Fluoride-promoted rearrangement of organo silicon compounds:A new synthesis of 2-(arylmethyl)aldehydes from 1-alkynes

A new approach to 2-(arylmethyl)aldehydes 4 based upon a 1,2-anionotropic rearrangement of an aryl group is presented. The synthetic sequence begins with a silylformylation reaction of terminal acetylenes 5 with aryl and heteroaryl silanes 6, followed by treatment of the products (Z)-1 with TBAF. The optimization of the experimental conditions of the fluoride-promoted step is described, together with the synthetic potentialities of the process. A plausible mechanism of the rearrangement reaction is reported that suggests the addition of the fluoride ion to the arylsilicon moiety of beta-silylalkenals (Z)-1 and the consequent migration of the aryl group to the adjacent carbon atom. Both aryl and heteroaryl substituents can rearrange without any loss of configuration. Bromo-functionalized substrates undergo an intramolecular reaction that affords exclusively carbacyclobenzyl aldehydes, further enhancing the high synthetic value of this method

Silylformylation - Fluoride-assisted aryl migration of acetylenic derivatives in a versatile approach to the synthesis of polyfunctionalised compounds

Polyfunctionalised aldehydes and dihydropyrans are prepared from easily available functionalised 1-alkynes through a two-step silylformylation/aryl migration sequence. The silylformylation process is performed under mild experimental conditions and affords the corresponding beta-silylalkenals in high yields. The fluoride-promoted migration step occurs instantaneously with quantitative conversion. The chemo-, regio- and stereoselectivity can be modulated according to the nature and the position of the functional group on the acetylene precursors. When a good leaving group is present in the omega position of the aliphatic chain of the alkyne a cyclisation product is obtained, while a,p-unsaturated aldehydes are generated from propargylic tosylamides. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Electrical and mechanical anharmonicities from NIR-VCD spectra of compounds exhibiting axial and planar chirality: the cases of (S)-2,3-pentadiene and Methyl-d3 (R)- and (S)-[2.2]paracyclophane-4-carboxylate

The IR and Near infrared (NIR) vibrational circular dichroism (VCD) spectra of molecules endowed with noncentral chirality have been investigated. Data for fundamental, first, and second overtone regions of (S)-2,3-pentadiene, exhibiting axial chirality, and methyl-d3 (R)- and (S)-[2.2]paracyclophane-4-carboxylate, exhibiting planar chirality have been measured and analyzed. The analysis of NIR and IR VCD spectra was based on the local-mode model and the use of density functional theory (DFT), providing mechanical and electrical anharmonic terms for all CH-bonds. The comparison of experimental and calculated spectra is satisfactory and allows one to monitor fine details in the asymmetric charge distribution in the molecules: these details consist in the harmonic frequencies, in the principal anharmonicity constants, in both the atomic polar and axial tensors and in their first and second derivatives with respect to the CH-stretching coordinates

Highly selective silylformylation of internal and functionalised alkynes with a cationic dirhodium(II) complex catalyst

The tetracationic complex [Rh(2)(MeCN)(2)(Naft)(4)](BF(4))(4) (Naft = mu-1,8-naphthyridine) was found to be an efficient catalyst for the silylformylation of internal and functionalised alkynes to yield useful synthetic intermediates. The complex exhibits an unprecedented chemoselectivity towards alkyne silylformylation instead of simple hydrosilylation, as well as a good stereoselectivity. The catalytic efficiency of the complex is markedly superior compared to that of previously reported catalysts such as [Rh(+)C(7)H(8)BPh(4)(-)] or Rh(4)(CO)(12); incidentally, the performance of the latter catalyst was found to vary dramatically with its shelf-life, which indicates that the catalyst evolves with ageing towards other species, most notably higher nuclearity rhodium carbonyl clusters, which are more chemoselective towards silylformylation. Preliminary results on the determination of the catalytically active species in the case of complex [Rh(2)(MeCN)(2)(Naft)(4)](BF(4))(4) indicate that the complex is reduced in situ to a dirhodium(I) species which maintains the dimeric, lantern-shaped structure

Cationic complexes of dirhodium(II) with 1,8-naphthyridine: Catalysis of reactions involving silanes

The synthesis of cationic dirhodium(II) complexes by partial or total substitution of the acetate groups of [Rh-2(OAC)(4)] with different homoleptic neutral bidentate ligands has been attempted. The ligand 1,8-naphthyridine gave the best results: substitution of one as well as of all four acetate ligands is possible, giving rise to mono-, di- and tetra-cationic complexes. One of the resulting tetrasubstituted complexes has been structurally characterised and found to exhibit the expected lantern-shaped structure. All cationic complexes have been investigated as catalysts in different reactions involving silanes: promising results have been obtained, particularly in the silylformylation of alkynes

Cationic carboxylato complexes of dirhodium(II) with oxo thioethers: Promising catalysts with unusual coordination modes

Removal of an acetato ligand from dirhodium(II) acetato complexes with thioethers of the general structure [Rh-2(mu-OAc)(4)(RSCH(2)Z)(2)] yields the cationic complexes [Rh-2(mu-OAc)(3)(RSCH(2)Z)(2)](BF4) (R = Me, Ph; Z = C(O)OEt, CH2(O)OMe). The methylthio complex with Z = C(O)OEt has been structurally characterized and found to exhibit an unusual bidentate O-S coordination of the oxo thioether ligands. Preliminary tests indicate that the complex is a promising catalyst of the silylformylation or hydrosilylation of 1-hexyne with dimethylphenylsilane

Novel Pt(0) catalysts supported on functional resins for the chemoselective hydrogenation of citral to the \u3b1,\u3b2-unsaturated alcohols geraniol and nerol

Nanoclustered Pt-0 catalysts based on cross-linked macromolecular matrices are evaluated in the hydrogenation of an alpha, beta-unsaturated aldehyde (citral). Matrices and catalysts are characterized by inverse steric exclusion chromatography, scanning electron microscopy, X-ray microprobe analysis, and transmission electron microscopy. The monometallic catalysts exhibit remarkable selectivity for geraniol/nerol when 2-3-nm, regularly shaped, spherical metal nanoclusters are deposited on the Supports from solutions of solvated platinum atoms prepared by metal vapor synthesis (MVS). The immobilization in the polymer framework of ions of a second metal such as Fe(II), Co(II), or Zn(II) enhances the selectivity of the Pt catalysts by up to more than 90%