A Novel Approach toward the Synthesis of Chiral 2,3-Dideoxy Nucleosides and Their Carbocyclic Analogs (original) (raw)

Photochemical ring-expansion of chiral2(S),3(R)-bis[(benzoy€oxy)methyllcyclobutanone (3) in the presence of alcohols and acidic N-H functional groups gives anomeric mixtures of acetals and N-amino acetals, respectively, with retention of stereochemistry of the ring substituents. In the presence of purine and 6-chloropurine the corresponding protected nucleosides are obtained. The photoadduct with 6-chloropurine is converted to the known medicinally active deprotected adenine nucleoside with methanolic ammonia. One-carbon homologation of ketone 3 with diazomethane produces the corresponding optically pure cyclopentanone 8 with retention of stereochemistry. This ketone is converted to the optically pure cyclopentylamine 10 in two steps. Racemic amine 10 has been used as a key intermediate in the preparation of carbocyclic nucleosides.