page_title: Cascade reaction
section_title: Multistep tandem reactions
hierarchical_section_title: Cascade reaction / Multistep tandem reactions
caption_attribution_description: English: Representative examples of synthetic targeting using polyring forming processes
context_page_description: A cascade reaction, also known as a domino reaction or tandem reaction, is a chemical process that comprises at least two consecutive reactions such that each subsequent reaction occurs only in virtue of the chemical functionality formed in the previous step. In cascade reactions, isolation of intermediates is not required, as each reaction composing the sequence occurs spontaneously. In the strictest definition of the term, the reaction conditions do not change among the consecutive steps of a cascade and no new reagents are added after the initial step. By contrast, one-pot procedures similarly allow at least two reactions to be carried out consecutively without any isolation of intermediates, but do not preclude the addition of new reagents or the change of conditions after the first reaction. Thus, any cascade reaction is also a one-pot procedure, while the reverse does not hold true. Although often composed solely of intramolecular transformations, cascade reactions can also occur intermolecularly, in which case they also fall under the category of multicomponent reactions.
context_section_description: 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. This kind of organic reactions are designed to construct difficult structures encountered in natural product total synthesis.
  In the total synthesis of spiroketal ionophore antibiotic routiennocin 1 (Fig. 1), the central spiroketal skeleton was constructed by a multistep tandem reaction (Fig. 2).  Fragment A and fragment B were coupled in a single step to form the key intermediate G that could be further elaborated to afford the final product routiennocin.
  Four chemical transformations happened in this tandem reaction. First, treating fragment A with n-butyllithium formed carbon anion that attacked the alkyliodide part of fragment B to generate intermediate C (step 1). Then a 3, 4-dihydropyran derivative D was formed through base-mediated elimination reaction on intermediate C (step 2). The protecting group on 1, 3-diol moiety in intermediate D was removed by acid treatment to give the diol product E (step 3). The spiroketal product G was generated via intramolecular ketal formation reaction. This multistep tandem reaction greatly simplified the construction of this complex spiroketal structure and eased the path towards the total synthesis of routiennocin.
caption: Fig. 2: Representative examples of synthetic targeting using polyring forming processes
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