Chemoselectivity and protecting groups
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This chapter describes chemoselectivity and protecting groups. Most organic molecules contain more than one functional group, and most functional groups can react in more than one way, so organic chemists often have to predict which functional group will react, where it will react, and how it will react. These questions are what can be called selectivity. Selectivity comes in three sorts: chemoselectivity, regioselectivity, and stereoselectivity. The chapter focuses on chemoselectivity (which group reacts). It begins by looking at reductions of carbonyl compounds, introducing a few more specialized reducing agents. The chapter then considers the other type of reduction in the salmefamol synthesis: catalytic hydrogenation.Keywords:
Chemoselectivity
Functional group
A copper-catalyzed process has been developed for the N-arylation reaction under very mild conditions in the absence of additional ligand. This protocol could not only tolerate an array of thermally sensitive functional groups, but also achieve high chemoselectivity.
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Abstract Digitalization of information on organic reactions is essential for developing next-generation organic syntheses with artificial intelligence and machine-learning (ML) methods. In this regard, reliable information on functional group compatibility and chemoselectivity is critical for understanding the applicability of the reactions. Herein, we report the digitalization of organic reactions using a functional group evaluation (FGE) kit that allows for accurate and rapid assessment of information on the functional group compatibility and chemoselectivity of given organic reactions. Our 26 FGE compounds were used to evaluate 4 types of organic reactions (i.e., cross-coupling, proline-catalyzed aldol, condensation, and ketimine synthesis reactions). As a result, we obtained valuable information for developing a new model of retrosynthetic analysis tools and a deeper understanding of these reactions.
Chemoselectivity
Functional group
Retrosynthetic analysis
Organic reaction
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Chemoselectivity
Functional group
Quinoline
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Regioselective C–H functionalizations of indoles reported to date with directing groups at C3 mainly rely on functional groups that are linked to the indole via C–C bonds. However, groups that are linked to the indole core by C–X linkages are also attractive due to the possibility of further modifications of the C–X bond. Herein, we report a 3-acetoxy directing group for the regioselective C2 alkenylation of indoles via a C–H activation-based, cross-dehydrogenative, oxidative Heck-type reaction. The reaction is catalyzed by Pd(II) and Ag(I) with stoichiometric Cu(II) as the oxidant and provides the 2-alkenylated indoles in yields of 52–84%. The reaction conditions are compatible with several functional groups at different positions as well as different N-protecting groups or free NH groups on the indole core. With respect to the alkene coupling partners, the reactions are successful with acrylates, vinyl sulfates, and phosphates. Specifically designed experiments, as well as density functional theory (DFT) computational studies, reveal that a heterodinuclear [Pd(μ-OAc)3Ag] bimetallic species is the actual catalyst responsible for the C–H alkenylation. A mechanistic path involving this catalytic species was also found to be favorable over other possible pathways for explaining the observed regioselectivity through DFT studies.
Bimetallic strip
Alkene
Functional group
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Cu-mediated C-2 chlorination of indoles was accomplished with copper(ii ) chloride through the use of a directing pyrimidyl protection group. A highly regioselective manner can be achieved on a range of indole substrates with excellent functional group tolerance.
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Copper chloride
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Abstract A sequential one‐pot Horner‐Wadsworth‐Emmons reaction followed by [Cu]‐catalyzed 1,4‐reduction for an efficient preparation of esters, is described. The protocol showed excellent chemoselectivity and broad functional group tolerance. In addition, the strategy was successfully applied for the synthesis of indanones by using a single column chromatography process.
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A RhIII -catalysed three-component synthesis of isoindolinone frameworks via direct assembly of benzoyl chlorides, o-aminophenols and activated alkenes has been developed. The process involves in situ generation of o-aminophenol (OAP)-based bidentate directing group (DG), RhIII -catalysed tandem ortho C-H olefination and subsequent cyclization via aza-Michael addition. This protocol exhibits good chemoselectivity and functional group tolerance. Computational studies showed that the presence of hydroxyl group on the N-aryl ring could enhance the chemoselectivity of the reaction.
Chemoselectivity
Tandem
Functional group
Cascade reaction
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The efficient synthesis of organic compounds requires the development of processes with enhanced selectivity. Selectivity is categorized according to chemical reactivity (chemoselectivity), orientation (regioselectivity), and spatial arrangement (diastereoselectivity and enantioselectivity). Recent developments in reduction-oxidation methods and C-C bond forming reactions illustrate some solutions to problems of selectivity. The design of selectivity-inducing groups and the increased role of main group and transition metals in enhancing selectivity are especially noted.
Chemoselectivity
Reactivity
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This chapter evaluates chemoselectivity and protecting groups. In a chemoselective reaction, one functional group within the molecule reacts, leaving further potentially reactive functionality unaffected. Many of the principal transformations involved in functional group interconversions (FGIs) were introduced in the third chapter of this text. The reactions may involve addition, substitution, elimination, reduction, and oxidation. There are now a plethora of mild and selective reagents available to effect specific transformations. As a general rule, when there are two functional groups of unequal reactivity within a molecule, the more reactive can be made to react alone. However, it may not be possible to react the less reactive functional group selectively.
Chemoselectivity
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