Arene-chromium chemistry

Abstract Planar-chiral ri -arene-Cr(CO)3 complexes represent highly valuable buUdlng blocks for the dlastereo- and enantloselectlve synthesis of complex natural products and related bloactlve compounds. Highly original and competitive overall syntheses of various classes of natural products, such as sesquiterpenes, diterpenes, alkaloids and compounds with axial chirality, have been developed. In certain cases, the whole strategy is based on arene chromium chemistry and the various chemical and stereochemical effects of the metal unit are exploited In several subsequent transformations. Cationic Cp-ruthenium complexes allow arylether formation by Sj Ar reactions and have found application in the synthesis of glyco-peptide antibiotics. 

As a consequence, arene-Cr(CO)3 complexes offer new and unique opportunities for the stereoselective multi-step synthesis of complex molecules. By focusing on applications in the enantioselective total synthesis of natural products (and relevant analogs), this review intends to highlight the state of the art of synthetic arene chromium chemistry. It will be shown that highly original and competitive overall syntheses can be achieved especially in those cases, where the whole strategy is based on arene chromium chemistry and the chemical and stereochemical effects of the Cr(CO)3 unit can be exploited in several subse-... 

One of the first eye-catching synthetic applications of arene-chromium chemistry was the synthesis of the sp/ro-sesquiterpenes ( )-acorenone and ( )-acorenone B (rac-7) disclosed by Semmelhack and Yamashita in 1980 [14]. These authors twice exploited the meta-selective nucleophile addition to anisole-Cr(CO)3 derivatives (Scheme 1). Starting from complex rac-1, such a reaction is first used for the regioselective introduction of an acyl sidechain to give 2 after oxidative workup. A few steps later, the nitrile rac-4 (obtained from rac-3 by complexation and separation of the diastereomeric products by preparative HPLC) is deprotonated to form the spiro addition product rac-5, from which the enone rac-6 is obtained after protonation and hydrolysis of the initially formed dienol ether. The final conversion of rac-6 into acorenone B (rac-7) efficiently proceeds over five steps and involves a diastereoselective hydrogenation of an exo-methylene group. 

As demonstrated by Schmalz and coworkers, arene chromium chemistry offers unique and highly efficient entries to the aglycones of such compounds. The most successful approach [25, 26] follows the retrosynthetic analysis shown in Scheme 6, where the pseudopterosin aglycone (31) derives from a seco-com-pound of type 32. Such intermediates can be traced back (via 33) to the planar-chiral complex 34 carrying the absolute stereochemical information. 

There are a number of additional examples where arene chromium chemistry has been successfully employed in the synthesis of organic nitrogen compounds related to natural products[46-49]. For instance, Davies has demonstrated that... 

Another important natural product containing an axially-chiral biaryl substructure is the antibiotic vancomycin 103, which represents a tough challenge for chemical synthesis (Fig. 5) [57]. Again, arene chromium chemistry offers interesting opportunities for the stereoselective construction of the biaryl part, i.e., actinoidinic acid (104). 

Density functional theory studies arene chromium tricarbonyls, 5, 255 beryllium monocyclopentadienyls, 2, 75 chromium carbonyls, 5, 228 in computational chemistry, 1, 663 Cp-amido titanium complexes, 4, 464—465 diiron carbonyl complexes, 6, 222 manganese carbonyls, 5, 763 molybdenum hexacarbonyl, 5, 392 and multiconfiguration techniques, 1, 649 neutral, cationic, anionic chromium carbonyls, 5, 203-204 nickel rj2-alkene complexes, 8, 134—135 palladium NHC complexes, 8, 234 Deoxygenative coupling, carbonyls to olefins, 11, 40 (+)-4,5-Deoxyneodolabelline, via ring-closing diene metathesis, 11, 219... 

Molecular-beam epitaxy, for semiconductor growth, with Group 3 nitrides, 12, 4-5 Molecular gyroscopes, via iron carbonyls, 6, 51 Molecular mass distributions, in olefin polymerization, 4,1113 Molecular materials, and crystal engineering, 12, 555 Molecular mechanics future directions, 1, 666 in hybrid computational chemistry, 1, 664 Rh-catalyzed hydroformylation, 7, 239 Molecular modeling, arene chromium tricarbonyls, 5, 255 Molecular orbitals, and photoelectron spectroscopy variations,... 

In July 1955, Harold Zeiss (Fig. 5.3) visited the chemistry department of the University (LMU) in Munchen and gave a seminar, in which he discussed the results of Minoru Tsutsui s doctoral thesis. In this context, he mentioned that Hein s polyphenylchromium compounds might be in fact 7r-arene chromium(I) complexes. Walter Hafner attended the seminar and instantly remembered the outcome of his previous experiments. A few days later, after having repeated the reaction of CrCl3, Al, A1C13 and... 

This class of amides has been made enantio-selectively - albeit in low yield and low ee -by an ortholithiation reaction (Scheme 10). More successful is Uemura s demonstration [19] that the arene-chromium tricarbonyl complex chemistry that works with atroposelectivc biaryl couplings is also successful with atropose-lective amide-forming reactions (Scheme 11). 

A25. H. Zeiss, P. J. Wheatley, and H. J. S. Winkler, Benzenoid Metal Complexes. Ronald Press, New York, 1966. Excellent account of the chemistry of arene-chromium complexes, now dated. 

Yet another major advance in arene-metal chemistry was made in 1957 by Fischer and Ofele 95) y who found that a sealed tube reaction involving chromium hexacarbonyl, bis(benzene)chromium, and benzene produced the half-sandwich compound benzene-chromium tricarbonyl (XXVII). 

Two other groups investigated P,N ligands for amination chemistry with secondary amines. Uemura and coworkers have prepared ligands similar to those of Kumada, but based on arene chromium complexes rather than ferrocenes64. Catalysts containing ligand... 

The chemistry outlined on the next page was used to produce a cyclic arene-chromium carbene complex.100... 

Uemura M (1991) Tricarbonyl(rt -arene)chromium complexes in organic synthesis. In Liebeskind LS (ed) Advances in metal organic chemistry, vol 2. Jai Press, London, p 195... 

Schlogl K (1989) Stereochemistry of arenetricarbonylchromium complexes—useful intermediates for stereoselective synthesis. In Werner H, Erker G (eds) Organometal-lics in organic synthesis 2. Springer, Berlin Heidelberg New York, p 63 Solladi -Cavallo A (1989) Chiral arene-chromium-carbonyl complexes in asymmetric synthesis. In Liebeskind LS (ed) Advances in metal organic chemistry, vol 1. Jai Press, London, p 99... 

In addition, several groups have bound ir-arene complexes to solid supports and constructed libraries of products derived from ir-arenes by the chemistry described in this section (Equation 11.57). - Oxidation of the final product releases the arene from the metal. The arene-chromium was bound to the support by a pendant phosphine or isocyanide. The isocyanide provides the benefit of maintaining the ir-accepting property of the three ancillary ligands. 

Chiral Catalysts Containing Group 6 Metals (Cr, Mo, and W). Although all the three metals have important role in organometallic chemistry (eg, carbonyl complexes), their catalytic properties are scarcely investigated in the past few years. The tricarbonyl(jj -arene)chromium structural unit (see Fig. 16)... 

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