A novel bifunctional allyldisilane as a triple allylation reagent in the stereoselective synthesis of trisubstituted tetrahydrofurans

Three for the price of two: A bifunctional allyldisilane undergoes a two-step triple allylation sequence with pairs of aldehydes to give all-cis trisubstituted tetrahydrofurans in excellent enantio- and diastereoselectivity (see scheme). The first allylation step, which sets up the key stereogenic

A modular approach to aryl-C-ribonucleosides via the allylic substitution and ring-closing metathesis sequence: a stereocontrolled synthesis of all four α-/β- andd-/l-C-nucleoside stereoisomers

Iridium(I)-catalyzed allylation of the enantiopure monoprotected copper(I) alkoxide, generated from (S)-5a, with the enantiopure allylic carbonates (R)-9a,b has been developed as the key step in a new approach to C-nucleoside analogues. The anomeric center was thus constructed via a stereocontrolled formation of the C-O rather than C-C bond with retention of configuration. The resulting bisallyl ethers 15a,b (>= 90% de and >99% cc) were converted into C-ribosides 29a,b via the Ru-catalyzed ring-closing metathesis, followed by a diastereoselective dihydroxylation catalyzed by OsO(4) or RuO(4) and deprotection. Variation of the absolute configuration of the starting segments 5a and 9a,b allowed a stereocontrolled synthesis of all four alpha/beta-D/L-combinations

Vicinal amino alcohols as organocatalysts in asymmetric cross-aldol reaction of ketones: Application in the synthesis of convolutamydine a

Leucinol and valinol have been identified as efficient organocatalysts for the aldol reaction of isatin and its derivatives (as examples of activated, non-enolizable ketones) with acetone. Uncommon mechanistic features were observed and used in the formulation of the transition state of the reaction

Global potentials for the interaction between rare gases and graphene-based surfaces: An atom-bond pairwise additive representation

Global potentials for the physisorption of rare-gas atoms on graphene and graphite, amenable for a variety of dynamics simulations, are reported. An atom-bond pairwise additive form of the potential is used, where the interaction pairs, represented by proper analytical functions, are constituted by the Rg atom (Rg = He, Ne, Ar, Kr) and the C-C bonds of the graphene sheet(s). The parameters of the atom-bond pair potential, derived from the polarizability of the interacting partners, are fine-tuned, exploiting calculations of the prototypical Rg-coronene system using high-level electronic structure methods and large basis sets. The atom-graphene/graphite potential is further expanded in a Fourier series, and it is found that for an accurate representation of the interaction only a small number of corrugation terms need to be added to the laterally averaged potential. Furthermore, this corrugation part of the potential is both identical for Rg-graphene and Rg-graphite; in other words, inner layers of graphite only play a role in the laterally averaged Rg-graphite potential. For all systems, the hollow at the center of the carbon ring is the preferred adsorption site, although diffusion barriers are low. The present results compare well with previous data regarding well depths and equilibrium distances at different adsorption sites and, for graphite, the long-range dispersion coefficient C3. In addition, binding energies (eigenvalues of the laterally averaged potentials) are in a fairly good agreement with experimental determinations, providing further support for the reliability of the potentials. © 2013 American Chemical Society.The work has been funded by Spanish grants FIS2010-22064- C02-02 and CSD2009-00038. Allocation of computing time by CESGA (Spain) and the COST-CMTS Action CM1002 “Convergent Distributed Environment for Computational Spectroscopy (CODECS)” are also acknowledged. F.P. acknowledges financial support from the Italian Ministry of University and Research (MIUR) for PRIN contracts.Peer Reviewe