(4+3) Cycloaddition Reactions of Nitrogen‐Stabilized Oxyallyl Cations

Abstract

The use of heteroatom-substituted oxyallyl cations in (4 + 3) cycloadditions has had a tremendous impact on the development of cycloaddition chemistry. Extensive efforts have been exerted toward investigating the effect of oxygen-, sulfur-, and halogen-substituents on the reactivity of oxyallyl cations. Most recently, the use of nitrogen-stabilized oxyallyl cations has gained prominence in the area of (4 + 3) cycloadditions. The following article will provide an overview of this concept utilizing nitrogen-stabilized oxyallyl cations.

Aromatic Interactions as Control Elements in Stereoselective Organic Reactions

“…39–41 The Hsung stereoselective route to 7-membered carbocycles is based on (4+3) cycloadditions of oxyallyls containing a chiral oxazolidinone. 42 As shown in Scheme 9, the oxyallyl is generated by oxidation of an allenamide and is trapped with a furan (or pyrrole or diene). While I and II may be formed, reactions of 12 with furan and 2-methylfuran favored cycloadduct I .…”

Synthesis of Azepine Derivatives by Silver‐Catalyzed [5+2] Cycloaddition of γ‐Amino Ketones with Alkynes

“…[1][2][3][4][5] This process is most frequently used to prepare five-and six-membered ring systems. [1][2][3][4][5] This process is most frequently used to prepare five-and six-membered ring systems.…”

“…[1][2][3][4][5] This process is most frequently used to prepare five-and six-membered ring systems. [1][2][3][4][5] The difficulties of such an approach are likely caused by a combination of entropic factors and the presence of non-bonding interactions in the transition state. [1][2][3][4][5] The difficulties of such an approach are likely caused by a combination of entropic factors and the presence of non-bonding interactions in the transition state.…”

“…[1] However, approaches using a cycloaddition strategy for constructing seven-membered ring systems, particularly seven-membered heterocyclic ring systems, are much less abundant. [1][2][3][4][5] Particular focus has been put on the synthesis of azepine derivatives, [4,5] because these are important skeletal units that are found in numerous natural products and in compounds with important chemical, biological, and medicinal properties ( Figure 1). Despite the impressive challenges in this field, the continuing identification of bioactive natural products that contain a seven-membered ring has led to considerable efforts to establish valuable cycloaddition methods for their construction.…”

Synthesis of naturally occurring tropones and tropolones

“…The subsequent section was organized by how the 7-membered rings were formed. Although seven-membered ring syntheses have been reviewed several times, these reviews often focus on one type of method, such as the [4+3] cycloaddition, 85–87 [5+2] cycloaddition, 88–89 or other reactions. 90–91 A recent review on synthetic strategies to access seven-membered carbocycles in natural products only discussed the total synthesis of a few tropone- and tropolone-containing natural products including pareitropone, imerubrine, isoimerubrine and grandirubrine.…”