Heterocycl. Commun. 2018, 24 (1), 11-17
DOI: 10.1515/hc-2017-0235
Slobodyanyuk E.; Artamonov O.; Kulik I.; Rusanov E.; Volochnyuk D.; Grygorenko O.
A convenient four-step approach to the synthesis of (S)-4-alkyl-2-(pyrrolidin-2-yl)oxazoles starting from l-Boc-proline inspired by naturally occurring oxazole-containing peptidomimetics is described. The key step is the cyclization of 1-Boc-N-(1-oxoalkan-2-yl)pyrrolidine-2-carboxamides – aldehyde intermediates which demonstrate low to moderate stability – under Appel reaction conditions. This method furnishes the target compounds with more than 98% ee and in a 17–51% overall yield and has been used at up to a 45-g scale.