Tandem/domino/cascade processes

Tandem/Domino/Cascade Processes on Zeolites and Zeolite-Like Materials... 

There is certain confusion in the Hterature with respect to terminology of one-pot/ tandem or domino/cascade-type processes. We understand under true domino/cascade processes, those where the intermediate cannot be isolated and the individual steps cannot be performed separately. Contrary conventional reactions performed sequentially are referred as tandem reactions, and they can provide significant process improvements when performed in a one-pot fashion. 

The one-pot multistep process has been named in various ways domino, cascade, tandem, timed, consecutive, transmissive, etc. Sometimes the word used does not describe the real meaning of the procedure in that there is no conformity between the customary use of the term and the chemical transformation. These terms were recently defined more pertinently [59]. 

A domino Diels-Alder reaction (the term was chosen from the well-known game) is a one-pot process involving two or more Diels-Alder reactions carried out under the same reaction conditions without adding additional reagents or catalyst such that the second, third, etc., cycloaddition is the consequence of the functionality generated in the previous reaction. A historical example is illustrated in Equation 1.28 [60]. This type of transformation is sometimes named tandem or cascade, but these terms seem less appropriate for describing a time-resolved transformation. 

In this chapter the combinations of different chemical steps in one process are always called domino process although some authors may have used the word tandem or cascade. We prefer the word domino over tandem and cascade since domino is not used in any other context in chemistry and thus facilitates the search for this type of transformation in the literature. On the other hand, the word tandem does not describe these time-resolved processes in a proper way, since it means two at the same time. 

In a narrower sense, this review covers intramolecular Mizoroki-Heck [1] reactions forming carbocycles [2] that is, the palladium-catalyzed intramolecular coupling of vinyl/aryl (pseudo-)halides with an alkene tethered by a hydrocarbon chain. Ring closures furnishing heterocycles are covered in Chapter 6 also beyond the scope of this chapter are the domino/cascade or tandem (Chapter 8) and asymmetric processes (Chapters 12 and 16) dealing with formation of a carbocycle. 

The living nature of acylpalladium and other organopalladium species permits a series of their interconversions under one set of conditions, one representative example being the Pd-catalyzed copolymerization of alkenes and CO (Sect. VL4.2). A series of such processes can also occur in cyclic manners, and they are the subject of this subsection. Some chemists call combinations of two same or different successive processes tandem processes. These chemists have tended to call successively occurring multiple processes cascade processes, which may include tandem processes. Other chemists, on the other hand, would call them domino processes. Since these are rather loosely defined terms involving fundamentally nonchemical words, selection among them is a subjective matter, and all are used here and throughout this Handbook. 

Patterns of cyclic carbopalladation. As discussed above, the fundamentally stoichiometric and living nature of carbopalladation imposes various difficulties to be overcome. Carbopalladation can, in principle, be either a single-stage process or double- or multiple-stage processes. Double-and multiple-stage carbopalladation reactions have often been called either domino or cascade carbopalladation reactions. In some cases, two-stage carbopalladation reactions have also been called tandem carbopalladation reactions. None of these three words is a chemical term, and choice between them is a matter of taste. In this chapter, the term cascade will be used for both double- and multiple-stage carbopalladation processes. 

Abstract Radical tandem reactions—and in a wider context radical dominos or cascades—have attracted a lot of attention because of their intrinsic elegance and the construction of a hroad and sometimes unique array of molecular architectiu es they allow in a single step. This review focuses on the latest progress in the design and development of new tandem reactions. The first part is devoted to intramolecular processes the second part covers tandem and domino processes involving both intra- and intermolecular steps. The third part introduces intermolecular-only reactions. Finally, the last part focuses on tandem reactions involving both radical and non-radical elementary steps. 

Radical tandem reactions and in a wider context radical dominos or cascades have attracted a lot of attention because of their intrinsic elegance and the construction of a broad and sometimes unique array of molecular architectures they allow. Contrary to a long-standing idea, efficiency and selectivity requirements can also be met. A good illustration is the one-pot assembly of hnear triquinane 2 from acychc precursor 1 (Scheme 1) [1]. In this ten-elementary radical step process, five C - C bonds are created as well as three quaternary centers and four stereogenic centers, almost all completely controlled. 

Since tandem reactions first appeared they have been given many diverse names such as cascade, consecutive, and coupled processes, domino reactions, interrupted polymerisation, one-pot, sequential and serial reactions, and tactical combinations. Some authors have tried to classify... 

One pot A term that refers to a chemical process involving more than one reaction step taking place in a single reaction vessel without having to isolate the intervening intermediates (see cascade, domino, multicomponent, tandem). 

C. TANDEM, CASCADE, OR DOMINO ACYLPALLADATION AND CARBOPALLADATION PROCESSES... 

A transannular 4 + 2-cycloaddition initiates the tandem 4 + 2/3+2-cycloaddion cascade of 1,3,4-oxadiazoles (1) to yield cycloadduct intermediates (2) used for the synthesis of analogues of vinblastine (Scheme 1)." The multi-component 4+ 2/3+2-domino cycloaddition reactions of 3-nitroindole derivatives with vinyl ethers and acrylates were studied computationally and experimentally. The 4+2-reaction follows a classical concerted asynchronous process while the 3 + 2-addition involves an electron donation by an electron-deficient reaction partner. ... 

Cascade Reactions. Cascade reactions can be defined as multi reaction one pot sequences in which the first reaction creates the functionality to trigger the second reaction and so on. Cascade reactions have also been termed tandem or domino processes by some authors. This section is concerned with Pd(PPh3)2Cl2- [to generate Pd(0)] or PdCl2-catalyzed processes in which two or more carbon-carbon/carbon-heteroatom bonds are formed. 

After this general overview, a brief survey of the key achievements in this area is given by highlighting some selected transformations according to the main classes of electrophiles. We will then summarize the asymmetric organocatalyzed F-C reaction in sequential processes (cascade, domino, tandem reactions) and, finally, illustrate its potential in some selected outstanding natural product syntheses. 

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