Crystalline derivatives preparation imides

In all cases except (2) the nitrogen is part of an imide system which forms a chelate complex after deprotonation to the enolate. We used a different approach by using the N,O-acetals 35/36. This was first performed in racemic form to test the diastereose-lectivity of the enolate alkylation (Scheme 8). The diastereomers 35 and 36 are readily separable by chromatography. Analogously, amides 35a and 36a are prepared from O-jV-Boc-amino benzaldehyde. Derivative 36a is crystalline and was submitted to an X-ray crystal structure analysis (Fig. 1). 

Wanzlick et al. were the first to attempt the preparation of saturated imid-azolin-2-ylidenes by a-elimination of chloroform from imidazoline derivatives. They could, however, only isolate the electron-rich entetraamines (see Scheme 1.2). It was Arduengo et al who presented the first stable crystalline... 

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