Palladium catalysed tandem cyclisation - Anion capture processes .2. Cyclisation onto alkynes or allenes with hydride capture.

A wide range of palladium catalysed regio- and stereo-specific 5-, 6- and 7-exo-dig mono-, bis- and tris-cyclisation processes of aryl and vinyl halides and allylic acetates are described. The mono- and bis-cyclisation processes terminate in hydride capture from piperidine-formic acid or sodium formate. Addition of TI2CO3 results in alkyne-allene isomerisation and leads, after cyclisation, to 1,3-dienes which give Diels-Alder adducts in good yield. Copyright (C) 1996 Elsevier Science Ltd

Synthesis of 2-Alkynoates by Palladium(II)-Catalyzed Oxidative Carbonylation of Terminal Alkynes and Alcohols

A homogeneous PdII catalyst, utilizing a simple and inexpensive amine ligand (TMEDA), allows 2-alkynoates to be prepared in high yields by an oxidative carbonylation of terminal alkynes and alcohols. The catalyst system overcomes many of the limitations of previous palladium carbonylation catalysts. It has an increased substrate scope, avoids large excesses of alcohol substrate and uses a desirable solvent. The catalyst employs oxygen as the terminal oxidant and can be operated under safer gas mixtures.

Synthesis and characterisation of new platinum-acetylide complexes containing diimine ligands

A new class of platinum-bipyridyl compounds has been synthesized by the dehydrohalogenative reaction of [4,4'-bis(tert-butyl)-2,2'-bipyridyl]platinum dichloride [PtCl2((t)Bu(2)bipy)] 1 with terminal alkynes HC=CR, in the presence of copper(I) iodide and diisopropylamine. The products [Pt(C=CR)(2)((t)Bu(2)bipy)] (R=C6H4NO2-p 2, C6H5 3, C6H4CH3-p 4 or SiMe3 5), have been characterised by spectroscopic and analytical methods, and a single crystal molecular structure determination has been carried out on 4. Extended Huckel molecular orbital calculations have also been carried out, and the results are used to help rationalise the voltammetric, EPR and spectroelectrochemical properties of the new compounds. These show that compounds 3, 4 and 5 undergo a one-electron bipyridyl based redox process, but that 2 has an unresolved two-electron process located on the nitro groups.

Highly regioselective platinum catalyzed hydrometallation of propargylic alcohols

A Pt catalysed hydrometallation reaction has been developed that provides b-metallated products as a single region and geometric isomer. The reaction is incredible tolerant of sterics and actually performs better in more sterically congested stubstrates. We have demonstrated this approach in hydrosilylations, hydrostannylations and hydroboronations. We have shown a wide range of silanes to participate in this reactions and a Denmark type one-pot hydrosilylation-Hiyama coupling has been achieved as a single regioisomer. The regioselectivity has been probed for internal alkynes and we have discovered that the regioselectively is determined by both steric and electronic factors. We can selectively form either the a or b-products as a single regioisomer by altering the steric environment and we have discovered that electronic effects overide the sterics.

Platinum catalysed hydrosilylation of propargylic alcohols

A facile and user-friendly protocol has been developed for the selective synthesis of E-vinyl silanes derived from propargylic alcohols using a PtCl2/XPhos catalyst system. The reaction is generally high yielding and provides a single regioisomer at the ß-position with E-alkene geometry. The reaction is extremely tolerant of functionality and has a wide scope of reactivity both in terms of alkynes and silanes used. The catalyst loading has been investigated and it is found that good reactivity is observed at extremely low catalyst loadings. This methodology has also been extended to a one-pot hydrosilylation Denmark–Hiyama coupling.

Selective Hydrogenation of Acetylene over Pd-Boron Catalysts: A Density Functional Theory Study

Boron-modified Pd catalysts have shown excellent performance for the selective hydrogenation of alkynes experimentally. In the current work, we investigated the hydrogenation of acetylene on boron-modified Pd(111) and Pd(211) surfaces, utilizing density functional theory calculations. The activity of acetylene hydrogenation has been studied by estimating the effective barrier of the whole process. The selectivity of ethylene formation is investigated from a comparison between the desorption and the hydrogenation of ethylene as well as comparison between the ethylene and the 1,3-butadiene formation. Formation of subsurface carbon and hydrogen on both boron-modified Pd(111) and Pd(211) surfaces has also been evaluated, since these have been reported to affect both the activity and the selectivity of acetylene hydrogenation to produce ethylene on Pd surfaces. Our results provide some important insights into the Pd B catalysts for selective hydrogenation of acetylene and also for more complex hydrogenation systems, such as stereoselective hydrogenation of longer chain alkynes and selective hydrogenation of vegetable oil.

CONVENIENT ONE-POT SYNTHESIS OF HEXA-N-BUTYLDITIN FROM BIS(TRI-N-BUTYLTIN) OXIDE

Hexa-n-butylditin is prepared in high yield (83%), by reduction of bis(tri-n-butyltin) oxide with sodium borohydride in ethanol. The first stage is reduction. to tri-n-butyltin hydride (not isolated), which rapidly gives hexa-n-butylditin with the Loss of hydrogen under the basic reaction conditions.

Nucleoside Azide-Alkyne Cycloaddition Reactions Under Solvothermal Conditions or Using Copper Vials in a Ball Mill

Novel nucleoside analogues containing photoswitchable moieties were prepared using 'click' cycloaddition reactions between 5 '-azido-5 '-deoxythymidine and mono- or bis-N-propargylamide-substituted azobenzenes. In solution, high to quantitative yields were achieved using 5mol% Cu(I) in the presence of a stabilizing ligand. 'Click' reactions using the monopropargylamides were also effected in the absence of added cuprous salts by the application of liquid assisted grinding (LAG) in metallic copper reaction vials. Specifically, high speed vibration ball milling (HSVBM) using a 3/32('') (2.38mm) diameter copper ball (62mg) at 60Hz overnight in the presence of ethyl acetate lead to complete consumption of the 5 '-azido nucleoside with clean conversion to the corresponding 1,3-triazole.