To complete the synthesis of an NCL-competent fragment, the Alloc group in 18 had to be removed, and two routes were investigated: deallylation/ligation/desulfurization (route A) and deallylation/trapping followed by ligation/desulfurization (route B). We attempted deallylation of 18 using Pd(II), TPPTS/MPAA followed by SEC and NCL with thioester 24a, but under these conditions, only thioester 24a remained (LCMS) indicating that the thiol sequestered the metal. Similarly, attempted trapping of the thiol with MMTS yielded no detectable product. Alloc removal with PdCl2dppf/PhSiH3 in DMSO followed by NCL with 24a or trapping with MMTS showed the presence of the desired products albeit in low yields (11% and 7%, respectively). The Ru(II)-based method with Cp*Ru(COD)Cl/MPAA 94 produced 19 in almost quantitative yield, but 19 decomposed slowly likely through the intermolecular splicing as described above (route A). Attempts at the ligation of 19 with 24a, followed by desalting to remove MPAA and immediate desulfurization produced 20 but in irreproducible yields (0-55%). Additionally, thiol 19 could be trapped with MMTS, and pure disulfide 21 could be sent into the ligationdesalting-desulfurization sequence, but the yield was low (33%) and difficult to scale up. The subsequent NCL of 21 with 24b produced Tau(157-290) 20 in 52%.