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Silicon makes the difference! In contrast to known imines from alkyl- or arylamines, imines derived from C,C-bis(trimethylsilyl)methylamine and enolizable aldehydes react, as shown below, with ketenes to afford exclusively β-lactams. Furthermore, the reaction is highly diastereoselective when asymmetric ketenes are used.
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Palomo et al. (1996) studied this question.
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