Silyl Nitronates reactions with amines

The TiCU-mediated reaction of enol silanes with imines was first introduced by Ojima and coworkers in 1977. The reaction was then extended to several similar substrates, i.e. nitrones, ot-methoxycarba-mates, aminals, 4-acetoxyazetidin-2-one, 40 anj to different Lewis acids, i.e. SnCU, TiCU-(0PH)2, catalytic ZnX2, catalytic TMSOTf, ° to give good yields of the addition products with low levels ( 80 20) or a complete lack of simple stereoselection. Moderate to good anti selectivities were reported in the addition of silyl ketene acetals to imines under particular reaction conditions (equation 9) significant results are summarized in Table 4. 

L-Daunosamine (166) (R=H), (3-amino-2,3,6-trideoxy-L-/yxo-hexose), is an essential component of both natural and unnatural anthracycline antitumor agents. The 1,3-addition of ketene silyl acetal 164 to the chiral nitrone (Z)-[(4i )- ra 5-2,2,5-trimethyl-l,3-dioxolan-4-yl]methylene[(l S)-l-phenylethyl] amine 7V-oxide (163), prepared by the conversion of 141 to 103 [62] and then reaction of 103 with the hydroxylamine 162, provides the 0-silylated addition product 165 in quantitative yield with an anti relative stereochemistry at C-3 and C-4 (anti syn =>100 1). Efficient transformation of 165 to 166 (R=COPh) is achieved in three steps [63] (Scheme 39). 

The Mannich reaction and its variants have been reviewed, mainly focussing on asymmetric catalysis thereof. Catalytic, enantioselective, vinylogous Mannich reactions have also been reviewed, covering both direct and silyl dienolate methods. Another review surveys Mannich-type reactions of nitrones, oximes, and hydrazones. A pyrrolidine-thiourea-tertiary amine catalyses asymmetric Mannich reaction of N-Boc-imines (e.g. Ph-Ch=N-Boc) with ethyl-4-chloro-3-oxobutanoate to give highly functionalized product (16). Addition of triethylamine leads to one-pot intramolecular cyclization to give an 0-ethyl tetronic acid derivative (17). ... 

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