Excellent enantioselectivities (up to 97 % ee) and diastereoselectivities (up to >99:1 d.r.) have been achieved in the desymmetrization of cyclopentenes by catalytic hydroformylation. This novel methodology provides an efficient and concise synthetic route to chiral cyclopentane carboxaldehydes. The key intermediate, (1S,3S)‐(3‐hydroxymethyl)cyclopentanol, for the synthesis of carbocyclic‐ddA was obtained
Bis-alkene complexes of triorgano-substituted cations of stannylium and germylium ions were synthesized by alkyl fragmentation reactions and were characterized by NMR spectroscopy and for the tin compound also by X-ray structure analysis of the corresponding perfluorinated tetraarylborate. According to experimental results and quantum mechanical computations, the central group 14 element adopts in these pentacoordinated cations a distorted trigonal-bipyramidal coordination geometry with the two C=C double bonds occupying the apical positions. This geometrical arrangement places seven carbon atoms at a distance less than the sum of the van der Waals radii around the central atom. Quantum mechanical computations at the MP2/6-311G(d,p) (C,H) SDI) (Sn, Ge, Si) level reveal substantial interaction energies between the group 14 element and the C=C double bond and electron density distributions that are typical for noncovalent pi-donor interactions.
Carbon-13 NMR spectra of carbonium ions in the solid state: The 2-norbornyl cation
作者:Costantino S. Yannoni、Volker Macho、Philip C. Myhre