Introduction: Analogous to carbon-carbon and carbon-oxygen
double bonds, carbon-nitrogen double bond has been an active site
of study in recent times. The reactivity of the carbon-nitrogen
double bond lies in between that of the carbonyl and olefinic functions.
The carbon-nitrogen double bond has an additional lone
pair of electrons which leads to its distinctive properties from
carbon-carbon double bond.
N -Sulfonylimine
[¹ ]
(also
known as sulfonylimine) is one such good example of azomethenic
carbon-nitrogen double bond. N -Sulfonylimines
are useful precursors for the synthesis of important synthetic intermediates
such as oxaziridines
[² ]
and
aziridines
[³ ]
as well as
for the synthesis of compounds of medicinal importance.
[4-5 ]
N -Sulfonylimines
also serves as heterodienes and heterodienophiles in [4+2] cycloadditions.
[6 ]
Preparation:
N -Sulfonylimines can be synthesised
by direct condensation of primary sulfonamides with aldehydes or
ketones in the presence of some dehydrating agents (TiCl4 ,
4 Å molecular sieve, MgSO4 , AlCl3 ).
[² ]
[7-9 ]
However,
only few methods are reported for the preparation of N -Sulfonylimines of enolizable and sterically
hindered ketones. Such reactions involve the in situ generation
of oxime O -sulfinyl derivatives
[¹0 ]
and their subsequent
homolytic rearrangement to sulfonylimines. Recently, a simple method has
been reported which involves the condensation of simple as well
as hindered ketones with 4-toluenesulfonamides in the
presence of TiCl4 and Et3 N.
[¹¹ ]
Scheme 1