The quest for single-enantiomer outcomes in free-radical chemistry

A significant challenge facing free-radical chemists is in the area of stereocontrol, specifically the ability to control the direction of reagent attack at a prochiral radical. While significant inroads have been made in the area of diastereoselective radical chemistry, less successful have been attempts to provide truly enantioselective processes. This article highlights recent efforts in the area of enantioselective free-radical reduction chemistry and describes how single-enantiomer outcomes are possible when simple enantiopure stannanes are used in conjunction with large, sterically-demanding Lewis acids. Selectivities in excess of 90% are now possible, with one example in excess of 99.5% ee provided.

Single enatiomer free-radical chemistry - Lewis acid-mediated reductions of racemic halides using chiral non-racemic stannanes

Additions of one to two equivalents of Lewis acids that include magnesium salts to free-radical reduction reactions involving ester functionalized radicals and (1R,2S,5R)-menthyldiphenyltin hydride 4, bis((1R,2S,5R)-menthyl)phenyltin hydride 5, tris((1R,2S,5R)-menthyl)tin hydride 6, bis((1R,2S,5R)-menthyl)-[8-(N,N-dimethylamino)naphthyl]tin hydride 12, bis((1R,2S,5R)-menthyl)-[1-((S)-N,N-dimethylaminoethyl)phenyl]tin hydride 13 or 3α-dimethylstannyl-5α-cholestane 14 result in remarkable enantioselectivities. Examples include (S)-naproxen ethyl ester 16, produced in 74% yield and greater than 99% ee at −78°C from the bromide and 5 in the presence of MgBr₂, and ethyl (R)-N-trifluoroacetyl-_D-phenylglycinate 18, obtained in 78% yield and 99% ee under identical conditions. Kinetic and computational studies provide insight into the origins of these observations.

Media/ting change: the print media's role in mediating education policy in a period of radical reform in Victoria, Australia

This paper draws upon critical discourse analysis, cultural studies and communication theory, studies on media and educational reform, and the work of Bernstein, Bourdieu and Luhmann in particular, to explore how the print and media 'mediated' a period of educational change marked by moves to self-management in schools in Victoria, Australia. It considers how the media was mobilized by various education stakeholders, and in turn informed relations between schools and government, through policy discourses and texts. It considers why and how particular themes became media 'issues', how schools and teachers responded to these issues, and how the media was used by various stakeholders in education to shape policy debates. It is based on a year-long qualitative study that explored critical incidents and representations about education in the print media over a year in the daily press. It illustrates the ways in which a neo-liberal Victorian government mobilized the media to gain strategic advantage to promote radical education reform policies, considers the media effects of this media/tion process on schools and teachers, and conceptualizes how school and system performance is fed from and into media representations, public perceptions and community understandings of schools and teachers' work.

Synthesis, characterization and enantioselective free radical reductions of (1R,2S,5R)-menthyldiphenylgermane and its enantiomer

(1R,2S,5R)-Menthyldiphenylgermane and its enantiomer have been prepared in a few steps from germanium tetrachloride. The initial step in this sequence, namely the reaction between germanium tetrachloride and menthylmagnesium chloride, produces menthylgermanium trichloride, which is the exclusive product of this Grignard reaction, presumably due to the bulk of the menthyl group. When used at a low temperature (−78 °C) and in conjunction with Lewis acids, such as magnesium salts, these chiral germanes are capable of reducing ester functionalized radicals in high enantioselectivity, but in low-moderate yield. For example, (R)-naproxen ethyl ester was obtained in 15% yield and 99% ee by reaction in toluene of 2-bromonaproxen ethyl ester with (1R,2S,5R)-menthyldiphenylgermane in toluene at −78 °C in the presence of magnesium bromide. At 80 °C, (1R,2S,5R)-menthyldiphenylgermane reacted with primary alkyl radicals with a rate constant of 1.02 × 10⁶ M⁻¹ s⁻¹. Kinetic studies reveal the Arrhenius expression for this reaction to be: log(k/M⁻¹ s⁻¹) = (11.1 ± 0.4) − (34.6 ± 3.1)/θ where θ=2.3RT kJ mol⁻¹.

Australia's radical predatory pricing reforms : what business must know

Radical changes to the Trade Practices Act have the potential to affect significantly, the ability of businesses to engage in vigorous price competition. These changes are designed to prohibit what is colloquially referred to as predatory pricing; the practice of a firm temporarily reducing its prices to a level designed to eliminate its competitors so that, free of competition, it can thereafter, lift them to supra-competitive levels. Unfortunately, because of its scope and the ambiguous new concepts it employs, the section has the potential to apply to all forms of vigorous.price competition and creates significant risks for those businesses who.seek to compete with their rivals by systematically, or irregularly, selling at lower prices than they do. This note examines the section's nature and scope and identifies the pitfalls that it presents for such firms.

Australia's radical predatory pricing reforms: what business must know

Radical changes to the Trade Practices Act have the potential to affect significantly the ability of businesses to engage in vigorous price competition. These changes are designed to prohibit what is colloquially referred to as predatory pricing; the practice of a firm temporarily reducing its prices to a level designed to eliminate its competitors so that, free of competition, it can thereafter lift them to supra-competitive levels. Unfortunately, because of its scope and the ambiguous new concepts it employs, the section has the potential to apply to all forms of vigorous price competition and creates significant risks for those businesses who seek to compete with their rivals by systematically, or irregularly, selling at lower prices than they do. This note examines the section’s nature and scope and identifies the pitfalls that it presents for such firms.

Principals, politics and change : confronting school resilience to radical renewal

Governments expect school principals to lead and manage significant change to implement school improvement agendas. Research evidence suggests, however, that schools are slow to change (Evans, 1996; Duignan, 2006), that many teachers resist change (Marzano, Waters & McNulty, 2005), and that change is often cursory or short lived – not disrupting dominant cultures and existing arrangements (Johnson, 2004). This paper discusses the resistance to major change encountered by Australian principals, and their perceptions of its causes. Emergent themes demonstrate that the success or otherwise of change rests heavily on the political astuteness of principals, which suggests the need for ongoing professional learning and leadership support around the issue of leading and managing change.