Aromatic rearrangements intramolecular reactions

In addition to these reactions in which the carbanions are supplied from carbonyl compounds, we will discuss in this chapter Grignard reactions, the benzilic acid rearrangement, the benzoin condensation, and the Kolbe synthesis of hydroxy aromatic acids. These reactions illustrate the addition of other kinds of carbanions to carbonyl groups. The benzilic acid rearrangement is an example of the intramolecular addition of a group with its pair of electrons to a carbonyl carbon atom. 

For photochemically generated (2-biphenylcarbonyl)phenylcarbene, several competing intramolecular reactions are observed, namely cyclopropanation of an aromatic nucleus (followed by norcaradiene to cycloheptatriene tautomerization), Wolff rearrangement, C-H insertion, and a carbene-to-carbene rearrangement (see Houben-Weyl, Vol. E19b, pl282). 

Poly phosphoric acid (PPA), a highly viscous liquid, is a useful reagent and catalyst in various rearrangements and isomerizations, especially in intramolecular reactions (24,25). Cyclization of various compovmds into aromatic rings and formation of heterocycles are the most important transformations where PPA usually ensures high yields. It is especially useful when Friedel-Crafts acylations are carried out with carboxylic acids. 

As the intermolecular multicomponent reactions, three-component cycloaddition reactions (21.2 [2+2-1-2] cycloaddition and 21.3 [3+2+1] cycloaddition) and two-component cycloaddition reactions (21.4 [4+2] cycloaddition) are described. As the intramolecnlar single-component reactions, cycloaromatization reactions (21.5 intramolecular hydroarylation of alkynes and cychzation via transition metal vinybdenes) are described. Aromatic ring constrnction reactions involving aryne reactions (Chapter 12), rearrangement reactions (Chapters 16 and 18), metathesis reactions (Chapter 17), and coupling reactions (Chapters 19 and 20) are described in these different chapters. 

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

Simple criss-cross cycloadditions described so far are in fact limited to aromatic aldazines and cyclic or fluorinated ketazines. Other examples are rather rare, including the products of intramolecular criss-cross cycloaddition. The criss-cross cycloadditions of hexafluoroacetone azine are probably the best studied reaction of this type. It has been observed that with azomethine imides 291 derived from hexafluoroacetone azine 290 and C(5)-C(7) cycloalkenes < 1975J(P 1)1902, 1979T389>, a rearrangement to 177-3-pyrazolines 292 competes with the criss-cross adduct 293 formation (Scheme 39). 

Wolff rearrangement of a-diazoketones to give ketenes or subsequent products is an often used synthetic procedure the scope and limitations of which are well established 13 390), so that only a few new features of this reaction need to be considered here. Concerning its catalytic version, one knows that copper, rhodium and palladium catalysts tend to suppress the rearrangement390). A recent case to the contrary is provided by the Rh2(OAc)4-catalyzed decomposition of ethyl -2-diazo-3-oxopent-4-enoates 404 from which the p,y-unsaturated esters 405 are ultimately obtained via a Wolff rearrangement 236). The Z-5-aryl-2-diazo-3-oxopent-4-enoates undergo intramolecular insertion into an aromatic C—H bond instead (see Sect. 4.1). 

The reactivity of allenyl ketones is also manifested in the Hg(II)-catalyzed ipso substitution that converts 54 to spirodione 55 (Eq. 13.17) [19]. The reaction presumably involves activation of the allene by Hg(II), followed by intramolecular electrophilic attack on the aromatic ring. Hydrolytic cleavage of the metal from the intermediate product of the reaction, followed by rearrangement leads to the observed spirocyclic dione. 

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