Allylsilane-Modified Amino Acids from the Claisen Rearrangement

✍ Scribed by Mustafa Mohamed; Michael A. Brook

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: German
• Weight: 180 KB
• Volume: 85
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200290002

✦ Synopsis

Abstract

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.