Marc C. Perry

Chiral N-heterocyclic carbene-transition metal complexes in asymmetric catalysis

Syntheses and applications of chiral N-heterocyclic carbenes are reviewed. The common features of successful enantioselective catalysts are identified, and the outlook for further investigations is discussed.

A modular approach to trans-chelating, N-heterocyclic carbene ligand complexes

The N-methyl bis-imidazolium salts 3 were converted to the silver carbenes 7, then reacted to give palladium(II) complexes 4 with trans-chelating, bidentate bis-imidazolylidine ligands. The similar salts 8, that do not have N-methyl substituents, gave the tetradentate complexes 9 in direct reactions with palladium chloride. The potential of these complexes for asymmetric catalysis is discussed.

Rhenium catalyzed sulfoxide reduction

Abstract A mild, efficient method for the catalytic reduction of sulfoxides to sulfides with triphenylphosphine and the catalyst ReOCl 3 (PPh 3 ) 2 ( I ) is reported. Aryl sulfoxides are reduced faster than alkyl, and the reaction is successful for sterically hindered sulfoxides and those with common organic functional groups.

Polystyrene-Supported (Catecholato)oxorhenium Complexes: Catalysts for Alcohol Oxidation with DMSO and for Deoxygenation of Epoxides to Alkenes with Triphenylphosphine

Polymer-supported catalysts offer practical advantages for organic synthesis, such as improved product isolation, ease of catalyst recycling, and compatibility with parallel solution-phase techniques. We have developed the (carboxypolystyrene-catecholato)rhenium catalyst 2 derived from tyramine (=4-(2-aminoethyl)phenol), which is effective for alcohol oxidation with dimethylsulfoxide (DMSO) and for epoxide deoxygenation with triphenylphosphine. The supported [Re(catecholato)]catalyst 2 is air- and moisture-stable and can be recovered and used repeatedly without decreasing activity. The procedures work with non-halogenated solvents (toluene). DMSO for Re-catalyzed alcohol oxidation is inexpensive and safer for transport and storage than commonly used peroxide reagents. The oxidation procedure was best suited for aliphatic alcohols, and the mild conditions were compatible with unprotected functional groups, such as those of alkenes, phenols, nitro compounds, and ketones (see Tables 1 and 2). Selective oxidation of secondary alcohols in the presence of primary alcohols was possible, and with longer reaction time, primary alcohols were converted to aldehydes without overoxidation. Epoxides (oxirans) were catalytically deoxygenated to alkenes with this catalyst and Ph3P (see Table 3). Alkyloxiranes were converted to the alkenes with retention of configuration, while partial isomerization was observed in the deoxygenation of cis-stilbene oxide ( cis-1,2-diphenyloxirane). These studies indicate that supported [Re(catecholato)] complexes are effective catalysts for O-atom-transfer reactions, and are well suited for applications in organic synthesis.

Rhenium catalyzed sulfurization of phosphorus(III) compounds with thiiranes: New reagents for phosphorothioate ester synthesis

Abstract A new method for the mild sulfurization of phosphorus(III) compounds with thiiranes catalyzed by ReOCl 3 (PPh 3 ) 2 ( I ) or ReOCl 3 (SMe 2 )OPPh 3 ) ( II ) is reported. The novel catalytic sulfur transfer reactions are rapid and occur efficiently under ambient conditions in organic solvents. This methodology enabled propylene sulfide to be used as a sulfurizing agent for the synthesis of a protected nucleotide phosphorothioate ester.

Novel 17α-ethynylestradiol derivatives: Sonogashira couplings using unprotected phenylhydrazines

Abstract The Pd/Cu catalyzed coupling of 17α-ethynylestradiol with halogenated amino-substrates was investigated. Iodophenylhydrazine and its protected derivatives reacted with 17α-ethynylestradiol to give 4-hydrazinophenyl derivatives without any degradation of the hydrazine group. Unprotected 3-, and 4-iodoaniline reacted similarly to produce the aminophenyl-derivatives. Protection of the amino group of halogenated benzylamines was required for alkyne coupling reactions, in order to avoid competing ortho -palladation of the benzylamine substrates.

Trichlorooxo(triphenylphosphine)(triphenylphosphine oxide)rhenium(V)

The title complex, [ReCl 3 O(C 18 H 15 OP)(C 18 H 15 P)], is produced in a reaction between [Re(O)Cl 3 (PPh 3 ) 2 ] and ethyl 2-hydroxymethyl sulfoxide. The structure is compared to that of [Re(O)Cl 3 (PPhEt 2 )(OPPhEt 2 )] The Re-Cl distances are shorter [2.361 (2)-2.384 (2) A] and the Re-P distance is longer [2.506 (2) A] in the title complex.

Kinetic studies on the reaction of chlorosulfonyl isocyanate with monofluoroalkenes: experimental evidence for both stepwise and concerted mechanisms and a pre-equilibrium complex on the reaction pathway.

Chlorosulfonyl isocyanate (CSI) is reported to react with hydrocarbon alkenes by a stepwise dipolar pathway to give N-chlorosulfonyl-β-lactams that are readily reduced to β-lactams. Substitution of a vinyl hydrogen for a vinyl fluorine changes the dynamics for reaction with CSI so that a concerted pathway is favored. Rate constants were measured for reactions of CSI with monofluoroalkenes and some hydrocarbon alkenes. Activation parameters for two hydrocarbon alkenes and two monofluoroalkenes support this change in mechanism. A plot generated from the natural log of rate constants vs ionization potentials (IP) indicates that fluoroalkenes with IP values >8.9 eV react by a concerted process. Electron-rich monofluoroalkenes with IP values <8.5 eV were found to react by a single-electron transfer (SET) pathway. Hydrocarbon alkenes were also found to react by this dipolar stepwise SET intermediate rather than the previously accepted stepwise dipolar pathway. Data support a pre-equilibrium complex on the reaction pathway just before the rate-determining step of the concerted pathway and a SET intermediate for the stepwise reactions. When the reactions are carried out at lower temperatures, the equilibrium shifts toward the complex or SET intermediate enhancing the synthetic utility of these reactions. Kinetic data also support formation of a planar transition state rather than the orthogonal geometry as reported for ketene [2 + 2] cycloadditions.