10 research outputs found
Halogenation effects in Intramolecular Furan Diels-Alder reactions:broad scope synthetic and computational studies
For the first time a comprehensive synthetic and computational study of the effect of halogen substitution on both furan and dienophile for the intramolecular Furan Diels-Alder (IMDAF) reaction has been undertaken. Contrary to our initial expectations, halogen substitution on the dienophile was found to have a significant effect, making the reactions slower and less thermodynamically favourable. However, careful choice of the site of furan halogenation could be used to overcome dienophile halogen substitution, leading to highly functionalised cycloadducts. These reactions are thought to be controlled by the interplay of three factors: positive charge stabilisation in the transition state and product, steric effects and a dipolar interaction term identified by high level calculations. Frontier orbital effects do not appear to make a major contribution in determining the viability of these reactions, which is consistent with our analysis of calculated transition state structural data
Silver Effect in Regiodivergent Gold-Catalyzed Hydroaminations
We
report a silver-induced switching of regioselectivity in gold-catalyzed
reactions, and we provide mechanistic evidence to suggest a true “silver
effect”: that is, one that is implicated in the catalytic process
itself, via σ-gold π-silver acetylides. These results
are of significance because they clearly show that the use of silver
as halide abstractors in gold-catalyzed reactions may result in “silver
effects” when terminal alkyne substrates are involved
Gold(I)-catalysed synthesis of cyclic sulfamidates : current scope, stereochemistry and competing ene-allene cycloisomerisation
AbstractSix-membered cyclic sulfamidates are prepared in high yields by treatment of allenic sulfamates with readily available Ph3PAuNTf2. The reaction enables formation of N-substituted quaternary centres in high yields. The relative stereochemistry has been unambiguously determined. A π-rearrangement is faster than hydroamination in the case of an allyl-substituted sulfamate and a mechanism is proposed for this process
Gold(I)-catalysed synthesis of cyclic sulfamidates by intramolecular allene hydroamination
Six-membered cyclic sulfamidates are prepared in high yields by treatment of allenic sulfamates with readily available gold(i) complexes. The reaction enables formation of N-substituted quaternary centres and complements existing processes for sulfamidate formation
Stablized phosphazides
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Gold(I)-catalysed synthesis of cyclic sulfamidates : current scope, stereochemistry and competing ene-allene cycloisomerisation
Experimental fil
Fluoride ion chelation by a bidentate phosphonium/borane Lewis acid
The phosphonium borane [1-Mes2B-2-MePh2P-(C6H4)]+ ([2]+) has been synthesized as an iodide salt by alkylation of 1-Mes2B-2-Ph2P-(C6H4) with MeI. This novel cationic borane complexes fluoride to afford the corresponding zwitterionic fluoroborate complex 1-FMes2B-2-MePh2P-(C6H4) (2-F) with a binding constant in MeOH exceeding that of 1-Mes2B-4-MePh2P-(C6H4) ([1]+) by at least 4 orders of magnitude. Structural and computational results indicate that the high fluorophilicity of [2]+ arises from both Coulombic and cooperative effects which lead to formation of a B-F→P interaction with a F→P distance of 2.666(2) Å. These results, which are supported by NBO and AIM analyses, show that the latent phosphorus-centered Lewis acidity of the phosphonium moiety in [2]+ can be exploited to enhance fluoride binding via chelation
A 1,1'-ferrocenyl phosphine-borane: synthesis, structure and evaluation in Rh-catalyzed hydroformylation
The new ambiphilic ligand Ph2P-(1,1′-ferrocenyl)-BMes 2, prepared by sequential lithiation/electrophilic trapping of 1,1′-dibromoferrocene, adopts a monomeric structure free of dative P → B and Fe → B interactions. This flexible phosphine-borane and the related o-phenylene bridged system have been evaluated in Rh-catalyzed hydroformylation