Introduction

The volumes of Annual Reports, Section B, offer a selective overview of advances in some aspects of organic chemistry, taken from the primary literature published over the previous year or two, with chapters written by experts in each field.

This year, a number of recurring themes are evident in several of the various chapters, particularly green chemistry, organocatalysis, and C–H activation. All of these topics appear in Gareth Rowlands’ discussion of free-radical reactions, and two of the three in several others. These include that by Benjamin Buckley and Stephen Neary on organocatalysis, a topic that has again expanded in interest in 2009, with over 800 articles in the primary literature; the Report is organized according to the mode of action of the catalyst, and includes theory and applications in complex synthesis. Paul Davies again discusses organotransition metal catalysis; particular highlights this year are provided by p-acid catalysis, iron catalysis, C–H activation, and metathesis.

Karl Hemming, in his second contribution on heterocyclic chemistry, focuses on synthesis of heterocycles with three to seven-membered rings containing nitrogen, oxygen, or sulfur. Andrew Whiting covers organo-oxygen and organo-nitrogen compounds, with an emphasis on catalytic methods for their synthesis, in his first article on heteroatom chemistry.

Also in his second chapter for Annual Reports, Simon Lewis provides an overview of oxidation and reduction methods; major sections cover the use of salen complexes, oxaziridinium salts, and dioxiranes for oxidation processes; for reduction, the development of new chiral phosphine ligands is still attracting considerable attention, as are oxazaborolidines, and asymmetric reductive alkylation. The author remarks on the increasing influence of green chemistry and the use of nanoparticulate catalysts.

Oscar Navarro and Mihai Viciu take over the mantle of Steven Nolan in reporting on the use of N-heterocyclic carbenes (NHCs) in catalysis, concentrating on recent trends and the potential impact of this important class of ligands, with the chapter organized according to the metal involved. Gideon Grogan again addresses biological catalysis in synthetic organic chemistry, with particular focus on lipases, esterases, laccases, reductases, and aldolases.

Yvette Jackson and Nadale Downer-Riley continue this year to describe highlights of total syntheses of complex natural products; the syntheses selected are grouped according to the key reaction type of the approach, and concentrate on the key strategic steps of each synthesis. Bob Hill reports new marine natural products with unusual structures or interesting biological activities, and his chapter is organised by biogenetic origin, from polyketides, terpenoids, alkaloids and peptides.

Scott Dalgarno provides his second commentary on significant developments in supramolecular chemistry, arranged under three headings covering molecular recognition, structure and assembly, and functional systems. Highlights include advances in host-guest systems, molecular capsules, anion sensing, programmed synthesis and assembly, and self-assembled systems.

Bioinspired organic chemistry is assessed by Salvador Tomas and Lilia Milanesi, who describe their selection of new science from researchers inspired by biomolecular systems. The first three sections discuss progress in organic chemistry inspired by three major classes of biomolecules, nucleic acids, proteins, and lipids. The last section focuses on recent developments in organic chemistry inspired by the complexity of biomolecular systems, now known by the name ‘systems chemistry.’

As for last year, Niek Buurma and Lavinia Onel have reviewed developments in reactivity in organised assemblies, focussing on micelles, vesicles, emulsions, but also covering DNA and polymers. The numerous highlights include one where a micellar environment induces autocatalysis in N-alkylation, another where water nucleophilicity varies within the interfacial region of a microemulsion, and a serendipitous discovery of a DNA sequence that hydrolyses a specific DNA site.

This year we welcome Thorfinnur Gunnlaugsson and Emma Veale with a chapter on the use of organic compounds as fluorescent sensors for anions and cations. In many cases the mode of sensing is based on enhanced emission following a reaction induced by the analyte ion; two examples involving Hg²⁺ and Ag⁺ mediated spiro ring openings are described. Among the many strategies described is the use of intramolecular fluorescence energy transfer, whereby the anion, for example sulphite, induces preferential emission from one part of the sensor relative to another part. This approach has been applied to detection of the largely organic anion geranyl pyrophosphate.

We welcome another new contributor, Anna Croft, who reports on polar reaction mechanisms. Among many highlights, a few stand out particularly. For example, an alkyl dinitrobenzene was found to deprotonate more readily on the aromatic ring than at the benzylic site. Also, several papers that deal with quantification of carbanion nucleophilicity, including the important case of carbanion stabilised by adjacent phosphorus, are reported in this chapter.

Jeehiun Lee and Dean Tantillo provide, yet again, a comprehensive report on pericyclic reaction mechanisms. An intriguing example reported is of an enantioselective Diels-Alder reaction where a Lewis acid-complexed aldehyde itself acts as a Lewis acid catalyst for reaction of further aldehyde. As usual computational studies figure large, and for dipolar cycloadditions a study is reported that emphasises the importance of the dipole bending mode in contributing to the activation energy. Many pericyclic reactions turn out to be more complex than might at first sight appear, and several such reactions are described this year; one example involves an apparent ‘forbidden’ disrotatory cyclobutene ring-opening.

Sadly, this year's contribution from Jim Tanko will be his last for Annual Report. As in previous years, this chapter throws up many interesting reactions in what was once regarded as a ‘wild and untamed’ area. Jim reports on, inter alia, an S_N2-like rear-side attack of a methyl radical on a disulphide, and then on one of an S_N2 reaction that can proceed by either front- or rear-side attack. Also reported is an interesting report of a boron-carbene complexation that confers tin hydride-like reactivity to a boron hydride. An unusual 7-endo cyclisation, favoured over a 6-exo one, is another curiosity, while an enantioselective radical addition to imine, and an aldehyde α-arylation using a chiral electron transfer reagent, serve to show how ‘tame’ radical have become.

Steven Bachrach reports on developments in computational organic chemistry during the year. The debate about “protobranching” (to explain the particular stability of branched alkanes) continues. Among the rather exotic molecules ‘accessible’ by computation are an octaphryn (an 8-pyrrole analogue of a porphyrin) and a dication that is predicted to have a specific rotation of several thousand degrees! The inadequacy of classical transition state theory is a recurrent theme, and an example taken from simple alkene hydroboration is discussed in the report.

Another report on developments in NMR spectroscopy is provided by Mark Edgar. A discussion of the potential uses of the latest 1 GHz spectrophotometer is followed by a discussion of Earth-field NMR. The re-emergence of enhancement by dynamic nuclear polarisation is also reported, while a mechanical device (moving NMR tube) is described. Although not generally considered to be an organic molecule, few will not be fascinated by the elegant simplicity of the ¹³C MAS NMR spectra of nano- and micro-diamond.

Ai-Lan Lee, for the second year, provides a topical report on the popular subject of enantioselective catalysis. She devotes a significant portion to enantioselective gold-catalysed reactions, but also expands upon the use, for enantioselective alkene metathesis, of Mo complexes, especially those that are stereogenic at Mo. The complexity of the mechanisms is highlighted by a report where both (R) and (S) enantiomers of a catalyst yield the same enantiomeric excess of the same product enantiomer.

---