Stereospecific synthesis of polysubstituted E-olefins by reaction of acyclic nitrones with free and platinum(II) coordinated organonitriles

Abstract

(Chemical Equation Presented) 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 CH 2Cl2, to afford stereoselectively the E-olefins (NC)(R)C=C(H)R′ (3a-3c and 3a′-3c′), 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 trans-[PtCl 2{N=C(CH2R)ON(Me)C(H)R′}2] (R = CO 2Me, Cl and R′ = 4-MeC6H4, 2,4,6-Me 3C6H2) (5a-5d). Upon heating in CH 2Cl2, 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 trans-[PtCl2{N=C(CH2Cl)ON(Me)C(H) (4-C6H4Me)}2] 5c, also by X-ray diffraction analyses. © 2007 American Chemical Society.