5631-95-8Relevant academic research and scientific papers
Dithiolopyranthione synthesis, spectroscopy, and an unusual reactivity with DDQ
Pimkov, Igor V.,Nigam, Archana,Venna, Kiran,Fleming, Fraser F.,Solntsev, Pavlo V.,Nemykin, Victor N.,Basu, Partha
, p. 879 - 886 (2013/08/23)
The pyranodithiolone rearranges to a more stable isomer and the pyran ring opens up in the presence of DDQ. The bicyclic pyran thiolone tetrahydro-3αH-[1,3]dithiolo[4,5-β]pyran-2-thione (3a) engages in a highly unusual fragmentation in the presence of DDQ
Stereoselective Synthesis of Alcohols containing (Z)- and (E)-Olefins, Dienes, Enynes and Styrenes: Cyclic β-Halogeno Scissions using Samarium Diiodide as the Electron-transfer Agent
Crombie, Leslie,Rainbow, Linda J.
, p. 673 - 688 (2007/10/02)
In contrast to the sodium-mediated ring scission of 2-substituted 3-chloro ethers of the tetrahydrofuran series, samarium diiodide gives olefins of high (E)-stereoselectivity and provides (E)-conjugated and unconjugated dienes, styrenes and enynes in good yield without appreciable over-reduction.Whilst the SmI2 scission of 3-chloro-2-alkyltetrahydropyrans gives (Z)-rich (Z)/(E) olefin mixtures, the 2-(alk-1'-ynyl) members give (Z)-enyne alkohols with high stereoselectivity, providing a valuable complement to the (E)-enyne synthesis employing the tetrahydrofuran series.In electron-transfer scissions using sodium, the stereochemistry of the product alcohols is related to the ground-state conformation of the cis- and trans-pyrans and -furans.The slow SmI2-mediated reactions appear to involve samarium-complexed intermediates having structures independent of the original conformation, or of the cis- or trans-geometry of the furan or pyran, and it is the transition states from these intermediates that determine the stereochemical outcome.Scissions in the tetrahydrofuran series can be accelerated by addition of HMPA or DMPU with only a little deterioration in stereoselectivity, but in the tetrahydropyran series there are drastic changes in product stereochemistry when DMPU is added.Brief comment is made on the synthesis of tetrahydro-furan and pyran precursors.
THE STERIC COURSE OF THE REACTIONS OF 2,3-DIHALOTETRAHYDROPYRANS WITH GRIGNARD REAGENTS
Berti, Giancarlo,Catelani, Giorgio,Monti, Luigi,Ventresca, Giovanni
, p. 3973 - 3980 (2007/10/02)
The steric course of some reactions of 2,3-dihalotetrahydropyrans with sodium methoxide and with methyl- and phenyl-magnesium bromides has been reinvestigated.Whereas the methanolysis of the cis- and trans-dichlorides occurs with practically complete inversion, it has been confirmed that their reactions, as well as those of dibromides, with methylmagnesium bromide are non-stereospecific, yielding mixtures of trans- and cis-3-halo-2-methyl-tetrahydropyrans in ratios that are independent of the configurations of the starting dihalides.It has been further established that grignard reagents cause equlibration of cis- and trans-dihalide mixtures in a reaction that is much faster than the Grignard coupling step.
β-Halogeno Ether Synthesis of Olefinic Alcohols: Stereochemistry and Conformation of 2-Substituted 3-Halogenotetrahydro-pyran and furan Precursors
Crombie, Leslie,Wyvill, Robert D.
, p. 1971 - 1982 (2007/10/02)
Ring-scission of cis- or trans-2-alkyl- (or aryl-) 3-chlorotetrahydropyrans proceeds regioselectively and highly stereoselectively to give (E)-alk-4-en-1-ols, but in the parallel tetrahydrofuran series (Z)-/(E)-mixtures, dependent on percursor geometry, are formed.In this paper the stereochemistry and conformation of the tetrahydro-pyran and - furan precursors are considered.The cis/trans-composition of 2,3-dihalogenotetrahydro-pyrans and-furans made by various routes is reported.Reaction with Grignard reagents gives separable cis-/trans-mixtures the stereoisomeric composition of which, in the cases examined, does not depend on the stereoisomeric composition of the dihalide, but does vary with the halogen and the composition of the Grignard or dialkylmagnesium; possible reasons are discussed.The stereochemistry and conformation of the 2-alkyl- (or aryl-)3-chlorotetrahydropyrans is analysed by n.m.r. methods (J2a,3acis ca. 1.5 Hz; J2a,3atrans ca. 9.8 Hz) but assignments for the two tetrahydrofuran series with J2,3 2.6-3.6 and 4.3-5.9 are made uncertain by pseudorotation.The stereochemical identity of the two series is rigorously proved by isolation of cis- and trans-2-allyl-3-chlorotetrahydrofuran.On the one hand the former is hydrogenated to the cis-2-propyl compound, correlated with other members of the alkyl series, but on the other it is oxidised and the acid is converted into the cis-p-bromophenyl ester.The stereochemistry and conformation of the latter is rigorously demonstrated by an X-ray structure.The stereochemistries and conformations of the 2-deuterio- and 2-methoxy-3-chlorotetrahydropyrans are discussed, and consideration is then extended to the 2-alkyl-3-chloro-2-methyltetrahydro-pyran and -furan series.
Pheromones, XXXV. - Stereoselective Syntheses of 1,4-Alkadienes
Bestmann, Hans Juergen,Koschatzky, Karl-Heinrich,Plenchette, Alain,Suess, Joachim,Vostrowsky, Otto
, p. 536 - 544 (2007/10/02)
The stereoselective synthesis of 1,4-alkadienes via Julia synthesis, Wittig reaction, Crombie synthesis and methylene interruption of conjugated alkadienylphosphonates is described.
SYNTHESIS OF DIASTEREOISOMERIC 2,4,7-TRIOXA-3-PHOSPHA-3-R-3-THIONOBICYCLO(4.4.0) DECANES AS A MODEL FOR PHOSPHORUS NUCLEOPHILIC SUBSTITUTION STUDIES.
Bouchu, D.,Dreux, J.
, p. 25 - 34 (2007/10/02)
2,4,7-Trioxa-3-chloro, 3-fluoro, 3-dimethylamino, 3-methoxy, 3-(2-propanoxy)-3-phospha-3-thionobicyclo (4.4.0) decanes (trans fusion) have been prepared.The precursor diol, 2-hydroxymethyl-3-hydroxytetrahydropyran (2R*, 3S*), was obtained in two steps from 3,4-dihydro-2H-pyran.The chloridates 7a and 7b were separated by high performance liquid chromatography and the stereochemistry of the nucleophilic substitution at phosphorus (with fluoride anion, dimethylamine, methanol, 2-propanol) for each isomer was studied.The substitution of chlorine was found to occur mostly with inversion of configuration for the two isomers.Equilibrium constants were measured for 7a7b and 9a9b making it possible to calculate the corresponding standard free energies.A kinetic study of the 2-propanolysis of 7a and 7b showed that 7b reacted more slowly than 7a.It was found that the difference between the free energy of activation (ΔΔG (b-a)=1 Kcal/mol for the two isomers is close to the calculated value of the standard free energy variation ΔG0 (b-a)=-1.3 Kcal/mol.The difference between the observed reaction rates is probably due to the relative thermodynamic stabilities of the reactants.
Halogenation par voie electrochimique de composes ethyleniques. III. Chloration du dihydropyranne en milieu acetonitrile
Verniette, Madeleine,Pouillen, Paulette,Martinet, Pierre
, p. 343 - 344 (2007/10/02)
The electrochemical chlorination of dihydropyran is realised in acetonitrile only if pyridine is added.The chlorination conducts to the 3-chloro 2-hydroxy tetrahydropyran.In the anhydrous dichloromethane, without any treatment in aqueous media, the 2,3-dichlorotetrahydropyran is isolated.
