Abstract
The synthesis of optically active sulfinic acid esters has been accomplished by the acid catalyzed alcoholysis of optically active sulfinamides. Sulfinates are formed in this reaction with a full or predominant inversion of configuration at chiral sulfur or with predominant retention of configuration. The steric course of the reaction depends mainly on the size of the dialkylamido group in the sulfinamides and of the alcohols used as nucleophilic reagents. It has been found that bulky reaction components preferentially form sulfinates with retention of configuration. It has been demonstrated that the stereochemical outcome of the reaction can be changed from inversion to retention and vice versa by adding inorganic salts to the acidic reaction medium. The unusual stereochemistry of this typical bimolecular nucleophilic substitution reaction, as confirmed by kinetic measurements, has been rationalized in terms of the addition-elimination mechanism, A-E, involving sulfuranes as intermediates which undergo pseudorotations.
Highlights
The mechanism and stereochemistry of nucleophilic substitution reactions at sulfur, SN-S, as well as at other heteroatoms (P, Si, Se, etc.), have been a subject of extensive studies of many research groups in recent decades [1]
Before discussing the mechanism of the acid catalyzed alcoholysis of sulfinamides it is necessary to emphasize that the stereochemistry of this reaction studied with optically active sulfinamides shows unique features
It was found that optically active sulfinates are formed with a full or predominant inversion or predominant retention of configuration at stereogenic sulfur
Summary
The mechanism and stereochemistry of nucleophilic substitution reactions at sulfur, SN-S, as well as at other heteroatoms (P, Si, Se, etc.), have been a subject of extensive studies of many research groups in recent decades [1]. Possible mechanisms for nucleophilic substitution reactions at sulfur. The second closely related problem is connected with the relationship between the structure of transiently formed sulfuranes and the stereochemical outcome of nucleophilic substitution reactions. It is generally accepted that diaxial or diequatorial disposal of entering, N, and leaving, L, groups in a trigonal bipyramidal structure of transient sulfurane intermediates should lead to inversion of configuration at sulfur while the steric course of axial-equatorial substitution is predicted to be retention. It is generally accepted that diaxial or diequatorial disposal of entering, N, and leaving, L, groups in a trigonal bipyramidal structure of transient sulfurane intermediates should lead to inversion of configuration at sulfur while the steric course of axial-equatorial substitution is predicted to be retention. (Scheme 2)
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