Indenes synthesis

A bismuth-catalyzed alkylation of warfarins has not been described, although a bismuth-mediated synthesis of the coumarin core structure 21 starting from phenols 19 and ethyl acetoacetate 20 is known (Scheme 17) [51]. The synthesis of coumarins proceeds in the same way as the above-described indene synthesis. The initial reaction of phenol 19 and ethyl acetoacetate 20 leads to the ester. 

The Friedel-Crafts alkylation of aromatics with ro-haloalkyl fluorides always favors the formation of ru-haloalkylarenes (9, 10). Symbiosis determines the selective C—X bond severance. Similarly, the indene synthesis by alkylation of benzene with 1-bromo-l-fluorocyclopropanes is shown to proceed via an electrocyclic ionization of the hard F (11). This behavior is opposite to the trend of the uncatalyzed thermal heterolysis of halocyclopropanes (see Chapter 11, Section 11.4). 

Coumarone—indene or coal-tar resins, as the name denotes, are by-products of the coal carbonization process (coking). Although named after two particular components of these resins, coumarone (1) and indene (2), these resins are actually produced by the cationic polymerization of predominantly aromatic feedstreams. These feedstreams are typically composed of compounds such as indene, styrene, and their alkylated analogues. In actuaUty, there is very tittle coumarone in this type of feedstock. The fractions used for resin synthesis typically boil in the range of 150—250°C and are characterized by gas chromatography. 

G-9 Aromatic Petroleum Resins. Feedstocks typically used for aromatic petroleum resin synthesis boil in the approximate range of 100—300°C at atmospheric pressure, with most boiling in the 130—200°C range. The C-9 designation actually includes styrene (C-8) through C-10 hydrocarbons (eg, methylindene). Many of the polymerizable monomers identified in Table 1 for coumarone—indene type cmdes from coal tar are also present in aromatic fractions from cracked petroleum distillates. Therefore, the technology developed for the polymerization of coal-tar cmdes is also appHcable to petroleum-derived aromatic feedstocks. In addition to availabiHty, aromatic petroleum resins offer several advantages over coumarone—indene resins. These include improved color and odor, as weU as uv and thermal stabiHty (46). 

Oxa-3aA ,4-dithia-l-azapentalenes synthesis, 6, 1067, 1068 8-Oxa-1,8aA -dithiacyclopent[a]indene CNDO/2 calculations, 6, 1052... 

Cyclopentadiene, b.p. 40°, is obtained by heating commercial 85% dicyclopentadiene (e.g., from Matheson, Coleman and Bell Company, Norwood, Ohio) under a short column (M in. diameter X 8-12 in. length) filled with glass helices. The distilled cyclopentadiene is collected in a receiver which is maintained at Dry Ice temperature until the cyclopentadiene is used. Methylcyclopentadiene and other substituted cyclopentadienes such as indene may also be employed for the synthesis of the correspondingly substituted ferrocenes. In these cases, the reaction of the hydrocarbon with sodium is much slower than with cyclopentadiene, and refluxing for several hours is required to complete the reaction. 

The diastereoselective intramolecular Michael addition of /(-substituted cyclohexcnoncs results in an attractive route to ra-octahydro-6//-indcn-6-ones. The stereogenic center in the -/-position of the enone dictates the face selectivity, whereas the trans selectivity at Cl, C7a is the result of an 6-exo-trig cyclization. c7.v-Octahydro-5//-inden-5-ones are formed as the sole product regardless of which base is used, e.g., potassium carbonate in ethanol or sodium hydride in THF, under thermodynamically controlled conditions139 14°. An application is found in the synthesis of gibberellic acid141. 

Imidazoles 775 /J-Iminosulphones 640 /J-Iminosulphoxides, synthesis of 69 Inclusion compounds 59, 287 Indanols 256 Indanones 338 Indenes 267 Indoles 323... 

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]. 

Scheme Z20 The synthesis of substituted indenes by intramolecular hydroarylation of aryl prop-argytic acetates...

The key step in the following synthesis of indenes by the azolide method is an intramolecular C-acylation of a fulvene intermediate. The added dimethylaminopyridine (DMAP) was thought to act as an acyltransfer agent, and diazabicycloundecene (DBU) as cyclization initiator via fulvene deprotonation [116]... 

The ease of the synthesis makes this a valuable general method for the preparation of a variety of indenes despite moderate yields and prolonged reaction times.[1163... 

Scheme 2.62. Synthesis of an enantio-enriched indene by a twofold nitro-aldol reaction.

Depending on the nature of the substrates, selectivity could be completely reversed between the two isomeric products. For example, switching R1 group between Buc and Ph gave high yields of the first and second product structures, respectively. The authors noted that the reaction did not proceed if the imine contained an ortho-MeO group at R2 or if the imine was replaced with an aldehyde, oxime, or hydrazone. The catalytic cycle is initiated by C-H activation of the imine, that is, the formation of a five-membered metallocycle alkyne insertion affords the intermediate drawn in Scheme 69. It is noteworthy that this is the first report of catalytic synthesis of indene derivatives via a C-H insertion mechanism (C-H activation, insertion, intramolecular addition). 

Because of the yield of only 16% in the synthesis of 239, the overall yields of cycloadducts with reference to indene according to Scheme 6.54 are rather low, however. A substantial improvement was achieved by the development of a one-pot procedure, which starts from indene and takes advantage of its dibromocarbene adduct (254) (Scheme 6.55). This was prepared at -60 °C with tetrabromomethane and MeLi as source for the carbene and remained unchanged in solution up to temperatures around 0 °C [92]. If an activated alkene and MeLi were added sequentially to such a solution at -30 C, cydoadducts of 221 were isolated in a number of cases in relatively good yields. In Scheme 6.55, this procedure is illustrated by the example of 1,3-cyclopentadiene, which furnished the [4 + 2]-cydoadducts 255 and 256, both as a mixture with endo exo= 2 1, in the ratio of 8 1 in 23% yield with reference to indene [67]. Analogously, the products from 221 and styrene, 1,3-butadiene [92] and 2,3-dimethylbutadiene [66], namely the compounds 240, 241, 246-249 and 250-253, were obtained in yields of 40, 24 and 25%, respectively, by means of the one-pot procedure from indene. 

Although only a few condensed 5 6 or 5 5 aromatic pyrazole derivatives can be isolated from biological sources, the chemistry of condensed pyrazoles has received considerable interest. Condensed pyrazoles with an indene skeleton can be considered as purine analogues and, as such, are expected to have biological activity. The discovery of the xanthene oxidase inhibitory action of pyrazolo[3,4-fiT pyrimidine and the cAMP phos-phodiasterase inhibitory action of pyrazolo[l,5-a]pyrimidines has stimulated considerable interest in the synthesis of analogues of both ring systems. 

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. ... 

The synthesis of photochromic compounds containing combinations of benzothiophene and thiophene 70 (04JPP(A)97, 09JMS100), indene 71 (06TL1267), or benzofuran rings 72 and 73 (06BCJ1100, 08BCSJ644) was documented (Scheme 22). 

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