Total Synthesis of the Pentacyclic Diterpenoid Tropone Hainanolidol

2000 ◽  
Vol 53 (10) ◽  
pp. 819 ◽  
Author(s):  
Barbara Frey ◽  
Adam P. Wells ◽  
Frances Roden ◽  
Ty Duong Au ◽  
David C. Hockless ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Oxidation Process ◽  
Aldol Reaction ◽  
Ring System ◽  
Protecting Group ◽  
X Ray ◽  
Catalysed Reaction ◽  
Process Methodology ◽  
The Stability ◽  
Carbonyl Function

The total synthesis of the unusual diterpenoid tropone, hainanolidol (1), discovered in the bark of the yew species, Cephalotaxus hainanensis, has been completed in 26 steps from 3,5-dimethylanisole. The intramolecular cyclopropanation reaction of the aryl ring in (30) by means of the rhodium mandelate-catalysed reaction of the diazoacetyl function was used to assemble the 5/7 ring system of (31), at the same time elaborating a cycloheptatriene moiety that could be transformed subsequently to the tropone functionality in the target molecule. While removing the acetal protecting group from (31) an unexpected Mukaiyama–type aldol process was induced by ZnBr2, affording (32), the structure of which was determined by X-ray analysis. With greater care, the aldehyde (33) could be obtained and the desired carbocyclic ring system completed by means of a base-catalysed aldol reaction with the newly formed hydroxyl being employed subsequently in the formation of the σ-lactone function in (35). Desilylation, reduction of the C-10 carbonyl function and brief exposure to acid finally afforded (1). This last step took advantage of the stability of the tropylium ion (40) to provide a ‘thermodynamic sink’ for the reaction outcome. The synthesis of (1) also constitutes a formal synthesis of the troponoid ether, harringtonolide (2), since this compound had been obtained previously from (1) by means of a transannular oxidation process. Methodology for the assembly of the tropone moiety in (1) and (2) was modelled on the simpler bi- and tricyclic systems, (13) and (22), respectively.

Exploratory Studies on the Synthesis of the Unusual Diterpenoid Tropone Harringtonolide.

1999 ◽  
Vol 52 (11) ◽  
pp. 1093 ◽  
Author(s):  
Daniel H. Rogers ◽  
Barbara Frey ◽  
Francis S. Roden ◽  
Friedrich-Wilhelm Russkamp ◽  
Anthony C. Willis ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Transition Metal ◽  
Total Synthesis ◽  
Aldol Reaction ◽  
Ring System ◽  
Aryl Ring ◽  
Mercuric Nitrate ◽  
Catalysed Reaction

Various approaches to the total synthesis of the unusual diterpenoid tropone (2), discovered in the yew species Cephalotaxus harringtonia and C. hainanensis, are described. The rhodium-catalysed intramolecular cyclopropanation reaction of an aryl ring by means of the transition metal catalysed reaction of a diazoacetyl function was used to assemble the 5/7 ring system and to provide a cycloheptatrienyl precursor to the tropone moiety, e.g.(28)→(29) and (38) →(39). In the most promising approach, the carbocyclic system was assembled by means of the aldol reaction (42) →(43) with the newly formed α-hydroxyl being employed subsequently in the formation of the δ-lactone function of (44). The tropone ring may be formed from the methoxycycloheptatriene moiety simply by treatment with mercuric nitrate. Tropone (45) was formed from (44) in this way, but attempts to convert it into harringtonolide by means of transannular oxidation based on the 4-hypoiodite failed. The crystal structure of an intermediate is reported.

A versatile method for the synthesis of γ-pyrones

2012 ◽  
Vol 90 (11) ◽  
pp. 954-964 ◽  
Author(s):  
Garrison E. Beye ◽  
Athanasios Karagiannis ◽  
Alieh Kazemeini ◽  
Dale E. Ward
Keyword(s):  
Total Synthesis ◽  
Ambient Temperature ◽  
Aldol Reaction ◽  
Trifluoromethanesulfonic Acid ◽  
Protecting Group ◽  
Triflic Acid ◽  
Step Procedure

A versatile three-step procedure to annulate a γ-pyrone onto a methylene ketone was developed involving (i) aldol reaction with a dithiolane-protected β-ketoaldehyde, (ii) oxidation of the aldol adduct to a β-diketone, and (iii) treatment of the resulting dithiolane-protected 1,3,5-trione with 2-iodoxybenzoic acid (IBX) and trifluoromethanesulfonic acid (triflic acid; TfOH) in acetonitrile at ambient temperature to give the corresponding γ-pyrone. Cyclization proceeded with IBX alone, but significantly improved yields were obtained with added acid, particularly triflic acid. A dithiolane was more effective than a dithiane or acyclic dithioacetal protecting group. The method was amenable to the preparation of a variety of substituted γ-pyrones simply by altering the initial aldol reactants. Overall yields of 50%–60% were obtained in six examples. The method was applied to prepare a key fragment for the total synthesis of baconipyrones A and C and siphonarin B.

scholarly journals Application of sequential proline-catalyzed α-chlorination and aldol reactions in the total synthesis of 1-deoxygalactonojirimycin

2018 ◽  
Vol 96 (2) ◽  
pp. 144-147 ◽  
Author(s):  
Michael Meanwell ◽  
Mathew Sutherland ◽  
Robert Britton
Keyword(s):  
Total Synthesis ◽  
Aldol Reaction ◽  
Single Step ◽  
Carbon Skeleton ◽  
Aldol Reactions ◽  
Protecting Group ◽  
One Pot ◽  
Enantioselective Total Synthesis ◽  
Epoxide Opening ◽  
Structural Analogues

A short enantioselective total synthesis of 1-deoxygalactonojirimycin (migalastat) has been achieved that does not rely on chiral pool starting materials or biocatalysis. Instead, this synthesis exploits a one-pot proline-catalyzed α-chlorination and aldol reaction of a commercially available aldehyde to assemble the entire carbon skeleton in a single step. The key role played by a nitrogen protecting group in the final epoxide opening reaction is highlighted as is the amenability to access structural analogues using this route.

scholarly journals First Stereoselective Total Synthesis of Tumonoic Acid A and its Derivatives

SynOpen ◽  
2018 ◽  
Vol 02 (03) ◽  
pp. 0251-0255 ◽  
Author(s):  
G. Nagalatha ◽  
Siva Narala ◽  
A. Narsaiah
Keyword(s):  
Total Synthesis ◽  
Acid Derivative ◽  
Inhibitory Activity ◽  
Magnesium Chloride ◽  
Aldol Reaction ◽  
Calcium Oscillations ◽  
Inflammatory Activity ◽  
Protecting Group ◽  
Available N ◽  
Neocortical Neurons

An efficient protecting-group-free synthesis of tumonoic acid A and its derivatives has been accomplished. The synthesis started from commercially available n-octanal and employs the magnesium chloride catalysed anti-aldol reaction under the Evans protocol as the key step. Ethyl tumonoate A is a new tumonoic acid derivative with anti-inflammatory activity and inhibitory activity towards calcium oscillations in neocortical neurons.

Fractionation of polymethylene chains: An electron crystallographic investigation

1986 ◽  
Vol 44 ◽  
pp. 794-795
Author(s):  
Douglas L. Dorset
Keyword(s):  
Cross Section ◽  
Binary Systems ◽  
Linear Chain ◽  
Pure Component ◽  
Organic Substrates ◽  
Crystallographic Investigation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Molecular Sizes ◽  
The Stability

A variety of linear chain materials exist as polydisperse systems which are difficultly purified. The stability of continuous binary solid solutions assume that the Gibbs free energy of the solution is lower than that of either crystal component, a condition which includes such factors as relative molecular sizes and shapes and perhaps the symmetry of the pure component crystal structures.Although extensive studies of n-alkane miscibility have been carried out via powder X-ray diffraction of bulk samples we have begun to examine binary systems as single crystals, taking advantage of the well-known enhanced scattering cross section of matter for electrons and also the favorable projection of a paraffin crystal structure posited by epitaxial crystallization of such samples on organic substrates such as benzoic acid.

Interactions of Ge Atoms with High- ê Oxide Dielectric Surfaces

2005 ◽  
Vol 879 ◽  
Author(s):  
Scott K. Stanley ◽  
John G. Ekerdt
Keyword(s):  
Oxide Layer ◽  
Photoelectron Spectroscopy ◽  
Chemical Vapor ◽  
Temperature Programmed Desorption ◽  
Tungsten Filament ◽  
X Ray ◽  
Dielectric Surfaces ◽  
Temperature Programmed ◽  
The Stability ◽  
Ge Nanocrystals

AbstractGe is deposited on HfO2 surfaces by chemical vapor deposition (CVD) with GeH4. 0.7-1.0 ML GeHx (x = 0-3) is deposited by thermally cracking GeH4 on a hot tungsten filament. Ge oxidation and bonding are studied at 300-1000 K with X-ray photoelectron spectroscopy (XPS). Ge, GeH, GeO, and GeO2 desorption are measured with temperature programmed desorption (TPD) at 400-1000 K. Ge initially reacts with the dielectric forming an oxide layer followed by Ge deposition and formation of nanocrystals in CVD at 870 K. 0.7-1.0 ML GeHx deposited by cracking rapidly forms a contacting oxide layer on HfO2 that is stable from 300-800 K. Ge is fully removed from the HfO2 surface after annealing to 1000 K. These results help explain the stability of Ge nanocrystals in contact with HfO2.

Tele-Substitution Reactions in the Synthesis of a Promising Class of Antimalarials

2020 ◽  
Author(s):  
Marat Korsik ◽  
Edwin Tse ◽  
David Smith ◽  
William Lewis ◽  
Peter J. Rutledge ◽  
...  
Keyword(s):  
Heterocyclic Ring ◽  
Ring System ◽  
Substitution Reactions ◽  
Laboratory Notebook ◽  
Polar Solvents ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Core ◽  
Nmr Data

<p></p><p>We have discovered and studied a <i>tele</i>substitution reaction in a biologically important heterocyclic ring system. Conditions that favour the <i>tele</i>-substitution pathway were identified: the use of increased equivalents of the nucleophile or decreased equivalents of base, or the use of softer nucleophiles, less polar solvents and larger halogens on the electrophile. Using results from X-ray crystallography and isotope labelling experiments a mechanism for this unusual transformation is proposed. We focused on this triazolopyrazine as it is the core structure of the <i>in vivo </i>active anti-plasmodium compounds of Series 4 of the Open Source Malaria consortium.</p> <p> </p> <p>Archive of the electronic laboratory notebook with the description of all conducted experiments and raw NMR data could be accessed via following link <a href="https://ses.library.usyd.edu.au/handle/2123/21890">https://ses.library.usyd.edu.au/handle/2123/21890</a> . For navigation between entries of laboratory notebook please use file "Strings for compounds in the article.pdf" that works as a reference between article codes and notebook codes, also this file contain SMILES for these compounds. </p><br><p></p>

Mukaiyama Aldol Reaction Catalyzed by (Benz)imidazolium-Based Halogen Bond Donors

2020 ◽  
Author(s):  
Revannath L. Sutar ◽  
Nikita Erochok ◽  
Stefan Huber
Keyword(s):  
Halogen Bond ◽  
Aldol Reaction ◽  
Mukaiyama Aldol Reaction ◽  
Mukaiyama Aldol ◽  
Background Reaction ◽  
Strong Performance ◽  
The Stability ◽  
Elemental Iodine

A series of cationic monodentate and bidentate iodo(benz)­imidazolium-based halogen bond (XB) donors were employed as catalysts in a Mukaiyama aldol reaction. While 5 mol% of a monodentate variant showed noticeable activity, a <i>syn</i>-preorganized bidentate XB donor provided a strong performance even with 0.5 mol% loading. In contrast to the very active BAr<sup>F</sup><sub>4</sub> salts, PF<sub>6</sub> or OTf salts were either inactive or showed background reaction. Repetition experiments clearly ruled out a potential hidden catalysis by elemental iodine and demonstrated the stability of our catalyst over three consecutive cycles.

Short Protecting Group-free Syntheses of CDE Synthon of Racemic Camptothecin

2020 ◽  
Vol 17 (7) ◽  
pp. 588-591
Author(s):  
Pingxuan Shao ◽  
Wei Lu ◽  
Lei Wang
Keyword(s):  
Total Synthesis ◽  
Future Development ◽  
Protecting Group ◽  
Short Route ◽  
The Future ◽  
Tricyclic Ketone

A practical and concise total synthesis of tricyclic ketone 7 (CDE ring), a valuable intermediate for the synthesis of racemic camptothecin and analogs, was described (8 chemical steps and 29% overall yield). The synthesis starts with two inexpensive, readily available materials and is operationally simple to perform. It is worth mentioning that the reported protecting group-free synthesis, with advantages of a short route, would be helpful for the future development of industry-scale syntheses of camptothecin-family alkaloids.

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