Silyloxycarbamate nucleophile

Imidazolidinone (94.pTSA) has been developed as an enantioselective organocata-lyst for the addition of various silyloxycarbamate nucleophiles (e.g. BnOCONHOTBS, having a raised HOMO) to a range of a,/3-unsaturated aldehydes RCH=CHCH=0, affording /i-aminoaldehydes (96) (<96% ee), which can be converted into /3-amino acids (97) in two steps. The reaction proceeds via the corresponding iminium species (95) with a lowered LUMO.144... 

Mac Millan and coworkers used a multicatalytic system composed of the imi-dazolidinone 8 and d- or L-proline for the diamination and the amino oxidation of crotonaldehyde [16]. Similar to the aryl- and alkylamination, the syn or the anti diastereomers were obtained in a stereoselective manner by using the catalyst combination containing l- or D-proline (dr up to 1/17) (Scheme 12.15). The cascade catalysis provided enantioselective access to differentially protected 1,2-diaminated products 34 and 35 by the use of a silyloxycarbamate in conjunction with dibenzyla-zodicarboxylate (yield 84-87%, ee 99%). A similar amine nucleophile was employed in a cascade catalysis sequence with nitrosobenzene to afford the 3-amino-2-hydroxy alcohols (yield 71-74%, ee 99%). 

Despite this early success, it was not until 2006 that MacMillan reported the first highly enantioselective intermolecular aza-Michael addition to enals [51]. In this work, MacMillan reported the use of N-silyloxycarbamates as nucleophiles. The N-O functionality would increase the nucleophUidty at the nitrogen center via the ct-effect, while the carbamate functionahty would decrease the basicity of the... 

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