In one aspect, the invention provides a process for the preparation of compounds of Formula I ##STR00001## wherein R.sub.1 is --CN, --OP, alkyl, aryl or heteroaryl; wherein P represents any suitable protecting group; and R.sub.2 is alkyl or aryl; by reacting a compound of Formula II ##STR00002## wherein R.sub.1 is --CN, --OP, alkyl, aryl or heteroaryl; wherein P represents any suitable protecting group; and R.sub.2 is alkyl or aryl; with a reducing agent (e.g. sodium borohydride) in the presence of a metal halid (e.g. CeCl.sub.3) or a metal alkoxid (e.g. Ti(OiPr).sub.4).