Stereocontrolled intramolecular iron-mediated diene/olefin cyclocoupling

A methodology for stereocontrol during the intramolecular coupling between cyclohexadiene-Fe(CO)₃ complexes and pendant alkenes is presented. Introduction of a methoxy group at the C(3) position of the diene moiety controls pre- and post-cyclization rearrangements of the diene Fe(CO)₃ unit, allowing the preparation of spirolactams with defined relative stereochemistry and with a cyclohexenone framework, thus making this reaction a potentially valuable tool for the construction of quaternary carbon centers.*; A new methodology for the formation of tricarbonyl(cyclohexadienyl)ketone iron complexes was also developed. This method involves the coupling of a Grignard reagent with an acyl mesylate iron complex, giving rise to ketone derivatives in excellent yields. The possibility of intramolecular coupling between diene-Fe(CO)₃ complexes and homoallylic olefin was demonstrated. The stereospecific formation of spiroketones occurred in excellent yields under thermal conditions, but appeared to be limited to the simpler, less substituted pendant alkenes. The control of the stereochemical outcome of these spirocyclization was achieved using the “C(3) substitution method” previously described. The same trends were observed in these series. Also illustrated in these studies is the extension of this spirocoupling to the formation of a spiro[5.5]undecane framework. It is the first time that this framework has been accessed using this intramolecular coupling.*; *Please refer to dissertation for diagram.