la (I) wherein R is a group ???CONRaRb; or (e.3) with a suitable aldehyde or ketone derivative of formula (X) under reductive operative conditions Ra???CO???Ra (X) wherein each Ra is the same or different as above defined, so as to obtain the above compound of formula (I) wherein R is a group ???CH(Ra)Ra; or (e.4) with an aromatic iodide or bromide of formula (XI) or (XII) Ra???I (XI) Ra???Br (XII