A Convenient Route to O-Glycosyl Lactates via Conjugate Addition to 2-Nitroglycals: Ring Closure to Novel Pyrano[2.3-b][1,4]-oxazines

Synthesis ◽  
2003 ◽  
Vol 2004 (01) ◽  
pp. 53-58
Author(s):  
Richard Schmidt ◽  
Ahmed Khodair ◽  
Kandasamy Pachamuthu
Keyword(s):  
Conjugate Addition ◽  
Ring Closure ◽  
Convenient Route

Conjugate addition approach for natural product synthesis inspired by gibberellin and solanoeclepin A targets

2013 ◽  
Vol 85 (6) ◽  
pp. 1149-1160 ◽  
Author(s):  
Minoru Isobe
Keyword(s):  
Oxygen Atom ◽  
Low Temperatures ◽  
Bond Formation ◽  
Conjugate Addition ◽  
Ring Closure ◽  
Natural Product Synthesis ◽  
Partial Synthesis ◽  
Unsaturated Ketones ◽  
Cyclobutane Ring ◽  
Zinc Enolate

Trimethylzincate is known to react through conjugate addition to α,β-unsaturated ketones, but adds much faster to α,β-unsaturated esters at low temperatures. Since the intermediate zinc enolate behaves differently from that of dimethylcuprate, it offers scope for application in a partial synthesis of gibberellin A3. A second example involving vinylsulfones having an oxygen atom on the γ-carbon strongly directs incoming nucleophiles in conjugate addition mode. Heteroatom-directed conjugate addition (HADCA) provides very reactive carbanion intermediates leading to cyclobutane ring formation, necessary for synthesis of solanoeclepin A. An alternative reaction for the four-membered carbocyclic ring closure was explored to make a bond formation between the propargylic cation of Nicholas type and allyltrimethylsilane nucleophile of Hosomi–Sakurai type. This method allowed a formation of tricyclo[5.2.1.01,6]decene framework.

Carbocyclic Construction: The Deng Synthesis of (-)-Plicatic Acid

2013 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Brefeldin A ◽  
Conjugate Addition ◽  
Oxidative Cyclization ◽  
Ring Closure ◽  
Silyl Ether ◽  
University Of Pittsburgh ◽  
University Of Wisconsin ◽  
Institute Of Technology ◽  
The University ◽  
Academy Of Sciences

Tehshik P. Yoon of the University of Wisconsin uncovered (J. Am. Chem. Soc. 2009, 131, 14604) conditions for the crossed photodimerization of acyclic enones. Minoru Isobe of Nagoya University extended (Synlett 2009, 1157) conjugate addition–intramolecular epoxide opening to substrates such as 4, leading to the cyclobutane 6 with high diastereocontrol. In the course of a total synthesis of (+)-brefeldin A, Jinsung Tae of Yonsei University established (Synlett 2009, 1303) conditions for the trans-selective cyclization of 7 to 8. Cyclization with TiCl4 gave the alternative cis diastereomer. Several methods have been put forward for the conversion of carbohydrate derivatives to carbocycles. Yeun-Mi Tsai of the National Taiwan University found (Tetrahedron Lett . 2009, 50, 3805) that acyl silanes such as 9 cyclized efficiently under free radical conditions, leading to the silyl ether 10. Tanmaya Pathak of the Indian Institute of Technology, Kharagpur, developed (Eur. J. Org. Chem. 2009, 872) the tandem conjugate addition– intramolecular alkylation conversion of 11 to 13. Slawomir Jarosz of the Polish Academy of Sciences, Warsawza, observed (Heterocycles 2009, 80, 1303) that the oxime derived from 14 cyclized to 15. The cyclization was accelerated by high pressure. Cyclohexanes can also be prepared from carbohydrates. Tony K. M. Shing of the Chinese University of Hong Kong showed (Organic. Lett. 2009, 11, 5070) that the nitrile oxide derived from 16 cyclized to 17, that he carried on to (-)-gabosine O. John K. Gallos of the Aristotle University of Thessaloniki described (Tetrahedron Lett. 2009, 50, 6916) related work. Paul E. Floreancig of the University of Pittsburgh devised (Organic. Lett. 2009, 11, 3152) conditions for the oxidative cyclization of 18 to 19. Ring closure proceeded with high equatorial selectivity. Kou Hiroya of Tohoku University found (J. Org. Chem. 2009, 74, 6623) that the single oxygenated stereogenic center of 20 directed the dissolving metal reduction–enolate trapping, leading to 21. Similarly, Susumu Kobayashi of the Tokyo University of Science showed (Synlett 2009, 1605) that the oxygenated stereogenic centers of 22 set the alkylated centers of 23. Many marine organisms are able to carry out brominative and chlorinative polyolefin cyclizations.

scholarly journals Scalable Route to Chiral Phosphoramidites

2016 ◽  
Vol 8 (2) ◽  
pp. 64
Author(s):  
Sergiy G. Krasutsky ◽  
Sheila H. Jacobo
Keyword(s):  
General Structure ◽  
Conjugate Addition ◽  
Highly Efficient ◽  
Excellent Yield ◽  
Convenient Route ◽  
Pdf Format

The chiral copper-catalyzed conjugate addition is a well-developed methodology to create asymmetric C-C bonds. Many efforts have been dedicated to design efficient systems and identifying highly efficient ligands. Among the most proficient ligands, the ones possessing a bis-phenol or a bis-naphthol moiety are the most prominent. Herein we describe a scalable convenient route that can afford phosphoramidites in excellent yield.<br />Please find "Figure 1. General structure and application of phosphoramidites" in PDF format.

scholarly journals Comparison of Substituting Ability of Nitronate versus Enolate for Direct Substitution of a Nitro Group

Molecules ◽  
2020 ◽  
Vol 25 (9) ◽  
pp. 2048 ◽  
Author(s):  
Yusuke Mukaijo ◽  
Soichi Yokoyama ◽  
Nagatoshi Nishiwaki
Keyword(s):  
Nucleophilic Substitution ◽  
Nitro Group ◽  
Conjugate Addition ◽  
Ring Closure ◽  
Dicarbonyl Compounds ◽  
Dicarbonyl Compound ◽  
Direct Substitution ◽  
Electron Withdrawing Group ◽  
Active Methylene

α-Nitrocinnamate underwent the conjugate addition of an active methylene compound such as nitroacetate, 1,3-dicarbonyl compound, or α-nitroketone, and the following ring closure afforded functionalized heterocyclic frameworks. The reaction of cinnamate with nitroacetate occurs via nucleophilic substitution of a nitro group by the O-attack of the nitronate, which results in isoxazoline N-oxide. This protocol was applicable to 1,3-dicarbonyl compounds to afford dihydrofuran derivatives, including those derived from direct substitution of a nitro group caused by O-attack of enolate. It was found the reactivity was lowered by an electron-withdrawing group on the carbonyl moiety. When α-nitroketone was employed as a substrate, three kinds of products were possibly formed; of these, only isoxazoline N-oxide was identified. This result indicates that the substituting ability of nitronate is higher than that of enolate for the direct SN2 substitution of a nitro group.

ChemInform Abstract: RULES FOR RING CLOSURE- RING FORMATION BY CONJUGATE ADDITION OF OXYGEN NUCLEOPHILES

1978 ◽  
Vol 9 (14) ◽  
Author(s):  
J. E. BALDWIN ◽  
R. C. THOMAS ◽  
L. I. KRUSE ◽  
L. SILBERMAN
Keyword(s):  
Conjugate Addition ◽  
Ring Formation ◽  
Ring Closure
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