CONCISE RACEMIC AND HIGHLY ENANTIOSELECTIVE APPROACHES TO KEY INTERMEDIATES FOR THE SYNTHESES OF CARBOCYCLIC NUCLEOSIDES AND PSEUDO-RIBOFURANOSES - FORMAL SYNTHESES OF CARBOVIR

A regio- and stereo-specific synthesis of cis-(+/-)-3-acetoxy-5-(acetoxymethyl)cyclopentene 3 from cyclopent-3-enecarboxylic acid 4 via a bromolactonisation strategy is described. Pd-catalysed coupling of the cis-(+/-)-diacetate 3 with 2-amino-6-chloropurine or 2.6-diaminopurine leads to the formal syntheses of carbovir 1. A synthesis of the (1R) cis-diacetate 15 (R = Ac) is described via a highly enantioselective rearrangement of cis-6-oxabicyclo[3.1.0] hexane-3-methanol 13 (also prepared from the acid 4) using the dilithium salt of (1S,2R) norephedrine.