All organic reagents, nickel chloride hexahydrate and zirconocene dichloride were purchased from Acros. Ni (acac) 2 was purchased from Merck and iodosobenzene diacetate was purchased from Aldrich. Schwartz reagent was synthesized on a 15 mmol scale from zirconocene dichloride in 75% isolated yield following a protocol by Buchwald. 1 Anhydrous nickel chloride was prepared from nickel chloride hexahydrate by stirring with thionyl chloride under absolute conditions followed by sublimation under reduced pressure. Guanidine 6b was obtained from E. Campos and Prof. J. González (Universidad de Oviedo, Spain). Dichloromethane, ethyl acetate and hexanes were dried over calcium chloride, distilled and used without further manipulation. Absolute dmf was obtained through an Innovative Technology Inc. solvent purification system. Column chromatography was performed with silica gel (Merck, type 60, 0.063-0.2 mm). Nmr spectra were recorded on a Bruker Avance 400 MHz spectrometer. All chemical shifts in nmr experiments are reported as ppm downfield from TMS. The following calibrations were used: CDCl3 δ= 7.26 and 77.00 ppm. MS (ESI-LCMS) experiments were performed using an Agilent 1100 HPLC with a Bruker micro-TOF instrument (ESI). Unless other wise stated, a Supelco C8 (5cm x 4.6 mm, 5µm particles) column was used with an linear elution gradient from 100% H2O (0.5% HCO2H) to 100% MeCN in 13min at a flow rate of 0.5 mL/min. MS (EI) and HRMS experiments were performed on a Kratos MS 50 within the service centers at the Kekulé-Department, Bonn.