Asymmetric Synthesis using Organoboranes. Relative Effectiveness of the B-Halobis(terpenyl)boranes for the Enantioselective Halogenative Cleavage of Representative meso-Epoxides

2007 ◽  
Vol 60 (11) ◽  
pp. 835 ◽  
Author(s):  
Chandra D. Roy ◽  
Herbert C. Brown
Keyword(s):  
Comparative Study ◽  
Asymmetric Synthesis ◽  
Ring Opening ◽  
Relative Effectiveness ◽  
Enantiomeric Excess ◽  
Significant Advance ◽  
Cyclohexene Oxide ◽  
Asymmetric Ring Opening

A comparative study of the relative effectiveness of various Ter2BX, such as dEap2BX, lEap2BX, 2-dIcr2BX, 4-dIcr2BX, and lCleap2BX along with dIpc2BX for the asymmetric ring opening of three representative meso-epoxides (cyclohexene, cyclopentene, and cis-2,3-butene oxides) is reported. Among all the reagents studied, 2-dIcr2BCl (78–80%) demonstrated significant improvement in enantiomeric excess over a previously explored reagent, dIpc2BCl (41%), especially for meso-cyclohexene oxide. Although all these three reagents, dIpc2BBr, dEap2BBr, and 2-dIcr2BBr provided comparable enantiomerically enriched 2-bromocyclohexan-1-ol (76–86%) from meso-cyclohexene oxide, the carene-based reagent, 2-dIcr2BBr showed considerable improvements in enantiomeric excesses in the cases of meso-cyclopentene oxide (67%) and meso-cis-2,3-butene oxide (78%) than those achieved with previously reported reagent, dIpc2BBr (57 and 61% respectively). The enantioselectivity of the reaction was observed to be highly substrate dependent. The present study represents a significant advance in asymmetric synthesis using the chiral organoborane chemistry.

ASYMMETRIC RING-OPENING OF CYCLOHEXENE OXIDE WITH VARIOUS THIOLS CATALYZED BY ZINCLq-TARTRATE

1985 ◽  
Vol 14 (11) ◽  
pp. 1643-1646 ◽  
Author(s):  
Hiroyuki Yamashita ◽  
Teruaki Mukaiyama
Keyword(s):  
Ring Opening ◽  
Cyclohexene Oxide ◽  
Asymmetric Ring Opening

Synthesis of Novel Chiral (Thio)ureas and Their Application as Organocatalysts and Ligands in Asymmetric Synthesis

2008 ◽  
Vol 61 (5) ◽  
pp. 364 ◽  
Author(s):  
Marcos Hernández-Rodríguez ◽  
Claudia Gabriela Avila-Ortiz ◽  
Jorge M. del Campo ◽  
Delia Hernández-Romero ◽  
María J. Rosales-Hoz ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Asymmetric Synthesis ◽  
Carbonyl Group ◽  
Ring Opening ◽  
Enantiomeric Excess ◽  
Quantitative Yield ◽  
Epoxide Ring ◽  
Chiral Auxiliaries ◽  
Epoxide Ring Opening

The synthesis of novel chiral (thio)ureas 1–10 and 14–26 is described. These (thio)ureas incorporate chiral auxiliaries derived from (R)- or (S)-α-phenylethylamine, (R)-phenylglycine, or (1R,2S)-ephedrine. The phenylethyl group in compounds 1–10 and 21–24 adopts a particular orientation in the molecular structure as a consequence of 1,3-allylic strain with the (thio)carbonyl group. Ureas 1–10 were tested as Lewis basic organocatalysts in epoxide ring opening and in aldolic condensation, and it was found that the tetrasubstituted urea (R,R)-2 afforded the best results in terms of reaction yields. (Thio)ureas 20–26 were examined as ligands in the enantioselective diethylzinc addition to benzaldehyde, observing that C2-symmetric chiral urea (R,S,R,S)-20 provides the expected carbinol in nearly quantitative yield and in up to 62% enantiomeric excess.

scholarly journals Ring-Opening Copolymerization of Cyclohexene Oxide and Cyclic Anhydrides Catalyzed by Bimetallic Scorpionate Zinc Catalysts

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1651
Author(s):  
Felipe de la Cruz-Martínez ◽  
Marc Martínez de Sarasa Buchaca ◽  
Almudena del Campo-Balguerías ◽  
Juan Fernández-Baeza ◽  
Luis F. Sánchez-Barba ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Reaction Mechanism ◽  
Catalytic System ◽  
Phthalic Anhydride ◽  
Ring Opening ◽  
High Selectivity ◽  
Zinc Complexes ◽  
Cyclohexene Oxide ◽  
Reaction Conditions ◽  
Cyclic Anhydrides

The catalytic activity and high selectivity reported by bimetallic heteroscorpionate acetate zinc complexes in ring-opening copolymerization (ROCOP) reactions involving CO2 as substrate encouraged us to expand their use as catalysts for ROCOP of cyclohexene oxide (CHO) and cyclic anhydrides. Among the catalysts tested for the ROCOP of CHO and phthalic anhydride at different reaction conditions, the most active catalytic system was the combination of complex 3 with bis(triphenylphosphine)iminium as cocatalyst in toluene at 80 °C. Once the optimal catalytic system was determined, the scope in terms of other cyclic anhydrides was broadened. The catalytic system was capable of copolymerizing selectively and efficiently CHO with phthalic, maleic, succinic and naphthalic anhydrides to afford the corresponding polyester materials. The polyesters obtained were characterized by spectroscopic, spectrometric, and calorimetric techniques. Finally, the reaction mechanism of the catalytic system was proposed based on stoichiometric reactions.

Iridium-Catalyzed Anti-Stereoselective Asymmetric Ring-Opening Reactions of Azabenzonorbornadienes with Carboxylic Acids

2017 ◽  
Vol 82 (6) ◽  
pp. 3167-3172 ◽  
Author(s):  
Meina Zhu ◽  
Jingchao Chen ◽  
Xiaobo He ◽  
Cuiping Gu ◽  
Jianbin Xu ◽  
...  
Keyword(s):  
Carboxylic Acids ◽  
Ring Opening ◽  
Ring Opening Reactions ◽  
Asymmetric Ring Opening
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