S1 Tandem RCM-isomerization-cyclopropanation reactions Álvaro Mallagaray, Gema Domínguez, Ana Gradillas and Javier Pérez- Castells* Facultad de Farmacia, Dpto. Química, Universidad San Pablo CEU, Urb. Montepríncipe, ctra. Boadilla km 5,300 Boadilla del Monte, 28668 Madrid jpercas@ceu.es General procedures: 1 H NMR and 13 C NMR spectra were taken on a Bruker AM-300 spectrometer. Chemical shifts (™) are in parts per million relative to tetramethylsilane at 0.00 ppm. IR spectra were determined on a Perkin-Elmer 780 spectrometer. TLC analyses were performed on commercial aluminium sheets bearing 0.25-mm layer of Merck Silica gel 60F254. Silica gel 60 Merk of 230-400 mesh ASTM was used for column chromatography. Medium pressure liquid chromatography (MPLC) was performed using Biotage Si 25+M 2593-2 compact columns. Elemental analyses were carried out at the Elemental Analysis Center of the Complutense University of Madrid, using a Perkin Elmer 2400 CHN. The solvents for the reactions carried under argon atmosphere were distilled just before their use. THF was refluxed over Na/Benzophenone, DCM and toluene over CaH. All reactives were bought to Aldrich and Across. NH OMe MeO Preparation of N-(2,4-dimethoxybenzyl)prop-2-en-1-amine. A solution of allylamine (3.4 g, 60.2 mmol), 2,4-dimethoxybenzaldehyde (10.0 g, 84.2 mmol) and sodium triacetoxyborohydride (17.8 g, 84.2 mmol) in 210 mL of 1,2- dichloroethane was stirred at room temperature for 24 h. 50 mL of Na 2 CO 3 (10%) were added and the 1,2-dichloroethane was eliminated under reduced pressure. The crude was extracted with diethyl ether (3 x 50 mL), dried with MgSO 4 and concentrated in vacuo. The resulting mixture was purified by flash