Stereospecific Synthesis of Polysubstituted E-Olefins by Reaction of Acyclic Nitrones with Free and Platinum(II) Coordinated Organonitriles

Free nitriles NCCH2R (1a R = CO2Me, 1b R = SO2Ph, and 1c R = COPh) with an acidic α-methylene react with acyclic nitrones -O+N(Me)C(H)R‘ (2a R‘ = 4-MeC6H4 and 2b R‘ = 2,4,6-Me3C6H2), in refluxing CH2Cl2, to afford stereoselectively the E-olefins (NC)(R)CC(H)R‘ (3a3c and 3a3c‘), whereas, when coordinated at the platinum(II) trans-[PtCl2(NCCH2R)2] complexes (4a R = CO2Me and 4b R = Cl), they undergo cycloaddition to give the (oxadiazoline)-PtII complexes (R = CO2Me, Cl and R‘ = 4-MeC6H4, 2,4,6-Me3C6H2) (5a-5d). Upon heating in CH2Cl2, 5a affords the corresponding alkene 3a. The reactions are greatly accelerated when carried out under focused microwave irradiation, particularly in the solid phase (SiO2), without solvent, a substantial increase of the yields being also observed. The compounds were characterized by IR and 1H, 13C, and 195Pt NMR spectroscopies, FAB+-MS, elemental analyses and, in the cases of the alkene (NC)(CO2Me)CC(H)(4-MeC6H4) 3a and of the oxadiazoline complex 5c, also by X-ray diffraction analyses.