Cyclopentadienide, lithium

The reaction of 1,2-dithiolanes with 2- and 4-picolyllithium has been examined <96PS(112)101> and the reactions of thioanhydrides such as 94 with both thiols <95JOC3964> and amines <96TL5337> have been reported. Treatment of 1,2-dithiolium salts with lithium or thallium cyclopentadienide results in formation of a variety of bi-, tri- and tetracyclic products <96LA109>. Reaction of 95 with trimethyl phosphite gives some of the desired coupling product but also the phosphonates 96 <96PS(109)557>. 

More recently, a very efficient asymmetric carbolithiation of N,N-dimethyl-aminofulvene 30, leading to a chiral cyclopentadienide anion, was reported by Hayashi et al. [6] for the synthesis of chiral metallocenes (Scheme 6). By adding an aryl lithium such as 31 complexed with a chiral ligand on fulvene 30, a cyclopentadienide ion 32 bearing a stereogenic center at the a position was generated. This anion was reacted with [RhCl(nbd)]2 to yield... 

The reaction of the crowded stibole 53 and bismole 54 with lithium followed by addition of lithium cyclopentadienide (Scheme 9) gives mixtures of the corresponding monostibaferrocene 69 and monobismaferro-cene 70, respectively, with ferrocene.25 The more volatile ferrocene is easily removed by sublimation. Rather small amounts of the crowded diheteroferrocenes 55 or 56 are formed in this reaction. 

Oeeasionally, very good enantioselectivities were achieved in the (-)-sparteine-mediated carbolithiation of 6-dimethylaminofulvene (470) by ort/zo-substituted aiyllithiums 471 (equation 129) . Here, (—)-sparteine (11) turned out the best chiral additive. The lithium cyclopentadienides 472 were converted to the corresponding Rh(l)-norbornadiene complexes 473. 

CuCl-catalyzed decomposition of iodonium ylides prepared from /3-keto esters and diacetoxyiodobenzene, has been developed (equation 151)331. 1-Methylbenzvalene is obtained in a good yield by treating a mixture of lithium cyclopentadienide and 1,1-dichloroethane with butyllithium332. The tandem cyclization substitution in l-selenyl-5-hexenyllithiums derived from corresponding selenacetals via selenium/lithium exchange produces bicyclo[3.1.0]hexane derivatives333. 

An interesting isomer of benzene is "benzvalene" (tricyclo[2.1.1.05,6]-2-hexene). This substance, which like prismane (Section 12-10) can decompose with explosive violence, has been synthesized by T. Katz from lithium cyclopentadienide, dichloromethane, and methyllithium ... 

There is a certain analogy between the aromatic anions of cyclopentadienide (C5H5 ) and boratabenzene (C5H6B ). l-Methylbora-2,5-cyclohexadienehas a more acidic proton connected to the, sp3-hybridized ring carbon atom than cyclopentadi-ene, due to the same tendency of aromatic anion formation [252, 253]. The related 1-phenyl-1,4-dihydroborabenzene affords the lithium salt of 1-phenylborataben-zene on treatment with tert-butyllithium. Like metallic complexes such as ferrocene formed by cyclopentadiene, boratabenzene also forms such sandwich -complexes with iron and cobalt. The iron complex can be acetylated under Friedel-Crafts conditions. 

Condensation of 3,5-diaryl-l,2,4-dithiazolium salts 46 with lithium cyclopentadienides affords tricyclic azadithia heterocycles 73 (Scheme 10) <1994TL3893, 1997LA221>. 

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. 

Unfortunately, the carbolithiation reaction of lithium species with 6-/V, /V-dimethylamino fulvene and subsequent transmetallation reaction leads to titano-cenes with stereoisomers, as an equimolar mixture of the R and S form of the substituted lithium cyclopentadienide is formed. Subsequently, this equimolar mixture of R and S configured substituted lithium cyclopentadienide is used for the transmetallation reaction and therefore, a mixture of the 25% of RJt, 25% of the S,S and 50% of the R.S form of the chiral titanocene dichloride is obtained. 

In order to avoid the presence of stereoisomers, a further pathway including a carbolithiation reaction delivering achiral titanocene dichlorides was explored. Different aryl or heteroaryl lithium species were reacted with 6-bis-/V,/V-di methyl -amino fulvene and therefore, the intermediate lithium cyclopentadienide and the resulting 6-bis-/V./V-dimethylamino-functionalised titanocene dichlorides become achiral. 

Within this review we describe a second reaction pathway, which includes a carbolithiation reaction and leads to achiral-substituted titanocene dichlorides also. Therefore, aryl lithium species are added to the identical substituted 6-aryl fulvenes. This leads to the formation of highly substituted, but achiral diarylmethyl-functionalised lithium cyclopentadienides as seen in Scheme 5, which can still be used in the transmetallation reaction with titanium tetrachloride. 

The first example of lithium-NHC complexes, in which the lithium is coordinated only to carbon centres, was reported by Arduengo and coworkers.10 Stable NHCs were reacted with lithium 1,2,4-n-A(trimethylsilyl) cyclopentadienide to give 2 (Fig. 2). A single crystal X-ray structure reveals a complex in which the lithium centre is coordinated in a r 5-fashion to the cyclopentadienyl ring, with a single cr-interaction between the lithium and carbene centre. The lithium centre lies 2.155(4) A from the carbene centre hence has a closer contact than in the previous example, possibly as a result of the carbene interacting with only one lithium centre. 

A solution of 9.66 g (0.05 mol) of trimethyltin chloridef is prepared in 20 mL of dry diethyl ether. The solution is cooled to 0° and is slowly injected through the serum cap into the lithium cyclopentadienide solution. This operation is carried out over a period of 1 hr with continuous stirring, during which time the white precipitate gradually becomes buff-colored. When all of the trimethyltin chloride solution has been added, the flask is allowed to reach room temperature and the reaction mixture is finally gently refluxed for 6 hr. 

VI. OTHER SUPRAMOLECULAR DIMERS WITH LITHIUM A. Dimers of Lithium Isodicyclopentadienide and Cyclopentadienide... 

D-Mannitol was also used as a precursor for trehazolamine via its conversion into the (/ )-(—)-epichlorohydrin (162),91,92 which gave the optically active l-(hydroxy-methyl)spiro[2,4]cyclohepta-4,6-diene (163) in 60% yield upon treatment with lithium cyclopentadienide (Scheme 21).49 Conversion of 163 into the corresponding trichloroacetimidate 164,93 followed by reaction with I(,yy/w-collidine)2CI04, afforded... 

An excellent review has discussed the synthesis of organophosphorus cages employing phosphaalkynes as precursors.68 In order to avoid unnecessary duplication of coverage, the results here reported are restricted to transition-metal-assisted transformations. An intramolecular [2+4] cycloaddition between an 7 -phosphaalkyne and an V-cyclopentadienylli-gand to yield compound 134 is observed during the reaction of complex 114 with lithium cyclopentadienide, as shown in Eq. (29).56c... 

Other routes involve treatment of a metal-trifluorophosphine halide with either sodium or lithium cyclopentadienide (method D), or direct reaction between a metal-PF3 complex and cyclopentadiene (method E). 

---