Six‐Membered Heterocycles: Pyridines

Abstract

Figure 16.5 Examples of agrochemical pyridine derivatives and their applications.1434j 16 Six-Membered Heterocycles: Pyridines IR DataThe pyridine IR spectrum is quite similar to the corresponding vibrations of benzene. Pyridine has C-H stretching frequencies in the range 3020-3070 cm À1 as well as C¼C and C¼N stretching frequencies at 1590-1660 cm À1 and near 1500 cm À1 . N J 2,3 = 4-6 J 2,4 = 0-2.5 J 2,5 = 0-2.5 2 3 4 5 6 J 2,6 = 0-0.6 J 3,4 = 7-9 J 3,5 = 0.5-2 1436j 16 Six-Membered Heterocycles: Pyridines R + Metal catalyst ∆ R = alkyl, vinyl, aryl Scheme 16.2 16.

From 3-Acyl-2-methylindoles to γ-Carbolines: Li-Promoted Cycloaddition Reaction and Its Quantum Chemical Study

“…As indole derivatives are commercially available, γ-carbolines synthesis via annulation of a pyridine ring to an indole core is the most convenient. A lot of strategies for pyridine ring synthesis have been developed, but the [4 + 2] cycloaddition is the most direct method for its formation …”

“…A lot of strategies for pyridine ring synthesis have been developed, but the [4 + 2] cycloaddition is the most direct method for its formation. 12 To create a pyridine core, four paths of an aza-Diels−Alder reaction are possible: addition of a dienophile to azadiene according to pathways a and b or addition of an azadienophile to diene according to pathways c and d (Scheme 1). 13 In our DFT B3LYP/6-311++G(d,p) calculations, values of Gibbs free energies ΔG ⧧ and ΔG (in kcal/mol) are, respectively, 37.2 and −13.5 (for pathway a), 34.6 and −21.3 (for pathway b), 33.8 and −11.0 (for pathway c), and 38.0 and −6.8 (for pathway d).…”

Synthesis of ortho‐Acylphenols through the Palladium‐Catalyzed Ketone‐Directed Hydroxylation of Arenes

“…ortho ‐Acylphenols are an important structural motif found in a diversity of bioactive molecules ranging from natural products to drugs (Figure 1). 1 Moreover, they also serve as versatile building blocks for the synthesis of various pharmaceuticals, such as warfarin,2 as well as agrichemicals, flavors, and fragrances 3. Classic approaches to the synthesis of o ‐acylphenols generally involve a two‐step process: acylation of phenols followed by Fries rearrangement of the resulting phenyl esters (Scheme ) 4.…”

Mechanistic Evaluation of the Ni(IPr)2-Catalyzed Cycloaddition of Alkynes and Nitriles To Afford Pyridines: Evidence for the Formation of a Key η1-Ni(IPr)2(RCN) Intermediate

“…Substantial progress has been made in the field of transition-metal-catalyzed [2 + 2 + 2] cocycloadditions of alkynes and nitrile partners for well over three decades . Owing to the ubiquitous presence of pyridines across all chemical disciplines and applications, this simple, one-step, three-component route to pyridines stands as a powerful strategy. The primary focus of these investigations has been expanding the substrate scope of these reactions, even to the point of their application in complex natural product synthesis .…”