ChemInform Abstract: A Surprising Eight-Membered Ring Synthesis Leading To Enantiomerically Pure Tricyclic Benzodiazepine Derivatives.

ChemInform ◽  
2010 ◽  
Vol 26 (29) ◽  
pp. no-no
Author(s):  
A. HAKIKI ◽  
M. MOSSADAK ◽  
M. MOKHLES ◽  
F. ROUESSAC ◽  
H. DUDDECK ◽  
...  
Keyword(s):  
Membered Ring ◽  
Enantiomerically Pure ◽  
Benzodiazepine Derivatives ◽  
Ring Synthesis

A surprising eight-membered ring synthesis leading to enantiomerically pure tricyclic benzodiazepine derivatives

Tetrahedron ◽  
1995 ◽  
Vol 51 (8) ◽  
pp. 2293-2296 ◽  
Author(s):  
A Hakiki ◽  
M Mossadak ◽  
M Mokhles ◽  
F Rouessac ◽  
Helmut Duddeck ◽  
...  
Keyword(s):  
Membered Ring ◽  
Enantiomerically Pure ◽  
Benzodiazepine Derivatives ◽  
Ring Synthesis

C-O Ring Containing Natural Products: Paeonilactone B (Taylor), Deoxymonate B (de la Pradilla), Sanguiin H-5 (Spring), Solandelactone A (White), Spirastrellolide A (Paterson)

2011 ◽  
Author(s):  
Douglass Taber
Keyword(s):  
Oxidative Coupling ◽  
Claisen Rearrangement ◽  
Cyclic Carbonate ◽  
Membered Ring ◽  
State University ◽  
Enantiomerically Pure ◽  
University Of Cambridge ◽  
Spirastrellolide A ◽  
The University ◽  
Oregon State University

Richard J. K. Taylor of the University of York has developed (Angew. Chem. Int. Ed. 2008, 47, 1935) the diasteroselective intramolecular Michael cyclization of phosphonates such as 2. Quenching of the cyclized product with paraformaldehyde delivered ( + )-Paeonilactone B 3. Roberto Fernández de la Pradilla of the CSIC, Madrid established (Tetrahedron Lett. 2008, 49, 4167) the diastereoselective intramolecular hetero Michael addition of alcohols to enantiomerically-pure acyclic sulfoxides such as 4 to give the allylic sulfoxide 5. Mislow-Evans rearrangement converted 5 into 6, the enantiomerically-pure core of Ethyl Deoxymonate B 7. The ellagitannins, represented by 10, are single atropisomers around the biphenyl linkage. David R. Spring of the University of Cambridge found (Organic Lett. 2008, 10, 2593) that the chiral constraint of the carbohydrate backbone of 9 directed the absolute sense of the oxidative coupling of the mixed cuprate derived from 9, leading to Sanguiin H-5 10 with high diastereomeric control. A key challenge in the synthesis of the solandelactones, exemplified by 14, is the stereocontrolled construction of the unsaturated eight-membered ring lactone. James D. White of Oregon State University found (J. Org. Chem. 2008, 73, 4139) an elegant solution to this problem, by exposure of the cyclic carbonate 11 to the Petasis reagent, to give 12. Subsequent Claisen rearrangement delivered the eight-membered ring lactone, at the same time installing the ring alkene of Solandelactone E 14. AD-mix usually proceeds with only modest enantiocontrol with terminal alkenes. None the less, Ian Paterson, also of the University of Cambridge, observed (Angew. Chem. Int. Ed. 2008, 47, 3016, Angew. Chem. Int. Ed. 2008, 47, 3021) that bis-dihydroxylation of the diene 17 proceeded to give, after acid-mediated cyclization, the bis-spiro ketal core 18 of Spirastrellolide A Methyl Ester 19 with high diastereocontrol.

The Sato/Chida Synthesis of Paclitaxel (Taxol®)

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Organic Synthesis ◽  
Conjugate Addition ◽  
Cyclic Carbonate ◽  
Membered Ring ◽  
Standard Protocol ◽  
Protecting Group ◽  
Enantiomerically Pure ◽  
Facial Selectivity ◽  
Starting Point ◽  
Nabh4 Reduction

Paclitaxel (Taxol®) 3 is widely used in the clinical treatment of a variety of cancers. Takaaki Sato and Noritaka Chida of Keio University envisioned (Org. Lett. 2015, 17, 2570, 2574) establishing the central eight-membered ring of 3 by the SmI2-mediated cyclization of 1 to 2. The starting point for the synthesis was the enantiomerically-pure enone 5, pre­pared from the carbohydrate precursor 4. Conjugate addition to 5 proceeded anti to the benzyloxy substituent to give, after trapping with formaldehyde and protection, the ketone 6. Reduction and protection followed by hydroboration led to 7, that was, after protection and deprotection, oxidized to 8. The second ring of 3 was added in the form of the alkenyl lithium derivative 9, prepared from the trisylhydrazone of the corresponding ketone. Hydroxyl-directed epoxidation of 10 proceeded with high facial selectivity, leading, after reduction and protection, to the cyclic carbonate 11. Allylic oxidation converted the alkene into the enone, while at the same time oxidizing the benzyl protecting group to the ben­zoate, to give 12. Reduction of the ketone 12 led to a mixture of diastereomers. In practice, only one of the diastereomers of 1 cyclized cleanly to 2, as illustrated, so the undesired diastereomer from the NaBH4 reduction was oxidized back to the enone for recycling. For convenience, only one of the diastereomers of 2 was carried forward. To establish the tetrasubstituted alkene of 3, the alkene of 2 was converted to the cis diol and on to the bis xanthate 13. Warming to 50°C led to the desired tet­rasubstituted alkene, sparing the oxygenation that is eventually required for 3. For convenience, to intercept 16, the intermediate in the Takahashi total synthesis, both xanthates were eliminated to give 14. Hydrogenation removed the disubsti­tuted alkene, and also deprotected the benzyl ether. Oxidation followed by Peterson alkene formation led to 15, that was carried on to the Takahashi intermediate 16 using the now-standard protocol for oxetane construction. It is a measure of the strength of the science of organic synthesis that Masahisa Nakada of Waseda University also reported (Chem. Eur. J. 2015, 21, 355) an elegant synthesis of 3 (not illustrated).

Chiral Mo−Binol Complexes:  Activity, Synthesis, and Structure. Efficient Enantioselective Six-Membered Ring Synthesis through Catalytic Metathesis

1999 ◽  
Vol 121 (36) ◽  
pp. 8251-8259 ◽  
Author(s):  
S. Sherry Zhu ◽  
Dustin R. Cefalo ◽  
Daniel S. La ◽  
Jennifer Y. Jamieson ◽  
William M. Davis ◽  
...  
Keyword(s):  
Membered Ring ◽  
Ring Synthesis

The mechanism investigation of the imidazolidinone catalyzed five-membered ring synthesis reaction

2012 ◽  
Vol 26 (3) ◽  
pp. 232-239 ◽  
Author(s):  
Lili Zhang ◽  
Huiling Liu ◽  
Yuhong Yang ◽  
Zhihui Chong ◽  
Tingting Feng ◽  
...  
Keyword(s):  
Membered Ring ◽  
Synthesis Reaction ◽  
Ring Synthesis

ChemInform Abstract: Highly Stereoselective 7-Membered Ring Synthesis Based upon the Oxidopyrylium-Alkene [5 + 2] Cycloaddition Reaction.

ChemInform ◽  
2010 ◽  
Vol 33 (6) ◽  
pp. no-no
Author(s):  
Naoki Ohmori ◽  
Toru Miyazaki ◽  
Satoshi Kojima ◽  
Katsuo Ohkata
Keyword(s):  
Cycloaddition Reaction ◽  
Membered Ring ◽  
Ring Synthesis

Enantiomerically pure (1S,5R) and racemic 3-(1-benzothiophen-2-yl)-8-azoniabicyclo[3.2.1]oct-2-ene acetate

2012 ◽  
Vol 68 (8) ◽  
pp. o298-o301
Author(s):  
Brian Frøstrup ◽  
Dan Peters ◽  
Andrew D. Bond
Keyword(s):  
Title Compound ◽  
Molecular Conformation ◽  
Thiophene Ring ◽  
Membered Ring ◽  
Group Symmetry ◽  
Asymmetric Unit ◽  
Enantiomerically Pure ◽  
Space Group ◽  
Compound C ◽  
Pure Enantiomer

The title compound, C15H16NS+·C2H3O2−, has been crystallized as both a pure enantiomer (1S,5R) and a racemate. The racemate crystallizes in the space groupCc, with molecules of opposite handedness related to each other by the action of thec-glide. The enantiomer is essentially isostructural with the racemate, except that the glide symmetry is violated by interchange of CH and CH2groups within the seven-membered ring. The space-group symmetry is reduced toP1 with two molecules in the asymmetric unit. The enantiomer structure shows disorder of the thiophene ring for one of the molecules in the asymmetric unit. The major component of the disorder has the thiophene ring in the same position as in the racemate, but generates a higher-energy molecular conformation. The minor disorder component has different intermolecular interactions but retains a more stable molecular conformation.

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