Domino reactions definition

Besides the numerous examples of anionic/anionic processes, anionic/pericydic domino reactions have become increasingly important and present the second largest group of anionically induced sequences. In contrast, there are only a few examples of anionic/radical, anionic/transition metal-mediated, as well as anionic/re-ductive or anionic/oxidative domino reactions. Anionic/photochemically induced and anionic/enzyme-mediated domino sequences have not been found in the literature during the past few decades. It should be noted that, as a consequence of our definition, anionic/cationic domino processes are not listed, as already stated for cationic/anionic domino processes. Thus, these reactions would require an oxidative and reductive step, respectively, which would be discussed under oxidative or reductive processes. 

An impressive combination of two Diels-Alder reactions is also described by Winkler [4] for the synthesis of the taxane skeleton, though two different Lewis acids must be used for the two cycloadditions. Thus, it does not strictly match the definition of a domino reaction. 

In transition metal-catalyzed domino reactions, more than one catalyst is often employed. In Tietze s definition and the classification of domino reactions, no distinction has been made between transformations where only one or more transition metal catalyst is used for the different steps, provided that they take place in a chronologically distinct order. Poli and coworkers [13] differentiated between these processes by calling them pure-domino reactions (which consisted of a single catalytic cycle driven by a single catalytic system) or pseudo-domino reactions . The latter type was subdivided into ... 

An interesting pericyclic-anionic-pericyclic domino reaction showing a high stereoselectivity is the cycloaddition-aldol-retro-ene process depicted in scheme 20.1581 The procedure presumably starts with a [4+2]-cycloaddition of diene 98 and S02 in presence of a Lewis acid. After opening of the formed adduct reaction with (Z)-silyl vinyl ether 99 leads to a mixture of alk-2-enesulfinic acids 101. It follows a retro-ene reaction which affords a 7 3 mixture of the products 102 and 103. The reaction described by Vogel et al is a nice example for the efficient generation of polypropionate chains with the stereoselective formation of three stereogenic centers and one (0-double bond in a three-component domino reaction in its strict definition. 

By definition, multi-component reactions (MCRs) belong to the class of domino reactions [7]. Generally, domino reactions are regarded as sequences of uni- or bi-molecular elementary reactions that proceed without intermediate isolation or workup as a consequence of the reactive functionality that has been formed in the previous step. In addition to uni- and bimolecular domino reactions that are generally referred to as domino reactions , a third class is called multimole-cular domino reactions or MCRs. Whereas uni- and bimolecular domino reac-... 

In transition-metal-catalysed domino reactions, often more than one catalyst is employed. In Tietze s definition and classification of domino reactions, no differentiation is made between domino reactions, whether it is just one or more than one transition-metal catalyst... 

In contrast, a much better efficiency could be accomplished using domino reactions, which have been defined by us as processes of two or more bond forming reactions under identical reaction conditions, in which the latter transformations take place at the functionahties obtained in the former bond forming reactions [4]. In the processes one, two, three, or more substrates can be involved. Thus, multicomponent transformations are domino reactions per definition. In the meantime, several excellent reviews have also been pubhshed by other authors on this topic [5]. 

Per definition, aU domino reactions take place in one reaction vessel without isolating any intermediates however, they are much more than the so-called one-pot reactions, where you just put together different substrates and reagents after each other. The planning of domino reactions is hke playing chess, where to be a reasonable player you will have to analyze four to five steps in advance. Thus, you have to predict the reaction pathways of aU substrates and intermediates in your reaction mixture and in contrast to chess, where the movement of the different chess pieces is fixed, the reactivity of the chemical compounds can even be altered, for instance, by changing the pH-value or using different catalysts. 

During the last decades, the number of total syntheses featuring domino reactions has increased exponentially. Accordingly, numerous reviews and book chapters have been dedicated to the subject. Thus, we do not aim to be comprehensive in the following survey on total syntheses, but rather want to give an overview of the most recent elegant examples, which not only meet the definition of domino reactions but also provide a maximum increase in structural complexity. 

Furthermore, Fogg and dos Santos categorized the different types of mnlticatalyzed one-pot reactions in 2004 [25], some years after Tietze set the definition of domino reactions [12]. In this categorization, domino/cascade catalysis, tandem catalysis, and multicatalytic one-pot reactions were distinguished depending on certain factors, snch as the moment when the (pre)catalysts are added and the number... 

The introductory chapter, written by internationally recognized expert in domino reactions Pellissier, discusses various aspects of selected examples of carbohydrate domino chemistry methodologies and proposes a novel strategy applicable to synthesizing certain molecular targets. It also describes the definition of domino reaction that was originally introduced by Thietze. 

A similar reaction (which is not a domino process in its strict definition but a useful one-pot transformation) was described by Queiroz and coworkers [116]. Reaction of bromobenzothiophene 6/1-233 with pinacolborane in the presence of Pd(OAc)2 and a phosphine followed by addition of 2-bromonitrostyrene 6/1-234 led to 6/1-235, normally in good yields (Scheme 6/1.60). 

The Heck-Mizoroki reaction has also been heavily applied in one-pot sequential reaction sequences. The topic of sequential, domino, consecutive, or tandem catalytic reactions is a very timely subject, as at its core is efficiency, economy, and waste minimization in organic synthesis. In 2010 [59], one of us published a review of this topic which explains the current state of play and includes relevant references on the subject. However, the topic is still rather murky in terms of definitions, and this is something that we feel needs urgent attention. The Heck-Mizoroki is a very suitable transformation for inclusion in a sequential catalytic process, given that it leads to the formation of C=C units, a common functionality for further catalytic transformation. 

In addition, the definition of a multicomponent domino process would discount any example in which the reaction conditions are altered during the process, the result of which is that some useful reactions have not been discussed. We have decided to briefly detail a recent strategy, involving uninterrupted sequences of one-pot organocatalytic reactions, used to streamline the preparation of active pharmaceutical ingredients, since this approach nicely testifies to the synthetic power of organocatalytic MCRs (Section 42.2.4). 

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