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.

The impossible infinite: Les Murray, poetry, and the sacred

In 1983, the provocative and idiosyncratic Australian poet Les Murray published a volume entitled The People's Otherworld. At the heart of that middle volume of Murray's work is a poem about grace entitled Equanimity. Here, McCredden examines how does the poetry of Murray seek to represent the sacred.

Deborah Walker : hommage to the infinite

Spirtuality is at the heart of Deborah Walker's enigmatically engaging works. Drawing on the interpretive nature of a philosophical world view, Walker presents a figurative structure imbued with a calmness, stillness, and sophistication. Elegantly dressed characters are warmly depicted witha touch of theatre and drama, their serene gaze gentle, sometimes melancholy and reflective. 

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.

Scope for further analytical solutions for constant flux infiltration into a semi-infinite soil profile or redistribution in a finite soil profile.

We attempt to generate new solutions for the moisture content form of the one-dimensional Richards' [1931] equation using the Lisle [1992] equivalence mapping. This mapping is used as no more general set of transformations exists for mapping the one-dimensional Richards' equation into itself. Starting from a given solution, the mapping has the potential to generate an infinite number of new solutions for a series of nonlinear diffusivity and hydraulic conductivity functions. We first seek new analytical solutions satisfying Richards' equation subject to a constant flux surface boundary condition for a semi-infinite dry soil, starting with the Burgers model. The first iteration produces an existing solution, while subsequent iterations are shown to endlessly reproduce this same solution. Next, we briefly consider the problem of redistribution in a finite-length soil. In this case, Lisle's equivalence mapping is generalized to account for arbitrary initial conditions. As was the case for infiltration, however, it is found that new analytical solutions are not generated using the equivalence mapping, although existing solutions are recovered.