Chiral tertiary alpha-hydroxy esters of known stereochemical configuration were transformed to alpha-azido esters by Mitsunobu reaction with HN3. Optimization of this reaction was shown to proceed at room temperature with high chemical yield using 1,1-(azodicarbonyl)dipiperidine (ADDP) and trimethylphosphine (PMe3). Complete inversion of configuration was observed at the alpha-carbon. Several alpha,alpha-disubstituted amino acids were synthesized in high overall chemical yield and optical purity.
The synthesis of several omega-chloroalkyl tetrazoles and their subsequent attachment to a solid support is described. Using an in situ Finkelstein reaction, a variety of nucleophiles were alkylated and then cleaved from the resin to give pure alkyl tetrazole derivatives. A sample library of 5 x 6 demonstrates the general utility of this sequence.
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