Indene complexes

TABLE 7. Activation parameters for epimerization of Uthiated sparteine and O -isosparteine complexed indenes (complexes 295 and 296)... 

An intermolecular Pauson-Khand reaction of a dihydrofuran intermediate was used to prepare a benz[ indenone, allowing for the first synthesis of a zirconocene benz[/]indene complex <03OL3153>. A stereoselective intermolecular Pauson-Khand reaction of 3-(R)-methyldihydrofuran was used to construct the desired diastereoisomer of oxabicyclo[3.3.0]octanone ring shown below in the total synthesis of the sesterterpene terpestacin <03JA11514>. 

In contrast to the reaction with indene, a triruthenium complex having a face-capping azulene ligand was isolated from the reaction of Ru3(CO)i2 with azulene, while formation of a tetrametallic azulene complex was also observed.It has been shown by means of X-ray diffraction studies that the azulene is coordinated to one of the ruthenium centers through its Cs ring in an / -fashion similar to the /t3-indene complex, and the seven-membered... 

Coumarone—Indene Kesins. These should be called polyindene resins (17) (see Hydrocarbon resins). They are derived from a close-cut fraction of a coke-oven naphtha free of tar acids and bases. This feedstock, distilling between 178 and 190°C and containing a minimum of 30% indene, is warmed to 35°C and polymeri2ed by a dding 0.7—0.8% of the phenol or acetic acid complex of boron trifluoride as catalyst. With the phenol complex, tar acids need not be completely removed and the yield is better. The reaction is exothermic and the temperature is kept below 120°C. When the reaction is complete, the catalyst is decomposed by using a hot concentrated solution of sodium carbonate. Unreacted naphtha is removed, first with Hve steam and then by vacuum distillation to leave an amber-colored resin. It is poured into trays, allowed to cool, and broken up for sale. 

The lithium-(-)-sparteine complex, generated by deprotonation of 1-methylindene, does not lose its configuration in diethyl ether solution even at room temperature80 presumably, the observed major diastcreonier is the thermodynamically determined product. Substitution with carbonyl compounds leads to 1-substituted (fl)-l-methyl-l//-indenes with >95% ee in high yields81. 

The highest enantioselectivities in the base-catalyzed Michael additions have so far been obtained using achiral bases complexed to chiral crown ethers. The addition of methyl 2,3-dihydro-l-oxo-1//-indene-2-carboxylate (1) to 3-buten-2-one using 4 mol% of a [l,T-binaphthalcnc]-2,2 -diol derived optically active crown ether 3 in combination with potassium AY/-butoxide as the base illustrates this successful method 259 260 It is assumed that the actual Michael donor is the potassium enolate complex of 1 and crown ether 3. 

The reaction of alkoxyarylcarbene complexes with alkynes mainly affords Dotz benzannulated [3C+2S+1C0] cycloadducts. However, uncommon reaction pathways of some alkoxyarylcarbene complexes in their reaction with alkynes leading to indene derivatives in a formal [3C+2S] cycloaddition process have been reported. For example, the reaction of methoxy(2,6-dimethylphenyl)chromium carbene complex with 1,2-diphenylacetylene at 100 °C gives rise to an unusual indene derivative where a sigmatropic 1,5-methyl shift is observed [60]. Moreover, a related (4-hydroxy-2,6-dimethylphenyl)carbene complex reacts in benzene at 100 °C with 3-hexyne to produce an indene derivative. However, the expected Dotz cycloadduct is obtained when the solvent is changed to acetonitrile [61] (Scheme 19). Also, Dotz et al. have shown that the introduction of an isocyanide ligand into the coordination sphere of the metal induces the preferential formation of indene derivatives [62]. 

The unconventional structure of fulvenes with a unique C=C bond conjugation leads to unusual cycloaddition reactions with other unsaturated systems. For example, alkenylcarbene complexes react with fulvenes leading to indanone or indene derivatives which can be considered as derived from a [6S+3C] cycloaddition process [118] (Scheme 72). The reaction pathway is well explained by an initial 1,2-addition of the fulvene to the carbene carbon followed by [1,2]-Cr(CO)5-promoted cyclisation. 

Chemoselectivity plays an important role in the benzannulation reaction as five-membered rings such as indene or furan derivatives are potential side products. The branching point is again the rf-vinylcarbene complex D intermediate which maybe formed either as a (Z)- or an ( )-metallatriene the (E)-configuration is required for the cyclisation with the terminal double bond. (Z)-Metallatriene D, however, leads to the formation of furan derivatives H (Scheme 8). Studies on the formation of (E)- and (Z)-isomers discussing stereoelectronic effects have been undertaken by Wulff [17]. 

The superior donor properties of amino groups over alkoxy substituents causes a higher electron density at the metal centre resulting in an increased M-CO bond strength in aminocarbene complexes. Therefore, the primary decarbo-nylation step requires harsher conditions moreover, the CO insertion generating the ketene intermediate cannot compete successfully with a direct electro-cyclisation of the alkyne insertion product, as shown in Scheme 9 for the formation of indenes. Due to that experience amino(aryl)carbene complexes are prone to undergo cyclopentannulation. If, however, the donor capacity of the aminocarbene ligand is reduced by N-acylation, benzannulation becomes feasible [22]. 

It is reported that the intermediate species in the CujO-Icrt-BuNC reaction system can undergo reactions with cyclopentadiene or with indene. The products obtained are C5HjCu(CNBu ) and indenylCu(CNBu )3 132). The postulate that a copper(I) isocyanide complex is the reaction intermediate here is reasonable. 

The analogous complex CjH5Cu(CNBu ) is obtained from CU2O, CNBu, and (132). The reaction with indene gave a complex of... 

Electronic factors also influenced the outcomes of these cyclization reactions cyclization of pyrrole 84 to bicyclic amine 85 is catalyzed by the sterically open complex 79a. In this reaction, initial insertion into the Y - H bond occurred in a Markovnikov fashion at the more hindered olefin (Scheme 19) [48]. The authors proposed that the Lewis basic aromatic ring stabilizes the electrophilic catalyst during the hydrometallation step, overriding steric factors. In the case of pyrroles and indenes, the less Lewis basic nitrogen contained in the aromatic systems allowed for the cyclization of 1,1-disubstituted alkenes. 

More subtle arguments have been invoked to rationalize the dichotomous behavior of so-called second-generation Mn-salen catalysts of type 7 toward unfunctionalized and nucleophilic olefins. For example, higher yields and ee s are obtained with the (i ,S)-complex for the epoxidation of indene (8). However, JV-toluenesulfonyl-l,2,3,4-tetrahydropyridine (10) gave better results using the (R,/ -configuration. An analysis of the transition-state enthalpy and entropy terms indicates that the selectivity in the former reaction is enthalpy driven, while the latter result reflects a combination of enthalpy and entropy factors <00TL7053>. 

Alkenyl Fischer carbene complexes can serve as three-carbon components in the [6 + 3]-reactions of vinylchro-mium carbenes and fulvenes (Equations (23)—(25)), providing rapid access to indanone and indene structures.132 This reaction tolerates substitution of the fulvene, but the carbene complex requires extended conjugation to a carbonyl or aromatic ring. This reaction is proposed to be initiated by 1,2-addition of the electron-rich fulvene to the chromium carbene followed by a 1,2-shift of the chromium with simultaneous ring closure. Reductive elimination of the chromium metal and elimination/isomerization gives the products (Scheme 41). 

Brunner, Leitner and others have reported the enantioselective transfer hydrogenation of alpha-, beta-unsaturated alkenes of the acrylate type [50]. The catalysts are usually rhodium phosphine-based and the reductant is formic acid or salts. The rates of reduction of alkenes using rhodium and iridium diamine complexes is modest [87]. An example of this reaction is shown in Figure 35.8. Williams has shown the transfer hydrogenation of alkenes such as indene and styrene using IPA [88]. 

A typical manganese-salen complex (27)[89] is capable of catalysing the asymmetric epoxidation of (Z)-alkenes (Scheme 18) using sodium hypochlorite (NaOCl) as the principle oxidant. Cyclic alkenes and a, (3-unsaturated esters are also excellent starting materials for example indene may be transformed into the corresponding epoxide (28) with good enantiomeric excess1901. The epoxidation of such alkenes can be improved by the addition of ammonium acetate to the catalyst system 911. 

Irradiation in air of the deoxycholic acid (DCA, 157) complex of indanone leads to oxidation of both the steroid and the guest, yielding 5- 3-hydroxy-DCA, 158, and optically active 3-hydroxyindanone (241). In the presence of air, irradiation of the DCA clathrates of isochromane, 159, and indene, 161, leads to reaction with oxidation of the host and of the allylic position of the guest to a keto group (e.g., 159 — 160 and 161 — 162).The detailed mechanisms of these oxidations remain to be elucidated. 

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