1.3- Cyclopentadiene preparation

The heterocyclic derivatives of cyclopentadiene prepared by the ring-closure reactions are listed in Table VI. 

Heterocyclic Derivatives of Cyclopentadiene Prepared by Ring-Closure Reactions... 

In a 100-mL, two-necked round-bottomed flask equipped with a nitrogen inlet and a magnetic stirring bar, 0.25 g (0.95 mmole) of hydrated ruthenium trichloride is completely dissolved, under nitrogen, in 7 mL of absolute ethanol. Freshly distilled cyclopentadiene, prepared by literature methods,8 (7.0 mL, 84.7 mmole) and zinc dust (2.5 g, 28.2 mmole) are added in that order and the mixture stirred for 2 hr at room temperature. The resulting yellow-brown solution is filtered, and the solid residue is washed with benzene (50 mL). The filtrate is evaporated to dryness under reduced pressure, and the solid residue obtained is extracted with pentane (2 X 60 mL). 

The Cr-N02 complexes reported to date do not appear to isomerize under photolysis conditions, but can decompose with release of NO when irradiated with light (88). However, the complex CpCr(N0)2(N02) (Cp = cyclopentadiene) prepared by metathesis of CpCr(NO)2Cl with NaN02 in methanol, exists in both the nitro and nitrito forms in solution (Figure 8), with the nitrito isomer favored both in solution and in the solid state (89). The equilibrium is temperature dependent as determined by H NMR spectroscopy, with the nitrito isomer favored at higher temperatures (AHeq = 1.8(3)kcalmol AS=9.3(9) eu) (89). In addition, H NMR and... 

Cyclopentadiene (2.5) was prepared from its dimer (Merck-Schuchardt) immediately before use. Dimineralised water was distilled twice in a quartz distillation unit. Ethanol (Merck) was of the highest purity available. Acetonitrile (Janssen) was mn over basic aluminium oxide prior to use. 2,2,2-Trifluoroethanol (Acros) was purified by distillation (bp 79 - C). Co(N03)2 6H20,... 

Pyridyl)hydrazine (Aldrich), 4-acetylpyridine (Acros), N,N,N -trimethylethylenediamine (Aldrich), methylrhenium trioxide (Aldrich), InQj (Aldrich), Cu(N0j)2-3H20 (Merck), Ni(N03)2-6Il20 (Merck), Yb(OTf)3(Fluka), Sc(OTf)3 (Fluka), 2-(aminomethyl)pyridine (Acros), benzylideneacetone (Aldrich), and chalcone (Aldrich) were of the highest purity available. Borane dimethyl sulfide (2M solution in THE) was obtained from Aldrich. Methyl vinyl ketone was distilled prior to use. Cyclopentadiene was prepared from its dimer immediately before use. (R)-l-acetyl-5-isopropoxy-3-pyrrolin-2-one (4.15) has been kindly provided by Prof H. Hiemstra (University of Amsterdam). 

The allyl-substituted cyclopentadiene 122 was prepared by the reaction of cyclopentadiene anion with allylic acetates[83], Allyl chloride reacts with carbon nucleophiles without Pd catalyst, but sometimes Pd catalyst accelerates the reaction of allylic chlorides and gives higher selectivity. As an example, allylation of the anion of 6,6-dimethylfulvene 123 with allyl chloride proceeded regioselectively at the methyl group, yielding 124[84]. The uncatalyzed reaction was not selective. 

Cyclodienes. These are polychlorinated cycHc hydrocarbons with endomethylene-bridged stmctures, prepared by the Diels-Alder diene reaction. The development of these insecticides resulted from the discovery in 1945 of chlordane, the chlorinated adduct of hexachlorocyclopentadiene and cyclopentadiene (qv). The addition of two Cl atoms across the double bond of the ftve-membered ring forms the two isomers of chlordane [12789-03-6] or l,2,4,5,6,7,8,8-octachloro-2,3,3t ,4,7,7t -hexahydro-4,7-methano-lJT-indene, QL-trans (mp 106.5°C) and pt-tis (32) (mp 104.5°C). The p-isomerhas signiftcantiy greater insecticidal activity. Technical chlordane is an amber Hquid (bp 175°C/267 Pa, vp 1.3 mPa at 25°C) which is soluble in water to about 9 fig/L. It has rat LD qS of 335, 430 (oral) and 840, 690 (dermal) mg/kg. Technical chlordane contains about 60% of the isomers and 10—20% of heptachlor. It has been used extensively as a soil insecticide for termite control and as a household insecticide. 

Preparation. The industrial production of malonic acid is much less important than that of the malonates. Malonic acid is usually produced by acid saponification of malonates (9). Further methods which have been recendy investigated are the ozonolysis of cyclopentadiene [542-92-7] (10), the air oxidation of 1,3-propanediol [504-63-2] (11), or the use of microorganisms for converting nitriles into acids (12). 

Reactions of acetylene and iron carbonyls can yield benzene derivatives, quinones, cyclopentadienes, and a variety of heterocycHc compounds. The cyclization reaction is useful for preparing substituted benzenes. The reaction of / fZ-butylacetylene in the presence of Co2(CO)g as the catalyst yields l,2,4-tri-/ f2 butylbenzene (142). The reaction of Fe(CO) and diphenylacetylene yields no less than seven different species. A cyclobutadiene derivative [31811 -56-0] is the most important (143—145). 

Halogenation. Halogens and halogen acids add readily to the unsaturated carbon linkages of the cyclopentadiene molecule. By such additions a series of halogenated derivatives range, in the case of the chloride, from 3-chlotocydopentene to tetrachlorocyclopentane. Of all the possible chloto derivatives of CPD, only hexachlorocyclopentadiene [77-47-4] ever reached commercial status. It was used as an insecticide, but this use has been discontinued because of its toxicity (see Chlorocarbons and chlorohydrocarbons, toxic aromatics). It can be prepared by a Hquid phase chlorination of CPD below 50°C (29). 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (76). Cyclopentadiene is also a component of supported metallocene—alumoxane polymerization catalysts in the preparation of syndiotactic polyolefins (77), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (78), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (79). 

Methylene thiirane is obtained by thermolysis of several spirothiirane derivatives which are formally Diels-Alder adducts of methylenethiirane and cyclopentadiene or anthracene <78JA7436). They were prepared via lithio-2-(methylthio)-l,3-oxazolines (c/. Scheme 121). A novel synthesis of the allene episulfide derivatives, 2-isopropylidene-3,3- dimethylthiirane (good yield) or its 5-oxide (poor yield), involves irradiation of 2,2,3,3-tetramethyl-cyclopropanethione or its 5-oxide (81AG293). Substituents on the thiirane ring may be modified to give new thiiranes (Section 5.06.3.9). The synthesis of thiirane 1-oxides and thiirane 1,1-dioxides by oxidation is discussed in Section 5.06.3.3.8 and the synthesis of 5-alkylthiiranium salts by alkylation of thiiranes is discussed in Section 5.06.3.3.4. Thiirene 1-oxides and 1,1-dioxides may be obtained by dehydrohalogenation of 2-halothiirane 1-oxides and 1,1-dioxides (Section 5.06.4.1.2). 

Substituted azulenes can be prepared in the same manner by the use of substituted cyclopentadienes or substituted pentamethinium salts. 

Cyclopentadiene was prepared by cracking dicyclopentadiene of 95% purity purchased from Aldrich Chemical Company, Inc. 

The methods of preparation of ferrocene have been reviewed by Pauson and by Fischer. Ferrocene has been made by the reaction of ferric chloride with cyclopentadienylmagnesium bromide, by the direct thermal reaction of cyclopentadiene with iron metal, by the direct interaction of cyclopentadiene with iron carbonyl, by the reaction of ferrous chloride with cyclopentadiene in the presence of organic bases such as diethyl-amine, by the reaction of ferrous chloride with sodium cyclo-[lentadienide in liquid ammonia, and from cyclopentadiene and... 

All precautions with regard to the purification of tetrahydrofuran, the quality of the iron powder, the rapid stirring, the maintenance of a nitrogen atmosphere, and the handling of cyclopentadiene, described in the preceding preparation, are followed. 

A standard method for preparing sodium cyclopentadienide (CjHjNa) is by the reaction of cyclopentadiene with a solution of NaNH2 in liquid ammonia. Write a net ionic equation for this reaction, identify the acid and the base, and use curved arrows to track the flow of electrons. 

Cobaltocene, [Co ()7 -C5H5)2], is a dark-purple air-sensitive material, prepared by the reactions of sodium cyclopentadiene and anhydrous C0CI2... 

Chiral aluminum catalyst 2, prepared from Et2AlCl and a Vaulted biaryl ligand, is reported to be an effective Lewis acid catalyst of the Diels-AIder reaction between methacrolein and cyclopentadiene, affording the adduct in 97.7% ee [4] (Scheme 1.2). Although the Diels-AIder reaction with other a,/ -unsaturated aldehydes has not been described, that only 0.5 mol% loading is sufficient to promote the reaction is a great advantage of this catalyst. 

Another chiral titanium reagent, 11, was developed by Corey et al. [17] (Scheme 1.24). The catalyst was prepared from chiral ris-N-sulfonyl-2-amino-l-indanol and titanium tetraisopropoxide with removal of 2-propanol, followed by treatment with one equivalent of SiCl4, to give the catalytically-active yellow solid. This catalyst is thought not to be a simple monomer, but rather an aggregated species, as suggested by NMR study. Catalyst 11 promotes the Diels-Alder reaction of a-bro-moacrolein with cyclopentadiene or isoprene. 

Since Evans s initial report, several chiral Lewis acids with copper as the central metal have been reported. Davies et al. and Ghosh et al. independently developed a bis(oxazoline) ligand prepared from aminoindanol, and applied the copper complex of this ligand to the asymmetric Diels-Alder reaction. Davies varied the link between the two oxazolines and found that cyclopropyl is the best connector (see catalyst 26), giving the cycloadduct of acryloyloxazolidinone and cyclopentadiene in high optical purity (98.4% ee) [35] (Scheme 1.45). Ghosh et al., on the other hand, obtained the same cycloadduct in 99% ee by the use of unsubstituted ligand (see catalyst 27) [36] (Scheme 1.46, Table 1.19). 

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