Chelation Controlled Aza-Claisen Rearrangements

In contrast to the well-investigated chelation controlled ester enolate Claisen rear-rangments, the corresponding rearrangement of N-allylated amides is much less appUed. Tsunoda et al. evaluated the synthetical potential of N-crotyl glycolamides and glycinamides 215 [125] and the results obtained are listed in Table 5.2.23. 

Excellent syn diastereoselectivities were observed for nearly all cases. The presence of an OH or NH2 group at the )S-position (entries 2 and 3) facilitated the rearrangement in comparison to unfunctionalized carboxamides (entry 1), possibly 

The substrate-induced diastereoselectivity was investigated using an (R)- or (S)-1-phenylethyl group as a chiral auxiliary on the amide nitrogen. The reactions with the unprotected compounds went smoothly and diastereomeric mixtures were obtained in excellent yield and syn diastereoselectivity ( 99% syn) (entries 6-8). The results were better than those obtained with the butylamides. The facial selectivity was in the range of about 8 1. The protection of the hydroxyl group lowered both the facial selectivity and the yield (entry 8). 

1 General reviews on [3,3]-sigmatropic rearrangements, including stereochemical aspects a) S. J. Rhoads, N. R. Raulins, Org. React. 1975, 22, 1-252  

Altenbach, M. Braun, K. Krohn, H.-U. Reissig (eds.) Wiley-VCH, Wein-heim, 1991, p lllf, p 116f i) S. Pereira, M. Srebnik, Aldrichimica Acta 1993, 26, 17 k) H. Frauenrath in Houben-Weyl E 21dG. Helmchen, R. W. Hoffmann, 

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