Synthesis of Dicyclopenta[a,e]pentalenes via a Molybdenum Carbonyl Mediated Tandem Allenic Pauson−Khand Reaction and the X-ray Crystal Structure of a Planar Dicyclopenta[a,e]pentalene

• Published in: Journal of the American Chemical Society Vol. 127; no. 3; pp. 933 - 943
• Main Authors: Cao, Hui, Van Ornum, Scott G, Deschamps, Jeffery, Flippen-Anderson, Judith, Laib, Frank, Cook, James M
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 26.01.2005; Amer Chemical Soc
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Aliphatic, non-condensed and condensed benzenic, and alicyclic compounds; Chemistry; Chemistry, Multidisciplinary; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Organic chemistry; Organic compounds; Physical Sciences; Physics; Preparations and properties; Science & Technology; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; CYCLOADDITION; ROUTE; DICYCLOPENTA<A,E>PENTALENE; CONJUGATED HYDROCARBONS; ENTRY; PI RESONANCE ENERGIES; RINGS; SYSTEMS; GENERATION; CYCLOPENTENONES; Catalytic reaction; Molecular structure; Molybdenum Carbonyl; Transition metal Carbonyl; Electron delocalization; NMR spectrometry; Tetracyclic compound; Complex catalyst; X ray diffraction; Organic synthesis; Electronic structure; Polyenic compound; Pauson Khand reaction; Carbon 13; Ultraviolet visible spectrometry; Crystalline structure
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja040120x

Two 14 π cross-linked annulenes which belong to the family of dicyclopenta[a,e]pentalenes have been synthesized, 14 π bis enol triflate ester 27 and the 3,7-diisopropylsilyl substituted 14 π dicyclopenta[a,e]pentalene 30. The new allenic tandem Pauson−Khand reaction mediated by Mo(CO)6 was employed as the key process to construct the core of the tetracycles. The two linear dicyclopenta[a,e]pentalenes 27 and 30 underwent significant electronic delocalization, perhaps even aromaticity, as revealed by the X-ray structure of 27. The tetracyclic rings in 27 assumed a flat geometry (Figure ); the bond lengths of the tetracycle in 27 also fit well into the criteria for aromatic compounds. A comparison of the NMR and UV spectra of both 27 and 30 demonstrated that they both exhibited similar electronic properties, therefore, the purple colored 14 π cross linked annulene 30 is planar as well as delocalized.