Low-Valent Titanium Induced Novel Reductive Cyclization of α,β-Unsaturated Nitrile Compounds

Synthesis ◽  
1998 ◽  
Vol 1998 (06) ◽  
pp. 851-854 ◽  
Author(s):  
Long-hu Zhou ◽  
Shu-jiang Tu ◽  
Da-qin Shi ◽  
Gui-yuan Dai ◽  
Wei-xing Chen
Keyword(s):  
Reductive Cyclization ◽  
Low Valent ◽  
Unsaturated Nitrile

Low-Valent Titanium Induced Reductive Cyclization of Nitriles to Symmetrically Substituted Tetraalkylpyrazines

Synthesis ◽  
1990 ◽  
Vol 1990 (08) ◽  
pp. 701-702 ◽  
Author(s):  
Wei-xing Chen ◽  
Jun-hu Zhang ◽  
Ming-yang Hu ◽  
Xiao-chun Wang
Keyword(s):  
Reductive Cyclization ◽  
Low Valent

A Novel Reductive Cyclization of o-Nitrochalcones Promoted by Low-Valent Titanium: An Access to 2-Arylquinolines (II) and 5,6-Dihydrobenz[c]acridines (IV).

ChemInform ◽  
2004 ◽  
Vol 35 (1) ◽  
Author(s):  
Daqing Shi ◽  
Liangce Rong ◽  
Juxian Wang ◽  
Qiya Zhuang ◽  
Xiangshan Wang ◽  
...  
Keyword(s):  
Reductive Cyclization ◽  
Low Valent

ChemInform Abstract: Low-Valent Titanium Induced Reductive Cyclization of Nitriles to Symmetrically Substituted Tetraalkylpyrazines.

ChemInform ◽  
2010 ◽  
Vol 22 (1) ◽  
pp. no-no
Author(s):  
W.-X. CHEN ◽  
J.-H. ZHANG ◽  
M.-Y. HU ◽  
X.-C. WANG
Keyword(s):  
Reductive Cyclization ◽  
Low Valent

The Carreira Synthesis of (±)-Gelsemoxonine

2015 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Carbon Monoxide ◽  
Aldol Condensation ◽  
Computational Study ◽  
Addition Product ◽  
Nitrile Oxide ◽  
Reductive Cyclization ◽  
Single Diastereomer ◽  
Open Face ◽  
Unsaturated Nitrile

The traditional Chinese pharmacopeia includes Gelsemium elegans benth, from which the alkaloid gelsemoxonine 3 was isolated. Erick M. Carreira of the Eidgenössische Technische Hochschule Zürich envisioned (J. Am. Chem. Soc. 2013, 135, 8500) that the unusual azetidine ring of 3 could be established by Brandi contraction of 1 to give 2. Following Brandi and Salaün (Eur. J. Org. Chem. 1999, 2725), the hemiketal 4 was carried onto the aldehyde 9. Condensation with nitromethane followed by dehydration gave the unsaturated nitrile oxide, which cyclized to 10. Epoxidation of 10 across the more open face gave an intermediate epoxide. Addition of 11 to the epoxide, promoted by InBr3, delivered 12 with good stereocontrol. CeCl3-mediated addition of 1-propynyl lithium completed the assembly of 1. A cyclopropanone could be seen as the addition product of carbon monoxide to an alkene. On exposure of 1 to acid, this formal addition was reversed, leading to the β-lactam 2. A computational study of this cleavage was recently reported (Eur. J. Org. Chem. 2011, 5608). Conceptually, one can imagine protonation activating the C–N bond for cleavage, leading to an intermediate such as 14, which then fragments to the acylium ion, leading to cyclization. It is unlikely that 14 would have any real lifetime. On warming with the Petasis reagent, the Boc-protected β-lactam was converted to the alkene 15. Hydroboration proceeded to give the alcohol 16 as a single diastereomer. Reduction followed by oxidation to 17 then set the stage for intramolecular aldol condensation to give 18. The last challenge was the diastereoselective assembly of the N-methoxyoxindole. To this end, oxidation and dehydration of 18 led to the bromo amide 20. As hoped, Heck reductive cyclization proceeded across the more open face of the alkene, leading to 21. Hydroxyl-directed hydrosilylation of the pendant alkyne to give the ethyl ketone then completed the synthesis of gelsemoxonine 3. Twice in this synthesis, advantage was taken of the preparation and reactivity of heteroatom-substituted alkenes. Dimethyl dioxirane, generated as a solution in acetone, was sufficiently water free that the epoxide derived from 10 could survive long enough to react in a bimolecular sense with the ketene silyl acetal 11.

ChemInform Abstract: An Efficient Synthesis of 2H-Indazoles via Reductive Cyclization of 2-Nitrobenzylamines Induced by Low-Valent Titanium Reagent.

ChemInform ◽  
2012 ◽  
Vol 43 (41) ◽  
pp. no-no
Author(s):  
Fang Sun ◽  
Xian Feng ◽  
Xuan Zhao ◽  
Zhi-Bin Huang ◽  
Da-Qing Shi
Keyword(s):  
Reductive Cyclization ◽  
Efficient Synthesis ◽  
Low Valent

Raney-Co Mediated Reductive Cyclization of an α,β-Unsaturated Nitrile

2008 ◽  
Vol 73 (8) ◽  
pp. 3212-3217 ◽  
Author(s):  
Jacob M. Janey ◽  
Charles J. Orella ◽  
Eugenia Njolito ◽  
Jenny M. Baxter ◽  
Jonathan D. Rosen ◽  
...  
Keyword(s):  
Reductive Cyclization ◽  
Unsaturated Nitrile

A Novel Reductive Cyclization of Arylmethylidenemalononitrile Promoted by Low-Valent Titanium.

ChemInform ◽  
2003 ◽  
Vol 34 (8) ◽  
Author(s):  
Daqing Shi ◽  
Hong Zhao ◽  
Xiangshan Wang ◽  
Changsheng Yao ◽  
Longhu Zhou
Keyword(s):  
Reductive Cyclization ◽  
Low Valent
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