Ozonolysis of (cyclohexa-1,4-dienyl)-L-alanine. An approach to the synthesis of new unnatural amino acids. X-Ray molecular structure of 2-hydroxy-7-methyl-3-phenylpyrazolo[1,5-a]pyrimidine

The aromatic ring in L-phenylalanine was transformed into isoxazolyl, N-phenylpyrazolyl, and the bicyclic pyrazolo[1,5-a]pyrimidinyl groups, by a combination of Birch reduction and ozonolysis, followed by condensation with the relevant binucleophiles. The ozonolysis was carried out on the N-acylated esters of cyclohexa-1,4-dienylalanine. The resulting N-acylated esters of heterocyclic alanine derivatives were obtained without isolation of the ozonolysis products. 4-Phenylpyrazolidine-3,5-dione was used as a ‘hydrazine donor’ in the construction of a pyrazolyl group, as direct condensation with hydrazine was successful.