Regio‐ and stereoselective preparation of ascomycin‐d 1 and FK 506‐d 1

The immunosuppressive macrolides ascomycin 1 and FK 506 2 were stereoselectively deuteriated at C(32) using Curran's radical translocating method. Both AIBN and Et 3 B/O 2 were tested as radical initiator for the radical translocation/reduction step with Bu 3 SnD as reducing agent. Despite only minor structural differences, ascomycin and FK 506 showed remarkably different behaviour under the radical translocation/reduction conditions. Higher stereoselectivities were observed with Et 3 B/O 2 as initiator, presumably due to lower reaction temperatures applied in this case. Copyright © 2002 John Wiley & Sons, Ltd.