The preparation of imidazolidinone and oxazolidinone chelated carbene complexes

The synthesis of several internally chelated imidazolidinone and oxazolidinone Fischer carbene complexes of the type (CO)4M=CC(R1)NCO(CHR2CHR3X) are reported where the M=chromium, tungsten; R1=methyl, ethyl, iso-propyl, phenyl, trans-propenyl, iso-propenyl, iso-butenyl, cyclohexenyl and 1-propynyl; R2=H, Ph, Bn, Me, Cy; R3=H, Me, Ph; X=O, NMe. Four different methods are used for the synthesis of these complexes. The imidazolidinone complexes are best prepared by adding an imidazolidinone or lithiated imidazolidinone to a methoxy carbene complex or to an in-situ generated acetoxy carbene complex. α,β-Unsaturated imidazolidinone complexes are prepared by aldol condensations of alkyl imidazolidinone complexes or by alkylaltion of these complexes with bromomethyl methyl ether and then elimination of methanol. The oxazolidinone complexes are best made by a two-step procedure that involves the addition of an β-aminoalcohol to a methoxy or acetoxy complex followed by closure of the resulting amino carbene complex to the oxazolidinone complex with phosgene.