Premium
Dynamic Solvation Effects in Ethylmagnesium Bromide Addition to (2 S )‐ O ‐( tert ‐Butyldimethylsilyl)lactal
Author(s) -
Cainelli Gianfranco,
Giacomini Daria,
Galletti Paola,
Orioli Paolo
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200112)2001:23<4509::aid-ejoc4509>3.0.co;2-8
Subject(s) - chemistry , selectivity , diethyl ether , diastereomer , anisole , ether , tetrahydrofuran , medicinal chemistry , tetrahydropyran , solvent , solvent effects , organic chemistry , solvation , catalysis , ring (chemistry)
The diastereofacial selectivity of (2 S )‐ O ‐( tert ‐butyldimethylsilyl)lactal towards nucleophilic addition of ethylmagnesium bromide is strongly solvent‐dependent. We have shown that solute−solvent interactions occurring in a series of ethers, such as tetrahydrofuran, tetrahydropyran, diethyl ether, dipentyl ether, tert ‐butyl methyl ether, diisopropyl ether, diisopentyl ether, and anisole, can govern a diastereomeric switch from the anti to the syn isomer. Determination of the temperature‐dependence of the anti / syn ratio has enabled the selectivity to be analysed in terms of the differential enthalpies and entropies of activation of the two diastereomeric reaction paths. We have demonstrated that the predominance of one isomer over the other is often due to an entropy effect on the diastereofacial selectivity. The phenomenon of the inversion temperature was evident in the corresponding Eyring plots.