The Chemistry of Laurenene. X. A New Carbon Skeleton by Rearrangement of Laurenan-2-β-ol

1990 ◽  
Vol 43 (1) ◽  
pp. 141 ◽  
Author(s):  
PJ Eaton ◽  
AR Hayman ◽  
RT Weavers
Keyword(s):  
Trifluoroacetic Acid ◽  
Major Product ◽  
Ring System ◽  
Membered Ring ◽  
Carbon Skeleton ◽  
Deuterium Labelling ◽  
Carbon Ring ◽  
Starting Point ◽  
Remote Part

Treatment of laurenan-2β-ol (2) with trifluoroacetic acid in dichloromethane at 0° gives as the major product the rearranged alkene (4). This compound has a new carbon-ring system containing three five-membered rings and one six- membered ring. The structure of (4) has been determined by a range of n.m.r. techniques applied to (4) and selected derivatives. Deuterium- labelling experiments have established that the rearrangement proceeds to a remote part of the molecule and then returns to its starting point.

The Chemistry of Laurenene. XIII. Formation of a New, Bridged, Tetracyclic Ring System

1991 ◽  
Vol 44 (8) ◽  
pp. 1139 ◽  
Author(s):  
RE Corbett ◽  
JR Guild ◽  
DR Lauren ◽  
RT Weavers
Keyword(s):  
Sodium Borohydride ◽  
Ring System ◽  
Membered Ring ◽  
Keto Ester ◽  
Carbon Ring

Attempted reduction of a laurenene-derived keto ester with sodium borohydride or lithium tri-t-butoxyaluminium hydride at 110° gave rise to products containing a new tetracyclic carbon ring system made up of one seven- and one six- membered ring and two five- membered rings.

Access to the Bicyclo[5.3.1]undecadiene Ring System by Two Carbon Ring Enlargement of Bicyclo[3.3.1]nonane Derivatives

Synlett ◽  
1996 ◽  
Vol 1996 (04) ◽  
pp. 385-386 ◽  
Author(s):  
Michel Miesch ◽  
Gaëtan Mislin ◽  
Michel Franck-Neumann
Keyword(s):  
Ring System ◽  
Ring Enlargement ◽  
Carbon Ring

The Boger Synthesis of (-)-Vindoline

2013 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Absolute Configuration ◽  
Secondary Alcohol ◽  
Ring System ◽  
Simple Solution ◽  
Relative Configuration ◽  
Amine Oxidation ◽  
Formidable Challenge ◽  
Starting Point ◽  
La Jolla ◽  
Stereogenic Center

The periwinkle-derived alkaloids vinblastine 2a and vincristine 2b are still mainstays of cancer chemotherapy. The more complex half of these dimeric alkaloids, vindoline 1, presents a formidable challenge for total synthesis. Building on his previous work (Organic Lett. 2005, 7, 4539), Dale L. Boger of Scripps/La Jolla devised (J. Am. Chem. Soc. 2010, 132, 3685) a strikingly simple solution to this problem based on sequential cycloaddition. The starting point for the synthesis was the ester 3, derived from D-asparagine. This was extended to 4, condensation of which with 5 gave the enol ether 6. On heating, 7 cyclized to 8, which lost N2 to give the zwitterion 9. Addition of the intermediate 9 to the indole then gave 10. In one reaction, the entire ring system of vindoline, appropriately oxygenated, was assembled, with the original stereogenic center from D-asparagine directing the relative and absolute configuration of the final product. To complete the synthesis, the pendant carbon on 11 had to be incorporated into the pentacyclic skeleton. After adjusting the relative configuration of the secondary alcohol, the N was rendered nucleophilic by reduction of the amide to the amine. Oxidation delivered 14, which on activation as the tosylate smoothly rearranged to the ketone 15. Reduction and regioselective dehydration then completed the synthesis of vindoline 1.

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).

scholarly journals Homocoupling Reactions of Azoles and Their Applications in Coordination Chemistry

Molecules ◽  
2020 ◽  
Vol 25 (24) ◽  
pp. 5950
Author(s):  
Steffen B. Mogensen ◽  
Mercedes K. Taylor ◽  
Ji-Woong Lee
Keyword(s):  
Coordination Chemistry ◽  
Reaction Mechanisms ◽  
Metal Organic Frameworks ◽  
Ring System ◽  
Membered Ring ◽  
Materials Chemistry ◽  
Structural Class ◽  
Basic Nitrogen ◽  
Metal Organic ◽  
Metal Catalyzed

Pyrazole, a member of the structural class of azoles, exhibits molecular properties of interest in pharmaceuticals and materials chemistry, owing to the two adjacent nitrogen atoms in the five-membered ring system. The weakly basic nitrogen atoms of deprotonated pyrazoles have been applied in coordination chemistry, particularly to access coordination polymers and metal-organic frameworks, and homocoupling reactions can in principle provide facile access to bipyrazole ligands. In this context, we summarize recent advances in homocoupling reactions of pyrazoles and other types of azoles (imidazoles, triazoles and tetrazoles) to highlight the utility of homocoupling reactions in synthesizing symmetric bi-heteroaryl systems compared with traditional synthesis. Metal-free reactions and transition-metal catalyzed homocoupling reactions are discussed with reaction mechanisms in detail.

Untersuchungen zur Ringkontraktion am 1,4-Dithia-2,6-diaza-3,5-diborinan-System/ Studies on Ring Contraction of the l,4-Dithia-2,6-diaza-3,5-diborinane System

1988 ◽  
Vol 43 (8) ◽  
pp. 959-962 ◽  
Author(s):  
Carl Habben ◽  
Anton Meiler ◽  
Stefan Pusch
Keyword(s):  
Mass Spectra ◽  
Ring System ◽  
Membered Ring ◽  
Ring Contraction ◽  
C Nmr

AbstractThe 1,4-dithia-2,6-diaza-3,5-diborinanes 1a-d react with elemental sodium with formation of the 1,3-diaza-2,4-diboretidines 2a-d. By use of more sodium in case of 1 d or 3,5-bis(diethylamino)- 2-cyclohexyl-6-trimethylsilyldiborinane, the 1,3-thiaza-2,4-diboretidines 3 were formed. 3.5-Dimethyl-2,6-bis(trimethylsilyl)-1,4-dithia-2,6-diaza-3,5-diborinane gives the borazine 4, The reaction of di-t-butyl-sulfurdiimide with 2,6-di-t-butyl-3,5-dimethyl-1,4-dithia-2,6-diaza-3,5-diborinane leads by ring contraction to the four-membered ring system 5. 1H, 11B, 13C NMR and mass spectra are reported and discussed.

Reaktion von N-Trimethylsilyl-N′(N″ -trimethylsilylammodiphenylphosphoranylidenimino) sulfamid mit Wolframoxitetrachlorid und die Struktur von (Cl3WNPPh2N)2 Reaction of N-Trimethylsilyl-N′(N″ -trimethylsilylaminodiphenylphosphoranylidene)sulfamide with Tungstenoxitetrachloride and the Structure of (Cl3WNPPh2N)2

1992 ◽  
Vol 47 (2) ◽  
pp. 171-174 ◽  
Author(s):  
H. W. Roesky ◽  
T. Raubold ◽  
M. Noltemeyer ◽  
M. Witt ◽  
R. Bohra
Keyword(s):  
Molecular Structure ◽  
Structure Analysis ◽  
Ring System ◽  
Membered Ring ◽  
X Ray

1The reaction of ClSO2N = PPh2Cl () with NH3 yields H2NSO2N = PPh2NH2 (2).This compound is converted to Me3Si(H)NSO2N = PPh2N(H)SiMe3 (3) by Me3SiNMe2. 3 reacts with WOCl4 under elimination of (Me3Si)2O and ClSO2NH2 to yield the eight-membered ring system (Cl3WNPPh2N)2 (4).The molecular structure of 4 was investigated by an X-ray structure analysis.

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