Z. R. Valiullina

Reaction of methyl-4-methylene-2,3-O-isopropylidene-β-D-ribofuranoside with N-bromosuccinimide in aqueous tetrahydrofurane

Methyl-4-methylene-2,3-O-isopropylidene-β-D-ribofuranoside prepared from D-ribose reacted in a system NBS-THF-H2O to give a mixture of stereoisomeric products of regioselective bromohydroxylation of a double bond. The reaction involved a hydrolysis of the glycoside bond, but the acetonide protective group was retained. The mechanism of the selective hydrolysis originating from the ring-chain tautomerism of bromohydrins obtained was proved by the 1H NMR spectra of the steroisomeric methyl-5-deoxy-5-bromo-4-hydroxy-2,3-O-isopropylidene-β-D-ribofuranosides. By crotonic cyclization of the formed masked 1,4-dicarbonyl compounds at heating in benzene in the presence of neutral Al2O3 a new chiral cyclopentenone block, 2-bromo-4,5-isopropylideneoxycyclopent-2-en-1-one, was obtained in a low yield.

Uncommon transformations of methyl (1S,2S,3R,4R)-2,3-isopropylidenedioxy-5-iodomethyl-2-tetrahydrofurylacetate initiated by bases

Methyl (1S,2S,3R,4R)-2,3-isopropylidenedioxy-5-iodomethyl-2-tetrahydrofurylacetate prepared in two stages from D-ribose acetonide underwent a series of uncommon transformations under the treatment with bases providing the following different products depending on the base applied: methyl 3-(5-acetyl-2,2-dimethyl-1,3-dioxol-4-yl)propionate (DBU), methyl 2,3-isopropylidenedioxy-7-oxabicyclo[2.2.1]heptane-6-carboxylate (t-BuOK), methyl {(5R)-2,2-dimethyl-5-[(2R)-oxiranyl]-1,3-dioxolan-4-ylidene}propionate and methyl-(E)-3-{(4S,5R)-2,2-dimethyl-5-[(1R)-(2-oxiranyl)]-1,3-dioxolan-4-yl}-2-propenoate (t-BuOK and LDA).

Unexpected transformation of methyl 3,6-anhydro-2,7-dideoxy-7-iodo-4,5-O-isopropylidene-D-allo-heptonate in the dehydroiodination reaction with 1,8-diazabicyclo[5.4.0]undec-7-ene

The reaction of methyl 3,6-anhydro-2,7-dideoxy-7-iodo-4,5-O-isopropylidene-D-allo-heptonate with 1,8-diazabicyclo[5.4.0]undec-7-ene affords methyl 3,6-anhydro-2,7-dideoxy-4,5-O-isopropylidene-D-ribo-hept-6-enonate, which undergoes the previously unknown rearrangement into a 2,2-dimethyl-1,3-dioxole derivative.

Aspects of stereoselectivity in electrophilic addition reactions of iodine with 5-allenyl-2,3,5-trichloro-4,4-dimethoxycyclopent-2-en-1-one and its derivatives

The reactions of 5-allenyl-2,3,5-trichloro-4,4-dimethoxycyclopent-2-en-l-one and related compounds with I2 were studied. The stereochemistry of the resulting 1,2-adducts with I2 at the terminal double bond of the allenic fragment depends in a complex way on the character of functionalization in the cyclopentene fragment of the starting molecule.

Haloiminolactonization of cyclopentene α,α-dichlorocarboxamides. Tandem rearrangement of iminolactones in epoxylactones

Electrophilic cyclization initiated by NBS and I2 of 2,2-dichloro-2-[(1R,5S)- and 2,2-dichloro-2-[(1S,5R)-5-hydroxy-2-cyclopent-2-en-1-yl]-N-[(1R)-1-phenylethyl]acetamides was investigated. Stable under conditions of chromatography on SiO2 bicyclic iminoesters, (2Z,3aS,4S,6S,6aS)-6-bromo-3,3-dichloro- and (2Z,3aS,4S,6S,6aS)-3,3-dichloro-6-iodo-2-{[(1R)-1-phenylethyl]imino}hexahydro-2H-cyclopenta[b]furan-4-ols were isolated and characterized, and a possible version was suggested of their step-by-step recyclization transformations. The halocyclization of carboxamides in water-organic mixtures afforded bicyclic epoxylactones (1aR,2aS,5aS,5bS)- and (1aS,2aR,5aR,5bR)-5,5-dichlorohexahydro-4H-oxireno[3,4]cyclopenta-[1,2-b]furan-4-ones, whose reductive dechlorination proceeded stepwise with successive removal of Cl atoms and led to the formation of (1aR,2aS,5aS,5bS)- and (1aS,2aR,5aR,5bR)-hexahydro-4H-oxireno[3,4]cyclopenta-[1,2-b]furan-4-ones.

New disaccharide blocks for OSW-1 and its analogs

A new disaccharide block for OSW-1 natural steroidal antitumor agent was described. Regioisomeric 2- and 3-O-p-methoxybenzoyl derivatives of phenyl 1-thio-β-d-xylopyranoside and phenyl 2-O-acetyl-1-thio-β-l-arabinopyranoside derivatives blocked at positions 3 and 4 by R3Si groups were synthesized with a view to use them in the preparation of OSW-1 analogs modified at the disaccharide fragment.

Cyclopentenone blocks for 15-deoxy-Δ12,14-prostaglandin J2

Proceeding from the [2+2]-adduct of dichloroketene and dimethylfulvene a synthesis was developed of methyl (5Z)-7-(2,2-dimethyl-4-oxo-1-oxaspiro[2.4]hept-6-en-5-yl)hept-5-enoate, the key block in the new synthetic approach to 15-deoxy-Δ12,14-prostaglandin J2.

Synthesis of (2S,3S,4S)-2,3-O-isopropylidene-4-(methoxycarbonylmethyl)cyclopentan-1-one

Abstract(2S,3S,4S)-2,3-O-Isopropylidene-4-(methoxycarbonylmethyl)cyclopentan-1-one was synthesized starting from D-ribose through methyl (Z)-3-(5-acetyl-2,2-acetoxyacetyl-2,2-dimethyl-1,3-dioxolan-4-yl)prop-2-enoate which was subjected to cyclization in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene, followed by decarboxylation.

Unusual course of “enolate-imine” condensation in approach to β-lactams

In reaction of methyl (Е)-3-(methoxycarbonyl)methylimino-2,2-dimethylpropanoate with enolate of ethyl 3-hydroxybutanoate an abnormal reaction product was isolated, 2-methyl 4-ethyl-(2S*,3S*,4S*,5S*)-3-methyl-5-(2-methyl-1-methoxy-1-oxopropan-2-yl)pyrrolidine-2,4-dicarboxylate.

Pyrrolidine synthons for β-lactams

Fused tricyclic aziridines, methyl rel-(2R,2aR,3R,4R,4aR,4bS)- and rel-(2S,2aR,3R,4R,4aR,4bS)-4-hydroxy-2,4a-dimethoxyhexahydro-1-oxa-2b-azacyclopropa[cd]pentalene-3-carboxylates, have been synthesized as possible precursors to β-lactams. The product structure has been determined by two-dimensional NMR techniques in combination with computational methods.