Ketimines enolizable

Enantiomerically pure /3-nitroamines of enolizable aldimines and ketimines have been accessed via a diastereoselective aza-Henry reaction of A-sulfinylimines and nitromethane.37 The reaction is catalysed by sodium hydroxide, but also by tetrabuty-lammonium fluoride, the latter species giving an inversion of stereochemistry. An CT -+N contact ion pair is proposed in the ammonium-catalysed route. 

The Maillard reaction is best known as the phenomenon responsible for the browning of untreated foodstuffs, by non-enzymic oxidation. It involves the condensation of amino acids on sugars, both aldoses (glucose) and ketoses (fructose) (Figure 8.27). When aldoses are involved, the primary condensation products are aldimines (Rj = H) (or Schiff base), while ketoses produce ketimine (Ri H). Due to their enoliz-able character, these imines develop according to two tautomeric equilibriums into enaminol and... 

The modification of the Peterson reaction using an N-trimethylsilylamide anion instead of an a-silyl carbanion offers a promising route to the corresponding imines. Treatment of N-(p-tolyl)-N-trimethylsilylamide anion with carbonyl compounds yields the corresponding ketimines [400]. In particular, LiHMDS has been utilized for the preparation of N-trimethylsilylimines, which are useful as masked imine derivatives in the synthesis of yS-lactam antibiotics [401-407]. Reactions of LiHMDS with non-enolizable aldehydes, enolizable aldehydes, ketones, a diketone, and a-keto esters give the respective imines (Scheme 2.153) [408-413]. Chloro-trimethylsilane is added to convert the generated lithium trimethylsilanolate into hexamethyldisiloxane. 

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