John Blacker

Efficient rhodium and iridium-catalysed asymmetric transfer hydrogenation using water-soluble aminosulfonamide ligands

Abstract A range of aromatic ketones was reduced asymmetrically under transfer hydrogenation conditions using enantiomerically pure catalysts derived from water-soluble diamine ligands and [Cp*MCl 2 ] 2 (Cp*=pentamethylcyclopentadienyl, M=Rh, Ir). High catalytic activity and enantioselectivity were observed in systems containing up to 51% water.

Synthesis of water-soluble aminosulfonamide ligands and their application in enantioselective transfer hydrogenation

Abstract Water-soluble analogues of Noyoris (1S,2S)-N-(p-tolylsulfonyl)-1,2-diphenylethylenediamine and Knochels (1R,2R)-N-(p-tolylsulfonyl)-1,2-diaminocyclohexane, containing an additional sulfonic acid group, have been synthesised. The ruthenium catalysed reduction of aromatic ketones using enantiomerically pure catalyst derived from water soluble ligands and [RuCl2(p-cymene)]2 has been examined. High enantioselectivity and moderate activity were observed in the 2-propanol/base system. The addition of water is necessary to stabilise the catalyst.

Developments in the Simmons−Smith-Mediated Epoxidation Reaction

The reaction between Et2Zn, ClCH2I, sulfide, and aldehyde furnishes terminal epoxides in high yields. The reaction occurs via a zinc carbenoid, which reacts with the sulfide to furnish an ylide, which in turn reacts with the aldehyde to give the epoxide. Chiral ligands capable of chelation to zinc [1,2-amino alcohols, amino acids, bis(oxazolines), taddols] were examined, but only low enantioselectivity was observed (up to 11% ee). A number of chiral sulfides were also examined, but again only low enantioselectivity was observed (up to 16% ee). However, linking a sulfide to a metal capable of chelation to zinc [a bis(oxazoline) bearing a sulfide at the 5 position] produced a reagent that gave up to 54% ee in the epoxidation process. The same system was applied to the preparation of terminal aziridines from imines. The optimum group on nitrogen was a sulfonyl group, although groups capable of chelation of zinc (o-methoxyphenyl) were also effective. Attempts to render the aziridination process asymmetric by using the above strategy were less successful (up to 19% ee).

A novel procedure for the synthesis of aziridines: application of Simmons–Smith reagents to aziridination

The reaction of Simmons–Smith carbenoids with imines in the presence of sulfides provides N-(p-toluenesulfonyl)- and N-[(1,1,1-trimethylsilyl)ethyl]sulfonyl-substituted aziridines in high yield.

The Strecker reaction: kinetic and equilibrium studies of cyanide addition to iminium ions.

Kinetics studies are reported of the reactions of benzylidene benzylamine 4a, and of benzylidene allylamine 4b, with cyanide in aqueous buffers to give the corresponding [small alpha]-aminonitriles. The results allow the calculation of values of rate and equilibrium constants for reaction of the iminium ions formed from 4a and 4b with cyanide ions. These values are compared with those, obtained from the hydrolysis reactions, for reaction of the iminium ions with hydroxide ions and with water. Comparison with some other iminium ions reveals that those formed from 4a and 4b are relatively unreactive due to the possibilities of charge delocalisation.