Mechanistic Studies on the Base-Promoted Ring Opening of Glycal-Derived -Dibromocyclopropanes.

In the presence of a nucleophilic base, ring-fused -dibromocyclopropanes derived from d-glycals undergo ring opening to give 2-deoxy-2-(-bromomethylene)glycosides. Such cleavage of an exocyclic cyclopropane bond contrasts with the more usual silver-promoted ring-expansion reactions in which endocyclic bond cleavage occurs. Experimental and theoretical studies are reported which provide insights into the reaction mechanism and the origin of its kinetic selectivity for -configured bromoalkene products.

Catalytic Asymmetric Staudinger-aza-Wittig Reaction for the Synthesis of Heterocyclic Amines.

Many natural products and medicinal drugs are heterocyclic amines possessing a chiral quaternary carbon atom in their heterocyclic ring. Herein, we report the first catalytic and asymmetric Staudinger-aza-Wittig reaction for the desymmetrization of ketones. This highly enantioselective transformation proceeds at room temperature to provide high yields-even on multigram scales-of nitrogen heterocycles featuring a chiral quaternary center.

Asymmetric synthesis of multiple quaternary stereocentre-containing cyclopentyls by oxazolidinone-promoted Nazarov cyclizations.

Carbometalation of oxazolidinone ()-substituted ynamides is used to generate highly substituted -divinyl (and aryl vinyl) ketones for use in Nazarov cyclizations. The -group serves as a remarkably effective chiral activating group, enabling the torquoselective Nazarov cyclization of these sterically congested substrates to be performed under mild conditions. It also serves as a charge-stabilizing group in the intermediate oxyallyl cation, suppressing undesired [1,2]-sigmatropic shifts of neighboring substituents and facilitating the regio- and stereoselective incorporation of nucleophiles to yield cyclopentanoids containing up to three contiguous all-carbon quaternary (4°) stereocentres.

Synthesis of spirocyclic orthoesters by 'anomalous' rhodium(ii)-catalysed intramolecular C-H insertions.

A tetrahydropyranyl acetal bearing a proximal phenyl diazoketone substituent underwent Rh(ii)-catalysed C-H insertion via an 'anomalous' C-O bond-forming, rather than C-C bond-forming, transformation, giving spirocyclic orthoesters. Density functional theory calculations with M06 show that the formation of these anomalous products involves hydride transfer to the rhodium carbene, giving an intermediate zwitterion which undergoes C-O bond formation in preference to C-C bond formation.

Multistereocenter-Containing Cyclopentanoids from Ynamides via Oxazolidinone-Controlled Nazarov Cyclization.

Achieving ready-enantioselective access to multistereocenter-containing cyclopentyl rings is an area of great significance to organic synthesis. In this work, we describe a general protocol for accessing multistereocenter-containing cyclopentanoids from simple N-alkynyloxazolidinones (Ox-ynamides). This protocol involves conversion of Ox-ynamides into Ox-activated divinyl and aryl vinyl ketones that undergo facile Nazarov cyclization with excellent chemo-, regio-, and stereocontrol.

A bidirectional synthesis of spiroacetals via Rh(ii)-catalysed C-H insertion.

Acyclic methylene acetals bearing two diazoester subunits have been converted to [5,5]-spiroacetals via bidirectional C-H insertion under Rh(ii) catalysis. Using a chiral Rh(ii) catalyst, the major diastereomer can be produced in high enantiomeric excess (89%).

Probing function and structure of trehalose-6-phosphate phosphatases from pathogenic organisms suggests distinct molecular groupings.

The trehalose biosynthetic pathway is of great interest for the development of novel therapeutics because trehalose is an essential disaccharide in many pathogens but is neither required nor synthesized in mammalian hosts. As such, trehalose-6-phosphate phosphatase (TPP), a key enzyme in trehalose biosynthesis, is likely an attractive target for novel chemotherapeutics. Based on a survey of genomes from a panel of parasitic nematodes and bacterial organisms and by way of a structure-based amino acid sequence alignment, we derive the topological structure of monoenzyme TPPs and classify them into 3 groups.