Mark Purdie

Counterintuitive kinetics in Tsuji-Trost allylation: ion-pair partitioning and implications for asymmetric catalysis.

The kinetics of Pd-catalyzed Tsuji-Trost allylation employing simple phosphine ligands (L = Ar3P, etc.) are consistent with turnover-limiting nucleophilic attack of an electrophilic [L2Pd(allyl)]+ catalytic intermediate. Counter-intuitively, when L is made more electron donating, which renders [L2Pd(allyl)]+ less electrophilic (by up to an order of magnitude), higher rates of turnover are observed. In the presence of catalytic NaBArF, large rate differentials arise by attenuation of ion-pair return (via generation of [L2Pd(allyl)]+ [BArF]-) a process that also increases the asymmetric induction from 28 to 78% ee in an archetypal asymmetric allylation employing BINAP (L*) as ligand. There is substantial potential for analogous application of [M]n+([BArF]-)n cocatalysis in other transition metal catalyzed processes involving an ionic reactant or reagent and an ionogenic catalytic cycle.

Direct acylation of aryl chlorides with aldehydes by palladium-pyrrolidine Co-catalysis.

A palladium catalyst system has been developed that allows for the direct acylation of aryl chlorides with aldehydes. The choice of ligand, as well as the presence of pyrrolidine and molecular sieves is shown to be critical to the catalysis, which appears to proceed via an enamine intermediate. The reaction was successful for a wide range of aryl chlorides and tolerant of functionality on the aldehyde component, giving easy access to alkyl aryl ketones in modest to good yields.

Expansion of the Ligand Knowledge Base for Chelating P,P-Donor Ligands (LKB-PP)

We have expanded the ligand knowledge base for bidentate P,P- and P,N-donor ligands (LKB-PP, Organometallics2008, 27, 1372–1383) by 208 ligands and introduced an additional steric descriptor (nHe8). This expanded knowledge base now captures information on 334 bidentate ligands and has been processed with principal component analysis (PCA) of the descriptors to produce a detailed map of bidentate ligand space, which better captures ligand variation and has been used for the analysis of ligand properties.

Double Arylation of Allyl Alcohol via a One-Pot Heck Arylation–Isomerization–Acylation Cascade

A one-pot, two-step catalytic protocol has been developed. A regioselective Heck coupling between aryl bromides and allyl alcohol leads to the generation of arylated allyl alcohols that in situ isomerize to give aldehydes, which then undergo an acylation reaction with a second aryl bromide. A variety of aryl bromides can be employed in both the initial Heck reaction and the acylation, providing easy access to a wide variety of substituted dihydrochalcones.

Enantioselective synthesis of α-hydroxyketones using the ditox asymmetric building block

The 2-(R)and 2-(S)-hydroxy-1-phenylbutan-1-ones have been prepared in high enantiomeric excesses and in five steps from propanal using a dithiane oxide unit as an asymmetric building block and a modified Sharpless enantioselective sulphur oxidation as the source of Chirality.