Diels-Alder reaction 1,3-dipolar cycloadditions

Chapter 6 looks at concerted pericyclic reactions, including the Diels-Alder reaction, 1,3-dipolar cycloaddition, [3,3]- and [2,3]-sigmatropic rearrangements, and thermal elimination reactions. The carbon-carbon bond-forming reactions are emphasized and the stereoselectivity of the reactions is discussed in detail. 

As with the Diels-Alder reaction, 1,3-dipolar cycloadditions can be used to start a domino process. In some examples, a second 1,3-dipolar cycloaddition, a rearrangement, a cleavage of the formed heterocycle, or an elimination may follow. 

Dipolar addition is closely related to the Diels-Alder reaction, but allows the formation of five-membered adducts, including cyclopentane derivatives. Like Diels-Alder reactions, 1,3-dipolar cycloaddition involves [4+2] concerted reaction of a 1,3-dipolar species (the An component and a dipolar In component). Very often, condensation of chiral acrylates with nitrile oxides or nitrones gives only modest diastereoselectivity.82 1,3-Dipolar cycloaddition between nitrones and alkenes is most useful and convenient for the preparation of iso-xazolidine derivatives, which can then be readily converted to 1,3-amino alcohol equivalents under mild conditions.83 The low selectivity of the 1,3-dipolar reaction can be overcome to some extent by introducing a chiral auxiliary to the substrate. As shown in Scheme 5-51, the reaction of 169 with acryloyl chloride connects the chiral sultam to the acrylic acid substrate, and subsequent cycloaddition yields product 170 with a diastereoselectivity of 90 10.84... 

Palladium cat. C-C-couplings, 43-44 Mitsunobu- and Diels-Alder reactions, 1,3-dipolar cycloadditions... 

Another gain in diversity is achieved by the combination of these cross couplings with uncatalyzed reactions. Because of their oligounsaturated character, the coupling products are obviously well suited for subsequent peri-cyclic reactions leading to additional cyclizations. These atom-efficient processes are especially attractive since they typically proceed with high chemo-, regio- and stereoselectivity [18]. This review is intended to cover Heck reactions and related palladium-catalyzed processes followed by Diels-Alder reactions, 1,3-dipolar cycloadditions or 6 -electrocyclizations. 

Electrocyclic reactions Diels-Alder reactions Hetero-Diels-Alder reactions 1,3-Dipolar cycloadditions... 

The regioselectivity of inverse electron-demand Diels-Alder reactions, 1,3-dipolar cycloadditions, and other cycloadditions can similarly be explained by resonance and orbital coefficient arguments. Determining which end of a 1,3-dipole is nucleophilic and which end is electrophilic can be dicey, though. In nitrones (R2C=NR-0), the O is the nucleophilic end, so it reacts with the electrophilic end of a dipolarophile. 

The versatile utility of transition-metal Lewis acids in catalytic organic synthesis has been thereby demonstrated in this decade to show high synthetic performance in a variety of reactions with high stereoselection and enantioselection, for example, for asymmetric Diels-Alder reactions, 1,3-dipolar cycloadditions, and other carbon-carbon or hetero atom bond-formation reactions. We hope that this review will stimulate further developments of this category Lewis acid catalyst and its application in a truly efficient chemical process in the future. 

A review detailing computational methods for determining transition-state geometry in stereoselective cycloaddition reactions has been presented. Diels-Alder reactions, 1,3-dipolar cycloadditions, sigmatropic rearrangements, electrocyclic reactions, and ene reactions have been extensively reviewed. Pressure-induced cycloadditions to strained arenes have been reviewed. ... 

Cycloaddition Cascades. These processes involve combinations of a starter molecule, which comprises a vinyl, aryl, al-lylic, or benzylic halide, triflate, etc., with one (or more) acceptor molecules (alkene, alkyne, 1,2-diene, 1,3-diene, etc.). Carbon monoxide is also a valuable one-carbon acceptor molecule. Other cycloaddition processes include Diels-Alder reactions, 1,3-dipolar cycloaddition reactions, etc., catalyzed by Pd (MeCN)2Cl2. 

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