Sigmatropic Rearrangement Reactions

Aromatic Substitution (Carey Sundberg, Chapter 11) Intramolecular Wittig Reaction Sigmatropic Rearrangements... 

Thomson - v Click Organic Interactive to predict products from a variety of sigmatropic rearrangement reactions. 

Keywords Diels-Alder reactions, dipolar cycloadditions, electrocyclic reactions, ene reactions, pericyclic reactions, sigmatropic rearrangements... 

Rearrangement reactions have provided access to some interesting azepinone or azepine dione systems. Curtius rearrangement followed by a [3,3] sigmatropic reaction on intermediate carbonyl azides gave azepin-2-one derivatives, for example 2, in fair to moderate yield. The precursor intermediates for this sequence were made, in turn, by treatment of 2-siloxysubstituted 2-alkenylcyclopropanecarboxylic acids (for example, 1) (Scheme 1) with diphenylphosphorazidate and triethylamine <00SL725>. 

The [3,3]-sigmatropic type rearrangement of propargyl thionophosphates 46 was catalyzed by PdCl2(NCMe)2 [63]. The rearrangement reaction took place stereospedfically and the allenyl thiolophosphates 47 were obtained in good yields (Scheme 3.27). 

This type of stereoselective reaction, in which a chiral unit is created and another destroyed, has been termed self-immolative by Mislow39 and an asymmetric transfer process by Pracejus40. Both terms are in use. but the latter is gaining ground in the mutated form of "chirality transfer 41, which is most often applied to sigmatropic rearrangement reactions such as the following37 ... 

This [3,3] sigmatropic rearrangement process, which represents a variant of the well-known Biichi reaction, does proceed through a transition state geometry which is boatlike in character. The rearrangement reaction has been applied to other lactones as well. One rather interesting example is provided by the rearrangement of the cls-fused lactone (646) to the bicyclic carboxylic acid (647 Scheme 148). 

Rearrangement reactions (Miscellaneous) (see also Electrocyclic rearrangements, Sigmatropic rearrangements, Wittig rearrangement)... 

The three principal types of pericyclic reactions are cycloaddition, electro-cyclic rearrangement, and sigmatropic rearrangement ... 

In this primer, Ian Fleming leads you in a more or less continuous narrative from the simple characteristics of pericyclic reactions to a reasonably full appreciation of their stereochemical idiosyncrasies. He introduces pericyclic reactions and divides them into their four classes in Chapter 1. In Chapter 2 he covers the main features of the most important class, cycloadditions—their scope, reactivity, and stereochemistry. In the heart of the book, in Chapter 3, he explains these features, using molecular orbital theory, but without the mathematics. He also introduces there the two Woodward-Hoffmann rules that will enable you to predict the stereochemical outcome for any pericyclic reaction, one rule for thermal reactions and its opposite for photochemical reactions. The remaining chapters use this theoretical framework to show how the rules work with the other three classes—electrocyclic reactions, sigmatropic rearrangements and group transfer reactions. By the end of the book, you will be able to recognize any pericyclic reaction, and predict with confidence whether it is allowed and with what stereochemistry. 

Experimental and computational approaches to elucidating mechanistic details in pericyclic rearrangements have been reviewed,1 as have preparations of alkenes by rearrangement reactions.2 The formation of saturated carbon atoms with no attached heteroatoms by sigmatropic or electrocyclic rearrangement reactions has been reviewed.3... 

Pericyclic processes comprise a broad and important class of concerted reactions of both theoretical and practical interest. These transformations, which are especially useful in the construction of carbon-carbon bonds,93 include electrocyclic reactions, sigmatropic rearrangements, and cycloadditions. Because they are not typically subject to general acid-general base chemistry but can be highly sensitive to strain and proximity effects, they are attractive targets for antibody catalysis. 

Keywords Thiocarbonyl compounds, Thiophilic addition, Cycloaddition reactions, Enethioli-sation, Eschenmoser reaction, Sigmatropic rearrangement. 

Overman has suggested a cyclic six-membered transition state 10 for the reaction [8]. The experimental result for the formation of substituted alkenes is similar to that observed for other [3,3]-sigmatropic rearrangements. Furthermore, the preferred formation of the trans-isomer of the di- and trisubstituted alkenes is consistent with transition state 10. The activation parameters for the [3,3]-sigmatropic rearrangements are similar to related rearrangement reactions. 

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