RESUMEN

We report the preparation of enantiomerically pure constrained geometry complexes (cgc) of the rare-earth metals bearing a pentadienyl moiety (pdl) derived from the natural product (1R)-(-)-myrtenal. The potassium salt 1, [Kpdl*], was treated with ClSiMe2 NHtBu, and the resulting pentadiene 2 was deprotonated with the Schlosser-type base KOtPen/nBuLi (tPen=CMe2 (CH2 Me)) to yield the dipotassium salt [K2 (pdl*SiMe2 NtBu)] (3). However, 3 rearranges in THF solution to its isomer 3' by a 1,3-H shift, which elongates the bridge between the pdl and SiMe2 NtBu moieties by one CH2 unit. This is crucial for the successful formation of various monomeric C1 - or dimeric C2 -symmetric rare-earth cgc complexes with additional halide, tetraborohydride, amido and alkyl functionalities. All compounds have been extensively characterised by solid-state X-ray diffraction analysis, solution NMR spectroscopy and elemental analyses.

RESUMEN

Targeting the synthesis of rare-earth-metal pentadienyl half-sandwich tetramethylaluminate complexes, homoleptic [Ln(AlMe4 )3 ] (Ln=Y, La, Ce, Pr, Nd, Lu) were treated with equimolar amounts of the potassium salts K(2,4-dmp) (2,4-dmp=2,4-dimethylpentadienyl), K(2,4-dipp) (2,4-dipp=2,4-diisopropylpentadienyl), and K(2,4-dtbp) (2,4-dtbp=2,4-di-tert-butylpentadienyl). The reactions involving the larger rare-earth-metal centers lanthanum, cerium, praseodymium, and neodymium gave selectively the desired half-sandwich complexes [(2,4-dmp)La(AlMe4 )2 ], [(2,4-dipp)La(AlMe4 )2 ], and [(2,4-dtbp)Ln(AlMe4 )2 ] (Ln=La, Ce, Pr, Nd) in high crystalline yields. Smaller rare-earth-metal centers yielded preferentially the sandwich complexes [(2,4-dmp)2 Ln(AlMe4 )] (Ln=Y, Lu) and [(2,4-dipp)2 Y(AlMe4 )]. Activation with fluorinated borate/borane co-catalysts gave highly active catalyst systems for the fabrication of polyisoprene, displaying molecular weight distributions as low as Mw /Mn =1.09 and a maximum cis-1,4 selectivity of 90.4 %. The equimolar reaction of half-sandwich complex [(2,4-dtbp)La(AlMe4 )2 ] with B(C6 F5 )3 led to the isolation and full characterization of the single-component catalyst {{(2,4-dtbp)La[(µ-Me)2 AlMe(C6 F5 )]}[Me2 Al(C6 F5 )2 ]}2 . The reaction of the latter complex with 10 equivalents of isoprene could be monitored by 1 H NMR spectroscopy. Also, a donor-induced aluminato/gallato exchange was achieved with [(2,4-dtbp)La(AlMe4 )2 ] and GaMe3 (OEt2 ) leading to [(2,4-dtbp)La(GaMe4 )2 ].

RESUMEN

Heavy metal on Lewis acid: The combination of lanthanide metals and AlCl3 has been employed for selective single C-F activation in benzofulvenes comprising an exocyclic CF3 substituent. Intermediate ϵ,ϵ-difluorinated metal-dienyl species react with a large variety of aldehydes in a highly regio- and diastereoselective fashion to afford 1,1-disubstituted indenes bearing a difluorovinyl group. These new building blocks have been further transformed through a hydrogenation-cyclization process into fluorinated heterocyclic spiro compounds.

RESUMEN

Dienoic acids and pentadienyl alcohols are coupled in a decarboxylative and dehydrative manner at ambient temperature using Pd(0) catalysis to generate 1,3,6,8-tetraenes. Contrary to related decarboxylative coupling reactions, an anion-stabilizing group is not required adjacent to the carboxyl group. Of mechanistic importance, it appears that both the diene of the acid and the diene of the alcohol are required for this reaction. To further understand this reaction, substitutions at every unique position of both coupling partners was examined and two potential mechanisms are presented.

RESUMEN

New variation in the Nazarov cyclization has been developed by preparing divinyl and arylvinyl epoxides as pentadienyl cation precursors for the first time. Highly substituted cyclopentadienes, hydrindienes, and indenes were synthesized to demonstrate the compatibility of this reaction with substrates bearing a variety of substitutions and having different types of epoxides. Application of this method in the synthesis of resveratrol-based natural products was also demonstrated.

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RESUMEN

In this work the synthesis and antiparasitical activity of new 1,5-diaryl-3-oxo-1,4-pentadienyl derivatives are described. First, compounds 1a, 1b, 1c and 1d were prepared by acid-catalyzed aldol reaction between 2-butanone and benzaldehyde, anisaldehyde, p-N,N-dimethylaminobenzaldehyde and p-nitrobenzaldehyde. Reacting each of the methyl ketones 1a, 1b, 1c and 1d with the p-substituted benzaldehydes under basic-catalyzed aldol reaction, we further prepared compounds 2a-2p. All twenty compounds were evaluated for antiproliferative activity, particularly for promastigote of Leishmania amazonensis and epimastigote of Trypanosoma cruzi. All compounds showed good activity while nitro compounds 2i and 2k showed inhibition activity at a few µM.

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