Solventless mechanosynthesis of N-protected amino esters
Mechanochemical derivatizations of N- or C-protected amino acids were performed in a ball mill under solvent-free conditions. A vibrational ball mill was used for the preparation of N-protected α- and β-amino esters starting from the corresponding N-unmasked precursors via a carbamoylation reaction in the presence of di-tert-butyl dicarbonate (Boc2O), benzyl chloroformate (Z-Cl) or 9-fluorenylmethoxycarbonyl chloroformate (Fmoc-Cl). A planetary ball mill proved to be more suitable for the synthesis of amino esters from N-protected amino acids via a one-pot activation/esterification reaction in the presence of various dialkyl dicarbonates or chloroformates. The spot-to-spot reactions were straightforward, leading to the final products in reduced reaction times with improved yields and simplified work-up procedures.
Studies on 2-Aziridinecarboxylic Acid. VI. Synthesis of β-Alkoxy-α-Amino Acids via Ring-opening Reaction of Aziridine
The reaction of aziridine derivatives having a urethane-type protecting group with several alcohols in the presence of boron trifluoride etherate afford the corresponding optically pure O-alkylserine and O-alkylthreonine derivatives via a ring-opening reaction of aziridine in good yield.
Process for t-butylating hydroxy- or thiol-substituted amino acids
Hydroxy- or thiol-substituted amino acids are t-butylated by reacting them with isobutylene in the presence of a catalyst comprising boron trifluoride and anhydrous phosphoric acid.
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(2008/06/13)
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