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Multistep tandem reactions (or cascade reactions) are a sequence of chemical transformations (usually more than two steps) that happens consecutively to convert a starting material to a complex product. [28] This kind of organic reactions are designed to construct difficult structures encountered in natural product total synthesis.
The proposed reaction mechanism involves an initial [2+2] cycloaddition between the vinylcyclopropane and TCNE, followed by rearrangement to furnish the seven-membered ring in the product. Evidences have shown that depending on the reaction conditions, the rearrangement step can occur via either radical or ionic intermediates. [7]
The Diels-Alder reaction is perhaps the most important and commonly taught cycloaddition reaction. Formally it is a [4+2] cycloaddition reaction and exists in a huge range of forms, including the inverse electron-demand Diels–Alder reaction, hexadehydro Diels–Alder reaction and the related alkyne trimerisation.
Trimethylenemethane cycloaddition is the formal (3+2) annulation of trimethylenemethane (TMM) derivatives to two-atom pi systems. Although TMM itself is too reactive and unstable to be stored, reagents which can generate TMM or TMM synthons in situ can be used to effect cycloaddition reactions with appropriate electron acceptors .
The Pauson–Khand (PK) reaction is a chemical reaction, described as a cycloaddition.In it, an alkyne, an alkene, and carbon monoxide combine into a α,β-cyclopentenone in the presence of a metal-carbonyl catalyst [1] [2] Ihsan Ullah Khand (1935–1980) discovered the reaction around 1970, while working as a postdoctoral associate with Peter Ludwig Pauson (1925–2013) at the University of ...
The nitrone-olefin (3+2) cycloaddition reaction is the combination of a nitrone with an alkene or alkyne to generate an isoxazoline or isoxazolidine via a (3+2) cycloaddition process. [1] This reaction is a 1,3-dipolar cycloaddition, in which the nitrone acts as the 1,3-dipole, and the alkene or alkyne as the dipolarophile.
An alkyne trimerisation is a [2+2+2] cycloaddition reaction in which three alkyne units (C≡C) react to form a benzene ring. The reaction requires a metal catalyst. The process is of historic interest as well as being applicable to organic synthesis. [1] Being a cycloaddition reaction, it has high atom economy.
Ketene [2 + 2] cycloaddition reactions have been used in many total syntheses since Corey's use of the [2 + 2] cyclization in synthesizing the prostaglandins. [35] Robert Ireland's synthesis of (±)-aphidicolin uses the Wolff rearrangement to do a tandem ring-contraction, and [2 + 2] cycloaddition. [38] Synthesis of (±)-aphidicolin