In this paper we aim to highlight the need to consider the possible role of autocatalysis in oxidation reactions when using molecular oxygen as the terminal oxidant. Oxygen in its ground state is a diradical, and depending on the reaction conditions, it can initiate oxidation through radical pathways through mechanisms which do not require the presence of a catalyst. Consequently, we contrast the oxidation of benzyl alcohol with oxidation of α-pinene. For benzyl alcohol oxidation the initial reaction is the oxidative dehydrogenation to form benzaldehyde, a non-radical process; but the subsequent over-oxidation to benzoic acid is a radical process. In this case the role of the autocatalysed reaction can be minimised. With α-pinene, the oxidation reaction is via radical pathways and now the autocatalysed reaction can be dominant and, indeed, can be the preferred pathway for the formation of high yields of the desired verbenone product.

The epoxidation of 2,5-dimethyl furan leads to the production of hex-3-ene-2,5-dione via a ring opening rearrangement reaction. A second epoxidation reaction could then enable a further ring closing rearrangement to form 4-hydroxy-2,5-dimethyl-3-furanone (furaneol). In this paper we report the use of gold and gold palladium supported on graphite and titania as catalysts for the ring opening reaction of 2,5-dimethyl furan. We show that by tuning the reaction conditions high selectivity towards hex-3-ene-2,5-dione can be achieved using green chemical methods and mild reaction conditions.

A one-pot synthesis of the trisubstituted imidazole derivatives from alpha-acetoxy-alpha-chloro-beta-keto-esters, aldehydes, and ammonium acetate has been developed.

A key discovery in the last two decades has been the realisation that gold, when prepared as supported nanoparticles, is exceptionally effective as an oxidation catalyst, particularly for the oxidation of alcohols. The catalytic efficacy is enhanced further by the alloying of gold with palladium. In this paper we study the effect of the method preparation of gold–palladium alloy nanoparticles supported on titania and investigate the activity of the materials for the selective oxidation of benzyl alcohol. We contrast impregnation and deposition–precipitation methods and demonstrate that the most active catalysts are prepared using the deposition–precipitation method.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

α-Chloro-α-acetoxy-β-keto-esters 9 were readily prepared from β-keto-esters 6 in good overall yields. These compounds reacted as α,β-diketo-ester equivalents 2 with amidrazones 1 yielding triazines 3, generally in good yields. Picolinates 10 provided an alternative source of α,β-diketo-ester equivalents 2 when treated with copper(II) acetate. A ‘one-pot’ reaction of the α,β-diketo-ester equivalents 2 with amidrazones 1 in the presence of 2,5-norbornadiene 5 in boiling ethanol yielded the pyridines 4 and 2,2′-bipyridines 4 (R1=2-pyridyl) directly without the need to isolate the corresponding triazines 3. Triazine 3c reacted with the aza-dienophiles 13 and 17 affording the products 16 and 18, respectively, in good yields.

The synthesis of trifluoromethyl-substituted pyridylboronic acids and pyrazolylboronic esters is described via lithiation-boronation protocols (Schemes 1, 3 and 4). A study of their palladium-catalysed cross-couplings with heteroaryl halides is presented. CF3-substituted aryl/heteroaryl-pyridines are thereby obtained (51-98% yields). Analogous cross-couplings have yielded heteroaryl-3-(trifluoromethyl)pyrazoles (60-85% yields); homocoupling of the pyrazolylboronic esters is suppressed by the addition of potassium formate, although competing protodeboronation is observed. Halogenation of the 4-position of selected pyrazole coupling products allows for further cross-couplings to yield tetra-substituted pyrazolyl derivatives (Scheme 5). X-Ray crystal structures are reported for selected pyridylboronic acids, pyrazolylboronic esters and derived trifluoromethyl-substituted heterobiaryl systems. These multi-ring CF3-substituted systems are of interest as building blocks for drug discovery and materials chemistry.

The 2,2′:6′,2″-terpyridines 8a and 8b were prepared in good yield by reacting α-acetoxy-α-chloro-β-keto-esters 1 (R1=nPr and Ph) with the bis-amidrazone 7 and 2,5-norbornadiene 5 in ethanol at reflux.

A general method for the synthesis of functionalized pyridazinylboronic acids/esters is described involving a directed ortho metalation (DoM)-boronation protocol (Schemes 1 and 2). A comprehensive study of the reactivity of the C-B bond in palladium -catalyzed cross-couplings with aryl/heteroaryl halides is presented. Aryl-/heteroarylpyridazines are thereby obtained in synthetically viable yields (typically 40-75%) although in some cases competing protodeboronation has been observed. A series of pyridazin-3(2H)-one derivatives, including 4,6-diaryl/heteroaryl derivatives, have been obtained from the corresponding 3-methoxypyridazines in straightforward procedures (Schemes 3 and 4). Several X-ray crystal structures of aryl-/heteroarylpyridazines and derived pyridazin-3(2H)-one derivatives are reported. These multi-ring systems are of considerable interest in contemporary N-heterocyclic chemistry.

We report the synthesis of (2,6-diinethoxy-3-pyridyl)boronic acid (2), (2,3-dimethoxy-4-pyridyl)boronic acid (4), (2,6-difluoro-3-pyridyl)boronic acid (6), (2,6-dichloro-3-pyridyl)boronic acid (8) and (2,3-dichloro-4-pyridyl)boronic acid (10) by directed ortho-metalation reactions on the corresponding disubstituted pyridine precursor, followed by the reaction with triisopropyl borate (TPB) or trimethyl borate. The reactivity of the pyridylboronic acids with heteroaryl halides in Suzuki-Miyaura cross-coupling reactions has been evaluated. New highly functionahzed heteroarylpyridine derivatives have thereby been obtained in moderate to high yields. The reaction of 8 and 3-amino-2-chloropyridine yielded the rare 5H-pyrrolo[2,3-b:4,5-b']dipyridine (i.e. 1,5-diazacarbazole) ring system by sequential cross-coupling and intramolecular cychsation reactions. The X-ray crystal structures are reported for the pyridylboronic acids 2, 4, 8 and 10. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

We report the synthesis of 2-chloro-5-pyrimidylboronic acid (6) and 2-amino-5-pyrimidylboronic acid (8) by lithium-halogen exchange followed by reaction with triisopropylborate. Their reactivity with heteroaryl halides in Suzuki-Miyaura cross-coupling reactions has been evaluated. New highly functionalized 5-heteroarylpyrimidine derivatives 24-33 (heteroaryl = quinoline, pyridine, pyrimidine, pyrazine, thiophene, benzothiazole) have been obtained in synthetically useful yields. The X-ray structure of 6 reveals extensive intermolecular O-H center dot center dot center dot N hydrogen bonding in the crystal. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).

The α-Chloro-α-acetoxy-β-keto-esters were prepared from β-keto-esters in good overall yields. These compounds reacted as α,β-diketo-ester equivalents with amidrazones yielding triazines, generally in good yields, or with an amidrazone and 2,5-norbornadiene in a one-pot aza Diels–Alder reaction to give the corresponding pyridines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A range of halogenated aromatics and heteroaromatics bearing a primary amine group are shown to be suitable substrates for Suzuki cross-coupling reactions with arylboronic acids and pyridylboronic acids under standard conditions, without the need for protection/deprotection steps. New amino-substituted arylpyridines, bipyridines, and pyrazinopyridines have thereby been obtained. Conditions for the efficient syntheses of 2-methoxy-5-pyridylboronic acid 1 and 2-methoxy-3-pyridylboronic acid 2 in ca. 75 g batches have been defined. A 2-fold reaction of 2-amino-5-bromopyrazine with 2,5-dimethoxy-1,4-benzenediboronic acid affords 1,4-dimethoxy-2,5-bis[2-(5-aminopyrazyl)]benzene 31. The X-ray crystal structures of 1 and 31.DMF are reported.

This paper describes the commercially-viable synthesis and isolation of 2-ethoxy-3-pyridylboronic acid on a ca. 70 g scale via a directed ortho-metalation reaction on readily-available 2-ethoxypyridine. A range of efficient cross-coupling reactions of 2-ethoxy-3-pyridylboronic acid with selected aryl/heteroaryl halides under palladium-catalysed Suzuki–Miyaura conditions yield novel 2-ethoxy-3-aryl/heteroaryl-pyridines in high yield (heteroaryl=pyridyl, pyrimidyl, pyrazyl). The X-ray crystal structure of 2-ethoxy-3-pyridylboronic acid reveals that the boronic acid group takes part in an intramolecular O–H⋯O bond with the adjacent ethoxy substituent, and an intermolecular O–H⋯N bond.