| abstract |
A process for preparing a compound of formula (3) in enantio-enriched form, comprises reducing a compound of formula (4) using an asymmetric enantiospecific reductant, wherein A1 = A2 = H or A1, A2 = O; B1 = B2 = H or B1, B2 = O; Z = H, C1-20 alkyl or a precursor thereof, or a removable protecting group for nitrogen, e.g. acyl or alkyloxycarbonyl; Y = H or a substituent; R1 = C1-20 alkyl; and R is an optional, additional substituent. |