Fulvenes—

Fulvenes are formed by the action of sodium cyclopentadienide, indenide, and fluorenide on chloroacetates RCHClOAc. Diaryl thioketones react with cyclopentadienyliron dicarbonyl and its molybdenum and tungsten analogues to yield 6,6-diaryl-fulvenes. The ester (20) dimerises stereoselectively to compound (21). Pyrolysis of phthalide at 740 C gives unstable fulveneallene 

Me) exist in equilibrium with the fulvene tautomers (27)/ Unstable peroxides (28 R = Me or Ph) are formed by the reaction of singlet oxygen with the corresponding fulvenes/ 6,6-Dimethylfulvene and cyclopentadienone give a 1 1 mixture of the Diels-Alder adduct (29) and the product (30) of its Cope 

Cyclopentadienones.— The stable perchlorocyclopentadienone derivative (40) results from the thermal electrocyclic reaction of the dione (39). Indenone (42) is conveniently prepared by heating the sulphoxide (41) 2,3-diphenyl-indenones (43 R = H, Me, Cl, OMe, or NHAc) are produced in low yields by 

4-addition and subsequent extrusion of carbon monoxide. Different types of products have been obtained from 2,5-diethyl-3,4-diphenylcyclopentadienone (44 R = Et) and various aromatic azides phenyl azide yields the cycloadduct (47), 3,5-dinitrophenyl azide the a-pyridone (48), and a-azidostyrene, N3CPh= CH2, gives compound (49), together with a trace of the Diels-Alder product (50)/ The indenones (51 R R = Me or Ph) are reduced electrochemically to the corresponding cw-indanones (52), which at pH 9.3 rearrange to the trans- 

Monahan, P. Campbell, S. Cheh, J. Fong, S. Grossman, J. Miller, P. Rankin, andJ. Vallee, Synth. Comm., 1977,7, 553. 

Part of the folklore of nonbenzenoid hydrocarbons suggests fulvenes are on the nonaro-matic/aromatic border. It is thus not obvious whether these species really belong in this chapter. Yet, because their aromaticity is so much less than that found for their isomeric benzenoid derivatives we feel confident to proceed. Other than the parent hydrocarbon species 103 [i.e. 127 wherein (R, R ) = (H, H) most of the other thermochemically char-acterized fulvenes have substimtion on the exomethylene carbon cf (R R ) = (H, Me), (Me, Me) and (Ph, Ph) for reference, the suggested enthalpies of formation of the (H, H), (H, Me), (Me, Me) and (Ph, Ph) species are 224, 185, 144 and 402 kJmor respectively. Were all differences in steric interactions and contributions from the dipolar resonance structures of the generic type 128 negligible, then AH (127, R R ) and A//f(CH2=CR R ) would be linearly related. We find that a nearly perfect straight line 

Consider now the one ring-substituted fulvene for which we have a measured enthalpy of formation, namely the ring tetramethylated derivative 131 with its value of 83 kJ mol . If benzene is the appropriate paradigm for fulvene, then reaction 37 is expected to be essentially thermoneutral. 

If an olefinic paradigm is appropriate for fulvene, then reaction 38 would be more likely to be thermoneutral. 

From the enthalpies of formation from Roth for the fulvenes and from Pedley for the other hydrocarbons in equations 37 and 38, we find the former reaction is exothermic by 12 kJmol while the latter is endothermic by 12 kJmol Ionic resonance structures analogous to 128 are expected to be of less importance for the ring alkylated species than for the parent species 103 negatively charged carbon is destabilized by adjacent 

The parent triafulvene, 104, is the sole representative of this hydrocarbon class for which there is a suggested enthalpy of formation, namely 423 kJmol . If the conjugative interactions of the ea c-methylene with cyclopropene and cyclopentadiene were the same, then equation 39 would be thermoneutral. 

These reactions, going from no sp2 carbon to one in a 3-membered ring, and from one 

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The first study was made on the benzene molecule [79], The S ISi photochemistry of benzene involves a conical intersection, as the fluorescence vanishes if the molecule is excited with an excess of 3000 crn of energy over the excitation energy, indicating that a pathway is opened with efficient nonradiative decay to the ground state. After irradiation, most of the molecules return to benzene. A low yield of benzvalene, which can lead further to fulvene, is, however, also obtained. 

In a photochemical experiment, irradiation of benzene leads to Sj, which connects to the ground-state surface via the conical intersection shown. Benzene, the much more stable species, is expected to be recovered preferentially, but the prebenzvalene structure which hansfomis to benzvalene is also fomied. Another possible route from the prebenzvalene, along a different coordinate, will lead to fulvene [90, p.357] after a hydrogen-atom transfer from... 

Interesting formation of the fulvene 422 takes place by the reaction of the alkenyl bromide 421 with a disubstituted alkyne[288]. The indenone 425 is prepared by the reaction of o-iodobenzaldehyde (423) with internal alkyne. The intermediate 424 is formed by oxidative addition of the C—H bond of the aldehyde and its reductive elimination affords the enone 425(289,290]. 

R = vinyl. With aromatic substituents the fulvenes ate deep ted. The aldehyde condensation products ate also strongly colored but tesinify so easily that it is difficult to isolate them in the pure form. 

Oxidation of thiophene with peracid under carefully controlled conditions gives a mixture of thiophene sulfoxide and 2-hydroxythiophene sulfoxide. These compounds are trapped by addition to benzoquinone to give ultimately naphthoquinone (225) and its 5-hydroxy derivative (226) (76ACS(B)353). The further oxidation of the sulfoxide yields the sulfone, which may function as a diene or dienophile in the Diels-Alder reaction (Scheme 88). An azulene synthesis involves the addition of 6-(A,A-dimethylamino)fulvene (227) to a thiophene sulfone (77TL639, 77JA4199). 

Alkylthio groups are replaced in nucleophilic substitutions. Such reactions are easy in cationic derivatives for example, in the 1,2-dithiolylium series (539), substituted cydopen-tadienyl ion gives fulvene derivatives (540) (66AHC(7)39). 2-Methylthio groups in... 

SKATTEB0L DihalocydapropaneRearrangemant Rearrangement of gem-ditialocyclopropanes to ailenes or of vinyt dihalocyclopropanes to eyciopentadienes and fulvenes by MeU... 

Cyclohexylidene fulvene [3141-04-6] M 134.2. Purified by column chromatography and eluted with -hexane [Abboud el al. J Am Chem Soc 109 1334 1987]. 

The resins tend to be dark in colour and it has been suggested that this is due to a fulvenation process involving the unsaturated end group of a polymer molecule. Hydrogenation of the polymer molecule, thus eliminating unsaturation, helps to reduce discolouration. 

Irradiation of benzene and certain of its derivatives results in bond reorganization and formation of nonaromatic products. Irradiation of liquid benzene with light of 254-nm wavelength results in the accumulation of fulvene and a very small amount of tricy-clo[3.1.0.0 ]hex-3-ene, also known as benzvalene. The maximum conversion to this product in liquid benzene is about 0.05%. The key intermediate is believed to be a biradical formed by 1,3-bonding. 

Fulvene-type enamines, which possess some nonbenzenoid aromatic character, have been synthesized by treating cyclopentadienylsodium with an amide-dimethyl sulfate eomplex (117aJ17b) or quaternary pyridinium salts (117c). One of the simplest ones produced is 6-(dimethylamino)fulvene (117a,117d). 

Bu4N F , n-CgHi7SH, 92-100% yield.The thiol is used to scavenge the liberated fulvene... 

This division is not possible for other hydrocarbons such as fulvene and hepta-fulvene (Figure 7.5). 

Tlie name fulvaleiie was first mentioned by R. Brown (49TFS296), who expanded the class of fulvenes for those compounds containing two cyclic poly-enic systems with a central double bond. Tlius, depending on the ring size, cy-clopropylidenecyclopropene 1, fulvaleiie 2, heptafulvalene 3 and the unsymmetrical hybrid molecules triapentafulvalene (calicene) 4, triaheptaful-valene 5, and pentaheptafulvalene (sesquifulvalene) 6 are members of this class of cyclic cross-conjugated systems (Scheme 1). 

Cycloaddition of 4-acylsubstituted fulvene 425 with the imine 427 in boiling toluene gave the tricyclic pyrroline 428. Treatment of 426 with 427 and subsequent reaction of the product 429 with malononitrile gave 428 (86S908) (Scheme 72). 

B. 6-(Dimetkylamino)fulvene. A 1-1. four-necked flask is equipped with mechanical stirrer, dropping funnel with calcium... 

The crude product is crystallized after treatment with activated carbon from ca. 1.5 1. of petroleum ether (b.p. 60-80°) or 800 ml. of cyclohexane. From the orange-yellow solution 84 g. (69%) of 6-(dimethylamino)fulvene separates in yellow leaflets, m.p. 67-68° (Note 4). Concentration of the filtrate and further recrystallization of the residue from petroleum ether or cyclohexane gives an additional 8 g. of product. The combined yield is 92 g. (76%). 

Dimethylamino)fulvene is light-sensitive and is stored in brown bottles. 

This procedure illustrates formylation by N,N-dimethylamino-methoxymethylium methyl sulfate, a compound which can be produced readily by reaction of easily available materials. 6-(Dimethylamino)fulvene is a useful intermediate for the synthesis of various f used-ring nonbenzenoid aromatic compounds. 

Dimethylamine, reaction with phosphorus trichloride, 46, 42 f-Dimethylami nobenzaldehyde, conversion to 0,/9-dichloro- -dimethyl-aminostyrene, 46, 34 tn-Dimethylaminobenzoic acid, 47, 71 /5-Dimethylaminobenzoic acid, 47, 71 6.(Dimethylamino)fulvene, 47, 52 -Dimethylaminophenylacetic acid, 47, 71... 

Phenylcyclopent[c]azcpine (33a) and 6,7-fused cyclopentazepines 33b-d are formed in moderate yields in a one-pot, two-stage process involving initial condensation of triphenyl-[(l-phenylvinyl)imino]phosphoranes 32 with 6-(dimethylamino)fulvene-2-carbaldehyde (30), followed by an intramolecular aza-Wittig reaction of the iminophosphorane with the pendant aldehyde function.5 The method fails with the unsubstituted vinylphosphorane 32 (R1 = R2 = H). 

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