Fulvenes reagents

The reductive coupling of fulvenes is a convenient method and a novel and versatile route for the preparation of ansa-bis-Cp titanium complexes with ethylene bridges. The ansa-bis-Cp complexes shown in Scheme 640 have been prepared by reduction of the appropriate fulvene reagent with TiCl2. The complexes in combination with MAO are highly active in ethylene polymerization and give linear, high density polymers.1654... 

Eq. (4.4 a) is satisfied in the position 1 of azulene. Eq. (4.4b) is valid in position 6 of fulvene, position 6 of azulene, position 3 of fluoranthene, and position 5 of acenaphthylene. Even in a few exceptional cases where the previous relations do not hold, a consideration of the coulombic effect of attacking reagents leads to a conclusion favorable to the hypothesis of frontier density growth. An example of such cases is position 3 of... 

Choose a suitable reagent and show the most likely product in a reaction between it and fulvene, 5 (R = H). 

Trifluoromethyl groups are aminolyzed by ammonia to yield carbonitriles, which works especially well with electron-rich-substituted trifluoromethane derivatives (e.g., 7), even when aqueous ammonia is used.41 45 It has been proposed that these substrates might react via a fulvene-like intermediate, which could be formed via an ElcB mechanism. With less reactive substrates, sodium amide or liquid ammonia has to be used as reagent in order to achieve carbonitrile formation.3,46 49... 

Which atom in fulvene will be most easily attacked by (a) electrophiles and (b) nucleophiles Is fulvene an electrophile, nucleophile or a non-discriminating reagent ... 

Cyclopentadienyl-SMA have been obtained through addition of triphenylsilylithium reagent to 6-(dimethylamino)fulvenes, hydrolysis and final treatment of the residue with methyl iodide.196... 

The nucleophilic addition of a hydride to the exocyclic double bond of fulvenes, using LiBEt3H as the hydride transfer reagent, resulted in the formation of the appropriately substituted lithium cyclopentadienide intermediates, which is insoluble under the reaction conditions chosen and can be isolated for purification purposes. Two equivalents of the substituted lithium cyclopentadienide undergo a transmetallation reaction when reacted with 1 mol equivalent of titanium tetrachloride in THF under reflux to give the appropriate non-bridged substituted titanocene dichloride in overall yields of up to 77% as seen in Scheme 2. 

Figure 29 shows the frontier molecular orbitals of fulvene, a molecule which can react as a 2 n, 4 7r, or 6 n addend. As we and others have discussed78,79 the very different localization of the HOMO and LUMO suggest different sites of attack by electrophilic and electrophilic reagents. This feature is common in non-alternant... 

Additions occur more easily if a carbanion with resonance or inductive stabilization is formed in the addition. Thus, fulvenes are very reactive, vinylsilanes and highly fluorinated alkenes somewhat less so. Styrene, 1,3-dienes, and enynes are more reactive than isolated alkenes, and Grignard reagents may be used to initiate anionic polymerization of styrenes, dienes, and acryhc monomers. Strained alkenes such as norbomenes and cyclopropenes are also more reactive. Examples of additions facilitated by resonance or substitution are shown in Scheme 8. 

Cycloadditions between substituted fulvenes and 1,3-dipolar reagents have been the subject of considerably less study than the corresponding diene-mediated chemistry, paralleling the situation seen in the tropone series. For the most part, however, the reactivity patterns formulated in the fulvene-diene studies are repeated in the analogous 1,3-dipole reactions. 

Fulvenes also add Grignard reagents. This represents a useful route to substituted cyclopentadiene derivatives, as the resulting Grignard reagent can reacted further to produce... 

Wittig (74) and Wittig-Homer (75) reagents of 1,3-dichalcogenoles are useful starting materials, and they have been used extensively for synthesis of extended fulvenes in the sulfur series as well as for their selenium analogues. As expected, the phosphonate esters are more reactive nucleophiles in these reactions as compared to the phosphoranes. 

When a 2-thiomethyl-l,3-selenothiolium iodide such as (84) reacts with an aryl ketone (85) in pyridine-acetic acid, fulvenes such as (86) are obtained reaction with a Wittig-Homer reagent takes place at both carbonyl groups (Equation (8)) <90PAC473,91JCS(Pl)157>. 

Oxidative work-up of the reaction of C0CI2, RI1CI3 and IrClg with 6.6-diphenyl fulvene 159,161) and Grignard reagent produces the complexes (38) with 6.6-dimethyl fulvene (39) is obtained 159>. 

Reaction with fulvenes. Amaro and Grohmann have studied the reaction of fulvenes with dichloromethyllithium under two conditions preformed reagent or reagent generated in the presence of the fulvene with lithium diisopropylamide. In both cases the reaction is carried out first at -75 to -95° and then eventually at 0°. In the case of fulvene itself or of 6,6-dimethylfulvene (1, R = CH3), yields of chlorospiro[2.4]heptadienes (2) are 55-80%. In the case of 6-mono-alkylfulvenes, two. isomeric products can be formed usually the thermodynamically less stable cis-isomer is obtained preferentially. 

Cydoadditlan. The pentalene (2) has been obtained by [6 + 2]cyclo-addition of dimethyl acetylenedicarboxylate with 1,3-di-/-butyl-6-dimethyl-aminofulvene (1) in benzene at room temperature. The fulvene lacking the two r-butyl groups undergoes Michael addition with the reagent. 

With these reagents the presence of an amine substituent on the 6-carbon atom markedly facilitates bromination [246]. This is an example of the way in which 6-amino groups activate the cyclopenta-diene ring to electrophilic attack these fulvenes can be regarded as enamines. Another example is provided by the ready formylation... 

The widespread use of silane reagents has found another application. The exocyclic double bond of fulvenes can be reduced with EtjSiH and CFjCOjH (1 1.8) at 333 K without the formation of hydrodimers. ... 

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