Ziegler modified

The short synthesis of the pyrrolophenanthridone alkaloid hippadine was accomplished by D.C. Harrowven and co-workers. " The key step of the synthetic sequence was the Ziegler modified intramolecular Ullmann biaryl coupling between two aryl bromides. One of the aryl halides was 7-bromoindole which was prepared using the Bartoli indole synthesis. The second aryl bromide was connected to 7-bromoindole via a simple A/-alkylation. 

The Ziegler-modified Ullmann reaction was used for the total synthesis of pyrrolophenanthridinium alkaloid tortuosine by L.A. Flippin and co-workers. First, A/-Boc-5-methoxyindoline was lithiated at C7 with s-BuLi in the presence of TMEDA, and then it was transmetallated to the corresponding organocopper species that smoothly underwent the Ullmann reaction with a 3-iodoaryl imine. The resulting biaryl product was treated with anhydrous HCI in chloroform, which promoted the cyclization followed by dehydration to give the natural product. 

Fig. 2. Estimated primary alcohol distributions for (H) Ethyl Corporation-modified Ziegler and (+) Vista Corporation Ziegler, at 4.0 moles ethylene per...

Most catalysts for solution processes are either completely soluble or pseudo-homogeneous all their catalyst components are introduced into the reactor as Hquids but produce soHd catalysts when combined. The early Du Pont process employed a three-component catalyst consisting of titanium tetrachloride, vanadium oxytrichloride, and triisobutjlalurninum (80,81), whereas Dow used a mixture of titanium tetrachloride and triisobutylalurninum modified with ammonia (86,87). Because processes are intrinsically suitable for the use of soluble catalysts, they were the first to accommodate highly active metallocene catalysts. Other suitable catalyst systems include heterogeneous catalysts (such as chromium-based catalysts) as well as supported and unsupported Ziegler catalysts (88—90). 

The low temperature limitation of homogeneous catalysis has been overcome with heterogeneous catalysts such as modified Ziegler-Natta (28) sohd-supported protonic acids (29,30) and metal oxides (31). Temperatures as high as 80°C in toluene can be employed to yield, for example, crystalline... 

In general, imines are too reactive to be used to protect carbonyl groups. In a synthesis of juncusol, however, a bromo- and an iodocyclobexylbnine of two identical aromatic aldehydes were coupled by an Ullmann coupling reaction modified by Ziegler. The imines were cleaved by acidic hydrolysis (aq. oxalic acid, THE, 20°, 1 h, 95% yield). Imines of aromatic aldehydes have also been prepared to protect the aldehyde during ring metalation with. -BuLi. ... 

Muhlhaupt R, Fischer D, JUngling S (1993) Donor- and acceptor-modified metallocene-based homogeneous Ziegler-Natta catalysts. Makromol Chem Macromol Syp 66 191-202... 

The experimental procedure described is essentially one reported by Ziegler and Wilms 8 as subsequently modified,9 except that the glutaraldehyde is prepared from 2-ethoxy-3,4-dihydro-2H-pyran instead of cyclopentene ozonide 8 or pyridine via dihydropyridine and glutaraldehyde dioxime.9 Essentially these procedures have also been reported briefly by other investigators.10... 

Idemitsu A process for making C6-C18 a-olefins from ethylene, catalyzed by a modified homogeneous Ziegler-Natta catalyst containing a zirconium chloride. Developed by the Idemitsu Petroleum Company in 1988. 

Fig. 1.9. POISSON product distribution during synthesis of the modified AMOCO-Ziegler...

Oleochemical alcohols are primary, even carbon-numbered structures with a high linearity (>95%), while the petrochemical derivatives can be even or odd numbered, and depending on the process, their linearity can be as high as the oleochemicals (Ziegler alcohols) or can exhibit variable branching (30% modified 0X0-60% standard OXO). 

With minor modifications that rubber is still used for passenger cars. It is not suitable for large trucks and bomber tires because of the excess of heat build-up in operation. Before the end of the rubber program, two of the companies, Firestone and Goodrich, had developed processes that produced rubber essentially like natural rubber. Firestone used a lithium catalyst for the polymerization, and Goodrich used a modified Ziegler catalyst. These materials were manufactured for a while until the oil prices became too prohibitive and the natural rubber was again used for heavy-duty tires. 

A soluble titanium-based modified Ziegler-Natta catalyst [Ti(OR)4-Et3Al, R = n-Bu, isoPr] is employed in the reaction.42 Since similar catalysts may be used for the oligomerization and polymerization of ethylene, the nature and oxidation state of the metal and reaction conditions determine selectivity. Ti4+ was found to be responsible for high dimerization selectivity, whereas polymerization was shown to be catalyzed by Ti3+. According to a proposed mechanism,42,43 this catalyst effects the concerted coupling of two molecules of ethylene to form a metal-lacyclopentane intermediate that decomposes via an intramolecular p-hydrogen transfer ... 

The low temperature limitation of homogeneous catalysis has been overcome with heterogeneous catalysts such as modified Ziegler-Natta solid-supported protonic adds and metal oxides. 

These ligands, as exemplified by (12 Figure 2), were first reported by Zinke and Ziegler.31 Synthetic design has since then been modified and improved.64,65 133"135 The attachment of an aliphatic chain bridging two opposite para positions in the calix[4]arenes (i.e. those composed of four phenol groups) has been used to fix the cone conformation in these somewhat flexible molecules.136... 

Conventional Ziegler catalysts are not suitable for use with acrylonitrile because, among other reasons, the monomer reacts with the catalyst or forms complexes with it. Recently, modified catalysts have been developed in Natta s laboratory (106), using such combinations as Chromium acetylacetone plus dibutyl zinc,... 

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