Ring Closure of Alkoxycarbonyl(tetracarbonyl)pyruvoyliron Complexes into Metallalactones Induced by Nucleophilic Attack of Carbanions

The reaction of carbanions with the pyruvoyl‐substituted iron complex [(CO) 4 Fe(CO 2 CH 3 ){C(O)C(O)CH 3 }] ( 1 ) affords the anionic trifunctionalized metallalactones [(CO) 3 Fe{C(O)C(CH 3 )(CRR′R″)OC 4 (O)(Fe–C 4 )}(CO 2 CH 3 )] – ( 3 ), whose formation results from the addition of the nucleophile to the β carbonyl of the pyruvoyl moiety, followed by attack of the oxygen of this β carbonyl on a terminal carbonyl ligand. These anionic lactones react, at low temperature, with HCl to give rise to the neutral lactones [(CO) 4 Fe{C(O)C(CH 3 )(CRR′R″)OC 4 (O)(Fe–C 4 )}] ( 2 ), which were previously obtained by addition of NuH nucleophiles to 1 . Complex 3(3) , whose lactonic ring formation has been performed using the diethyl malonate anion (R = R′ = CO 2 C 2 H 5 ; R″ = H), and the dimethyl‐substituted neutral lactone 2(1) (R = R′ = R″ = H) have been characterized by X‐ray diffraction studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)