A 1,2-metallate rearrangement of the putative higher order cuprate 17 derived from reaction of the metallated dihydrofuran 15 with the homocuprate 16 occurred with clean inversion of configuration to give the alkenylcuprate 18. Methylation of 18 followed by five simple transformations completed the synthesis of the C16-C23 effector domain of the immunosuppressant FK-506.