Introduction
One of the most important sections of modern organic chemistry is asymmetric synthesis,
and in this field particularly attractive are problems relating to asymmetric catalysis.
In the recent two decades, special attention is focused on (S )-proline and its derivatives, which are known as versatile organocatalysts (‘aminocatalysts’).[1 ]
[2 ] It was found that the introduction of the protecting silyl moiety into the prolinol
structure results in a remarkable increase of catalytic activity, thus allowing decrease
in catalyst loading and shorter reaction times without compromising the level of enantioselectivity.[
3
] In addition, this modification leads to significant broadening of the substrate
scope. First examples of applications of the O -silyl prolinol derivatives in asymmetric synthesis were independently reported by
Hayashi[
3
] and Jørgensen.[
4
] Since then these compounds have been used efficiently as ‘privileged catalysts’[
2b
] in diverse organic transformations, such as epoxidations, aldol, anti -selective Mannich, Friedel–Crafts and Diels–Alder reactions, etc.[5 ]
[6 ] Probably, the most prominent representative of diarylprolinol derivatives containing
the silyl moiety is (S )-α,α-diphenylprolinol trimethylsilyl ether (1 ).
Preparation
A straightforward synthesis of compound 1 is based on the O-protection of commercially available (S )-α,α-diphenylprolinol (2 ) with trimethylsilyl chloride (3 ) at room temperature in the presence of imidazole.[
7
]
Scheme 1
