Cross-conjugated 3-ferrocenylmethylidene-2,4-dimethylpenta-1,4-diene in cationic cycloaddition and proton-catalyzed cyclodimerization reactions

Cationic cycloaddition of cross-conjugated 3-ferrocenylmethylidene-2,4-dimethylpenta-1,4-diene to 1-ferrocenyl-2-isopropenyl-3,3-dimethylallylium tetrafluoroborate and its proton-catalyzed cyclodimerization result in diferrocenylbicyclo[3.3.1]nonene derivatives. The spatial structure of one of the reaction products, viz., ferroceno[4,5]-{9-ferrocenylmethylidene-1,3,3,8,10-pentamethyltricyclo[6.3.1.0^2,6]dodec-2(6)-ene}, was established based on the data from X-ray diffraction analysis.     

Synthesis and characterization of cross-conjugated cruciforms with varied functional groups

A series of novel oligo(p-phenylenes) (OPPs) derivatives with bisdiene side-chains are synthesized and fully characterized. These cruciforms are soluble in common organic solvents and show good thermal stability. Absorption and emission spectra are recorded to study the effect of different electron-withdrawing and electron-donating groups on photophysical properties. Powder XRD shows crystalline structures for all the cruciforms. Single crystal XRD studies show tight-packing along the planar bisdiene axis but significant twisting along phenylene units, which correlate the role of functionalization along the bisdiene axis in tuning the band gaps of the cruciforms.     

Asymmetric Brønsted Base Catalyzed and Directed [3+2] Cycloaddition of 2‐Acyl Cycloheptatrienes with Azomethine Ylides

Conjugated cyclic trienes have the potential for different types of cycloaddition reactions. In the present work, we will, in a novel asymmetric cycloaddition reaction, demonstrate that the organocatalytic reaction of 2‐acyl cycloheptatrienes with azomethine ylides proceeds as a [3+2] cycloaddition, which is in contrast to the Lewis acid‐catalyzed reaction, in which a [3+6] cycloaddition takes place. In the presence of a chiral organosuperbase, 2‐acyl cycloheptatrienes react in a highly enantioselective manner in the [3+2] cycloaddition with azomethine ylides, providing the 1,3‐dipolar cycloaddition product in high yields and up to 99 % ee. It is also shown that the diene formed by the reaction can undergo stereoselective dihydroxylation, bromination, and cycloaddition reactions. Finally, based on experimental observations, some mechanistic considerations are discussed.     

1-Cyclohepta-2,4,6-trienyl-selanes--a 77Se NMR study: indirect nuclear 77Se--13C spin-spin coupling constants and application of density functional theory (DFT) calculations

1-Cyclohepta-2,4,6-trienyl-selanes Se(C(7)H(7))(2) (2c), R--Se--C(7)H(7) with R = Bu, (t)Bu, Ph, 4-F--C(6)H(4) (12a,b,c,d) were prepared by the reaction of the corresponding silanes, Si(SeMe(3))(2) and R--Se--SiMe(3), respectively, with tropylium bromide C(7)H(7)Br. In spite of the low stability of the selanes even in dilute solutions and at low temperature, they could be characterised by their (1)H, (13)C and (77)Se NMR parameters. Coupling constants (1)J((77)Se,(13)C) were measured and calculated by DFT methods at the B3LYP/6-311+G(d,p) level of theory. The comparison of experimental and calculated coupling constants (1)J((77)Se,(13)C) included numerous selenium carbon compounds with largely different Se--C bonds, revealing a satisfactory agreement. Both the spin-dipole (SD) and the paramagnetic spin-orbital (PSO) terms contributed significantly to the spin-spin coupling interaction, in addition to the Fermi contact (FC) term.     

From propargylic biscarbonate to diaryl[n]dendralenes

An efficient cross-coupling reaction using a low cost carbon-supported palladium (Pd/C) catalyst for the synthesis of cross-conjugated compounds, diaryl[n]dendralenes, has been developed. The reaction of a propargylic biscarbonate with phenylboronic acid using Pd/C and phosphine ligand (S-Phos) gave 2,3-diphenyl[2]dendralene in high yield. We found that Pd/C was an effective catalyst for the synthesis of dialyl[n]dendralenes. The synthesis of various dendralenes was successfully achieved under the optimized conditions, giving dialyl [2] and [4] dendralenes in good yields.     

Cycloaddition reactions of cross-conjugated enaminones

A detailed study on the cycloaddition reactions of cross-conjugated enaminones 1 and 9 with dimethyl acetylenedicarboxylate (DMAD) and ketenes is described. The reactions provide a variety of pyran (4, 11), pyran-2-one 14 and pyrrol-3-ylidene 8 derivatives having great pharmacological and medicinal significance. Moreover, the preferred formation of product 8 over 7 has been explained on the basis of molecular dynamics (MD) simulations performed on the intermediate 5 in the gas phase. The synthetic potential of enaminones 9 has further been explored by treating them with Lawesson's reagent (LR) and trapping the in situ generated enaminothiones 16 with some acrylates 17 leading to the formation of thiopyran derivatives 19. To the best of our knowledge, this is the first report in which cross-conjugated enaminothiones 16 have been utilized in cycloaddition reactions.     

Synthesis of Δ-15-deoxy-PG-J1 methyl ester and epi-Δ-15-deoxy-PG-J1

The synthesis of racemic Δ^12,14-15-deoxy-PG-J₁ is readily achieved in six steps employing as the key transformation a one-pot conjugate addition-Peterson olefination sequence using exo-2-trimethylsilyl-3a,4,7,7a-tetrahydro-4,7-methanoinden-1-one. Additionally a Noyori-type three-component coupling approach is employed for the synthesis of enantioenriched epi-Δ¹²-15-deoxy-PG-J₁ from 4(S)-tert-butyldimethylsilyloxycyclopent-2-enone.     

Consecutive Rh(I)-catalyzed Alder-ene/Diels-Alder/Diels-Alder reaction sequence affording rapid entry to polycyclic compounds

Conversion of acyclic allenynes to polycyclic compounds using consecutive transition metal catalyzed carbon-carbon bond forming reactions in a single chemical operation is described. Reaction of an allenyne with a Rh(I) catalyst affords a cross-conjugated triene via a formal Alder-ene reaction. The triene then participates in a Rh(I)-catalyzed intramolecular [4+2] cycloaddition reaction to generate a new conjugated diene. An external dienophile is added to this diene which then undergoes a second [4+2] cycloaddition reaction to afford a complex polycyclic ring system. This reaction sequence demonstrates the synthetic potential of allenynes and cross conjugated trienes and highlights the rapid increases in molecular complexity that are possible by one-pot sequential transition metal catalyzed carbon-carbon bond forming reactions.