Selective transformations of secologanin: dihydroxylation

1981 ◽  
Vol 59 (2) ◽  
pp. 210-214 ◽  
Author(s):  
John Richard Purdy ◽  
Raymond G. Hamilton ◽  
Lalarukh Akhter ◽  
Stewart McLean
Keyword(s):  
High Yield ◽  
Side Chain ◽  
Conformational Preference ◽  
Large Excess ◽  
Reaction Proceeds ◽  
Small Excess

Sweroside tetraacetate (2b) has been converted in high yield by osmylation to the epimeric glycols 3 and 4 (R = H) which have been separated. This reaction proceeds with high chemoselectivity for reaction at the vinyl side chain but with low stereoselectivity, leading to a small excess of the 3-R isomer. Secologanin derivatives appear to show a much lower chemoselectivity in this reaction, but the stereoselectivity is considerably higher, and opposite to that in the sweroside example. Conditions have been found for oxidizing the dimethylacetal 5b of secologanin tetraacetate in useful yields to the epimeric glycols 6 and 7 (R = H); in this reaction a large excess of the 3-S isomer is formed. The reasons for these differences in selectivity appear to be related to differences between the two series in conformational preference.

Phosphonium salts. III. The action of cyanide ion and other nucleophiles on some bis-phosphonium salts

1969 ◽  
Vol 22 (7) ◽  
pp. 1405 ◽  
Author(s):  
JJ Brophy ◽  
MJ Gallagher
Keyword(s):  
Sodium Azide ◽  
Sodium Methoxide ◽  
Sodium Acetate ◽  
Potassium Cyanide ◽  
Dimethyl Sulphoxide ◽  
High Yield ◽  
Phosphonium Salts ◽  
Elimination Reaction ◽  
Cyanide Ion ◽  
Reaction Proceeds

Cyclic and acyclic bis-phosphonium salts with a two-carbon bridge are smoothly cleaved to phosphines in high yield by potassium cyanide in dimethyl sulphoxide. Evidence is presented that the reaction proceeds by an elimination-addition sequence. An elimination reaction also occurs when sodium methoxide, sodium azide, sodium acetate, and triethylamine react with ethane-1,2-bis(tri-phenylphosphonium) dibromide. ��� In a novel reaction, triphenylphosphine is converted into its oxide by a mixture of sodium azide and dimethyl sulphoxide.

Highly Diastereoselective and Irreversible Aldol Reactions of N-Sulfonylimidates

Synthesis ◽  
2016 ◽  
Vol 48 (19) ◽  
pp. 3413-3419 ◽  
Author(s):  
Hannah Bartrum ◽  
Sébastien Carret ◽  
Jean-François Poisson
Keyword(s):  
Lewis Acid ◽  
High Yield ◽  
Aldol Reactions ◽  
Titanium Complex ◽  
Reaction Proceeds

A mild method for the aldolization of N-sulfonylimidates was developed. The reaction proceeds in excellent diastereoselectivity to provide a range of useful β-hydroxyimidates in high yield. The innate reversibility of the reaction is suppressed by the use of a titanium complex as a Lewis acid.

scholarly journals Effect of Fe Additives on the Catalytic Performance of Ion-Exchanged CsX Zeolites for Side-Chain Alkylation of Toluene with Methanol

Catalysts ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 829 ◽  
Author(s):  
Zhang ◽  
Yuan ◽  
Miao ◽  
Li ◽  
Shan ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Catalytic Performance ◽  
High Yield ◽  
Side Chain ◽  
Impregnation Method ◽  
Basic Sites ◽  
Lewis Acidic Sites ◽  
X Zeolite ◽  
Acidic Sites ◽  
Negative Effect

The side-chain alkylation of toluene with methanol was investigated over some Fe-modified Cs ion-exchanged X zeolite (CsX) catalysts prepared via the impregnation method using different iron sources. The absorption/activation behaviors of the reactants on the surface of the catalysts were studied by in situ Fourier-transform infrared (FT-IR) spectroscopy and temperature programmed desorption (TPD) mass measurements. Modification of CsX with a small amount of FeCl3 could result in a considerable decrease in catalytic activity, due mainly to the remarkable decrease in the density of acidic and basic sites of the catalysts. Interestingly, the Fe(NO3)3-modified CsX with an optimum Fe loading of 0.15 wt.% shows improved catalytic activity and high yield compared to the side-chain alkylation products. Modification of CsX with Fe(NO3)3 could also result in a decrease in basic sites of the catalyst. However, such a change does not bring an obvious negative effect on the adsorption/activation of toluene, while it could effectively inhibit the generation of the undesired bidentate formate. Furthermore, the introduced FeOx species (derived from the decomposition of Fe(NO3)3) may also act as new Lewis acidic sites to participate in the activation of methanol and to stabilize the formed active intermediates (i.e., unidentate formate). Therefore, modification of CsX with a suitable amount of Fe(NO3)3 may adjust its adsorption/activation ability for reagents by changing the acid–base properties of the catalyst, which can finally enhance the catalytic performance for the side-chain alkylation of toluene with methanol.

An Efficient Two-Step Protocol for the Isoprenylation of Xanthone at the C2 Position Starting from 1-Fluoroxanthone Derivative

Synlett ◽  
2020 ◽  
Vol 31 (14) ◽  
pp. 1423-1429
Author(s):  
Takashi Matsumoto ◽  
Yuuki Fujimoto ◽  
Chisato Furukawa ◽  
Kanae Takahashi ◽  
Miho Mochizuki ◽  
...  
Keyword(s):  
Silica Gel ◽  
Room Temperature ◽  
Claisen Rearrangement ◽  
High Yield ◽  
Side Chain ◽  
Snar Reaction

The SNAr reaction of 1-fluoroxanthone derivatives with alkoxide of 1,1-dimethylallyl alcohol cleanly afforded the corresponding ethers, which have thus far been unavailable. The obtained ethers underwent the Claisen rearrangement at room temperature by treatment with silica gel in toluene. This two-step protocol provides expeditious and high-yield access to xanthones possessing isoprenyl or the related allylic side chain at the C2 position.

Experiments Directed Towards the Synthesis of Anthracyclinones. XXVIII. Titanium(IV)- and Tin(IV)-Mediated Cyclizations of ortho-Methallyl-Substituted Homochiral Dioxans

1996 ◽  
Vol 49 (6) ◽  
pp. 677 ◽  
Author(s):  
RC Cambie ◽  
KC Higgs ◽  
JJ Rustenhoven ◽  
PS Rutledge
Keyword(s):  
Lewis Acid ◽  
Major Product ◽  
Metal Chloride ◽  
High Yield ◽  
Side Chain

Metal chloride cyclizations of the 4-demethoxy anthraquinonyl 1′,3'-dioxan (6) are highly diastereoselective , giving 9-chloro-9-methylanthracyclinones in high yield. The selectivity is inversely proportional to the strength of the Lewis acid, with the mild Lewis acid tin(IV) chloride/ dimethylformamide affording an 82% yield of the diastereomer (21). The predominant products have a (7S) configuration and a trans relationship between the C7 side chain and the 9-chloro substituent. Cyclization of the analogous dimethoxy 1′,3′-dioxan (4) with tin(IV) chloride/ dimethylformamide is considerably less selective, but the major product also has a (7S)-trans stereochemistry. Titanium(IV) chloride effects stereorandom cyclization of (4).

4,5-Seco-4,6-cyclosteroids. III. Observations on the course of reductive rearrangement of 6β-Bromo-4β,5-epoxy-5β-cholestan-3β-ol

1969 ◽  
Vol 22 (4) ◽  
pp. 807 ◽  
Author(s):  
DJ Collins ◽  
JJ Hobbs ◽  
RJ Rawson
Keyword(s):  
Hydrogen Bromide ◽  
High Yield ◽  
Lithium Aluminium Hydride ◽  
Experimental Conditions ◽  
Lithium Aluminium ◽  
Reaction Proceeds ◽  
Derivatives Of

It has been shown that reductive rearrangement of 6β-bromo-4β,5-epoxy- 5β-cholestan-3β-ol (I) to 4,5-seco-4,6-cycle-6β-cholestane-3β,5α-diol (IXa) with lithium aluminium hydride in tetrahydrofuran proceeds via 6β-bromo-5β-cholestane-3β,5-diol (IIa). Relevant reactions of the latter and the corresponding 3-ketone are discussed. ��� Similar conversion of the 3-epimer of (I) into 4,5-seco-4,6-cyclo- 6β-cholestane-3α,5α-diol (XIIIa) in high yield indicates that reductive rearrangement of the 6β-bromo-5β-hydroxy moiety proceeds without participation of the 3-aluminate complex. Some derivatives of (XIIIa) are described. ��� Experimental conditions required for the conversion of (I) into (IXa) are defined. ��� Combined evidence indicates that the reaction proceeds in a concerted manner by essentially base-catalysed, 1,3-elimination of hydrogen bromide from diol (IIa) with 4,5-bond migration to give the formal intermediate 3β-hydroxy-4,5-seco-4,6-cyclo-6β-cholestan-5-one (VI), further reduced to (IXa).

scholarly journals Copper(I)-Catalyzed Boryl Substitution of Allyl Aminals: Selective Synthesis of Linear γ-Aminoallylboronates

Synthesis ◽  
2017 ◽  
Vol 49 (21) ◽  
pp. 4738-4744 ◽  
Author(s):  
Hajime Ito ◽  
Yuta Takenouchi
Keyword(s):  
Amino Alcohol ◽  
High Yield ◽  
Selective Synthesis ◽  
Novel Approach ◽  
Reaction Proceeds ◽  
High Stereoselectivity

A novel approach for the selective synthesis of α-substituted γ-aminoallylboronates through a copper(I)-catalyzed γ-boryl-substitution of allyl aminals is developed. The reaction proceeds with high yield (up to 88%) and good E/Z selectivity (up to >95:5). Subsequent aldehyde allylation using allylboronates affords (Z)-anti-1,2-amino alcohol derivatives with high stereoselectivity (up to 91% yield, and up to 17:83 E/Z).

Anhydropenicillin: a key intermediate for the stereocontrolled introduction of the 6-R-hydroxyethyl side chain of the penem and carbapenem antibiotics

1987 ◽  
Vol 65 (9) ◽  
pp. 2179-2181 ◽  
Author(s):  
Alain Martel ◽  
Jean-Paul Daris ◽  
Carol Bachand ◽  
Marcel Menard
Keyword(s):  
Hydroxy Group ◽  
Aldol Condensation ◽  
Reductive Dehalogenation ◽  
High Yield ◽  
Side Chain

Aldol condensation of the magnesium enolate derived from anhydro-6,6-dibromopenicillin with acetaldehyde allows for the stereospecific introduction of a 1-R-hydroxyethyl substituent at C-6. Protection of the hydroxy group followed by reductive dehalogenation provides anhydro-6(α)-[(1-R)-(tert;-butyldimethylsilyloxy)-ethyl]-penicillin, an intermediate in the synthesis of thienamycin. A high yield conversion of this anhydro derivative to (4-R)-acetoxy-(3-S)-[(1-R)-(tert-butyldimethylsilyloxy-ethyl]-azetidin-2-one (5) is also reported.

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