthesized as starting materials for disaccharides. The C(4) and C(6) hydroxyl groups of the amino sugar were initially blocked by an acetal group. After introduction of the protecting group at C(3), the acetal group was removed by acid hydrolysis, and the C(6) hydroxyl group was selectively acylated or sulfonylated. The 3,6-di-O-benzoate has also been prepared by dimolar benzoylation of the amino sugar, whereby the 4,6-isomer was obtained as a by-product.     

S(N)1-like reactions of bicyclic alpha-amino ethers with sulfur,nitrogen, and carbon nucleophiles. Synthesis of 1-azabicyclo[3.2.2]nonanes functionalized at carbon C2 and C6 with complete stereocontrol

[reaction: see text] In the presence of nucleophiles, Lewis acid mediated cleavage of alpha-amino ethers derived from quincorine and quincoridine affords a variety of C2-substituted and C6-vinylated 1-azabicyclo[3.2.2]nonanes. These are enantiopure and are formed in S(N)1-like reactions with complete stereocontrol. There is no leakage into 2-Nu en route to product 1-Nu or vice versa. Me(3)SiCN provides new Strecker-type alpha-amino nitriles. In the presence of TTMPP-BF(3).OEt(2), the ketene acetal Me(2)C=C(OMe)OSiMe(3) delivers enantiopure bicyclic beta-amino acid esters.     

Totalsynthese eines Neobetanidin-Derivates und des Neobetenamins

The total synthesis of a neobetanidine derivative ( 3b ) is described. Preliminary experiments led to the synthesis of neobetenamine ( 4 ), which presents the ring system of neobetanidine ( 3 ). A general method for the synthesis of several compounds containing the essential neobetanidine chromophore (a 1, 7-diazaheptamethine system incorporating a pyridine ring) consisted of Vilsmeier-Haack condensations involving the active (enolizable) methyl group of γ-picoline. Neobetenamine ( 4 ) resulted from this reaction with N-formyl-indoline, and also by an amine exchange between indoline and the Vilsmeier-Haack product from γ-picoline and N-methyl-formanilide. The methyl group of γ-picoline-2, 6-dicarboxylic ester 9 , however, was resistant to the Vilsmeier-Haack condensation, but could be activated by introduction of a carboxyl into it: 4-chloropyridine-2, 6-dicarboxylic ester ( 11a ) (from chelidamic ester) was used to alkylate malonic ester. The product ( 12a ) lost only one carboxyl group when saponified. The resulting 2, 6-dicarboxy-pyridine-4-acetic acid ( 13a ) readily underwent a novel decarboxylative condensation with the Meerwein acetal of dimethyl formamide to 4-(2-dimethylamino-vinyl)-2, 6-dimethoxycarbonyl-pyridine ( 14b ), the first synthetic derivative of a neobetalaine. The enamine 14b was subjected to amine exchange reactions with indoline to 2-decarboxy-5, 6-dideoxy-neobetanidine dimethyl ester ( 15 ), and with (S)-cyclodopa ( 16 ) 5, 6-di-O-methyl-neobetanidine trimethyl ester ( 3b ). The latter was identical with the diazomethane transformation product of betanidine ( 1 ), the aglucone of the pigment of the red beet, betanine. A few proton resonance and electron spectral properties, as well as the basicities of several of the synthesized compounds, are tabulated and discussed as far as they express special structural and electronic features of the common 1, 7-diazaheptamethine chromophore.     

Cyclic Acetal-Photosensitized Polymerization. XII. Photopolymerizations of Styrene and Methyl Methacrylate in the Presence of Polycyclic Acetals

Styrene (St) and methyl methacrylate (MMA) were photopolymerized in the presence of poly-2-vinyl-1,3-dioxolane (PVDO), poly-2-vinyl-4-hydroxymethyl-1,3-dioxolane (PVHDO), or the terpolymer of vinyl formal/vinyl acetate/vinyl alcohol (PVFAcA) at 30 or 40°C. The ability to accelerate the photopolymerization increased in the order PVFAcA < PVHDO < PVDO; the ability of pendent cyclic acetal was larger than that of cyclic acetals which are not pendent. Moreover, the promoting ability per cyclic acetal increased with the increase in the number of cyclic acetal cyclic acetal group in the molecule.