A DIASTEREOSELECTIVE SYNTHESIS OF (DL)-1,3-DIPHENYL-1,3-PROPANEDIAMINES

A large-scale and practical synthesis of (dl)-1,3-diphenyl-1,3-propanediamine (1) has been achieved by a highly diastereoselective phenylcerium dichloride addition to 1-tert-butoxycarbonyl-4,5-dihydro-5-phenylpyrazole (3). Alkylcerium addition reaction to the corresponding 5-alkyl substituted 1-Boc-4,5-dihydropyrazoles was less satisfactory mainly giving ring-cleaved products. Further elaboration of the diamine 1 to the N-substituted derivatives 8 a-f bearing N-methyl, N-ethyl, N-isopropyl, N-neopentyl, N-benzyl, and N-mesitylmethyl groups is described.