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Base‐promoted cyclization of N‐Boc‐ω‐(4‐(chloromethyl)oxazol‐5‐yl)alkylamines led to the corresponding "dimerization" products containing fused 10‐, 12‐, and 14‐membered rings. Experimental data showed that the formation of these ring systems is favored over the corresponding 5‐/6‐/7‐membered ones, which was partially confirmed by DFT calculations; this effect was especially significant in the case of the 5‐/10‐membered pair. [ABSTRACT FROM AUTHOR]

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 oxazolecontaining 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. [ABSTRACT FROM AUTHOR]

A stereolibrary of conformationally restricted oxazole-containing amino acids, namely all isomers of 5-pyrrolydinyl- and 5-piperidinyloxazole-4-carboxylic acids, were designed and synthesized in three steps by the reaction of the corresponding N-Boc-protected amino acids and ethyl isocyanoacetate. These natural productsinspired amino acids are valuable building blocks for the synthesis of peptidomimetics and potential lead compounds for drug discovery. [ABSTRACT FROM AUTHOR]