Base-promoted diastereoselective α-alkylation of borane <i>N</i>-((<i>S</i>)-1′-phenylethyl)azetidine-2-carboxylic acid ester complexes
作者:Eiji Tayama、Ryotaro Nishio、Yoshiaki Kobayashi
DOI:10.1039/c8ob01395k
日期:——
base-promoted α-alkylation of N-((S)-1-phenylethyl)azetidine-2-carboxylic acid esters 1 was investigated. The use of diastereomerically pure borane complexes 3 as substrates, which are easily prepared from 1, dramatically improved the yields and diastereoselectivities of α-alkylated products 2. For example, the treatment of tert-butyl ester (1S,2S,1′S)-3a with 2.4 equivalents of lithium bis(trimethysilyl)amide
Facile and straightforward syntheses of both enantiomers of azetidine-2-carboxylicacid are described. The syntheses depart from inexpensive chemicals and allow for the production, in five to six steps, of practical quantities of each enantiomer. Synthetic highlights include the construction of the azetidine ring using an intramolecular alkylation and the use of optically active α-methylbenzylamine