The configurational stability of some lithiated fluorinated styrene oxides has been investigated. Chemical studies have shown that in ethereal solvents α-lithiated ortho-, meta-, and para-fluorostyrene oxides (2-Li, α-5-Li, and α-6-Li) are all configurationally stable in the reaction time scale, whereas a-lithiated ortho-, meta-, and paratrifluoromethylstyrene oxides (9-Li, 13-Li, and 14-Li) are configurationally unstable. Optically active oxiranyllithiums 2-Li and 9-Li, could be stereospecifically generated and quenched with electrophiles. The corresponding derivatives were then successfully subjected to regiospecific ring-opening reactions with amines to give fluorinated ßamino alcohols with a stereodefined quaternary carbinol center, which are useful synthons in medicinal chemistry. The barriers of inversion have been calculated (Eyring equation) for oxiranyllithiums 9-Li, 13-Li, and 14-Li by determining the enantiomeric ratios after electrophilic quenching on aging the enantioenriched organolithium for different times in THF; in the case of 9-Li, activation parameters have also been determined. Mechanisms that may be responsible of the racemization oxiranyllithiums 9-Li, 13-Li, and 14-Li undergo once generated are also discussed.
Lithiated Fluorinated Styrene Oxides: Configurational Stability, Synthetic Applications, and Mechanistic Insight
CAPRIATI, Vito;PERNA, FILIPPO;Salomone, A.
2010-01-01
Abstract
The configurational stability of some lithiated fluorinated styrene oxides has been investigated. Chemical studies have shown that in ethereal solvents α-lithiated ortho-, meta-, and para-fluorostyrene oxides (2-Li, α-5-Li, and α-6-Li) are all configurationally stable in the reaction time scale, whereas a-lithiated ortho-, meta-, and paratrifluoromethylstyrene oxides (9-Li, 13-Li, and 14-Li) are configurationally unstable. Optically active oxiranyllithiums 2-Li and 9-Li, could be stereospecifically generated and quenched with electrophiles. The corresponding derivatives were then successfully subjected to regiospecific ring-opening reactions with amines to give fluorinated ßamino alcohols with a stereodefined quaternary carbinol center, which are useful synthons in medicinal chemistry. The barriers of inversion have been calculated (Eyring equation) for oxiranyllithiums 9-Li, 13-Li, and 14-Li by determining the enantiomeric ratios after electrophilic quenching on aging the enantioenriched organolithium for different times in THF; in the case of 9-Li, activation parameters have also been determined. Mechanisms that may be responsible of the racemization oxiranyllithiums 9-Li, 13-Li, and 14-Li undergo once generated are also discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
