ChemInform Abstract: Synthesis of AB Ring Model System of Taxol via Allylation of 8- Membered Ring Compound and Intramolecular Aldol Condensation.

ChemInform ◽  
2010 ◽  
Vol 26 (33) ◽  
pp. no-no
Author(s):  
T. MUKAIYAMA ◽  
I. SHIINA ◽  
K. KIMURA ◽  
Y. AKIYAMA ◽  
H. IWADARE
Keyword(s):  
Aldol Condensation ◽  
Model System ◽  
Membered Ring ◽  
Ring Model ◽  
Ab Ring

Synthesis of AB Ring Model System of TaxolviaAllylation of 8-Membered Ring Compound and Intramolecular Aldol Condensation

1995 ◽  
Vol 24 (3) ◽  
pp. 229-230 ◽  
Author(s):  
Teruaki Mukaiyama ◽  
Isamu Shiina ◽  
Kaname Kimura ◽  
Yuji Akiyama ◽  
Hayato Iwadare
Keyword(s):  
Aldol Condensation ◽  
Model System ◽  
Membered Ring ◽  
Ring Model ◽  
Ab Ring

A Synthesis of AB-Ring Model System of Taxane Framework by Way of Intramolecular Knoevenagel Cyclization

2002 ◽  
Vol 31 (1) ◽  
pp. 92-93 ◽  
Author(s):  
Hidehiro Arai ◽  
Ayako Ohno ◽  
Yu-ichirou Tani ◽  
Shouhei Imachi ◽  
Teruaki Mukaiyama
Keyword(s):  
Model System ◽  
Ring Model ◽  
Ab Ring

ChemInform Abstract: A Synthesis of AB-Ring Model System of Taxane Framework by Way of Intramolecular Knoevenagel Cyclization.

ChemInform ◽  
2010 ◽  
Vol 33 (24) ◽  
pp. no-no
Author(s):  
Hidehiro Arai ◽  
Ayako Ohno ◽  
Yu-ichirou Tani ◽  
Shouhei Imachi ◽  
Teruaki Mukaiyama
Keyword(s):  
Model System ◽  
Ring Model ◽  
Ab Ring

scholarly journals Five-membered ring annelation in [2.2]paracyclophanes by aldol condensation

2014 ◽  
Vol 10 ◽  
pp. 2021-2026 ◽  
Author(s):  
Henning Hopf ◽  
Swaminathan Vijay Narayanan ◽  
Peter G Jones
Keyword(s):  
Structural Analysis ◽  
Spectroscopic Data ◽  
Acid Treatment ◽  
Aldol Condensation ◽  
Membered Ring ◽  
X Ray

Under basic conditions 4,5,12,13-tetraacetyl[2.2]paracyclophane (9) cyclizes by a double aldol condensation to provide the two aldols 12 and 15 in a 3:7 ratio. The structures of these compounds were obtained from X-ray structural analysis, spectroscopic data, and mechanistic considerations. On acid treatment 12 is dehydrated to a mixture of the condensed five-membered [2.2]paracyclophane derivatives 18–20, whereas 15 yields a mixture of the isomeric cyclopentadienones 21–23. The structures of these elimination products are also deduced from X-ray and spectroscopic data. The sequence presented here constitutes the simplest route so far to cyclophanes carrying an annelated five-membered ring.

The Ding Synthesis of Steenkrotin A

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Intramolecular Cyclization ◽  
Aldol Condensation ◽  
Secondary Alcohol ◽  
Folk Medicine ◽  
Equilibrium Concentration ◽  
Membered Ring ◽  
Silyl Ether ◽  
Enol Ether ◽  
Bond Forming ◽  
Open Face

Steenkrotin A 3 was isolated from Croton steenkampianus Gerstner, widely used in folk medicine for the treatment of coughs, fever, malaria, and rheumatism. Hanfeng Ding of Zhejiang University envisioned (Angew. Chem. Int. Ed. 2015, 54, 6905) that the intriguingly compact core of 3 could be assembled by reductive cyclization of the alde­hyde 1 to 2, followed by intramolecular aldol condensation. The diastereoselective assembly of 1 from the cycloheptenone core 4 depended on the conformational preferences of the seven-membered ring. Enol ether forma­tion followed by Rubottom oxidation led to the silyl ether 5. Oxidative rearrange­ment of the tertiary alcohol generated by 1,2-addition to 5 of in situ generated allyl lithium established the enone 6. Again taking advantage of the conformational pref­erence of the seven-membered ring, cyclopropanation of the silyl enol ether derived from 6 proceeded across the open face of the electron-rich alkene to give 7. The other oxygenated quaternary center of 1 was constructed by O-alkylation of 7 with diazo malonate followed by methylation and reduction. Acetylation of the diol 8 proceeded with 10:1 diastereoselectivity, to give, after oxidation, the aldehyde 9. In the first of a sequence of three intramolecular bond-forming reactions, HF.py cyclized the aldehyde onto the endocyclic alkene, and also freed the alcohol, that was alkylated with the dibromide 10 to give 11 as a 1.5:1 mixture of diastereomers. On exposure to SmI2, the major diastereomer cyclized to give a intermediate that was carried on to 1. The minor diastereomer was merely reduced, to a product that could be recycled to 11. With 1 in hand, the stage was set for the second intramolecular cyclization. Even though 1 was predominantly in the lactol form, there was enough of an equilibrium concentration of aldehyde present for the SmI2-mediated cyclization to proceed smoothly to 2. With 2 in hand, in addition to the last intramolecular cyclization, the two stereo­genic centers (marked by an asterisk) had to be inverted. The methyl group adjacent to the ketone was readily equilibrated. The secondary alcohol could be inverted by late-stage oxidation and reduction, and the authors did do that. However, they also observed a small amount of the desired epimeric alcohol 14 from the intramolecu­lar aldol condensation of 12.

The Procter Synthesis of (+)-Pleuromutilin

2015 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Aldol Condensation ◽  
Secondary Alcohol ◽  
Primary Alcohol ◽  
Conjugate Addition ◽  
Alkoxy Group ◽  
Membered Ring ◽  
Allylic Alcohol ◽  
Silyl Ether ◽  
Radical Reduction ◽  
The University

The fungal secondary metabolite (+)-pleuromutilin 3 exerts antibiotic activity by binding to the prokaryotic ribosome. Semisynthetic derivatives of 3 are used clinically. The central step of the first synthesis of (+)-pleuromutilin 3, devised (Chem. Eur. J. 2013, 19, 6718) by David J. Procter of the University of Manchester, was the SmI2-mediated reductive closure of 1 to the tricyclic 2. The starting material for the synthesis was the inexpensive dihydrocarvone 4. Ozonolysis and oxidative fragmentation following the White protocol delivered 5 in high ee. Conjugate addition with 6 followed by Pd-mediated oxidation of the resulting silyl enol ether gave the enone 7. Subsequent conjugate addition of 8 proceeded with modest but useful diastereoselectivity to give an enolate that was trapped as the triflate 9. The Sakurai addition of the derived ester 10 with 11 led to 12 and so 1 as an inconsequential 1:1 mixture of diastereomers. The SmI2-mediated cyclization of 1 proceeded with remarkable diastereocontrol to give 2. SmI2 is a one-electron reductant that is also a Lewis acid. It seems likely that one SmI2 bound to the ester and the second to the aldehyde. Electron transfer then led to the formation of the cis-fused five-membered ring, with the newly formed alkoxy constrained to be exo to maintain contact with the complexing Sm. Intramolecular aldol condensation of the resulting Sm enolate with the other aldehyde then formed the six-membered ring, with the alkoxy group again constrained by association with the Sm. Hydrogenation of 13 gave 14, which could be brought to diastereomeric purity by chromatography. Elegantly, protection of the ketone simultaneously selectively deprotected one of the two silyl ethers, thus differentiating the two secondary alcohols. Reduction of the ester to the primary alcohol then delivered the diol 15. Selective esterification of the secondary alcohol followed by thioimidazolide formation and free radical reduction completed the preparation of 16. Ketone deprotection followed by silyl ether formation and Rubottom oxidation led to the diol 17. Protection followed by the addition of 18 and subsequent hydrolysis and reduction gave the allylic alcohol 19.

Synthetic Studies toward Tubiferal A: Asymmetric Synthesis of a Model ABC-ring Compound

Synlett ◽  
2021 ◽  
Author(s):  
Yuki Yukutake ◽  
Takahiro Hiramatsu ◽  
Ryusei Itoh ◽  
Kazutada Ikeuchi ◽  
Takahiro Suzuki ◽  
...  
Keyword(s):  
Asymmetric Synthesis ◽  
Claisen Rearrangement ◽  
Ring System ◽  
Alkylation Reaction ◽  
Ring Model ◽  
Stereoselective Addition ◽  
Stereogenic Centers ◽  
Rearrangement Reaction ◽  
Synthetic Studies ◽  
Ab Ring

Synthetic studies on an ABC-ring model of Tubiferal A, a triterpenoid isolated from the fruit bodies of the Tubifera dimorphotheca myxomycete, are described. The stereogenic centers at the angular positions were constructed through the stereoselective addition of a C-ring allylborane followed by an Eschenmoser–Claisen rearrangement reaction prior to the formation of the AB-ring system by a double intramolecular alkylation reaction of a dichloro nitrile intermediate.

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