Iridoids : on the synthesis and structure of specionin

Recently, structure $\text{8b}$ has been assigned to the iridoid specionin. In the present letter the total synthesis of $\text{8b}$ is described. Comparison of spectral data reveals that the final product is not identical with natural specionin. Therefore the original structural assignment of specionin must be revised.     

Homoallylic substitution reactions of lithium dialkyl cuprates with cyclopropylcarbinyl halides: mechanistic considerations

Highly reactive lithium dialkyl cuprates and l-bromo-l-cyclo-propylalkanes, $\text{4}$, react to give good yields of the homoallylic substitution product, $\text{6}$. Less reactive organocuprates react with $\text{4}$ to give mixtures of $\text{6}$ and the direct substitution product, $\text{7}$. These results are consistent with a copper(I) radical intermediate which undergoes facile rearrangement prior to reductive coupling.     

Stereoselektive c-glycosidsynthese durch titan-(iv)-katalysierte addition von silylenolethern an 2-acyloxy-3-keto-glycale

C-Glycosides are stereoselectively formed by the titan-(IV)-catalysed addition of silyl enolethers $\text{2}$ to 2,4,6-tri-O-acyl-1-deoxy-D-erythro-hex-1-enopyran-3-uloses $\text{1}$ followed by elimination of the 4-acyloxy substituent. Cyclohexenyl silylether $\text{2a}$ reacts with 2-acetoxy-3-keto-glycal derivative $\text{la}$ forming only one product $\text{3a}$. Thus, the reaction seems to be diastereospecific with respect to both new chiral centers of the product.     

Cyclic enediol phosphoranes obtained from the reaction of trimethyl phosphite with biacetyl and hexafluorobiacetyl give strikingly different acylation products

Cyclic enediol phosphoranes (2,2,2-trimethoxy-2,2-dihydro-l,3, 2-dioxaphospholenes), prepared from α-diketones, RCOCOR, and trimethyl phosphite (TMP), give strikingly different acylation products depending on the electronic properties of the groups, R, that occupy the 4,5-positions in the dioxaphospholene ring with pentacovalent phosphorus. Reaction of acetyl chloride or bromide with the hexafluorobiacetyl-TMP phosphorane gives exclusively the product of $\text{endo}$cyclic O-acylation, dimethyl(2-acetoxy-$\text{cis}$-1,2, -$\text{bis}$trifluoromethylvinyl) phosphate. Acylation of the biacetyl-TMP phosphorane gives mixtures of the product of $\text{exo}$cyclic O-acylation (a cyclic enediol phosphate) and the product of C-acylation (an α-hydroxy-β-diketone phosphate), the proportions depending on the structure of the acyl halide and the solvent. The parent 1,3,2-dioxaphospholene, i.e., the glyoxal-TMP phosphorane where R = H, gives exclusively the product of $\text{endo}$cyclic O-acylation with both acyl halides in all solvents.     

Crotylzirconium derivatives as a new reagent for the threo selective synthesis of β-methylhomoallyl alcohols

Crotylzirconium derivatives, prepared from the reaction of crotylmagnesium chloride or crotyllithium with bis (cyclopentadienyl) zirconium dichloride, undergo a rapid reaction with aldehydes to afford the threo product predominantly. The ratio of Cram/anti-Cram product via this reagent is ca. $\text{75}\text{25}$ ~ $\text{60}\text{40}$.     

The high pressure mediated intramolecular Diels-Alder reaction of furan dienes: a synthetic approach towards daphnanes.

Furan $\text{2}$ undergoes intramolecular Diels-Alder reaction when subjected to high (14kbar) pressures to give a mixture of $\text{endo}$ and $\text{exo}$ adducts in which the $\text{exo}$ adduct is formed as the kinetic product, at variance with the expected course of events.     

Heavenly blue anthocyanin II trans-4-0-(6-0-(trans-3-0-(β -d-glucopyranosyl)caffeyl)-β-d-glucopyranosyl)- caffeic acid,a novel component in heavenly blue anthocyanin

Structure of an alkaline hydrolysis product of heavenly blue anthocyanin was determined to be $\text{trans}$-4-0-(6-0-($\text{trans}$-3-0-(β-D-glucopyranosyl)caffeyl)-β-D- glucopyranosyl)caffeic acid ($\text{1}$).     

Reaction of bicyclo[3.2.1]octadiene with 4-methyl-1,2,4-triazoline-3,5-dione: competitive dipolar and homo-cycloaddition

The nonconjugated bicyclo[3.2.1]octa-2,6-diene ($\text{1}$) affords with 4-methyl-1,2,4-triazolin-3,5-dione (MTAD) the homo-cycloadduct ($\text{2}$) product and the rearranged urazoles ($\text{3}$) and ($\text{4}$) through dipolar cycloaddition, while ene-reaction and (2+2)-cycloaddition are not observed.     

Studies in claisen rearrangement - novel thermal and mercuric trifluroacetate induced transformations of 2,4-di(N-aryl)amino-1,3,5-triazin-6yl-prop-2-y

The thermal rearrangement of 2,4-di(N-aryl)amino-1,3,5-triazin-6yl-prop-2-ynyl ethers $\text{1}$ yield a mixture of 6-methyleneimidazo(1,2-a)-1,3,5-triazine-4-one $\text{6}$ and 6-methylimidazo(1,2-a)-1,3,5-triazine-4-one $\text{7}$, whereas under the influence of mercuric trifluroacetate the ethers $\text{1}$ yield only $\text{6}$, at room temperature. Mechanisms invoking [3,3] sigmatropic rearrangement of ethers $\text{1}$ were proposed to account for the product formation.     

Crahamimycin A1 synthesis and determination of configuration and chirality

The two hydroxyacid derivatives $\text{10}$ and $\text{11}$, obtained from (S)-β-hydroxybutanoate and (S)-lactate, respectively, are joined to give the acetylenic ester $\text{12}$. Cyclization and functional group manipulations lead to (S,S)-(+)-grahamimycin A₁, the enantiomer of the natural product.     

5,12-dihydro-6,11-didehydronaphthacene,A derivative of 1,4-didehydronaphthalene

Treatment of the di-lithium derivative of 1,2-diethynyl-benzene ($\text{1}$) with $\text{o}$-xylene-α,α′-diol di-$\text{p}$-toluenesulphonate ($\text{2}$) in tetrahydrofuran led to 5,12-dihydronapthacene ($\text{5}$) as the only identifiable product. This reaction presumably involves 5,12-dihydro-6,11-didehydronaphthacene ($\text{4}$) as an intermediate, and this was confirmed by the formation of 5,12-dihydro-6,11-dideuterio-naphthacene when the reaction was carried out in tetrahydrofuran-$\text{d}$₈.     

A facile synthesis of 3,4-homoadamantanediol via the reaction of 1-adamantyl triflate with carbon monoxide

The reaction of 1-adamantyl triflate ($\text{1}$) with carbon monoxide and adamantane catalyzed by triflic acid affords 3-hydroxy-4-homoadamantyl 1-adamantanecarboxylate ($\text{2}$) as a major product, which is easily converted to 3,4-homoadamantanediol ($\text{5}$) — a promising starting material for 3,4-bifunctional homoadamantane derivatives.     

Chemical synthesis of the 5-́half molecule of E.coli tRNA2GLY

A tritriacontanucleotide which has the sequence of the 5$\text{-}\text{?}$half molecule of E.coli glycine tRNA₂, was synthesized by the phosphotriester method involving p-anisidate protection for the 3$\text{-}\text{?}$phosphate ends. Di- and trinucleotide units were prepared from 5$\text{-}\text{?}$dimethoxytrityl-2$\text{-}\text{?}$O-tetrahydrofuranyl-3?-O-(o-chlorophenyl)phosphoryl derivatives of uridine, N-benzoylcytidine, N-benzolyadenosine and N-iso-butyrylguanosine by condensation with 3$\text{,}\text{?}$5$\text{-}\text{?}$unprotected nucleosides followed by phosphorylation to give 3$\text{-}\text{?}$phosphodiester blocks. The 3$\text{-}\text{?}$terminal dimers and trimers were synthesized by using 3$\text{-}\text{?}$(o- chlorophenyl)phosphoro-p-anisidates instead of 3?,5?-unprotected nucleosides. The 3?-phosphodiesters of oligonucleotides with a chain length of larger than 5 were obtained by removal of the 3?-phosphoro-p-anisidate with isoamyl nitrite. The 5$\text{-}\text{?}$dimethoxytrityl group was removed by treatment with zinc bromide under anhydrous conditions. Fragments were designed to use common dimer blocks and to reduce the step for 5$\text{-}\text{?}$deblocking of larger fragments. Finally a 3$\text{-}\text{?}$phosphodiester block with a chain length of 20 was condensed with a 5$\text{-}\text{?}$OH component (tridecanucleotide). The fully protected 33 mer was deblocked and purified by chromatography. The structural integrity of the product was confirmed by mobility shift analysis and complete digestion with RNase T2.     

Electrophilic reactions of DMAD with a cyclic dienamine: Solvent influence upon the competitive formation of [4+2]−,[2+2]− and michael type adducts

The reaction course of DMAD with dihydroazepine $\text{3}$ depends strongly on the solvent: under appropriate conditions either $\text{4}$, $\text{5}$ or $\text{6}$(E) is formed as the exclusive addition product.     

Oxygenation of 4-(N-alkylimino)methyl-2,6-di-t-butylphenols mediated by Co(II)-Schiff base complex

4-(N-Alkylimino)methyl-2,6-di-$\text{t}$-butylphenols ($\text{1}$), Schiff bases of 3,5-di-$\text{t}$-butyl-4-hydroxybenzaldehyde can be oxygenated in the presence of Co(Salpr), a five coordinate Co(II)-Schiff base complex to give N-alkyl-3-$\text{t}$-butyl-5-formyl-2-hydroxy-2-pivaloyl-1,2-dihydropyridines ($\text{2}$ as the main product together with 3-formyl-2,5-di-$\text{t}$-butyl-2,4-cyclopentadienone ($\text{3}$) and 2,6-di-$\text{t}$-butyl-4-formyl-6-hydroxy-4,5-epoxy-2-cyclohexenone ($\text{4}$). These products result from dioxygen incorporation into the ortho position of $\text{1}$.     

Inept-29Si NMR study of a TiCl4-mediated reaction of an enol silyl ether

Condensation of 1,3-bis(trimethylsiloxy)-1-methoxybutadiene ($\text{1}$) and 2-phenyl-2,2-dimethoxyethanal ($\text{2}$) under TiCl₄ condition gave the γ-hydroxycyclopentenone product $\text{3}$. The reaction was followed by INEPT²⁹Si NMR. Implication to the mechanism of the reaction was discussed.     

Stereochemistry of electrophilic addition to dimethyl tricyclo[4,2,2,02,5] Deca-3,7-diene-9,10-dicarboxylate. Molecular structure of Hg(OAc)2-addition product

The molecular structure of the $\text{trans}$ addition product of Hg(OAc)₂ to diester $\text{1}$ has been determined by X-ray diffraction (represented by formula $\text{3}$) which leads to a revision of previously claimed $\text{cis}$-additions in this series.     

Condensation of a p-diazooxide with dimethyl acetylenedicarboxylate: formation of a spiro [4.5] Decatetraenone and a nonenolizable naphthalenone in a single reaction

The condensation of p-diazooxide $\text{1}$ with dimethyl acetylenedicarboxylate at 90°–100°C yields two C₂₆H₃₂O₉ products, corresponding to addition of two molecules of ester to one of the carbene $\text{2}$. The major product is the novel spirodecatetraenone $\text{4}$, and the minor product is the remarkable, nonenolizable naphthalenone $\text{5}$. Spirodecatetraenone $\text{4}$ is not a precursor of $\text{5}$, since the former is stable to acids and rearranges only above 200° to give the blocked azulenone $\text{8}$. A mechanism for the concomitant formation of product $\text{4}$ and $\text{5}$ is proposed.     

A new synthesis of spirobenzylisoquinolines. Analogues of sibiricine and corydaine

The reduction product of dehydrocordrastine, $\text{6}$, with di-isobutylaluminum hydride spontaneously rearranged to the spirobenzylisoquinolines $\text{7a}$ and $\text{7b}$, analogous to the alkaloids sibiricine ($\text{5a}$), corydaine ($\text{5b}$), and yenhusomidine ($\text{5c}$).     

The ring closure and rearrangement of 1-(2-amino)-benzoyl-1-methylhydrazones of β-dicarbonyl compounds: on the formation and crystal structure of 3a,9a-dihydro- -1,3,3a,9a-tetramethyl-4H-pyrazolo[3,4-b]quinolin-4-one

The conversion of 1-(2-amino)-benzoyl-1-methylhydrazones of β-dicarbonyl compounds into heterocyclic derivatives yielded in addition to the already known type of product $\text{2}$ further three novel pyrazole derivatives $\text{3}$, $\text{4}$ and $\text{5}$. The structures of these products have been established by chemical and spectroscopic (MS) methods. The crystal structure of $\text{5}$ has been determined by X-ray diffraction.