Isoindene

Because of its great reactivity PTAD has found wide use in the interception of reactive, unstable dienes. For example, unstable isoindenes,226 3a//-indenes,146 1,3-divinylallenes,227 and benzene oxides228 have all been successfully trapped with PTAD. 4-(4-Bromophenyl)-l,2,4-triazole-3,5-dione (5, R = 4-Br—C6H4) is often used if the derivatives ai e required for X-ray structure determination.229 Azodicarboxylic esters have been used to trap tetra(trifluoromethyl)cyclobutadiene,230 and spiro[4.4]nonatetraene.231... 

These cycloadditions with o-quinodimethanes provide a broad variety of useful fullerene functionalizations, since o-quinodimethanes can be prepared using several routes and the resulting cycloadducts are thermally stable [42], There exist several alternatives to the iodide-induced bromine 1,4-elimination of 1,2-bis (bromomethyl)-benzenes [44-47]. o-Quinodimethanes have been prepared by thermolysis of 3-isochromanone (42) [43], benzocyclobutenes (43) [48-50], isobenzothiophene 2,2-dioxides (44) [42] and sultines [51,52] or by photolysis of o-alkylphenones such as 45 [53-55] and could be added to Cjq in good yields (Scheme 4.7). Indene, thermally rearranged to isoindene, also adds to Cjq in similar fashion to quinodimethanes [56]. 

McCullough JJ (1980) A review on o-xylylenes and isoindenes as reaction intermediates, Acc Chem Res 13 270... 

The conjugated base of 1,3-diphenylindene and -isoindene is the same molecule obtainable by proton abstraction from a (c) or (d) precursor ... 

It has been suggested that walk rearrangements are responsible for the photoisomerization of benzanelated heterocycles and carbocycles (30). A remarkable example is the indene-isoindene rearrangement (31). Irradiation of 1,1-dimethyl-indene 28 produces the relatively stable 2,2-dimethylisoindene 29, an o-chino-dimethane derivative which was also synthesized by independent routes (32). 

Figure 3. Possible pathways for the indene - isoindene rearrangement.

Thermal rearrangements of indenes (8) to isoindenes by hydrogen shifts have been revealed by some early investigations9,22 Z4. 

By using a stereospecifically deuterated substrate, it can be shown that the cpimcrization 15 16 and the rearrangement to and from 17 mainly occurs by a series of suprafactal [1,5] sigmatropic hydrogen shifts via a common isoindene-type intermediate 15a (cf. 9)26. 

When heated with maleic anhydride, indene gives a 4 + 2 adduct whose structure suggested that an isomerization to isoindene had occurred (Scheme 10.1). ... 

Iso- and pseudoindenes have been prepared. The former was generated and found to dimerize. The latter, as its 2,2-dimethyl derivative, was prepared and found to give the isoindene with an activation energy of 18.9 kcal/mol (Scheme 10.5). ... 

In addition to the o-xylylene intermediate 2, isoindene 14 and 2,3-dihy-dronaphthalene 15 were generated by the 1,4-eliminations from 1,3-dibromoin-dan and 1,4-dibromotetralin, respectively, using activated nickel (Figure 7.4). 

Indene (benzcyclopentadiene) 99 also reacts with MA. In this case, a 1,4 addition requires rearrangement to isoindene 100 and hence loss of aromaticity during the reaction occurs as shown below ... 

Isobutyl vinyl sulfide, MA reactivity ratios, 303 Isohexene, MA ene reaction, 165 Isoindene, MA Diels-Alder reaction, 120 Isomaleimides, 86, 88-90 alkyl substituted, 89, 90 alternating copolymerization, 307 aryl substituted, 88-90 radical polymerizations, 266 rearrangement catalyst, 89, 90 rearrangement to maleimides, 89, 90 Isomerization, maleate-fumarate during polymerizations, 484 Isonicotinic acid, use in polyesters, 490 Isooctyl acrylate, MA copolymerization, 279 Isooctyl methacrylate, MA copolymerization, 279 Isophthalic acid... 

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