Synthesis and Stereochemistry of New Cyclic Phosphate-phosphonates

1,3,2alloxaphoSPhorinanederivahveshavbeengenetallypwibythcPhoSI)horylatiowith(thio)PhOSPhorylchlorideinliteraturd'].bor,studiesonthepeeSsandstemeheInistIyofl,3,2choxaphoSPhorinane2-suffidcs(selenideStythetriS(diethyndno~nem~weretwmprted.Furthermore,a-hydroxyphoSPhonatedCriVativarebiologitallyaodvd2]andhavboshowntoinhibittheempmesrenin,EPSPtwse,andHIVProtcascI'1.DuetothebiQlOgitalandStereochendcalintereSt,wedCsi~andrynthchndthenoVelcyClicpbOSPhate-PhoSI)bonateS7a4tyaoneWprocedu…     

Stereochemistry of α-aminoacetophenone oximes : Study of solvent effects

The aminolysis of Z-α-halogenoacetophenone oximes results in different mixtures of E- and Z-α-aminoacetophenone oximes depending on the solvent used. Assignment of configuration can be achieved by ¹³C NMR spectroscopy even if only one isomer is available using a strong solvent dependence of the methylene chemical shift in the case of the Z-isomers. This effect is due to the presence of different conformations in the solvents chloroform and dimethyl sulfoxide. Together with a study by vapor pressure osmometry the results provide an unambiguous proof of intramolecular hydrogen bonding of Z-α-aminoacetophenone oximes in chloroform.     

Synthesis and Stereochemistry of α-Aryl-β-Nitroalkylphosphinate

Abstract

Twenty-three new α -aryl-β -nitroalkylphosphinates 3a - g were synthesized in high yields under very mild conditions. Compounds 3 consist of two pairs of diastereomeric isomers (A) and (B)     

Stereochemistry in alkylations of dianions of β-hydroxysulfoxides and β-hydroxysulfones

Alkylations of dianions of β-hydroxysulfoxides and β-hydroxysulfones have been found to be affected by chelation of a Li cation with a sulfinyl group and by coordination of the cation with tetrahydrofuran rather than a sulfonyl group, respectively.     

Stereochemistry of the asymmetric alkylation of Δ9,10-octahydroquinolin-4-ones

The asymmetric character of the alkylation of a series of metallated bicyclic enaminoketones has been established and its stereoselectivity has been investigated. The enantiomers of (3S*)-methyl- and (3S*)- and (3R*)-3-methyl-3-butyl-^9,10-octahydroquinolin-4-ones have been obtained. The possibility of inducing chirality at the 3 position of the enaminoketone molecule during methylation in the presence of chiral lithium amides has been established in principle.M. V. Lomonosov Moscow State University, Moscow 119899. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1531–1542, November, 1995. Original article submitted November 10, 1995     

Total Synthesis and Stereochemistry of 13-Hydroxy-α-eudesmol

Recently, 13-hydroxy-α-eudesmol 1a was first isolated from C. uncata Cunn. by King and Robinson et aL and its structure was determined by high field NMR techniques, however, the absolute configuration of C-11 remained unsolved. Herein, we report the first total synthesis and determination of the stereochemistry of 13-hydroxy-α-eudesmol. In our synthesis (+)-α-selinene has also been accomplished.     

Stereochemistry of Substitution of the α-Dimethylamino Group by Dialkylzinc in Chiral Benzylferrocene

The stereochemistry of the substitution of the α-dimethylamino group by dimethylzinc in the presence of acetyl chloride in the chiral benzylferrocene backbone was examined. The reaction with the benzylferrocene bearing an o-bromo substituent at both ferrocene and the phenyl ring proceeded with inversion of configuration, while the reaction with the benzylferrocene bearing an o-bromo substituent at either ferrocene or the phenyl ring proceeded with retention of configuration.     

The Stereochemistry of the Migrating Groups in the Pyrolysis of Stable Steroidal Ozonides

ＴｈｅＳｔｅｒｅｏｃｈｅｍｉｓｔｒｙｏｆｔｈｅＭｉｇｒａｔｉｎｇＧｒｏｕｐｓｉｎｔｈｅＰｙｒｏｌｙｓｉｓｏｆＳｔａｂｌｅＳｔｅｒｏｉｄａｌＯｚｏｎｉｄｅｓＪｉｏｎｇＹＡＮＧ；ＴｏｎｇＳｈｕａｎｇＬＩａｎｄＹｕＬｉｎＬＩ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅ...     

Synthesis and Stereochemistry of Some new Derivatives of 1,2-O-Cyclohexylidene-α-D-Xylofuranuronic Acid

Abstract

1,2-O-Cyclohexylidene-α-d-xylofuranuronic acid (2) has been converted into its 3-O-acetyl derivative and consecutively to the corresponding acid chloride and ethyl ester. Direct reaction of 2 with ethanol in the presence of p-to-luene sulphonic acid gave the ethyl ester. Reaction of 2 with phosphorus pentachloride in dry ether gave the acid chloride of 1,2-O-cyclohexylidene-3-O-dichlorophosphoryl–α-d-xylofuranuronic acid. Conformational data have been obtained from ¹H and ¹³C NMR measurements.     

Stereochemistry of the Addition of Organometallic Reagents to Methyl 2,3-O-Isopropylidene-β-D-ribo-pentodialdo-1,4-furanose

Methyl 2, 3-O- isopropylidene-β-D-ribo-pen tod ialdo-1,4-furanoside, upon reaction with either methyl lithium or methyImagnesium iodide/ gave a ca. 2-3:1 mixture of β-D-allo to α-L-talo adducts. Reaction with 2-lithio-l,3-d ithiane gave much improved stereoselectivity, in line with either the Cram or Felkin model, to give the dithianyl adducts in a ratio of 97:3 of β-D-allo to α-talo isomers.     

Stereochemistry of the coupling step in photo-S_(RN) 1 reaction

The photo-S_(RN) 1 reaction of (+)-camphor and aryl halides was investigated in order toestimate the stereochemistry of the coupling step of aryl radicals with a nucleophile. The ratio of endo toexo products determined by ~1H NMR and CD spectra was found to be 99:1. MNDO calculationsof the orbital parameters showed a favorable one-sided overlap of the enolate ion with the SOMO of arylradical. In addition, fragmentation of (ArX)~- was found to be related to the energy of SOMO of(ArX)~-.     

Stereochemistry of Phosphite Addition to Azomethine Bond of Achiral 2,6-Pyridinedicarbaldimines and Isophthalaldimines—A Comparative Study

Abstract

The addition of dialkyl H-phosphonates to isophthalaldimines 1a–d and pyridine-2,6-dicarboxaldimines 2a–d was investigated and led to the corresponding aminophosphonates. Diastereoselectivity of the addition to pyridine-2,6-dicarboxaldimines was lower than to isophthalaldimines. In contrast, addition of bis(trimethylsilyl) H-phosphonate to both groups of aldimines demonstrated that the diastereoselectivity in case of pyridine-2,6-dicarboxaldimines is comparable or even better than that for the isophthalic derivatives.     

Stereochemistry and mechanism of the Brønsted acid catalyzed intramolecular hydrofunctionalization of an unactivated cyclic alkene

Through employment of deuterium-labeled substrates, the triflic acid catalyzed intramolecular exo addition of the X-H(D) (X=N, O) bond of a sulfonamide, alcohol, or carboxylic acid across the C=C bond of a pendant cyclohexene moiety was found to occur, in each case, with exclusive formation (≥90%) of the anti-addition product without loss or scrambling of deuterium as determined by (1)H and (2)H NMR spectroscopy and mass spectrometry analysis. Kinetic analysis of the triflic-acid-catalyzed intramolecular hydroamination of N-(2-cyclohex-2'-enyl-2,2-diphenylethyl)-p-toluenesulfonamide (1a) established the second-order rate law: rate=k(2)[HOTf][1a] and the activation parameters ΔH(++)=(9.7±0.5) kcal mol(-1) and ΔS(++)=(-35±5) cal K(-1) mol(-1). An inverse α-secondary kinetic isotope effect of k(D)/k(H) =(1.15±0.03) was observed upon deuteration of the C2' position of 1a, consistent with partial C-N bond formation in the highest energy transition state of catalytic hydroamination. The results of these studies were consistent with a mechanism for the intramolecular hydroamination of 1a involving concerted, intermolecular proton transfer from an N-protonated sulfonamide to the alkenyl C3' position of 1a coupled with intramolecular anti addition of the pendant sulfonamide nitrogen atom to the alkenyl C2' position.     

Studies on the Total Synthesis of Hainanolide (VII) - Analysis of the Relative Stereochemistry of key Intermediate 2

The natural product, hainanolide 1, also under the name harringtonolide2 demonstrated antitumor and antiviral activities in preliminary test. Its structure was determined by X-ray diffraction. The total synthesis of 1 was reported recently by Mander3. A different scheme of its synthesis has been studied in our laboratory4. Here the determination of the stereochemical structure of the key intermediate 2 in the synthesis was reported. HMBC and HMQC spectra identified the skeleton and H,…     

Stereochemistry of organic sulfur compounds: Part 18. Configurational assignment of conformationally homogeneous β-oxygenated acyclic sulfoxides

The different nature of hydrogen bonding interactions (inter vs. intramolecular) found in each diastereomer of 3,3-dimethyl-1-methylsulfinyl-2-butanol (1α and 1β) allowed their configurational assignment by ¹H-NMR and IR. The intermolecularly-bonded epimer (1α) was assigned the R*, R* configuration. Lanthanide shift reagent studies performed on their acetates reinforced the assignment. Both assignment and the strong intermolecular association in 1α were confirmed by X-ray diffraction analysis.     

Stereochemistry of nitrogenous heterocycles. 71. Isomerization — Equilibration of stereoisomeric ethinylcarbinols epimeric at the carbinol center

Equilibration of stereoisomeric cyclic ethinylcarbinols, epimeric at the carbinol center, was conducted for the first time and it was shown that the equilibrium is shifted toward the equatorial alcohol (at 50C for 2e-methyl-4-hydroxy-4-phenylethinyl-trans-decahydroquinoline, 2e-methyl-4-hydroxy-4-ethinyl-trans-decahydroquinoline, 4-hydroxy-4-ethinyl-trans-decahydroquinoline —(78±1)% equatorial and (22±1)% axial alcohol, for 1,2e,5e-trimethyl-4-ethinylpiperidol-4 (74±1)% equatorial and (26±1)% axial alcohol). The epimerization of stereoisomeric ethinylcarbinols can be used as a method for determination of the configuration of the quaternary carbinol center.See [1] for Communication 70.The data was presented at the VI International IUPAC Conference on Organic Synthesis [2].Translated from Khimi-ya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1072–1076, August, 1991.     

Studies on the origin of cis-diastereoselectivity of the titanium-mediated cyclopropanation of carboxylic esters with Grignard reagents. Stereochemistry of the intramolecular cyclization of β-metalloketones

Datа on the stereochemistry of the intramolecular cyclization of β-metaloketones into 1,2-disubstituted cyclopropanols are in agreement with the cyclopropanation of carboxylic esters with alkoxytitanacyclopropane reagents proceeding via the β-titanoketone intermediates with the metal atom bound to a secondary carbon. Hypothesis for the origin of cis-diastereoselectivity of the cyclization of the β-titanoketones is suggested. It explains the tendency for the preferable formation of cis-1,2-disubstituted cyclopropanols by relief of repulsion strain between the ligands at the octahedral titanium atom.     

Stereochemistry Control in Direct 1α-Hydroxylation of 5,6-trans-Vitamin D3 by Solid Support

1α-Hydroxyvitamin D3 1 (1α-hydroxycholecalciferol) is a biologically active form ofvitamin D3 2 which exhibits a much broader spectrum of biological activities thanvitamin D3 . 1,2 Recently a number of analogues have been found to have specificenhanceme…     

Stereochemistry of transition metal catalyzed asymmetric intramolecular allyl transfer in chiral α-sulfinyl allylic esters

The stereochemistry of palladium or nickel catalyzed asymmetric intramolecular allyl transfer in chiral α-sulfinyl allylic esters was determined. The participation of the catalyst and the chiral sulfinyl functionality in these transformations, presumably by the coordination of the sulfinyl group to the catalyst, is discussed, and a novel mechanism is proposed for the rationalization of the results obtained.