Organometallic complexes in synthesis. Part VI. Some oxidative cyclisations of tricarbonylcyclohexadieneiron complexes

Abstract

Tricarbonylcyclohexadienyliron salts of type (2; R2 = +), after reaction successively with a P-diketone or a pketo-ester and manganese dioxide or lead dioxide, give tricarbonyl-cis-3a.7a-dihydrofuraniron complexes of type (3). Use of deuteriated intermediates indicated that the cyclisation occurs with specific loss of the 6-endoproton.THE reactions with nucleophiles of some carboniuni salts derived from tricarbonylcyclohexadieneiron derivatives have been r e p ~r t e d . ~, ~ Such processes are potentially useful in organic synthesis if the tricarbonyliron group can be removed in good yield. This question is discussed el~ewhere,~ the usual reagents being iron(rr1) chloride or cerium(1v) salts.that manganese dioxide removes the tricarbonyliron group from its complex with 1methoxycyclohexa-1,3-diene (l), but not from the coniplex with 2-methoxycyclohexa-l,3-diene (2; R2 = H, R1 = OMe), in experiments with a mixture of the two dieiie complexes. We have now separated these complexes chromatographically, and have confirmed the original observations, although (1) was oxidised to give anisole rather than l-methoxycyclohexa-1,3-diene and (2; R1 = ORk, R2 = H) was relatively stable.In order to investigate further the capabilities of the We have reported

Nucleophilic addition to coordinated cyclic .pi.-hydrocarbons: mechanistic and synthetic studies

“…Hydride addition to a variety of other ring systems was examined and found to be exo: Mn(CO)3(C6H6)+> Mn(CO)3(C6H7), Re(CO)3(C6Me6)+, Fe(CO)3(C6H7)+, Cr(CO)2-(NO)(C6H6)+. 27,28,111,116,117 These results and our X-ray structures show that endo addition to 24 is not due to steric congestion around the carbon being attacked.…”

The Oxidation of Organic Compounds by Active Manganese Dioxide

“…7a-dihydrobenzofurantricarbonyliron) in 90% yield. 510 The oxidative cyclization reaction. as suggested.…”

Iron(0) Tricarbonyl Complexes of Microbially Derived Cyclohexadiene Ligands Containing Quaternary Stereocenters

“…Three examples have been reported for tricarbonyliron complexes of other dienol ligand types (cyclobutadiene and acyclic dienes), but far more prevalent in the literature are examples of manganese dioxide effecting oxidative cleavage of the tricarbonyliron fragment from the diene . Also, a preference for transfer of an endo hydride to the oxidant has been noted in manganese dioxide induced cyclizations of tricarbonyl(diene)iron complexes, in contrast to the example at hand, which necessarily involves exo hydride removal.…”