Indenes cycloaddition

UV irradiation of hexafluorobenzene with indene or cycloalkenes gives high yields of 2+2 adducts, which undergo further intramolecular cycloaddition to form hexafluoropolycycloalkanes [754] (equation 38) Photolysis of fluormated deriva tives of vinylbenzenes afford benzocyclobutenes, whereas allyl benzenes yield Dewar benzene-type products [755]... 

By analogy with the formation of3//-azepines by cycloaddition of 2//-azirines withcyclopenta-dienones, l,3-diphenyl-2//-inden-2-one (58) and its dibenzo analog 60 enter into [4 + 2] cycloadditions with 27/-azirines to give 3//-2-benzazepines 59 and phenanthro[9,10-e]azepincs 61, respectively.96... 

While (Z)-l,2-bis(phenylsulfonyl)ethylene (140) does not add to dienes such as furan, cyclopentadiene, cyclo-octatetraene, indene and /f-naphthol, ( )-l,2-bis(phenylsulfonyl)ethylene (141) is more reactive and the reaction with furan proceeds at room temperature for 2 h to give the adduct in 95% yield. The reactivity of dienophiles having sulfonyl group in the [4 + 2]cycloaddition is shown in equation 10393,101. 

The reaction of alkoxyarylcarbene complexes with alkynes mainly affords Dotz benzannulated [3C+2S+1C0] cycloadducts. However, uncommon reaction pathways of some alkoxyarylcarbene complexes in their reaction with alkynes leading to indene derivatives in a formal [3C+2S] cycloaddition process have been reported. For example, the reaction of methoxy(2,6-dimethylphenyl)chromium carbene complex with 1,2-diphenylacetylene at 100 °C gives rise to an unusual indene derivative where a sigmatropic 1,5-methyl shift is observed [60]. Moreover, a related (4-hydroxy-2,6-dimethylphenyl)carbene complex reacts in benzene at 100 °C with 3-hexyne to produce an indene derivative. However, the expected Dotz cycloadduct is obtained when the solvent is changed to acetonitrile [61] (Scheme 19). Also, Dotz et al. have shown that the introduction of an isocyanide ligand into the coordination sphere of the metal induces the preferential formation of indene derivatives [62]. 

The unconventional structure of fulvenes with a unique C=C bond conjugation leads to unusual cycloaddition reactions with other unsaturated systems. For example, alkenylcarbene complexes react with fulvenes leading to indanone or indene derivatives which can be considered as derived from a [6S+3C] cycloaddition process [118] (Scheme 72). The reaction pathway is well explained by an initial 1,2-addition of the fulvene to the carbene carbon followed by [1,2]-Cr(CO)5-promoted cyclisation. 

Dihydro-1-vinylnaphthalene (67) as well as 3,4-dihydro-2-vinylnaphtha-lene (68) are more reactive than the corresponding aromatic dienes. Therefore they may also undergo cycloaddition reactions with low reactive dienophiles, thus showing a wider range of applications in organic synthesis. The cycloadditions of dienes 67 and 68 and of the 6-methoxy-2,4-dihydro-1-vinylnaphthalene 69 have been used extensively in the synthesis of steroids, heterocyclic compounds and polycyclic aromatic compounds. Some of the reactions of dienes 67-69 are summarized in Schemes 2.24, 2.25 and 2.26. In order to synthesize indeno[c]phenanthrenones, the cycloaddition of diene 67 with 3-bromoindan-l-one, which is a precursor of inden-l-one, was studied. Bromoindanone was prepared by treating commercially available indanone with NBS [64]. 

Since dihydroarylethenes are more reactive than the corresponding fully aromatic compounds, their use in the cycloaddition reactions is preferred in order to carry out the reactions under mild conditions with higher yields. Some reactions of 3,4-dihydro-1-vinylnaphthalene (103) [33], 3,4-dihydro-2-vinyl-naphthalene (104) [34], and l,2-dihydro-4-vinylphenanthrene (105) [35] with 4-acetoxy-2-cyclopentenone (98) and 2-inden-l-one (106) are summarized in Schemes 5.11-5.13. 

The only reported 1,2-addition providing a relatively stable adduct is that of a 1,2-cycloaddition of phthalazinedione to indene (Scheme 40). Compound 162 was isolated and characterized (66JOC3862 71CC695). A similar 1,2-addition reaction to the 9,10-double bond of phenanthrene was also reported but not firmly documented (66JOC3862). 

Rhenium-catalyzed [3 + 2]-cycloaddition reactions between imines and nitriles affording indene derivatives were reported by Kuninobu et al. these authors demonstrated that only 3 mol.% of [ReBr(CO)3(THF)]2 allowed the transformation to proceed in high yield (Scheme 69).311... 

Thermolysis of 44 produced products derived from the Myers-Saito cyclization reaction. However, when 43 having a trimethylsilyl substituent at the acetylenic terminus was subjected to heating in the presence of 1,4-CHD at 70 °C for 3 h, the 1H-cyclobut[a]indene 46 was produced. A reaction mechanism involving an initial Schmittel cyclization to generate the benzofulvene biradical 45 followed by an intramolecular radical-radical coupling was proposed to account for the formation of the formal [2 + 2]-cycloaddition product 46. 

Several derivatives of lH-cycloprop[/]indene have been synthesized. The di-fluoro compounds 212 (X = 0,S) were obtained by the cycloaddition route from 188 in analogy to the synthesis of 191 and 192. The cycloaddition of diene 213 to 1,2-bromochlorocyclopropene (27) provided 214, which was aromatized to 217. Twofold Curtius degradation of 214 afforded the ketone 215. While attempted aromatization of 215 with base afforded no cycloproparene, the corresponding alcohol 216 reacted with base to 218 in acceptable yield. The alcohol 218 is also accessible from 219. ... 

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]. 

Photochemical cycloaddition reactions between sydnones (1) and 1,3-dipolarophiles take place to give products which are different from, but isomeric with, the thermal 1,3-dipolar cycloaddition products. These results are directly interpreted in terms of reactions between the 1,3-dipolarophiles and Ae nit mine (316). The photochemical reactions between sydnones and the following 1,3-dipolarophiles have been reported dicyclopentadiene, dimethyl acetylene dicarboxylate, dimethyl maleate, dimethyl fumarate, indene, carbon dioxide, and carbon disulfide. ... 

The transition state of singlet carbene cycloaddition to alkenes involves an electrophilic approach of the vacant p orbital to the n bond of alkenes. By contrast, the first step of the triplet addition process may involve the in-plane a orbital of the carbene. As in the case of C—H insertion (see Section 5.1), the difference in the transition structure between the singlet and triplet cycloaddition becomes important in the intramolecular process, especially when approach to a double bond is restricted by ring strain. Direct photolysis of ( )-2-(2-butenyl)phenyldiazomethane (99) in the presence of methanol gives l-ethenyl-l,la,6,6fl-tetrahydrocycloprop [fljindene [100, 29%, (E/Z)= 10 1] and l-(2-butenyl)-2-(methoxymethyl)benzene (101, 67%). Triplet-sensitized photolysis results in a marked increase in the indene (52%, EjZ) = 1.3.T) at the expense of the ether formation (4%) (Scheme 9.30). On the other hand, direct photolysis of phenyldiazomethane in an equimolar mixture of... 

Imines derived from aniline and glyoxylic acid esters can be regarded as electron-poor 2-azadienes, in which an aromatic carbon—carbon double bond takes part of the diene system. In this context, Prato and Scorrano et al. were able to achieve the [4 + 2] cycloaddition of ethyl N-phenyl glyoxylate imines with dihydrofuran and indene leading to hexahydrof-uro[3,2-c]- and tetrahydro-7//-indeno[2,l-c]quinolines, respectively, in moderate to good yields (88JHC1831). Similarly, tetrahydroquinoline derivatives were formed by [4 + 2] cycloaddition of 1,2-bis(trimethylsily-... 

Acenaphthylene, indene, and styrene undergo periselective 4 + 2-cycloaddition with 3-ethoxycarbonyl-2//-cyclohepta[Z>]furan-2-one in high yield.152... 

Cycloaddition of styrene with p-quinone methides.2 In the presence of this Lewis acid, p-quinone methides and styrenes undergo a formal [3 +2]cycloaddi-tion to form dihydro-lff-indenes. The reaction shows some stereoselectivity. Thus the geometry of the (E)-styrene is largely retained (17 1) and only two of the four possible products are formed. Presumably, any electron-rich alkene could participate in this cycloaddition. 

In some cases radical cations may undergo cycloadditions with an acceptor derived intermediate without prior proton transfer. This is observed especially for radical cations without sufficiently acidic protons, although it is not limited to such species. For example, the photoreaction of chloranil with 3,3-dimethylindene results in two types of cycloadducts [141]. In the early stages of the reaction a primary adduct is identified, in which the carbonyl oxygen is connected to the p-position of the indene (type B) in the later stages this adduct is consumed and replaced by an adduct of type A, in which the carbonyl oxygen is connected to the a-position. CIDNP effects observed during the photoreaction indicate that the type B adduct is formed from free indene radical cations, which have lost their spin correlation with the semiquinone anions. 

Benzyl cations generated from benzyl alcohols or quinone methides by the action of S11CI4 undergo [3-(-31-cycloaddition of allylsilanes leading to tetrahydronaphthalenes.1 With secondary and tertiary benzyl cations, a competing [3 + 2]-pathway forms dihydro(177)indenes. 

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