Introduction

The volumes of Annual Reports 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.

Gareth Rowlands' report on radical chemistry this year is dominated by two topics: the use of metals in radical transformations, where the use of potassium tert-butoxide in conjunction with a diamine ligand as a means of forming aryl radicals has potential for great impact, and photoredox catalysis for the generation of alkyl radicals, where one of the more exciting advances is the use of a simple organic dye instead of the more common ruthenium complexes.

Advances in oxidation and reduction chemistry are addressed by Chris Hyland and James Howard, new authors for Annual Reports. In the field of oxidation, highlights include Shi's detailed studies on the regioselectivity of the Cu(I)-catalysed deamination of conjugated dienes, and advances in the area of C–H oxidation, with Stambuli showing the stereoselectivity of cis-vinylsilane allylic acetoxylation to be dependent upon the nature of the oxidant used. In the field of reduction chemistry, Ward has developed an artificial metalloenzyme, where an iridium-catalyst was incorporated into a chiral enzyme for the asymmetric transfer of hydrogen for the production of enantiopure amines, and Strotman has demonstrated the first intramolecular reductive amination between dialkyl ketones and aliphatic amines.

The first article for Annual Reports by Hon Lam, with co-authors Daniel Best, Alan R. Burns, and Graham Pattison, focuses on advances in organohalogen, organoboron, organosilicon, organonitrogen, organosulfur, and organooxygen chemistry, with an emphasis on catalytic methods.

John Fossey, in his chapter on organometallic chemistry, selects a range applications of organometallic compounds from uses in supramolecular chemistry, as catalysts, for example in drug synthesis, through to photovoltaics.

Benjamin Buckley, Marc Kimber, and Natasha H. Slater provide a cross-section of developments in a number of areas of organocatalysis, including iminium/enamine catalysis, SOMO catalysis, hydrogen bonding catalysis, counterion catalysis, N-heterocyclic carbine-mediated organocatalysis, and tandem metal-organo-catalysis, and finishes with a discussion of natural products prepared using organocatalytic reactions.

Fawaz Aldabbagh, discussing heterocyclic chemistry in his first contribution to Annual Reports, discusses a number of modes of ring synthesis, including cycloadditions, cyclizations, multi-component reactions, and ring-expansions, particularly using copper(I), gold(I), iron, palladium and rhodium catalysts.

Robert Hill's report, as in previous years, focuses on marine natural products with unusual structures and interesting biological activities. The compounds are organized loosely under their biogenetic origins of polyketides, terpenoids, meroterpenoids, alkaloids and peptides.

Yvette Jackson and Nadale Downer-Riley describe a selection of natural product syntheses focusing on a few exemplary syntheses which employed novel and concise strategies towards popular or complex targets, including daphmanidin E, aspidophylline A, and cyanolide A.

The year 2011 produced many advances in supramolecular chemistry. Jian Tian, in his first article for Annual Reports, has divided his report into three broad sections covering in the areas molecular recognition, structure and assembly, and functional systems.

We also welcome new authors Dan Pantos and Koujito Tambara who report on the important supramolecular chemistry of donor–acceptor interactions. They begin by reporting recent advances in light-harvesting molecules for dye-sensitized solar cells, and materials for polymer solar cells. Turning to mechanically-interlocked molecules, they feature work on a combinatorial approach to catenanes with unusual donor–acceptor–acceptor–donor (DAAD) and DADD motifs. A remarkable ‘pirouette’ by a polyether loop in a catenane is also described, along with the latest advances in rotaxane chemistry. Their report ends with a brief review of donor–acceptor chromophores.

Gideon Grogan reviews significant developments in applications of biological catalysis in synthetic organic chemistry. Highlights include the use of lipases in dynamic kinetic resolutions of amines at low-temperature using radical-based racemisation methods; a system has also been developed for the lipase-catalysed desymmetrization of allenic diols. An unusual promiscuous activity of formate dehydrogenase has been described in which the enzyme catalysed a hydrolytic reaction. In reductase biotransformations, ene reductases of the Old Yellow Enzyme family have been applied to the asymmetric reduction of Baylis–Hillman adducts and also shown, in some cases, to catalyse oxazete formation in the transformation of nitro-alkenes. New developments in oxidase biocatalysis include a Baeyer–Villiger monooxygenase that catalyses a dynamic kinetic resolution using racemic substrates susceptible to racemization at alkaline pH. Artificial metalloenzymes based on the streptavidin-biotin system have been applied to asymmetric imine reduction, dihydroxylation and alkene metathesis.

As last year Ute Wille reports on radical mechanisms. Although radicals have very much been ‘tamed’ nowadays for use in organic synthesis, the key to maintaining control is an understanding of mechanism. This chapter reports many examples of mechanistic studies of synthetically-useful radical reactions. Not least is the use of a zinc compound, as a useful alternative to tin, in an addition/cyclisation of an enyne, and a cyclisation reaction that proceeds via two different, but converging, diastereotopic aryl radicals. Cascade mechanisms are often proposed in radical reactions, and an example involving an autooxidation step is reported. Unsurprisingly, radical mechanisms feature strongly in the chemistry of biological systems, and these are well represented in this chapter.

Further new authors this year are Edyta Greer and Christopher Cosgriff who report developments in pericyclic mechanisms. Even in such a well established field, there are some surprises, for example, the cyclopropenone [4 + 2] cycloaddition to cyclopentadiene follows a synchronous, exo pathway, in contrast to cyclobutenone, cyclopentenone and cyclohexenone. Interesting new reactions are being explored, for example, a [4 + 2]/[3,3] tandem reaction of a nitroso alkene (as dienophile) with diene. The interplay of experiment and computation is particularly important in this field, and this is shown in many examples; the unusual diastereoselectivity of a furan [4 + 3] cycloaddition to oxazolidinone-substituted oxyallyl is a good example of this. Unusual reactions feature, including pericyclic and coarctate cyclisations of an azo-ene-yne.

Anna Croft again reports on advances in polar mechanisms. She highlights the importance of water as a proton-delocalisation matrix in coupled proton/electron transfers. Carbocations continue to be important in organic reaction mechanisms and the chemistry of a tricationic carbenium ion intermediate is reported. Mechanistic studies of ever more complex reactions are now being made; one example involves organocatalysis of the addition of aldehyde to nitrostyrene, and this reaction includes a cyclobutane resting state. Many mechanistic studies are designed to model enzymic reactions, and a good example is reported here, with the aldehyde-facilitated deprotonation of glycine being studied to understand the mechanism of action of pyridoxal-5′-phosphate. The importance of solvent on the course of an organic reaction can often be striking, and an example is given where selective displacement of bromide over chloride is influenced by the ratio of two co-solvents.

Of all the physical methods used by organic chemists, NMR spectroscopy is paramount, but the vast range of techniques and procedures available can be bewildering. Mark Edgar has again written a detailed report on the latest developments, but importantly for the chemist has supported it with examples of applications. Amongst the many are a multiple quantum coherence method that allows intermolecular interactions to be observed, an ultrafast HSQC method used to probe mechanism, and procedures to improve on the ¹³C–¹³C coupling INADEQUATE experiment. Organic chemists still prefer to do NMR spectroscopy in the solution state, and in contrast to the situation with ATR-FTIR, solid-state NMR spectroscopy is rare. Mark gives a detailed account of the latest developments in this particular field, and examples exploring glycine polymorphs, the ²H solid state NMR spectrum of camphor, and the determination of interatomic distances in amyloid fibril proteins will surely stimulate greater use of this technique.

Niek Buurma reports once again on reactivity in organised assemblies. The subtleties of reactivity in even fairly simple micellar systems can be surprising, and a good example is a system where Diels–Alder reactions take place neither in an aqueous phase, nor in a organofluorous phase, but in the interface zone. With an increasing number of reactions being subjected to micellar catalysis nowadays, there is a need to develop new surfactants, and this chapter includes a report of one that was designed be efficient, cheap and green. As expected, systems involving surfactant and zinc complexes for phosphate ester cleavage feature strongly. The selectivity of the DNA base pairing process is now frequently utilised for selective couplings of attached reactants, and highlights are reported in this chapter. Niek reports that 2011 was a relatively quiet year for DNA-based catalysis, but nonetheless, finds an interesting example of a G-quadruplex DNA hemin catalyst that mimics the horseradish peroxidise enzyme. Finally, several of the latest developments in nanoparticle-supported catalysts are reported.

A field that is now particularly important in physical organic chemistry is that of computational organic chemistry, and Steven Bachrach has again critically reviewed the latest publications. He includes a report on the effect of tunnelling on the competing paths for hydroxycarbene rearrangement, and a study of ‘roaming’ reactions where two dissociated parts form a loose complex and ‘wander’ before recombining. To a large extent, interpretation of NMR spectra is still the preserve of the organic chemist's own brain, but in this report the latest developments in structure elucidation using computed spectra are examined. More traditional uses of computational chemistry include modelling of reaction mechanisms, and of unusual or unstable molecules, and both of these topics are well represented by examples from the recent literature.

This year we welcome Enda Bergin who has written a report on asymmetric catalysis that highlights the drive towards replacement of expensive late transition metal catalysts by cheaper early transition ones. The use of chiral iron-porphyrins for asymmetric oxidation has struggled to live up to initial expectation, but Enda describes research that suggests a renaissance; a ‘Binap-style’ iron-phenanthroline complex is also reported. Turning to reduction, he reports useful asymmetric hydrogenations catalysed by iron species. The latest developments in Co- and Cu-catalysed asymmetric reactions are also reviewed; a Cu alternative to the Rh, Ru, and Ir hydrogenation catalysts looks particularly promising, as do some new Cu-catalysed asymmetric alkyl- and aryl-ation reactions.

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