Stereoisomerization of β-Hydroxy-α-sulfenyl-γ-butyrolactones Controlled by Two Concomitant 1,4-Type Nonbonded Sulfur−Oxygen Interactions As Analyzed by X-ray Crystallography
摘要:
We have synthesized nine beta-hydroxy-alpha-sulfenyl-gamma-butyrolactones having different substituents. The syn-anti or syn-syn lactones (or any mixture of both) invariably isomerized into syn-anti/syn-syn lactones in a ratio of similar to 6/4. The other two possible isomeric lactones (anti-syn or anti-anti) were never observed. The crystal structures of syn-syn lactones have been determined. We found sulfur-oxygen distances to be less than the sum of the van der Waals radii (3.3 angstrom), with the angle formed among the hydroxylic oxygen, sulfur, and quaternary aromatic carbon being close to 180 degrees. In addition, carbonylic oxygen-sulfur is directed <40 degrees from the perpendicular to the C-S-C. Theoretical calculations were performed which emphasize the directionality of the sulfur-oxygen interaction. The X-ray and theoretical studies demonstrate that two concomitant, attractive 1,4 intramolecular interactions of divalent sulfur with both carbonyl and hydroxyl oxygens are the driving force for the aforementioned stereochemical preference. Then nonbonded sulfur-oxygen interactions would control the stereoselectivity of the reaction. The same features are observed in the X-ray structure of a beta-hydroxy-alpha-sulfinyl-gamma-butyrolactone.
Highly Stereoselective Epoxidation of α-Methyl-γ-hydroxy-α,β-unsaturated Esters: Rationalization and Synthetic Applications
摘要:
The diastereoselectivity of the nucleophilic epoxidation of gamma-hydroxy-alpha, beta-unsaturated esters having a methyl substituent at the alpha- or beta-position was investigated. Epoxidation of the alpha-methyl-substituted enoate was highly stereoselective, giving rise to the syn isomer. This finding was used to perform an enantioselective synthesis of a natural product having a beta-hydroxy-alpha-methylene-gamma-butyrolactone motif. The nucleophilic epoxidation of enoates was found to be irreversible. Models to explain the observed stereoselectivities are proposed.
Highly Stereoselective Epoxidation of α-Methyl-γ-hydroxy-α,β-unsaturated Esters: Rationalization and Synthetic Applications
作者:Irakusne López、Santiago Rodríguez、Javier Izquierdo、Florenci V. González
DOI:10.1021/jo0709955
日期:2007.8.1
The diastereoselectivity of the nucleophilic epoxidation of gamma-hydroxy-alpha, beta-unsaturated esters having a methyl substituent at the alpha- or beta-position was investigated. Epoxidation of the alpha-methyl-substituted enoate was highly stereoselective, giving rise to the syn isomer. This finding was used to perform an enantioselective synthesis of a natural product having a beta-hydroxy-alpha-methylene-gamma-butyrolactone motif. The nucleophilic epoxidation of enoates was found to be irreversible. Models to explain the observed stereoselectivities are proposed.
Stereoisomerization of β-Hydroxy-α-sulfenyl-γ-butyrolactones Controlled by Two Concomitant 1,4-Type Nonbonded Sulfur−Oxygen Interactions As Analyzed by X-ray Crystallography
作者:Florenci V. González、Amit Jain、Santiago Rodríguez、José A. Sáez、Cristian Vicent、Gabriel Peris
DOI:10.1021/jo1009454
日期:2010.9.3
We have synthesized nine beta-hydroxy-alpha-sulfenyl-gamma-butyrolactones having different substituents. The syn-anti or syn-syn lactones (or any mixture of both) invariably isomerized into syn-anti/syn-syn lactones in a ratio of similar to 6/4. The other two possible isomeric lactones (anti-syn or anti-anti) were never observed. The crystal structures of syn-syn lactones have been determined. We found sulfur-oxygen distances to be less than the sum of the van der Waals radii (3.3 angstrom), with the angle formed among the hydroxylic oxygen, sulfur, and quaternary aromatic carbon being close to 180 degrees. In addition, carbonylic oxygen-sulfur is directed <40 degrees from the perpendicular to the C-S-C. Theoretical calculations were performed which emphasize the directionality of the sulfur-oxygen interaction. The X-ray and theoretical studies demonstrate that two concomitant, attractive 1,4 intramolecular interactions of divalent sulfur with both carbonyl and hydroxyl oxygens are the driving force for the aforementioned stereochemical preference. Then nonbonded sulfur-oxygen interactions would control the stereoselectivity of the reaction. The same features are observed in the X-ray structure of a beta-hydroxy-alpha-sulfinyl-gamma-butyrolactone.