A novel one-pot procedure for the stereoselective synthesis of alpha-hydroxy esters from ortho esters was developed. Key steps were multi-heteroatom Cope rearrangements of O-acylated N-hydroxy-l-tert-leucinol-derived oxazoline N-oxides leading to alpha-acyloxy oxazolines and, after methanolysis, to the target molecules in 67-80% yield and 94-98% ee.
SummaryAn enantioselective route to four tricyclic amino acids and N-tosylamides, composed of a central norbornane framework with a 2-endo,3-endo-annelated pyrrolidine ring and a 5-endo-C1 or -C2 side chain, has been developed. A key intermediate was the chiral, N-Boc-protected ketone (1R,2S,6S,7R)-4-azatricyclo[5.2.1.02,6]decan-8-one, available from inexpensive endo-carbic anhydride in five steps and 47% yield. The rigid scaffold makes these amino acid derivatives promising candidates for β-turn-inducing building blocks in peptidomimetics and for chiral auxiliaries in asymmetric organocatalysis.
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