Demonstration of the facile reversibility of fulvene formation

Cleavage of fulvenes under mild conditions and interchange between electron-deficient fulvenes and their constituent cyclopentadienes and imines is demonstrated for the first time. A series of cyclopentadienes and imines are investigated to probe the dependence of fulvene equilibration on structure. The exchange of one fulvene for another is demonstrated in the first reported example of transfulvenation. Finally, the metathesis of two fulvenes to generate all four possible cross products is shown.     

Facile synthesis of alkylidene cyclopentenes via palladium catalyzed ring opening of fulvene derived bicyclic hydrazines

A facile synthesis of substituted alkylidene cyclopentenes through a palladium catalyzed ring opening of fulvene derived bicyclic hydrazines with various organometallic reagents is described. The products are versatile synthons with multiple points for functionalization and can be used in the synthesis of a number of biologically active molecules.     

Reaction of Substituted Cyclopentadienyl-magnesium-Chloride with Carbonyl Compound ( Ⅰ )——Reaction of (1, 1-Dialkyl-3-Butenyl) Cyclopentadienyl-magnesium-chloride with Ketones

The substituted cyclopentadienyl-magnesium-chloride, obtained by exocyclic addition of 6,6-dialkylfulvene and allyl-magnesium-chloride, reacted with the ketone 3, the product was hydrolyzed and dehydrated to give the 2-(1 ,1-dialkyl-3-butenyl)-6,6-dialkyl-fulvene 5. The structure of 5 was determined by using the 1H NMR spectra of 5 and the adducts of 5 with tetracyanoethylene.     

Novel organotin antibacterial and anticancer drugs

From the reaction of 6-(p-methoxyphenyl) fulvene (1a), 6-(p-N,N-dimethylaminophenyl) fulvene (1b) and 6-(3,4-dimethoxyphenyl) fulvene (1c) with LiBEt₃H, lithiated cyclopentadienide intermediates (2a–c) were synthesised. These intermediates were then transmetallated to tin with SnCl₄ to yield tetra-substituted bis(cyclopentadienyl)tin dichloride complexes (3a–c). Further reaction with tin tetrachloride yielded the benzyl-substituted derivatives bis-[(p-methoxybenzyl)cyclopentadienyl] tin(IV) dichloride (4a), bis-[(p-N,N-dimethylaminobenzyl)cyclopentadienyl] tin(IV) dichloride (4b), and bis-[(3,4-dimethoxyphenyl)cyclopentadienyl] tin(IV) dichloride (4c). Preliminary antibacterial tests were carried out using the Kirby–Bauer disk-diffusion method, in which 4a–c showed little to no activity against the Gram-negative bacterium Escherichia coli, but medium activity against Gram-positive bacteria (MRSA, MSSA). In addition, the organotin complexes had their cytotoxicity investigated through preliminary in vitro testing on the LLC-PK (pig kidney epithelial) cell line in order to determine their IC50 values. Compound 4c showed no cytotoxic activity, while 4a and 4b were found to have IC50 values of 15 and 205 μM, respectively.     

Pentafulvenkomplexe des Titans — Synthese,Struktur und Fluktuierendes Verhalten von Cp′Ti{η6‐C5H4=C(p‐Tol)2}Cl (Cp′ = Cp*, Cp)

Complexes of Titanium — Synthesis, Structure, and Fluxional Behaviour of CpTi{η⁶‐C₅H₄=C(p‐Tol)₂}Cl (Cp′ = Cp*, Cp) The reaction of Cp′TiCl₃ (C′ = Cp* or Cp) with magnesium and 6, 6‐di‐para‐tolylpentafulvene generates good yields of pentafulvene complexes Cp*Ti{η⁶‐C₅H₄=C(p‐Tol)₂}Cl ( 4 ) and CpTi{η⁶‐C₅H₄=C(p‐Tol)₂}Cl ( 5 ), respectively. The crystal and molecular structure of 4 have been determined from X‐ray data and exhibits compared to known η⁶‐pentafulvene complexes an unusual large Ti—C(p‐Tol)₂ (Fv)‐distance (2.535(5)Å) evoked by the bulky substituents at the exocyclic carbon. Dynamic ¹H‐NMR and spin saturation transfer experiments point out a rotation of the fulvene ligand around the Ti—Ct2 axis (Ct2 = centroid of the fulvene ring carbon atoms) with an activation barrier ΔG^≠_C = 60.6 ± 0.5 kJ mol⁻¹ (T_C = 314 ± 2 K). For 5 this barrier is significantly larger. Analogous dynamic behaviour is well known for diene complexes, but to our knowledge, it is here first‐time described for a pentafulvene complex.     

Palladium‐Catalyzed Cascade Oligocyclizations Involving Competing Elementary Steps Such as Thermal [1,5]‐Acyl Shifts

Palladium(Pd)‐catalyzed oligocyclizations of 2‐bromotetradec‐1‐ene‐7,13‐diynes with an unsubstituted terminal acetylene moiety like 3 and 5 and 15‐bromohexadec‐15‐ene‐3,9‐diyn‐2‐ones like 4 and 6 afforded fulvene derivatives 20 and 21 (Scheme 7) and bis(cyclohexane)‐annulated methylenecyclopentene systems 16 and 18 (Schemes 5 and 6), respectively. These transformations constitute cascades of cyclizing carbopalladation steps with ensuing [1,5]‐sigmatropic H‐atom and acyl shifts, respectively (Scheme 8). In contrast, analogous substrates with one three‐atom and one four‐atom tether between the unsaturated C,C‐bonds, such as 1 and 2 , behave differently in that the Pd‐substituted hexa‐1,3,5‐triene intermediates 12 undergo a 6π‐electrocyclization instead of a 5‐exo‐trig carbopalladation followed by β‐hydride elimination to furnish tricyclic bis‐annulated benzene derivatives 13 and 14 (Scheme 4).     

Theoretical studies on titanium pentafulvene complexes

A series of six titanium pentafulvene complexes are thoroughly investigated using the B3LYP/6-31G(d) level of theory. Excellent agreement with the available structural data is obtained. Relevant structural parameters indicate that a gradual change of the fulvene ligand coordination to the titanium center. Depending on the nature of the exocyclic fulvene substituents dianionic η⁵, η¹-and olefinic η⁶-coordination modes are found. This behavior is further supported by NBO and AIM population analyses which predict differences in the bond nature meanly of the contacts between titanium and the exocyclic carbon atom. In an excitation study, several theoretical approaches are evaluated against the available recorded UV-Vis spectra of the six complexes. The “best” approach, time-dependant DFT calculations reproduce the experimental UV data reasonably well, although systematically slightly too small values (abut 50 cm⁻¹) are obtained. The other levels of theory are significantly more erratic. It could further be testified that the absorption maxima correspond to a ligand-to-metal charge transfer from the HOMO to the LUMO+1 of the complexes.