Allylsilane‐Modified Amino Acids from the Claisen Rearrangement

The Claisen rearrangement of the N ‐protected, silylated allyl glycinates 11 and 12 led to the formation of allyl/silyl‐functionalized amino acids 13 and 14 in yields up to 80%. The diastereoisomer ratio varied from 2 : 1 to 29 : 1 for 11mb , and from 2 : 1 to 46 : 1 ( syn / anti ) for 12mb , depending on reaction conditions, as shown by X‐ray crystallographic analysis of 14mb . The relationship between the size of the alkyl groups on the chlorosilane reagent (Me 2 R″SiCl, R″=Cl, Me, t ‐Bu, Ph) used as an enolate trap and the observed stereoselectivity was investigated in the case of the Ireland – Claisen variant. Me 3 SiCl gave the best results. However, the size of the alkyl groups on the silylated ester (Me 2 R″Si, R=Me, t ‐Bu, Ph, i‐Pr) did not exert a significant effect on the diastereoselectivity or yield of the rearrangement.