Ketene acetals, with mines

Table 4 Ratio of Diastereoisomers in the Lewis Acid Mediated Reactions of Silyl Ketene Acetals with (mines...

To address the design criteria listed above, Kobayashi and co-workers prepared the mildly Lewis acidic zirconium[BINOL]2 complexes 78a,b from Zr(Of-Bu)4and (i )-BINOL and theimines 76 derived from 2-aminophenol [51a, 51b, 51c, 51d] (Scheme 26). In the presence of catalytic amounts of 78a the tri-methylsilyl ketene acetal of methyl 2-methylpropanoate (77) reacted with 76a to afford the adduct 79 quantitatively and with 34% ee. The use of N-methylim-idazole (NMI) in equal amoimts markedly improved the selectivity to 70% ee as did the use of 78b which provided 79 in 90% ee. By chemical correlation the products were shown to be of the i -configuration. The reaction displayed some generality with aromatic aldimines (83-98% ee), but the one enoHzable aldi-mine gave only modest results (56% yield, 80% ee) [51e]. 

The methods for generating acyl ketenes (Scheme 7-V) and their subsequent in situ participation in [4 + 2] cycloadditions with a wide range of hetero- or olehnic and acetylenic dienophiles (Scheme 7-VI), including acyl ketenes, carbonyl compounds,nitriles,isocyanates and isothiocyanates,ketenes,(mines,carbo-diimides, ynamines, ketene acetals, enol ethers,and V-sulfinylamines have been extensively reviewed.Two reports have detailed the 4tt participation of allenic ketones in [4 + 2] cycloaddition reactions [Eq. (51)]. ... 

Highly enantioselective Mannich-type reactions of A-(2-hydroxyphenyl) aldi-mines with ketene trimethylsilyl acetals and of A-Boc-aldimines with acetyl acetone or furan are catalyzed by chiral phosphonic acids 9 derived from 3,3 -diaryl-(l )-BlNOL and POCI3 (Scheme 12.7). ... 

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