1,3-Dipolar Cycloadditions of D-Erythrose- and D-Threose-Derived Alkenes with Nitrones

2003 ◽  
Vol 68 (5) ◽  
pp. 951-964 ◽  
Author(s):  
Iva Blanáriková-Hlobilová ◽  
Lubor Fišera ◽  
Naďa Prónayová ◽  
Marian Koman
Keyword(s):  
Steric Hindrance ◽  
Cyclic Acetal ◽  
Cyclic Acetals ◽  
Dipolar Cycloadditions ◽  
Terminal Alkenes

The new chiral terminal alkenes derived from cyclic acetals of D-erythrose 1-3 and D-threose 5, 6 were prepared. The alkenes 1, 2 and 5 react with chiral nitrones to afford the corresponding diastereomeric isoxazolidines 19-21. The stereoselectivity was dependent on the steric hindrance of the nitrone. In all cases the cycloadditions are endo-selective. The major products were found to have the C-3/C-4 erythro- and C-3/C-3a cis-configuration. Its formation can be rationalized by a less hindered endo-attack of the (Z)-nitrone in an antiperiplanar manner with respect to the largest group of the cyclic acetal.

STUDIES ON REACTIONS RELATING TO CARBOHYDRATES AND POLYSACCHARIDES. XXVII. SYNTHESIS AND STRUCTURE OF TRICHLOROETHYLIDENE GLYCEROL

1930 ◽  
Vol 2 (2) ◽  
pp. 131-143 ◽  
Author(s):  
Harold Hibbert ◽  
J. G. Morazain ◽  
A. Paquet
Keyword(s):  
Sulphuric Acid ◽  
Methyl Ether ◽  
Ring Closure ◽  
Cyclic Acetal ◽  
Satisfactory Explanation ◽  
Carbonyl Derivative ◽  
Cyclic Acetals ◽  
Polyhydroxy Compounds

A discussion is given as to the nature of the factors involved in the mechanism of the formation of cyclic acetals and ketals from carbonyl and polyhydroxy derivatives. It is shown that in the two reactions involved, namely, the primary formation of a half-acetal, followed by removal of water and ring-closure, the polarity of the carbonyl derivative plays a very important rôle. Chloral combines with polyhydroxy compounds to give exceptionally stable half-acetals, which can be converted into the cyclic derivatives by the use of strong dehydrating agents.In contrast with the behavior of other aldehydes it is found that the condensation of chloral with glycerol yields only one ring compound, namely the five-membered derivative. No satisfactory explanation of this can, as yet, be given.The identity of the trichloroethylidene glycerol obtained by the condensation of glycerol and chloral under the influence of concentrated sulphuric acid has been established as a five-membered cyclic acetal by a comparison of the properties of its methyl ether with those of trichloroethylidene glycerol α-methyl ether prepared from glycerol α-methyl ether.

scholarly journals Cyclic acetals as cleavable linkers for affinity capture

2015 ◽  
Vol 13 (31) ◽  
pp. 8445-8452 ◽  
Author(s):  
Siyeon Lee ◽  
Wei Wang ◽  
Younjoo Lee ◽  
Nicole S. Sampson
Keyword(s):  
Cyclic Acetal ◽  
Affinity Capture ◽  
Cyclic Acetals

A cyclic acetal moiety is an acid-sensitive linker for affinity capture and which provides an aldehyde for further elaboration.

Steric hindrance influence of a diazo link upon mesogenic properties of some ligands and related copper complexes

1997 ◽  
Vol 94 ◽  
pp. 1695-1714 ◽  
Author(s):  
P Lesot ◽  
F Perez ◽  
P Judeinstein ◽  
JP Bayle ◽  
H Allouchi ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
Copper Complexes

ANIPE-Cu Catalyst Enables Highly Enantioselective Markovnikov Hydroboration of α-Olefins

Synlett ◽  
2020 ◽  
Author(s):  
Shi-Liang Shi ◽  
Yuan Cai
Keyword(s):  
Petrochemical Industry ◽  
Future Directions ◽  
Asymmetric Hydroboration ◽  
Terminal Alkenes ◽  
Cu Catalyst

AbstractAsymmetric hydroboration of simple and unactivated terminal alkenes (α-olefins), feedstock chemicals derived from the petrochemical industry, has not been efficiently realized for past decades. Using a bulky ANIPE ligand, we achieved a rare example of highly enantioselective copper-catalyzed Markovnikov hydroboration of α-olefins. The chiral secondary alkylboronic ester products were obtained in moderate to good yields and regioselectivities with excellent enantioselectivities.1 Introduction2 Conditions Optimization3 Substrate Scope4 Application5 Mechanistic Discussion6 Conclusions and Future Directions

METABOLISM OF 17α-HYDROXYPROGESTERONE-4-14C-17α-CAPROATE BY HOMOGENATES OF RAT LIVER AND HUMAN PLACENTA

1961 ◽  
Vol 36 (4) ◽  
pp. 511-519 ◽  
Author(s):  
Margaret Wiener ◽  
Charles I. Lupa ◽  
E. Jürgen Plotz
Keyword(s):  
Rat Liver ◽  
Human Placenta ◽  
Steric Hindrance ◽  
Placental Tissue ◽  
Caproic Acid ◽  
Major Product ◽  
Side Chain ◽  
Anaerobic Conditions ◽  
Prolonged Action ◽  
Long Acting

ABSTRACT 17α-hydroxyprogesterone-4-14C-17α-caproate (HPC), a long-acting progestational agent, was incubated with homogenates of rat liver and human placenta. The rat liver was found to reduce Ring A of HPC under anaerobic conditions to form allopregnane-3β,17α-diol-20-one-17α-caproate and pregnane-3β,17α-diol-20-one-17α-caproate, the allopregnane isomer being the major product. The caproic acid ester was neither removed nor altered during the incubation. Placental tissue did not attack HPC under conditions where the 20-ketone of progesterone was reduced. It is postulated that this absence of attack on the side chain is due to steric hindrance from the caproate ester, and that this may account for the prolonged action of HPC.

Tyrosine-Selective Bioconjugation with Iminoxyl Radicals

2020 ◽  
Author(s):  
Katsuya Maruyama ◽  
Takashi Ishiyama ◽  
Yohei Seki ◽  
Kounosuke Oisaki ◽  
Motomu Kanai
Keyword(s):  
Reaction Time ◽  
Steric Hindrance ◽  
Room Temperature ◽  
Water Soluble ◽  
Light Irradiation ◽  
Sodium Ascorbate ◽  
Iminoxyl Radical ◽  
Short Reaction Time ◽  
Modified Peptides ◽  
The Stability

A novel Tyr-selective protein bioconjugation using the water-soluble persistent iminoxyl radical is described. The conjugation proceeded with high Tyr-selectivity and short reaction time under biocompatible conditions (room temperature in buffered media under air). The stability of the conjugates was tunable depending on the steric hindrance of iminoxyl. The presence of sodium ascorbate and/or light irradiation promoted traceless deconjugation, restoring the native Tyr structure. The method is applied to the synthesis of a protein-dye conjugate and further derivatization to azobenzene-modified peptides.

Synthesis of Conjugated Triynes via Alkyne Metathesis

2019 ◽  
Author(s):  
Idriss Curbet ◽  
Sophie Colombel-Rouen ◽  
Romane Manguin ◽  
Anthony Clermont ◽  
Alexandre Quelhas ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
High Selectivity ◽  
Alkyne Metathesis ◽  
Cross Metathesis ◽  
Synthetic Strategy ◽  
Sterically Hindered ◽  
Site Selective

<div> <div> <div> <div> <p>The synthesis of conjugated triynes by molybdenum-catalyzed alkyne metathesis is reported. Strategic to the success of this approach is the utilization of sterically-hindered diynes that allowed for the site- selective alkyne metathesis to produce the desired con- jugated triyne products. The steric hindrance of alkyne moiety was found to be crucial in preventing the for- mation of diyne byproducts. This novel synthetic strategy was amenable to self- and cross-metathesis providing straightforward access to the corresponding symmetrical and dissymmetrical triynes with high selectivity. </p> </div> </div> </div> </div>

Thioether-Facilitated Iridium-Catalyzed Hydrosilylation of Steric 1,1-Disubstituted Olefins

2019 ◽  
Author(s):  
Shengtao Ding
Keyword(s):  
Side Chains ◽  
Feasible Method ◽  
Iridium Catalysis ◽  
Efficient Strategy ◽  
Terminal Alkenes ◽  
And Control ◽  
Sulfur Containing ◽  
Organosilicon Polymers

<p>One facile and efficient strategy for the hydrosilylation of steric 1,1-disubstituted terminal alkenes is demonstrated. Investigations on substrate scope and control experiments revealed the necessity of thioether in promoting this process under a simple iridium catalysis system. This convenient and feasible method is expected to be useful in the synthesis of sulfur-containing organosilicon polymers with different side-chains.</p><p><br></p>

Regioselectivity of nucleophilic aromatic photosubstitution in the biphenyl series. Photohydrolysis of some dimethoxynitrobiphenyls

1987 ◽  
Vol 52 (10) ◽  
pp. 2482-2491 ◽  
Author(s):  
Ján Urban ◽  
Petr Kuzmič ◽  
David Šaman ◽  
Milan Souček
Keyword(s):  
Nitro Group ◽  
Steric Hindrance ◽  
The Other ◽  
Quantum Yields ◽  
Hydroxide Anion ◽  
Tert Butanol ◽  
Nitro Derivatives

Anaerobic photolysis of dimethoxynitrobiphenyls IIIa-VIa in aqueous alkaline tert-butanol gave products of nucleophilic photosubstitution of methoxyl by hydroxide anion, while the dimethoxybiphenyls Ia and IIa were found unreactive. Regioselectivity of the reaction was examined in view of a possible “extended meta activation” by the nitro group. The most reactive substrate IIIa gives both C-3 and C-4 substitution products with an unsubstantial preference for the latter, which opposes the “extended meta selectivity” rule. All of the other compounds obey the rule, and 3,4-dimethoxy-3'-nitrobiphenyl (IVa) even displayed absolute selectivity by yielding C-3 substituted compound as the only product. 2,5-Dimethoxy substituted compounds underwent photosubstitution which much lower quantum yields than their 3,4-substituted counterparts, most probably due to some steric hindrance of conjugation. Similarly, 3-nitro-substituted biphenyls exhibited much lower overall reactivity than 4-nitro derivatives.

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