Efficient synthesis of β-halogeno protected l-alanines and their β-phosphonium derivatives

✍ Scribed by Franck Meyer; Abdelhamid Laaziri; Anna Maria Papini; Jacques Uziel; Sylvain Jugé

• Book ID: 104359969
• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 265 KB
• Volume: 14
• Category: Article
• ISSN: 0957-4166
• DOI: 10.1016/s0957-4166(03)00484-1

✦ Synopsis

Ring opening of oxazolines, prepared from L-serinates, with trimethylsilyl halides (TMSX) led to b-halogeno-N-benzoyl-a-amino esters in good to excellent yields. Quaternization of triphenylphosphine by the b-bromo or -iodo amino esters gave the corresponding b-phosphonium salts in overall yields of up to 93% and with e.e. >96%. Hydrolysis of the ester function afforded the phosphonium salt bearing an N-benzoyl-a-amino acid substituent, with partial racemization. However, the reaction of the TMSX with the carboxylic salt, prepared by saponification of the starting oxazoline ester, furnished the corresponding b-halogeno-N-benzoyl-a-amino acids in 70-95% yields. Quaternization of triphenylphosphine by the bromo or iodo derivatives led to the phosphonium salts bearing a free acid function in 95% yield, without racemization. The efficiency of this synthesis was demonstrated by the preparation of these phosphonium salts in excellent overall yields, by a one-pot procedure starting from the oxazoline.