Saponification of the ester group resulted in the formation of interesting amino acids "c." The reaction of the Bpin-compounds with potassium fluoride in an acetone/water mixture smoothly gave trifluoroborates "d." The reaction of compound 19 with Me2NCH(OMe)2 led to the formation of a mixture of two Scheme 4. Synthesis of azetidine-containing building blocks for medicinal chemistry. isomeric products 19e:19f=3:1, from which the pure isomer 19e was isolated in 74% yield by column chromatography. The cyclization of 19e with hydrazine hydrate provided pyrazole 39 in 75% yield. We also obtained the isomeric pyrazole 40 via the reaction of 19e+19f with hydrazine hydrate and the separation of the isomeric products by column chromatography. The structure of compound 40 was proven by X-ray analysis. Acidic deprotection of the N-Boc group formed unique isomeric scaffolds 41 and 42. Cyclization of 19e with hydroxylamine allowed isolating isoxazole 43 in 87% yield. Acidic N-Boc deprotection of the latter provided scaffold 44. Condensation of compound 19e with guanidine smoothly afforded pyrimidine 45 in 83% yield.