Synthesis of β-hydroxypiperidine alkaloids by anodic oxidation of carbamates and hydroboration

1996 ◽  
Vol 74 (12) ◽  
pp. 2444-2453 ◽  
Author(s):  
Mark Plehiers ◽  
Claude Hootelé
Keyword(s):  
Key Words ◽  
Anodic Oxidation ◽  
Nucleophilic Addition ◽  
Piperidine Ring ◽  
Anodic Methoxylation

The β-hydroxypiperidine alkaloids (±)-pseudoconhydrine, (±)-N-methylpseudoconhydrine, (−)-5-hydroxysedamine, and (+)-sedacryptine were synthesized. Successive functionalization of the piperidine ring via anodic methoxylation allowed the regio- and stereoselective introduction of the substituents. The α and α′ substituents were introduced by application of the sequence elimination–nucleophilic addition from 2- or 2,5-substituted 6-methoxycarbamates. Hydroboration – oxidation of enecarbamates, obtained by elimination of methanol from α-methoxycarbamates, allowed the introduction of the β-hydroxy function. Key words: alkaloid, Sedum, N-acyliminium, enecarbamate.

Sedum alkaloids. XI. Synthesis of sedinone and sedacrine by application of anodic oxidation

1991 ◽  
Vol 69 (2) ◽  
pp. 211-217 ◽  
Author(s):  
Frank Driessens ◽  
ClaUDE Hootelé
Keyword(s):  
Nucleophilic Substitution ◽  
Key Words ◽  
Anodic Oxidation ◽  
Methoxy Group ◽  
High Yield ◽  
Piperidine Alkaloids ◽  
Piperidine Derivative ◽  
Sedum Acre ◽  
Anodic Methoxylation

α-Methoxycarbamate 12, synthetic precursor of the 2,6-disubstituted alkaloids of Sedum acre, was obtained in high yield from 2-phenacylpiperidine 5; the key step of the synthesis rests on the anodic methoxylation, which allows the functionalization of carbon 6. Nucleophilic substitution of the methoxy group by an acetonyl chain leads, after the required transformations, to sedinone 23. Bromomethoxylation of the enecarbamate 19 followed by dehydrohalogenation and nucleophilic substitution of the methoxy group leads to sedacrine 33. In both cases, the nucleophilic substitution of the methoxy group leads to a cis 2,6-disubstituted piperidine derivative. Key words: synthesis, piperidine alkaloids, anodic methoxylation

Sedum alkaloids XII. Synthesis of the new piperidine alkaloids homosedinone and dihomosedinone

1992 ◽  
Vol 70 (11) ◽  
pp. 2722-2725 ◽  
Author(s):  
Alex Durant ◽  
Claude Hootelé
Keyword(s):  
Nucleophilic Addition ◽  
Piperidine Alkaloids ◽  
Anodic Methoxylation

The new piperidine alkaloids homosedinone 2 and dihomosedinone 3, isolated from Sedumacre, have been synthesized from (−)-norsedamine 7 by application of the sequence: anodic methoxylation – elimination – nucleophilic addition.

Controlled diastereoselection in 2-lithio-1,3-dithiane additions onto α-substituted γ-lactols. Model studies toward bryostatins from (R)-pantolactone

1991 ◽  
Vol 69 (1) ◽  
pp. 62-69 ◽  
Author(s):  
René Roy ◽  
Allan W. Rey
Keyword(s):  
Key Words ◽  
Absolute Configuration ◽  
Nucleophilic Addition ◽  
Major Product ◽  
Model Studies ◽  
Nuclear Overhauser Enhancement ◽  
The Absolute ◽  
Nuclear Overhauser ◽  
Very High

Homochiral α-substituted γ-lactols 3 and 4 derived from (R)-pantolactone 1 were used in 2-lithio-1,3-dithiane additions to afford very high controls in diastereoselectivities arising from 1,2-asymmetric inductions. Thus non-chelation controlled nucleophilic addition on 3 gave the anti diastereomer 5 as the major product (92% de), while the chelation controlled addition on 4 furnished the syn diastereomer 7 (96% de) as the almost exclusive product. The stereochemical outcomes of these reactions were proven unambiguously by locking the conformation of the syn- and anti-triol adducts 7 and 8 through their respective acetonides and by nuclear Overhauser enhancement measurements. The lack of 1,3-dioxolane formation in the case of the anti-triol 8 was taken as a further confirmation of the absolute configuration at the newly created stereocenter. Key words: byrostatin, pantolactone, α-hydroxylactol, dithiane.

Stereochemistry and kinetics of amines addition to acetylenic esters

1991 ◽  
Vol 69 (9) ◽  
pp. 1445-1449 ◽  
Author(s):  
Saber M. Sharaf ◽  
Samir K. El-Sadany ◽  
Ezzat A. Hamed ◽  
Abdel-Hamid A. Youssef
Keyword(s):  
Key Words ◽  
Nucleophilic Addition ◽  
Nmr Spectra ◽  
Acetylenic Esters ◽  
H Nmr ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Step Mechanism

The reactions of a series of methyl para-substituted phenylpropiolates 1a–e with piperidine, morpholine, and diethylamine in methanol and dimethylformamide (DMF) have been studied and their rates measured. The products were methyl β-(N,N-dialkylamino)-p-substituted cinnamates 2–4a–e. 1H NMR spectra were used to determine the configuration of the products. The ρ values in methanol ranged between 0.34 and 1.24 whereas in DMF they were between 0.85 and 1.88. The values of ΔS≠ favor a bimolecular rate-limiting step mechanism. Key words: nucleophilic addition to acetylenic esters.

Electroreduction of 1-methyl 5-nitroindole, 5-nitrobenzofurane, and 5-nitrobenzothiophene in acidic and basic hydroorganic media: Generation and trapping of iminoquinone-type intermediates and electrosynthesis of ring-substituted amino derivatives

2003 ◽  
Vol 81 (10) ◽  
pp. 1108-1118 ◽  
Author(s):  
Luc Bouchard ◽  
Ian Marcotte ◽  
Jean Marc Chapuzet ◽  
Jean Lessard
Keyword(s):  
Key Words ◽  
Nucleophilic Addition ◽  
Acidic Medium ◽  
Cycloaddition Reaction ◽  
Am1 Calculations ◽  
Electrolytic Solution ◽  
Preparative Electrolysis ◽  
Regioselective Addition ◽  
Amino Derivatives ◽  
Type Intermediate

Preparative electrolysis of 1-methyl-5-nitroindole (1b, X = NCH3), 5-nitrobenzofurane (1c, X = O), and 5-nitrobenzothiophene (1d, X = S) at Hg, in acidic hydromethanolic media, leads to the formation of the corresponding 4-substituted amino derivatives 5, which result from the 100% regioselective addition to iminoquinone-type intermediate 4 of methanol or of any other good nucleophile present in the electrolytic solution. In acidic medium, the iminoquinonium intermediates 4b and 4c were trapped in a cycloaddition reaction with cyclopentadiene added to the electrolysis medium. The regiochemistry of the nucleophilic addition is discussed in light of AM1 calculations. Key words: 1-methyl-5-nitroindole, 5-nitrobenzofurane, 5-nitrobenzothiophene, iminoquinone, electrosynthesis.

Multislice imaging of gastrointestinal stromal tumors

2018 ◽  
pp. 3-14
Keyword(s):  
Computed Tomography ◽  
Key Words ◽  
Gold Standard ◽  
Gastrointestinal Stromal Tumors ◽  
Mesenchymal Tumors ◽  
Stromal Tumors ◽  
Preferential Localization ◽  
Multislice Imaging ◽  
Computed Tomography Diagnosis

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the digestive tract (1%). These tumors express the CD 117 in 95% of cases. The stomach is the preferential localization (70%). Diagnosis is difficult and sometimes late. Progress of imaging has greatly improved the management and the prognosis. Computed tomography (CT) is the gold standard for diagnosis, staging, and treatment follow-up. The increasing recognition of GIST’s histopathology and the prolonged survival revealed some suggestive imaging aspects. Key words: gastro-intestinal stromal tumors; computed tomography; diagnosis

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