scholarly journals Chemical Studies on the Oriental Plant Drugs. XXVII. The Acid Catalyzed Reactions and the Absolute Configuration at C(20) of Dammarane Type Triterpenes

1972 ◽  
Vol 20 (6) ◽  
pp. 1204-1211 ◽  
Author(s):  
NOBUTOSHI TANAKA ◽  
MASAHIRO NAGAI ◽  
TOMIHIKO OHSAWA ◽  
OSAMU TANAKA ◽  
KENICHI KAWAI ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Chemical Studies ◽  
Acid Catalyzed ◽  
Plant Drugs ◽  
The Absolute ◽  
Catalyzed Reactions

Configurationally Stable Doubly Bridged Biphenyl Azocines through Copper-Catalyzed Double Carbene Insertions into the Corresponding Azepines

Synthesis ◽  
2016 ◽  
Vol 48 (19) ◽  
pp. 3254-3262 ◽  
Author(s):  
Steven Harthong ◽  
Elodie Brun ◽  
Stéphane Grass ◽  
Céline Besnard ◽  
Thomas Bürgi ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Single Step ◽  
Starting Material ◽  
Axial Chirality ◽  
Configurational Stability ◽  
The Absolute ◽  
Catalyzed Reactions

Doubly bridged biphenyl azocines can be prepared in a single step through copper-catalyzed reactions of a doubly bridged biphenyl azepine and diazodiester reagents. Double [1,2]-Stevens rearrangements occur at 100 °C to afford doubly tethered eight-membered rings (49 to 61%) as trans and cis regioisomers (1:1 ratio). These products present an axial chirality. ECD and VCD analyses of the separated enantiomers (CSP-HPLC) were used to assign the absolute configuration. High configurational stability is observed for both regioisomers as racemization does not occur after 1 week of heating at 208 °C in dodecane (ΔG ‡ > 41 kcal·mol–1). Interestingly, reactions performed at 40 °C retain a certain level of enantiospecificity (82–86%), avoiding, for the most part, thermal racemization of the starting material.

SOME ASPECTS OF THE CHEMISTRY OF CATHARANTHINE AND CLEAVAMINE

1965 ◽  
Vol 43 (5) ◽  
pp. 1545-1552 ◽  
Author(s):  
James P. Kutney ◽  
Richard T. Brown ◽  
Edward Piers
Keyword(s):  
Absolute Configuration ◽  
Asymmetric Center ◽  
Reaction Products ◽  
Spectroscopic Evidence ◽  
X Ray ◽  
Transannular Cyclization ◽  
Acid Catalyzed ◽  
The Absolute

Chemical and spectroscopic evidence is presented for an interesting acid-catalyzed rearrangement of the alkaloid catharanthine. Four reaction products (descarbomethoxycatharanthine and cleavamine and its two dihydro derivatives) were isolated, and their formation is rationalized by a mechanism involving ring-opened intermediates. Evidence is presented in support of the proposed mechanism and, in particular, a novel transannular cyclization leading to the Iboga alkaloid skeleton is shown in support of the steps postulated for the formation of descarbomethoxycatharanthine.The X-ray analysis of cleavamine methiodide established the absolute configuration of the lone asymmetric center present in the molecule and, from these results, the absolute configuration of the Iboga alkaloids can be derived.

Isomeric oxatricyclodecanones with non-planar lactone groups: Synthesis, absolute configuration, NMR and X-ray study

1984 ◽  
Vol 49 (2) ◽  
pp. 513-532 ◽  
Author(s):  
Miloš Tichý ◽  
Ahmed Farag ◽  
Miloš Buděšínský ◽  
Ludmila P. Otroshchenko ◽  
Tatjana A. Shibanova ◽  
...  
Keyword(s):  
Carboxylic Acid ◽  
Absolute Configuration ◽  
Nmr Spectra ◽  
X Ray ◽  
Acid Catalyzed ◽  
The Absolute

Several rigid polycyclic lactones, potentially suitable as models for investigation of the lactone grouping geometry, were synthesized. (3S)-4-Oxatricyclo[4.3.1.03,7]decan-5-one ((+)-I), (3R)-5-oxatricyclo[4.3.1.03,8]decan-4-one ((+)-III) and (4S)-5-oxatricyclo[5.2.1.04,8]decan-6-one ((-)-VIII) were prepared by acid-catalyzed lactonization of (2R)-endo-bicyclo[2.2.2]oct-5-ene-2-carboxylic acid. (1S)-4-Oxatricyclo[4.4.0.03,8]decan-5-one ((-)-II) was synthesized from (2S, 5S)-endo,endo-bicyclo[2.2.2]-octane-2,5-dicarbolyxic acid. The structure of VIII was unequivocally proved by its NMR, spectra and the geometry of III was determined by X-ray analysis. The absolute configuration of (+)-III was assigned by correlation with (1R)-bicyclo[3.2.1]nonan-6-one. The acid-induced interconversion of I, II, III and VIII was studied. Lactones II and III represent suitable rigid models for investigations of non-planar lactone groups of known chirality and geometry.

Evaluation of Different Synthetic Routes to (2R,3R)-3-Hydroxymethyl-2-(4-hydroxy- 3-methoxyphenyl)-1,4-Benzodioxane-6-Carbaldehyde

2020 ◽  
Vol 23 (26) ◽  
pp. 2960-2968
Author(s):  
Renáta Kertiné Ferenczi ◽  
Tünde-Zita Illyés ◽  
Sándor Balázs Király ◽  
Gyula Hoffka ◽  
László Szilágyi ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Stereoselective Synthesis ◽  
Cotton Effect ◽  
Enantioselective Synthesis ◽  
Aryl Group ◽  
Target Molecule ◽  
Synthetic Routes ◽  
The Absolute

The reported enantioselective synthesis for the preparation of (+)-(2R,3R)-2-(4- hydroxy-3-methoxyphenyl)-3-hydroxymethyl-1,4-benzodioxane-6-carbaldehyde, precursor for the stereoselective synthesis of bioactive flavanolignans, could not be reproduced. Thus, the target molecule was prepared via the synthesis and separation of diastereomeric O-glucosides. TDDFT-ECD calculations and the 1,4-benzodioxane helicity rule were utilized to determine the absolute configuration. ECD calculations also confirmed that the 1Lb Cotton effect is governed by the helicity of the heteroring, while the higher-energy ECD transitions reflect mainly the orientation of the equatorial C-2 aryl group.

Absolute configuration at C(20) of the derivatives of 21-nor-5α-cholane-20,24-diol

1980 ◽  
Vol 45 (9) ◽  
pp. 2443-2451
Author(s):  
Vladimír Pouzar ◽  
Miroslav Havel
Keyword(s):  
Absolute Configuration ◽  
Side Chain ◽  
Chemical Correlation ◽  
The Absolute ◽  
Derivatives Of

Derivatives of 21-nor-5α-cholane-20,24-diol XI and XIX were prepared by stepwise construction of the side-chain in the position 17β. Their absolute configuration at C(20) was determined on the basis of chemical correlation with the derivatives of 21-nor-5α-cholan-20-ol, XVI and XXIV. The absolute configuration of alcohols XVI and XXIV was determined from the ratio of the yields in which they are formed during the reduction of ketone X and using the benzoate rule. To compounds XI-XVIII the configuration 20R and to compounds XIX-XXVI the configuration 20S has been assigned.

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