Reactivity of carbonyl group at alpha position of

Reactivity of carbonyl group at alpha position of ferrocenyl group Autumn Andras and Uttam Pokharel Department of Chemistry & Physical Sciences, Nicholls State University, Thibodaux, LA 70301 Introduction In this project, we are interested in investigating the reactivity of carbonyl group lying at alpha position of the ferrocenyl moiety. Our long-term goal of the project is to develop the methodologies of conjugating carboxyclic rings to the cyclopentadienyl rings and their subsequent aromatization to extend the π-conjugation in ferrocene. Results Friedel-Crafts acylation between ferrocene and glutaric anhydride • On acidic workup, the reaction yields two products: acidic and neutral. • The acidic product, separated by base extraction followed by acidification, gives a mixture of acid and a neutral compound indicating the formation of 1’ as an intermediate product. • The formation of the lactone, 4 was confirmed by singlecrystal X-ray analysis. Proposed Mechanism Background When the keto group in 3 -carboxypropionyl ferrocene is reduced to methylene under Clemmensen conditions, the cyclopentadienyl (Cp) ring makes a nucleophilic attack to the carboxylic acid in the presence of trifluoroacetic anhydride giving 1, 2 -(αketotetramethylene)ferrocene as shown below. When attempted to close the ring without reducing the keto group, we isolated lactone due to the nucleophilic attack of carbonyl oxygen to the trifluoroacetate activated carboxy group. There was no indication of the formation of the desired diketone. • Reaction of ferrocene with glutaric anhydride in a 1: 1 ratio in DCE gave a mixture of succinic anhydride with ferrocene gives a mixture of (4 -carboxy-1 -oxobutyl)ferrocene, 1 (25%), 1, 1’bis(4 -carboxy-1 -oxobutyl)ferrocene, 2 (44%), and 1, 1’’-(1, 5 dioxo-1, 5 -pentanediyl)bisferrocene, 4 (9%) • The complex 1 is soluble in DCM but the complex 2 is insoluble. • The complex 3 is separated from unreacted ferrocene by silica gel column chromatography. • Double Friedel Crafts acylation of ferrocene with glutaric anhydride to give complex 3 has not been reported in literature yet. • The complex three was crystallized from the mixture of diethyl ether and hexane by slow evaporation. • An asymmetrical unit of the complex 3 contains its two molecules Reduction of carbonyl group with Na. BH 4 Conclusions • The Friedel-Crafts acylation of ferrocene with glutaric anhydride (1: 1) gives a mixture of two carboxylic acids, 1 and 2 along with neutral compound, 3. • The complex 2 has poor solubility in common organic solvents • Attempts to reduce the keto group of 1 to secondary alcohol followed by acidification resulted in the formation of lactone • The complex 2 lost one arm completely and gave similar products as complex 1 on reduction with Na. BH 4. Acknowledgements Although the carboxypropinoyl ferrocene gave the trifluroroacetate substituted unsaturated lactone, its stability was poor possibly due to ring strain. That prompted us to explore the chemistry with 4 -carboxy butanoyl ferrocene. • We were interested in breaking the conjugation of carbonyl group to secondary alcohol. • The reaction requires 3 equivalents of Na. BH 4 in Na. OH(aq) as a solvent under reflux conditions. • Financial support • SURE, Louisiana Board of Regents • X-ray crystallography • Frank Fronczek, LSU Reference • Pokahrel, U. ; Curole, B. ; Daigle, D. Unpublished results. Nicholls State University.