Aspects of tautomerism. Part 16. Influence of the y-keto function on the reactions of sulphonic acids

Reaction of sodium 2-formylbenzenesulphonate (1) with thionyl chloride or phosphorous pentachloride gives a mixture of pseudo (2) and normal (3) sulphonyl chlorides. Whereas ammonium 2-carboxybenzenesulphonate (6) gives only the normal sulphonyl chloride (7) on reaction with thionyl chloride, a mixture of normal (7) and pseudo (8) isomers are formed on reaction with phosphorous pentachloride. Sodium 2-benzoylbenzenesulphonate (15), on the other hand, gives the corresponding normal sulphonyl chloride (16) on reaction with both of the reagents mentioned above. Based on these observations it is concluded that γ-keto sulphonic acids are amenable to the influence of γ-carbonyl group as in the case of γ-keto carboxylic acids but to a lesser extent.     

Models of folate cofactors 18. Application in an approach to the synthesis of indoloquinolizine alkaloids

The substituted 5,10-methylenetetrahydrofolate models 5b and 7, prepared by the addition of glutaconate ester anion to 1-acetyl-3,4,4-tri-methyl-2-imidazolinium iodide (2b) and 1-acetyl-3-aethyl-1,4,5,6-tetrahydro-pyrimidinium iodide (3) transfer the C(2)-carbons with the attached functional groups to give an indole derivative which serves as a convenient precursor for the synthesis of nor-deplancheine (21) and nor-epigeissoschizoate (27).     

The effect of sulfur and selenium substitutents on the regiochemistry of diels-alder reactions

2-Phenylthio-1,3-butadiene (1) and 2-phenylseleno-1,3-butadiene (2) have been generated in situ from their SO₂ adducts and reacted with a series of unsymmetrical dienophiles. The regiochemical results have been analyzed in terms of qualitative perturbation theory.     

Two new xenicin diterpenoids from the octocoral anthelia edmondsoni

From the soft coral Antheliaedmondsoni two new diterpenoids, waixenicin-A (1) and -B (2) have been Isolated. Their structures were elucidated by¹H and¹³C NMR analysis and the relative stereochemistry was determined by x-ray diffraction of crystalline waixenicin-B (2).     

2H-Pyrrolo[3,4-b]pyridine and 2H-pyrrolo[3,4-c]pyridine: synthesis of the parent ring system and the Diels-Alder reaction

2H-Pyrrolo[3,4-b]pyridine (1) and 2H-pyrrolo[3,4-c]pyridine (2) were prepared and reacted with N-phenylmaleimide to give Diels-Alder adducts.     

Nonreducing-Sugar Subunit Analogs of Bacterial Lipid a Carrying the Ester-Bound (3R)-3-(Acyloxy)Tetradecanoyl Group

Abstract

In order to elucidate further the relationship between the composition of the fatty acyl groups in the nonreducing-sugar subunit of bacterial lipid A and its biological activity, 3-O-[(3R)-3-(acyloxy)tetradecanoyl]-2-deoxy-2-[(3R)-3-hydroxytetradecanamido]-4-O-phosphono-D-glucose [GLA-63(R, R) and GLA-64(R, R)], and 3-O-[(3R)-3-(acyloxy)tetradecanoyl]-2-deoxy-4-O-phosphono-2-tetradecanamido-D-glucose [GLA-67(R), GLA-68(R) and GLA-69(R)] have been synthesized. Benzyl 2-[(3R)-3-(benzyloxymethoxy)tetradecanamido]-2-deoxy-4,6-O-isopropylidene-β-D-glucopyranoside (5) and benzyl 2-deoxy-4,6-O-isopropylidene-2-tetradecanamido-β-D-glucopyranoside (6) were each esterified with (3R)-3-dodecanoyloxytetradecanoic acid (1), (3R)-3-tetradecanoyloxytetradecanoic acid (2) or (3R)-3-hexadecanoyloxy-tetradecanoic acid (3), to give 7-11, which were then transformed, by the sequence of deisopropylidenation, 6-O-tritylation and 4-O-phosphorylation, into a series of desired compounds.     

Stereospecific synthesis of (+)-oxybiotin from D-xylose. Preparation of the final chiral (+)-oxybiotin precursor

A stereospecific synthesis of 2(S)-carbomethoxy-butyl-3(R), 4(S)-diacetamido-tetrahydrofurane (11), the final chiral precursor in a new synthesis of (+)-oxybiotin has been achieved from 2, 5-anhydro-D-xylose derivative1.     

HPLC Separation of the Diastereomeric Glutathione Adducts of Styrene Oxide

Abstract

The four diastereomeric thioether adducts resulting from the addition of glutathione to racemic styrene oxide were separated on a Radial Pak C₁₈ column using pH 7 Tris-phosphate buffer solution containing methanol as eluent. The benzylic thioether (1) eluted earlier than the benzylic alcohol (2) regioisomers. A complete stereochemical profile was established with the first eluting stereoisomer assigned as (S,R)-1, followed by (R,R)-1, (S,R)-2, and (R,R)-2,. The diastereomers with S configuration at the benzylic carbon emerged first for each set of regioisomers. The use of glutathione as a chiral probe for the analysis of enantiomerically enriched epoxides was illustrated with β-methylstyrene oxide formed from (1R, 2S)-N,N-dimethylephedrium bromide during the course of a chiral phase-transfer synthesis of oxiranes.     

Asymmetric synthesis of anthracyclinones using chiral acetal: synthesis of a new chiral AB-synthon, ()-2-bromo-6-ethynyl-6-hydroxy-5, 6, 7, 8-tetrahydro-1, 4-naphthoquinone,and its application for ()-7-deoxydaunomycinone

A synthesis of a new chiral AB-synthon (4) for preparing the optically active anthracyclinones was attained through a stereospecific nucleophilic addition of trimethylsilylethynylmagnesium chloride to the chiral 2-tetralone-1-acetal (2). Synthesis of ()-7-deoxydaunomycinone (1c) was achieved by a regiospecific cycloaddition of4 to 4-acetoxy-8-methoxyhomophthalic anhydride (5).     

Synthesis of Glycosyl Cyanides and C-Allyl Glycosides by the use of Glycosyl Fluoride Derivatives

A treatment of 2,3,5-tri-O-benzyl-B-D-ribofuranosyl fluoride (1) with cyanotrimethylsilane in the presence of boron trifluoride diethyl etherate gave 2,3,5-tri-O-benzyl-α- (2α) and -β-D-ribofuranosyl (2β) cyanide in 46.2% and 46.6% yields, respectively. Confirmation of the corresponding isocyano isomer (3) formation and its conversion into 2 under boron trifluoride catalysis at -78°C made it possible to deduce that both 2α and 2β were produced by way of 3 which was formed preponderantly in the initial stage of the reaction. On the other hand, the reaction of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride (4) with cyanotrimethylsilane in diethyl ether by the use of boron trifluoride diethyl etherate (0.05 mol. equiv.) gave 2,3,4,6-tetra-O-benzyl-α -D-glucopyranosyl cyanide (5α), 2,3,4,6-tetra-O-benzyl-α- (6α), and -β-D-glucopyranosyl isocyanide (6β) as a 30:61:9 mixture (94% yield) but that in dichloromethane by the use of the catalyst (1.0 mol. equiv.) gave 5α (85% yield) as a sole product.

The reactions of 1 and of 4 with allyltrirnethylsilane under the same catalysis afforded C-allyl 2,3,5-tri-O-benzyl-α-D-ribofuranoside (7)(93.5% yield), and C-allyl 2,3,4,6-tetra-O-benzyl-α- (8α)(71.8% yield) and -β-D-glucopyranoside (8β) (22.4% yield), respectively.     

Stereospecific synthesis of (+) -cahbocyclic 2'-deoxyadenosine. an improved procedure for the preparation of (+)-(1r,2s,4r)-4-amino-2-hydroxy-1-hydroxymethylcyclopentane.

An improved procedure for the preparation of a versatile synthetic precursor, (+)-13, of carba-2'-deoxyribonucleosides and the first stereospecific way to enantiomerically pure carbocyclic 2'-deoxyadenosine, (+)-14, are presented from bicyclic lactone diol (+)-1. An unexpected formation of the disubstituted 2-oxabicyclo[2.2.1]heptane skeleton 15 through a hypervalent iodo species derived from 6 is also reported.     

2-benzopyrylium salts. XXXVII. Oxygen analogs of reissert compounds : molecular structure and reactions with sodium hydroxide

The weak intensity of the CN stretching band in IR spectra for 1-cyanoiso chromenes is obviously determined by the steric position of the CN group in the molecule, as it was established by X-ray structural analysis for the cyanide addition product 2d of 1-isopropyl-3-methyl-2-benzopyrylium salts. Depending on the other substituent in position 1, 1-cyanoisochromenes in aqueous solutions of sodium hydroxide eliminate hydrogen cyanide 2a, b, e, undergo inter-3a, b or intra-mlecular 2c, d recyclisation, or hydrolysis of the cyano group in 2f ; reaction products include α-naphthols 7c, e, β-naphthol 7d, acylchrysenes 5a, b, or the iso chromene-amide 11f , a stable 1-alkylideneisochromene 3e was obtained, and the intermediacy of 3-hydroxy-1-alkylideneiso chromenes was proved by their isolation in the cases of 10c, d     

Base-Catalyzed Decomposition of Acena Phtheneouinone Bissulfonylhydrazones to 1,8-Dicyanonaphthalenes,the Presumed Thermal Chemistry of 1,2,3,4-Tetrazine

In the course of our investigation of the chemistry of diazoacenaphthene, we needed 2-benzylidene-1-diazoacenaphthene (2). As a possible precursor to 2, benzylideneacenaphthenone (1) was treated with one equivalent of tosylhydrazine with the expectation that 2 would be formed following basic decomposition. Surprisingly, acenaphthenequinone bistosylhydrazone (3) was produced instead (Eq. 1).     

Synthesis of natural triisopentenylated flavanone, euchrenone a2

Euchrenone a₂ (7) isolated from the roots ofEuchresta japonica has been synthesised from 3-prenylphloroacetophenone (1) by other workers. We carried out its cyclodehydrogenation with dichloro dicyano quinone (DDQ) to obtain 6-acetyl-5,7-dihydroxy-2,2-dimethylchromene (2) which was ethoxymethylated in the 7-position to give 6-acetyl-7-ethoxymethoxy-5-hydroxychromene (3). Chalcone condensation of3 and 4-ethoxymethoxy-3-C-prenylbenzaldehyde (4) gave 4,6′-bisethoxymethoxy-2′-hydroxy-6″, 6″-dimethyl-3-C-prenylpyrano (2″, 3″–4,3) chalcone (5) which cyclised with methanolic sodium acetate to give protected 5,4′-bisethoxymethoxy-6″, 6″-dimethyl-3′-C-prenylpyrano (2″, 3″–7,8) flavanone (6). Deprotection of6 with 4% methanolic HCl yielded (7) with melting point and spectral data identical to that of the natural compound.     

Homoallylic rearrangement in the peracid oxidation of 19-iodo-5-androsten derivative

3-Chlorperbenzoic acid oxidation of steroidal homoallylic iodide1c in ether afforded the rearranged products2a, 2b and4 arising from highly labile hypervalent iodine intermediate.     

A new method for the synthesis of branched oligoribonucleotides using a fully protected branched triribonucleoside diphosphate unit

A fully protected key intermediate (2) for the synthesis of branched oligoribonucleotides was prepared by a four-step reaction from N⁶-benzoyl-adenosine 3′-phosphorodianilidate (9). To demonstrate the utility of this synthetic unit, a branched ribonucleotide of CUGA^G_C was synthesized.     

Synthesis and structure of hexakis (p-hydroxyphenyloxy)benzene: A versatile analogue of the hydrogen-bonded hexameric unit of β-hydroquinone

The title hexaphenol (1), a direct analogue of the -hydroquinone hexameric unit, has been prepared by six-fold demethylation of hexakis (p-methoxyphenyloxy)benzene (2) with BBr₃. Host1 forms a trigonal adduct, space groupR3,a=22.088(3),c=12.232(3) Å, containing 6 molecules of pyridine per host molecule: a detailed X-ray study of this inclusion compound reveals a true clathrate structure, the closed cages of which accommodate a small, non-stoichiometric amount of water.     

On the Stereoselectivity of Fluorine and Acetylhypofluorite Additions to Glycals: The Synthesis of 2-Deoxy-2-Fldorohexoses

Electrophilic syn additions of fluorine and acetylhypofluorite across double bonds in 3,4,6-tri-0-acetyl-D-glucal (1a) and D-glucal (1b) followed by acid hydrolysis gave mixtures of 2-deoxy-2-fluoro-D-glucose (8) and 2-deoxy-2-fluoro-D-mannose (9). These addition reactions were conducted in various solvents with a view to investigating the reaction mechanism based on the product distribution analysis by ¹⁹F NMR. Tight ion pair intermediates (4 and 5) have been invoked to explain the stereospecific characteristics of the addition of fluorine or acetylhypofluorite to glycals. The relative stabilities of these intermediates control the product distributions and are governed by a) the anomeric effect (axial vs equatorial preference of C(1) electronegative substituents in pyranose rings), b) dipole-dipole interactions of the lone pairs of electrons on the ring oxygen and the electronegative substituents on C(2), and c) the gauche relationship that exists between the C(2) fluorine and polar groups in the molecule. The overall contribution of these three factors largely depends upon the polarity of the solvent. A rationale for the ¹⁹F NMR chemical shifts as well as the anomeric distributions of the α and β anomers of 2-FDG (8) and 2-FDM (9) has been proposed.     

Intramolecular formal iron-catalyzed ene reactions: The stereoselective and regiocontrolled formation of substituted tetrahydropyrans

The iron-catalyzed six-membered ring carbocyclizations of 5-oxa-2, 8, 10-undecatriene derivatives proceed with high regio- and stereoselectivity to yieldtrans-3, 4-disubstituted tetrahydropyrans. Substrates containing an alkyl substituent at the 4- or the 7-position of the starting triene ether cyclize with high secondary stereoinduction to producetrans, trans-trisubstituted derivatives. Diastereomeric (2Z)- and (2E)-substrates cyclize via complementary [4+4]- and [4+2]-ene reaction pathways.     

Regioselective Synthesis of Flindersine Analogues

6-Alkylpyrano [3,2-c] quinolin-5(2H)-ones(11a-e) were obtained in excellent yields by simply refluxing propynyl and butymyl ethers (6) of 4-hydroxy-1-alkylquinolin-2H-ones (2) in chlorobenzene for 10h, 5-Prop-2-ynyloxy-2H-pyrano [3,2-c] quinoline (12) was also obtained from the thermal rearrangement of 2,4-bis prop-2-ynyloxyquinoline (4).