ENANTIOSELECTIVE SYNTHESIS OF (1R,4S)-1-AMINO-4-(HYDROXYMETHYL)-2-CYCLOPENTENE A PRECURSOR FOR CARBOCYCLIC NUCLEOSIDE SYNTHESIS

(1R,4S)-1-Amino-4-(hydroxymethyl)-2-cyclpentene, an important precurso r for the synthesis of carbocyclic nucleosides, has been prepared from D-glucono-delta-lactone in enantiomerically pure form (er > 99/1). Th e synthesis proceeded from the lactone via the diisopropylidene-2-amin o-2-deoxymannonate and hydrolysis of the terminal isopropylidene group . Selective oxidation of the primary alcohol and esterification gave t he corresponding mannarate which was deoxygenated at C5. Further trans formations by regiospecific eliminative cleavage of the ketal and hydr ogenation gave dimethyl (2S,3R)-2-amino-3-hydroxyadipate. Dieckmann cy clization through specific carbanion formation at C5 led to the aminoh ydroxy(methoxycarbonyl)cyclopentanone which was readily converted in a series of high-yielding steps to the target cyclopentene. Throughout the synthesis, stereo- and regioselectivities were strongly influenced by the sterically demanding 9-phenyl-9-fluorenyl protecting group on nitrogen.