Dioxygenase-catalysed sulfoxidation of bicyclic alkylaryl sulfides and chemoenzymatic synthesis of acyclic disulfoxides

Toluene- and naphthalene-dioxygenase-catalysed oxidation of six bicyclic disulfide substrates, using whole cells of Pseudomonas putida, gave the corresponding monosulfoxides with high ee values and enantiocomplementarity, in most cases. Two alcohol-sulfoxide diastereoisomers, formed from the reaction of the (R)-1,3-benzodithiole-1-oxide metabolite with n-butyllithium and benzaldehyde, were separated and stereochemically assigned. Treatment, of enantiopure (1R,3R)-benzo-1,3-dithiole-1,3-dioxide, obtained by chemoenzymatic synthesis, with alkyllithium reagents, resulted in a novel ring-opening reaction which proceeded with inversion of configuration to yield a series of acyclic disulfoxides. (C) 2003 Elsevier Ltd. All rights reserved.

Chemoenzymatic synthesis of enantiopure dihydroxy-1,2,3,4-tetrahydronaphthalenes from naphthalene and dihydronaphthalene precursors

cis-Dihydrodiol, cis-tetrahydrodiol and arene hydrate bacterial metabolites, of naphthalene and 1,2-dihydronaphthalene, have been used as synthetic precursors; chemoenzymatic and enzyme-catalysed syntheses have been used to obtain all possible enantiopure samples of dihydroxy-1,2,3,4-tetrahydronaphthalene stereoisomers.

Efficient heterogeneous asymmetric catalysis of the Mukaiyama aldol reaction by silica- and ionic liquid-supported Lewis acid copper(II) complexes of bis(oxazolines)

Lewis acid complexes based on copper(II) and an imidazolium-tagged bis(oxazoline) have been used to catalyse the asymmetric Mukaiyama aldol reaction between methyl pyruvate and 1-methoxy-1-tri-methylsilyloxypropene under homogeneous and heterogeneous conditions. Although the ees obtained in ionic liquid were similar to those found in dichloromethane, there was a significant rate enhancement in the ionic liquid with reactions typically reaching completion within 2 min compared with only 55% conversion after 60 min in dichloromethane. However, this rate enhancement was offset by lower chemoselectivity in ionic liquids due to the formation of 3-hydroxy-1,3-diphenylbutan-1-one as a by-product. Supporting the catalyst on silica or an imidazolium-modified silica using the ionic liquid or in an ionic liquid-diethyl ether system completely suppressed the formation of this by-product without reducing the enantioselectivity. Although the heterogeneous systems were characterised by a drop in catalytic activity the system could be recycled up to five times without any loss in conversion or ee.

One-pot multistep synthetic strategies for the production of fenpropimorph using an ionic liquid solvent

The one-pot synthesis of the fungicide fenpropimorph has been achieved using two different synthetic strategies in an ionic liquid. The first pathway consists of a Heck coupling followed by reductive amination; the second pathway consists of an aldol condensation followed by hydrogenation/reductive amination. Homogeneous and heterogeneous palladium catalysts have been utilised in the ionic liquid to provide a catalyst/solvent system that is suitable for recycling and process optimisation.

Lewis acid platinum complexes of conformationally flexible NUPHOS diphosphines: Highly efficient catalysts for the carbonyl-ene reaction

Enantiopure Lewis acid complexes of conformationally flexible acyclic and monocyclic NUPHOS diphosphines, delta- and lambda-[(NUPHOS)Pt(OTf)(2)], are efficient catalysts for the carbonyl-ene reaction between various unsymmetrical 1,1'-disubstituted alkenes and phenylglyoxal or ethyl glyoxylate. While catalyst performance was substrate dependent, ee values as high as 95% and yields up to 90% have been obtained. In a number of cases catalysts generated from delta- and lambda-[(NUPHOS)Pt{(S)-BINOL}] showed marked enhancements in enantioselectivity in ionic liquids compared with organic media. Although an enhancement in enantioselectivity was not obtained for all substrate combinations in such cases, the enantioselectivities were comparable to those obtained in dichloromethane. Furthermore, although the ee's are initially comparable in both the ionic liquid and dichloromethane, a gradual erosion of ee with time was found in the organic solvent, whereas the ee remained constant in the ionic liquid. Preliminary kinetic investigations suggest that the decrease in ee may be due to a faster racemization of the catalyst in dichloromethane compared with the ionic liquid.

Comparative study of diastereoisomer interconversion in chiral BINOL-ate and diamine platinum complexes of conformationally flexible NUPHOS diphosphines

A thorough and detailed study of diastereointerconversion in the chiral platinum complexes [(NUPHOS)Pt{(S)-BINOL}] (3a-e) has been undertaken and compared with the results of a similar study with [(BIPHEP)Pt{(S)-BINOL}]. Rate data revealed that this process obeys first-order relaxation kinetics, and rate constants for conversion of the minor to the major diastereoisomer have been obtained. Eyring analysis of the data gave DeltaH(double dagger) and DeltaS(double dagger) values of 22-25 kcal mol(-1) and -1 to -16 eu, respectively. In combination with computational analysis, these studies indicate that atropinversion most likely occurs via an on-metal pathway involving a planar seven-membered transition state. Substitution of (S)-BINOL for (S,S)-DPEN results in a marked reduction in the barrier to atropinversion; a DeltaH(double dagger) value of 17 kcal mol(-1) has been determined for the conversion of delta-[(Ph-4-NUPHOS)Pt{(S,S)-DPEN}]Cl-2 to lambda-[(Ph-4-NUPHOS)Pt{(S,S)-DPEN}]Cl-2, which could indicate that an alternative mechanism operates.