Fulvene derivative

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... 

Dilithium compound 210, obtained from the lithiation of hexasilylfulvene 209 in THF at room temperature (Scheme 72), represents the first X-ray structural analysis of a dUithi-ated fulvene derivative. In the solid state, one lithium centre is capping the central five-membered ring, while the second lithium centre is located at the exocyclic carbon atom of the fulvene unit (Figure 27) . 

Two additional synthetic routes to ( )-j8-vetivone (350) have been developed. In one of these a suitably substituted spirocyclic system [cf. (349)] is constructed by addition of Me2CuLi to the fulvene derivative (348)/ Subsequent functional group modification (cf. Scheme 32) provides ( )-j8 -vetivone (350). In the other total synthesis d the well-known intramolecular alkylation of para-substituted phenols has been used to produce a spirocyclic intermediate (353) which can be converted into ( )-/3-vetivone (350) (cf. Scheme 33). 

Arylsubstituted cyclopentadienes such as 1,2,3,4-tetraphenylcyclo-pentadiene (369) give rise to isolable endoperoxides249 which can be thermally rearranged to m-diepoxides. From the corresponding fulvene derivative (372) only the diepoxide 374 was isolated which probably originates from a thermally unstable endoperoxide 37i.249,250... 

An inter-intra-intramolecular carbopalladation cascade, initiated by the alkenylpalladium bromide intermediate from /3-bromostyrene 74 inserting into one of the triple bonds of the diyne 73, yields the ring-annelated fulvene derivative 75 (Scheme 22). ... 

Oxaquadricyclanes with a-H-containing substituents on C2 and C4 may undergo a competing thermal or acid-catalyzed rearrangement to afford enol ethers.46 Acid or Lewis acid catalysis may also lead to fulvene derivatives.46... 

Treatment of bis(dimethylaminomethylene)pyrrolizinium perchlorate (29) with cyclopentadiene-NaH in DMF gave the diatropic cyclopenta-[fc]cycl[4,2,2]azine (77), which was also obtained from the fulvene derivative (78) and 3//-pyrrolizine (25). Electrophilic substitutions (deuteration, nitration, nitrosation, acylation, bromination, Mannich reaction) occur in the 6- and 8-positions.32... 

Irradiation of benzene in quartz gives fulvene (Formula 416) (183). Toluene, isopropylbenzene, and anisole give fulvene derivatives to a... 

The most remarkable results for this group of monomers are those obtained with the fulvene derivatives 229-231. Their ROMP is initiated by both 7 (R = Me) and 8 (R = Me) in toluene at 20 °C, the latter giving the faster reaction. For each initiator the rate decreases in going from 229 to 230 to 231 i.e. as the bulk of the substituents becomes larger. Surprisingly the cis content of each polymer is independent of the catalyst 20% for 229, 0% for 230 and 100% for 231. The NMR spectra of the polymers of 230 are in keeping with an all-HT structure306. 

Another nucleophilic displacement of the methylthio group is observed with indole as a reactant. Heating indole with the 2-methylthio-l,3-dithiolylium iodide (195) at 50 °C in acetonitrile produces the salt (210) in 58% yield. Subsequent treatment of (210) with l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base forms the fulvene derivative (211) in quantitative yield (80BCJ1661). 

There are at least two issues to be addressed regarding the Type lie circular cascade process shown in Scheme 42. One is the regioselectivity in the initial intermolecular carbopalladation. Since it is not very difficult to differentiate the two terminal positions of a. j-diyncs, this is not a serious problem in most cases. A more serious problem is the exclusive formation of fulvene derivatives observed in a couple of cases [124] (Scheme 45). It is not very clear what the scope of the fulvene formation is and whether the course of the reaction could be altered to give benzene derivatives. 

In the usual manner the salt (44) can also be condensed with the reactive nitriles (24 h) and (24 i) and finally cyclized to the azulenes (48), (49), and (50). Starting with (24 h), one obtains passing over the fulvene derivative (47), the dihydro-naphtho-azulene (48) as the main product (45%), together with a small amount (6%) of the azulene (49). Bromosuccinimide in carbon tetrachloride dehydrogenates (48) to (49) in 89% yield, without any substitution by bromine. 

Based on mechanistic considerations, 171 has been suggested as an intermediate in the base-induced transformation of 170 to benzocyclopropene (172) (150). On treatment of 173 with lithium dimethylamide at — 75°C, the fulvene derivative 175 could be isolated (151). The mechanism by which the fulvene arises was elucidated by several isotope labeling experiments. These results require the formation of triene 174 as an intermediate in the base-induced elimination reaction of 173 (151). 

Heteroanalogous fulvene derivatives, such as diazocyclopentadiene 16 and tetra-ferf-butylcyclopentadienone 19 have also been of great interest as reactive precursors to other theoretically interesting molecules. Irradiation of diazocyclopentadiene 16 readily generates the cyclopentadienylidene 17 which has been trapped with alkynes to form spiro-fused cyclopentadiene derivatives such as 18 (Scheme 4) [14]. It has been demonstrated by UV spectroscopy [15] and calculations [16] that these spiro[2.4]heptatrienes (so-called [1.2]spirenes) 18 are spiroconjugated across their central sp3 carbon. 

The formylation of styrene derivatives has been extended to several related alkene derivatives indene (52) gives 2-formylindene (53 20%), polyenes (54) and (55) afford aldehydes (56 92%) and (57 29-65%), and fulvene derivative (58) yields (59). In several cases, the products of monosubstitution described above are accompanied by products of polysubstitution, particularly under forcing conditions. For example, 2-phenylpropene reacts with salt (1) to give 4-phenylpyridine-3-carbaldehyde (60) after treatment with aqueous ammonium chloride solution. A useful synthesis of biphenyls (61 30-98%) from alcohol derivatives (62) and salt (1) has recently been reported. ... 

A partially intermolecular verison is possible, but less efficient. Thus the bromocnync 4 and 3-hexync cyclize to 5 under the same conditions in 40% isolated yield (equation 1). However, cocyclization of (E)-/f-bromostyrcne and the diync 6 results in a fulvene derivative 7 (equation II). 

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