Tandem reactions definition

Recently, Denmark and coworkers have developed a new strategy for the construction of complex molecules using tandem [4+2]/[3+2]cycloaddition of nitroalkenes.149 In the review by Denmark, the definition of tandem reaction is described and tandem cascade cycloadditions, tandem consecutive cycloadditions, and tandem sequential cycloadditions are also defined. The use of nitroalkenes as heterodienes leads to the development of a general, high-yielding, and stereoselective method for the synthesis of cyclic nitronates (see Section 5.2). These dipoles undergo 1,3-dipolar cycloadditions. However, synthetic applications of this process are rare in contrast to the functionally equivalent cycloadditions of nitrile oxides. This is due to the lack of general methods for the preparation of nitronates and their instability. Thus, as illustrated in Scheme 8.29, the potential for a tandem process is formulated in the combination of [4+2] cycloaddition of a donor dienophile with [3+2]cycload-... 

Alkynes substituted with one or two trifluoromethyl groups are also highly reactive dienophiles [9] Indeed, hexafluoro-2-butyne is used increasingly as a definitive acetylenic dienophile in "difficult Diels-Alder reactions. It was used, for example, to prepare novel inside-outside bicycloalkanes via its reaction with cir,trnns -l,3-undecadiene [74] (equation 67) and to do a tandem Diels-Alder reaction with a l,l-bis(pyrrole)methane [75] (equation 68) Indeed, its reactions with pyrrole derivatives and furan have been used in the syntheses of 3,4-bis(tri-fluoromethyl)pyrrole [76, 77] (equation 69) and ],4-bis(trifluoromethyl)benzene-2,3-oxide [78] (equation 70), respectively. 

Short tandem repeat (STR) or microsatellite loci consist of DNA sequence motifs that have core repeats of two to seven base pairs. Examples include the dinucleotide 5 CACACACA 3 and the tetranucleotide 5 TTTATTTATTTA 3". Thousands of STRs are scattered throughout the genome. Because they are flanked by unique sequences, each can be specifically amplified with the polymerase chain reaction (PGR) for analysis. In populations of individuals, multiple alleles may be present based on differences in the number of repeated motifs at the locus. STRs have many characteristics that make them ideal for identity testing (1) They can be analyzed in fluorescent automated systems (2) alleles can be assigned in a definitive manner following analysis (3) STR loci are almost always transmitted in families in a Mendelian fashion (4) the loci may have 10 or more alleles, often with... 

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 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. 

Unfortunately, despite many attempts, no definition of a tandem process in chemical synthesis has been universally accepted. The Oxford English Dictionary defines tandem as one behind the other [ 10] but the continuum of chemical reactivity makes the strict application of this definition very difficult. For example, conducting several reactions in sequence (with or without purification) fits such a definition. However, we assert that this use of the term is inappropriate and when used as such diminishes the clarity of definitions that describe a special class of transformations that have... 

By definition, a diene contains two carbon-carbon double bonds each potentially can be a 2ti-component in a cycloaddition reaction. A [4 + 2] cycloaddition of a 1,3,4-oxadia-zole with a diene can proceed via one or both of two routes. In the first case, only one of the carbon-carbon double bonds from separate molecules reacts in each step, leading to a tandem, double intermolecular cycloaddition. This reaction is not much different from similar reactions with two molecules of an alkene described previously. However, in the second case, the carbon-carbon double bond remaining from the diene after the [4 + 2] cycloaddition step reacts in the [3 + 2] cycloaddition intramolecularly, which leads to a tandem, intermolecular-[4 + 2]/intramolecular-[3 + 2] cycloaddition. 

This chapter has refined the definition of a tandem process and its three variants cascade, consecutive, and sequential. Unlike a more intuitive definition of a tandem process, which is essentially synonymous to a multistep reaction sequence, this definition of a tandem process focuses on the presence of a special connection between its components. As a consequence, this definition is not concerned whether or not an intermediate can be isolated. Moreover, one or even several additional reactions may take place between the components of a tandem process (e.g.. Scheme 16.6). 

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