Stereospecific Ring Research Articles

New Stereospecific Ring Closure Reaction of 1,2-Diaxial Azido Alcohols

7β-Azidoneopine possessing 1,2-trans-pseudodiaxial azido and hydroxyl groups gave thiazolidinethione derivative in the presence of triphenylphosphine (TPP) and CS 2 which is a new stereospecific ring closure reaction. This procedure can be used on a carbohydrate model as well. The reaction mechanism is also discussed

ChemInform Abstract: Exceptionally Mild and Stereospecific Ring Fragmentations Promoted by Dimethylboron Bromide.

Abstract2‐(Iodomethyl)tetrahydropyran (I) is cleaved with dimethylboron bromide to give the 5‐hexenol (II).

Partial synthesis of 4-epi-trachylobagibberellin A12

The partial synthesis of 4-epi-trachylobagibberellin A12, starting from the natural diterpene trachinodiol (ent-7α,18-dihydroxytrachylobane) is reported. The stereospecific ring B contraction was carried out by treatment of a bromohydrin with silver oxide. The structure of a monoester of this gibberellin analogue was determined by X-ray analysis.

Exceptionally mild and stereospecific ring fragmentations promoted by dimethylboron bromide

A stereospecific and exceptionally mild fragmentation of β-iodoethers and allylic iodoethers by Me 2BBr in the presence of nBu 4NI was developed.

Sulphur in the Strategy of Natural Products Synthesis

Abstract Syntheses of secondary metabolites of α-and β-mercapto aminoacids are described. The strategy in the first class of compounds consists of using N-hydroxy-α-amino acid derivatives as intermediates and of converting them into α-functionalized, in particular thiol-substituted amino acids; as examples serve syntheses in the gliotoxin and sporidesmin series. In the second class of compounds the cycloaddition products of indole derivatives, having sulfide substituents, and nitroso olefins are transformed into indole alkaloids, in particular tryptathionins, by rearrangement and further reactions. The antitumor agent sparsomycin has been synthesized via an amino sultine and its stereospecific nucleophilic ring opening. Bioassays done with this compound and sixteen of its structural analogs gave insight in the structural features that are required for sparsomycin's antitumor activity.

Reduction–oxidation properties of organotransition-metal complexes. Part 22. Stereospecific oxidative cyclopropane ring opening and reductive cyclobutane ring formation in polycyclic hydrocarbon complexes of iron; X-ray crystal structures of [Fe2(CO)6(η5:η′5-C16H16)][PF6]2·CH3NO2and [Fe2(CO)6(η4:η′4-C16H16)

Electrochemical studies show that [Fe2(CO)6(η4:η′4-C16H16)](2) undergoes irreversible two-electron oxidation at a platinum electrode in CH2Cl2. Chemical oxidation with [Fe(η-C5H5)2][PF6] gives [Fe2(CO)6(η5:η′5-C16H16)][PF6]2(3), X-ray structural studies on the nitromethane solvate of which reveal the detailed stereochemistry of the polycyclic hydrocarbon ligand. Two cycloheptadienyl moieties, each η5-bonded to Fe(CO)3 units, are fused to a central cyclohexene ring at C(2)–C(3) and at C(2′)–C(3′). The six-membered ring adopts a very flattened chair conformation with C(4) and C(4′)(bonded to iron as terminal members of pentadienyl units) in pseudo-axial sites, at 3.78 A apart. Complex (3) is reduced by K[BH(CHMeEt)3] to [Fe2(CO)6(η4:η′4-C16H16)](4), X-ray structural studies on which show stereospecific cyclobutane ring formation via the linking of atoms C(4) and C(4′) of (3). This linking is accompanied by ring inversion of the cyclohexene residue and by significant twisting of the ring double bond [C(2)–C(1)–C(1′)–C(2′) torsion angle –8.6(5)°]. The C(4)–C(4′) bond formed is the longest in the cyclobutane ring at 1.596(4)A[cf. others, average 1.548(3)A]. The ring inversion is required to bring C(4) and C(4′) into adjacent pseudo-equatorial sites and hence proximity [the C(4)–C(3)–C(3′)–C(4′) torsion angle is 159.7(4)° in (3) and 25.2(2)° in (4)]. Complex (4) is oxidised by [Fe(η-C5H5)2][PF6] to (3) which reacts with PPh3 and with iodide ion to give [Fe2(CO)6{η4:η′4-C16H16(PPh3)2}][PF6]2(5) and [Fe2l2(CO)4(η5:η′5-C16H16)](6), respectively.

A stereospecific synthesis of (±) α-conhydrine and (±) β-conhydrine.

(±) α-Conhydrine and (±) β-Conhydrine are easily obtained by an intramolecular regio and stereospecific ring opening of the corresponding trans and cis ω-aminoepoxides.

Synthesis and Stereospecific Ring Opening of the (Z/E)-Isomers of 2-Methyl(Phenyl)-4-(thienylmethylene)-5(4H)-oxazolones

Synthesis and Stereospecific Ring Opening of the (<i>Z</i>/<i>E</i>)-Isomers of 2-Methyl(Phenyl)-4-(thienylmethylene)-5(4<i>H</i>)-oxazolones

1,3,2-Oxazaphospholidine-2-thiones from (+)-norephedrine: stereospecific ring opening, possibly by an elimination–addition mechanism

1,3,2-Oxazaphospholidine-2-thiones derived from (+)-norephedrine react with alkoxide to give a product of kinetic control, formed by endocyclic P–O cleavage with inversion of configuration, and one of thermodynamic control, formed by endocyclic P–N cleavage also with inversion of configuration. It is suggested that the product of kinetic control is formed by an elimination–addition process involving a metaphosphorimidate intermediate, and that of thermodynamic control by a mechanism involving nucleophilic attack opposite endocyclic nitrogen.

Synthesis of Lignin Model Dimers by Novel Techniques

Abstract A new procedure has been developed for the synthesis of g-substituted β-aryl ether lignin model dimers: models capable of generating quinonemethides in alkaline solutions. The process involves selective alkylation of the β-carbon of an unprotected a-keto-β-aryl ether model, followed by borohydride reduction and treatment with acetylchloride. A sampling of different alkylating agents Indicates that the process Is limited to very simple electrophiles. Attempts to prepare α-hydroxy-β-aryl ether lignin models by stereospecific ring openings of styrene and substituted styrene oxides met with no success.

Metabolism of testosterone and progesterone by liver homogenates of the seawater turtle (Chelonia mydas mydas) in vitro

The metabolism of testosterone and progesterone was studied in the liver of the sea turtle. Chelonia mydas mydas. Liver homogenate preparations (50 mg/50 ml) from the male turtle were incubated at 25°C for 4 h with either [4- 14C]-testosterone (I) of [4- 14C]-progesterone (II) in a medium supplemented with a NADPH-generating system. Metabolites were isolated and identified by column, thin-layer, and radio gas chromatography. After liquid-liquid partition between petroleum ether-methanol/water, 30% (incubation I) or 7% (incubation II) of the radioactive material was found in the nonpolar phase. In incubation I, the free steroid liberated after treatment with 5% sulphuric acid in methanol was identified as 5β-androstane-3α,17β-diol. The main metabolite of incubation was 5β-androstane-3α,17β-diol. Other metabolites identified were 3β-hydroxy-5β-androstan-17-one, 3α-hydroxy-5β-androstan-17-one, and 5β-androstane-3β,17β-diol. Less than 1% unmetabolized testosterone was recovered. The main metabolite of incubation II was 3α-hydroxy-5β-pregnan-20-one (about 75%). The following steroids were also identifed: 5βprcgnane-3,20-dione, 3β-hydroxy-5β-pregnan-20-one, 5β-pregnane-3α,20β-diol, and 5β-pregnane-3α,20α-diol. Unmetabolized progesterone was less than 1%. The results indicate that under the present conditions the stereospecific ring A reduction of progesterone and testosterone proceeds via a 5β-pathway in liver homogenates of C. mydas. Interestingly, the main metabolite of testosterone is a dihydroxysteroid—5β-androstane-3α,17β-diol—which exists both as the free compound and a fatty acid ester.

ChemInform Abstract: REGIOSPECIFIC, STEREOSPECIFIC RING CLOSURE OF ALKENYLPEROXY RADICALS GENERATED BY OXYGENATION OF BENZENETHIOL‐TRIENE MIXTURES

Chemischer InformationsdienstVolume 11, Issue 38 Heterocyclic Compounds ChemInform Abstract: REGIOSPECIFIC, STEREOSPECIFIC RING CLOSURE OF ALKENYLPEROXY RADICALS GENERATED BY OXYGENATION OF BENZENETHIOL-TRIENE MIXTURES A. L. J. BECKWITH, A. L. J. BECKWITHSearch for more papers by this authorR. D. WAGNER, R. D. WAGNERSearch for more papers by this author A. L. J. BECKWITH, A. L. J. BECKWITHSearch for more papers by this authorR. D. WAGNER, R. D. WAGNERSearch for more papers by this author First published: September 23, 1980 https://doi.org/10.1002/chin.198038209AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume11, Issue38September 23, 1980 RelatedInformation

Regiospecific, stereospecific ring closure of alkenylperoxyl radicals generated by oxygenation of benzenethiol–triene mixtures

Oxygenation of mixtures of benzenethiol and octa-1,3,6-triene (1a) or 5-methylhepta-1,3,6-triene (1b) with free-radical initiation affords, after treatment of the initial products with triphenylphosphine, the 1,2-dioxolans (9a) and (9b), respectively, via mechanisms involving stereospecific and regiospecific ring closure of the alkenylperoxyl radicals (4a) and (4b).

Redox-photosensitised reactions. Part 6. Stereospecific ring cleavage of 1-phenoxy-1,2,2a,3,4,8b-hexahydrocyclobuta[a]naphthalene-8b-carbonitrile and its 2-methyl derivatives by redox-photosensitisation

Ring cleavage of endo-1-phenoxy-1,2,2a,3,4,8b-hexahydrocyclobuta[a]naphthalene-8b-carbonitrile (1a) occurs to give phenyl vinyl ether and 3,4-dihydronaphthalene-1-carbonitrile in a 1 : 1 ratio upon the selective photoexcitation of phenanthrene, naphthalene, or triphenylene at 313 nm in the presence of p-dicyanobenzene in acetonitrile. With the cis- and trans-2-methyl derivatives of (1a), the photosensitised ring cleavage is stereospecific. The key mechanistic pathway is suggested to be the formation of a π-complex between the cyclobutanes and the cation radicals of the arenes, in which the phenoxy-group of the cyclobutanes plays important roles. It is speculated that the ring cleavage reaction proceeds by means of a concerted-like mechanism via the π-complex without complete hole transfer.

Substitutions allyliques : Nouvelle voie d'accès aux amino-2 didésoxy-2,3 hexopyrannoses synthèse d'un derivé de la tobrosamine

Synthesis of the methyl α-D-glycoside of N,N-diacetyl tobrosamine 16 from methyl α-D-mannoside 3 is described. Selective introduction of an azido function at C-6 cave 4. Regio- and stereospecific ring opening of benzylidene derivative 7, after O-methylation, afforded 8. Elimination of bromine followed by O-debenzoylation on C-2 led to enose 10. Azidolysis of 10 by means of alkoxyphosphonium salt (triphenylphosphine, diethylazodicar-boxylate and N 3H) gave 12 with high stereoselectivity. Reduction, acetylation and acid hydrolysis furnished N,N-diacetylbrosamine. Alternative way to 13, epimeric 2-amino derivative of 14, is also described.

Stereospecific ring opening of conduritol-B-epoxide by an active site aspartate residue of sucrase-isomaltase

Conduritol-B-epoxide inactivates sucrase-isomaltase (sucrose α-glucohydrolase, EC 3.2.1.48 - dextrin 6-α-glucohydrolase, EC 3.2.1.10) irreversibly with incorporation of 1 mol inhibitor/mol subunit, the affinity label being bound in both subunits to a β-carboxyl group of an aspartic acid (Quaroni, A. and Semenza, G. (1976) J. Biol. Chem. 251, 3250–3253). Conduritol-B-epoxide is a racemic mixture of 1- l-1,2-anhydro- myo-inositol and 1- d-1,2-anhydro- myo-inositol, but only the latter one is the reactive component, since 1- l-1,2-anhydro- myo-inositol alone did not inactivate the enzyme. After inactivation by 1- d-1,2-anhydro- myo-inositol the label was released by hydroxylamine and identified as scyllo-inositol. One can decide now which C atom of the epoxide ring has been attacked by the enzyme's aspartate residue. This explains why only the d-enantiomer is the reactive species and provides further information about the role of the carboxylate residue during enzymic hydrolysis.

Acid-induced reactions of 1-cyclopropyl-1-ferrocenyl-ethanols and -methanols

The reactions of some 1-cyclopropyl-1-ferrocenyl-ethanols and -methanols under mild acidic conditions are described. The stereospecific ring opening observed in some cases is rationalized in terms of a preferred conformation of the bisected carbocation. The influence of substituents upon the reaction is discussed.

Rearrangements of heterocyclic compounds. IV. Base-promoted elimination reactions in the 2-aza-5-norbornene system. Stereospecific ring opening of 2-(p-toluenesulfonyl)-exo-3-(trichloromethyl)-2-azabicyclo[2.2.1]hept-5-ene by lithium alkyls

Rearrangements of heterocyclic compounds. IV. Base-promoted elimination reactions in the 2-aza-5-norbornene system. Stereospecific ring opening of 2-(p-toluenesulfonyl)-exo-3-(trichloromethyl)-2-azabicyclo[2.2.1]hept-5-ene by lithium alkyls

Contraction de cycle a partir de la tosyloxy-8 bicyclo[4.2.0]octanone-7 cis

Cis 8-endo tosyloxybicyclo[4.2.0]oct-3-en-7-one treated with H 4AlLi undergoes a stereospecific ring contraction to give endo 7-formyl bicyclo[4.1.0]hept-3-ene and endo 7-hydroxymethyl bicyclo[4.1.0]hept-3-ène. On the contrary, the same compound treated with MeONa in ether or methanol (conditions of the Favorski rearrangement) gives, beside solvolysis products when CH 3OH is solvent, the two epimeric esters 7-endo and 7-exo carbomethoxybicyclo[4.1.0]hept-3-ène. Several pathways are postulated for the rearrangement.

Rearrangements of 8-chloro-8-methylbicyclo[4.2.0]oct-2-en-7-one

The endo- and exo-methyl isomers of 8-chloro-8-methylbicyclo[4.2.0]oct-2-en-7-one were separately treated with aqueous sodium carbonate, aqueous sodium hydroxide, silver nitrate in methanol, and sodium methoxide in methanol. A stereospecific ring contraction and an allylic substitution involving the enol form of the bicyclic ketone were found to be dependent on the base. Thermal rearrangement of the title compound resulted in the formation of propiophenone.