Dimethylcarbodi-imide. Improved synthesis, cyclic trimer, and reaction with α-hydroxy-esters

1971 ◽  
Vol 0 (0) ◽  
pp. 3827-3829 ◽  
Author(s):  
G. Rapi ◽  
G. Sbrana ◽  
N. Gelsomini
Keyword(s):  
Cyclic Trimer ◽  
Hydroxy Esters

Diastereoselective Reduction of Selected α-substituted β-keto Esters and the Assignment of the Relative Configuration by 1H-NMR Spectroscopy

2020 ◽  
Vol 07 ◽  
Author(s):  
Christian Trapp ◽  
Corinna Schuster ◽  
Chris Drewniok ◽  
Dieter Greif ◽  
Martin Hofrichter
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
1H Nmr Spectroscopy ◽  
Selective Reduction ◽  
Reducing Agents ◽  
Relative Configuration ◽  
Curtius Rearrangement ◽  
Keto Esters ◽  
Hydroxy Esters ◽  
Diastereoselective Reduction

Background:: Chiral β-hydroxy esters and α-substituted β-hydroxy esters represent versatile building blocks for pheromones, β-lactam antibiotics and 1,2- or 1,3-aminoalcohols. Objective:: Synthesis of versatile α-substituted β-keto esters and their diastereoselective reduction to the corresponding syn- or anti-α-substituted β-hydroxy esters. Assignment of the relative configuration by NMR-spectroscopy after a CURTIUS rearrangement of α-substituted β-keto esters to 4-substituted 5-methyloxazolidin-2-ones. Method:: Diastereoselective reduction was achieved by using different LEWIS acids (zinc, titanium and cerium) in combination with complex borohydrides as reducing agents. Assignment of the relative configuration was verified by 1H-NMR spectroscopy after CURTIUS-rearrangement of α-substituted β-hydroxy esters to 4-substituted 5-methyloxazolidin-2-ones. Results:: For the syn-selective reduction, titanium tetrachloride (TiCl4) in combination with a pyridine-borane complex (py BH3) led to diastereoselectivities up to 99% dr. High anti-selective reduction was achieved by using cerium trichloride (CeCl3) and steric hindered reducing agents such as lithium triethylborohydride (LiEt3BH). After CURTIUS-rearrangement of each α-substituted β-hydroxy ester to the corresponding 4-substituted 5-methyloxazolidin-2-one, the relative configuration was confirmed by 1H NMR-spectroscopy. Conclusion:: We have expanded the procedure of LEWIS acid-mediated diastereoselective reduction to bulky α-substituents such as the isopropyl group and the electron withdrawing phenyl ring.

Bu4N+-Controlled Addition and Olefination with Ethyl 2-(Trimethylsilyl)acetate via Silicon Activation

Synlett ◽  
2017 ◽  
Vol 28 (18) ◽  
pp. 2401-2406 ◽  
Author(s):  
Donal O’Shea ◽  
Manas Das ◽  
Atul Manvar ◽  
Ian Fox ◽  
Dilwyn Roberts
Keyword(s):  
Room Temperature ◽  
Product Formation ◽  
Unsaturated Ester ◽  
Reaction Conditions ◽  
Diverse Range ◽  
Inorganic Cation ◽  
Tetrabutyl Ammonium ◽  
Aldehydes And Ketones ◽  
Subsequent Elimination ◽  
Hydroxy Esters

Catalytic Bu4NOAc as silicon activator of ethyl 2-(trimethylsilyl)acetate, in THF, was utilized for the synthesis of β-hydroxy esters, whereas employing catalytic Bu4NOTMS gave α,β-unsaturated esters. The established reaction conditions were applicable to a diverse range of aromatic, heteroaromatic, aliphatic aldehydes and ketones. Reactions were achieved at room temperature without taking any of the specialized precautions that are in place for other organometallics. A stepwise olefination pathway via silylated β-hydroxy esters with subsequent elimination to form the α,β-unsaturated ester has been demonstrated. The key to selective product formation lies in use of the weaker acetate activator which suppresses subsequent elimination whereas stronger TMSO– activator (and base) facilitates both addition and elimination steps. The use of tetrabutyl ammonium salts for both acetate and trimethylsilyloxide activators provide enhanced silicon activation when compared to their inorganic cation counterparts.

Substituent and catalyst effects on GAC lactonization of γ-hydroxy esters

2017 ◽  
Vol 7 (7) ◽  
pp. 1497-1507 ◽  
Author(s):  
Elisabetta Brenna ◽  
Francesco Distante ◽  
Francesco G. Gatti ◽  
Giuseppe Gatti
Keyword(s):  
Leaving Group ◽  
Hydroxy Esters

The effect of catalyst, substituent and leaving group on reactivity was probed experimentally and computationally rationalized.

ChemInform Abstract: Preparation of α-Bromo-β-hydroxy Esters Using MgBr2·OEt2.

ChemInform ◽  
2016 ◽  
Vol 47 (4) ◽  
pp. no-no
Author(s):  
Brandin Lieberman ◽  
Adi Cohen ◽  
Aaron Schechter ◽  
Daniel Lim
Keyword(s):  
Hydroxy Esters

ChemInform Abstract: Asymmetric Dehydration of β-Styryl-β-hydroxy Esters and Application to the Synthesis of a Neoflavonoid.

ChemInform ◽  
2008 ◽  
Vol 39 (34) ◽  
Author(s):  
Eui Ta Choi ◽  
Kyoung Hee Kang ◽  
Min Hee Lee ◽  
Yong Sun Park
Keyword(s):  
Hydroxy Esters
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