Substitution chemistry

Quinonoid compounds have been thoroughly reviewed (4,6). More recent trends in quinone addition and substitution chemistry were reviewed in 1993 (7). The quinone system in natural products has also been covered (8) there has been a fascinating discussion of the quinone problem (9). 

Nucleophilic Substitution Reactions. Many of the transformations reali2ed through Michael additions to quiaones can also be achieved usiag nucleophilic substitution chemistry. In some iastances the stereoselectivity can be markedly improved ia this fashion (100), eg, ia the reaction of ben2enethiol with esters (R = CH C O) and ethers (R = 3) 1,4-naphthoquiaones. 2-Bromo-5-acetyloxy-l,4-naphthoquiQone [77189-69-6J, R = Br, yields 75% of 2-thiophenyl-5-acetyloxy-l,4-naphthoquinone [71700-93-1], R = SC H. 3-Bromo-5-methoxy-1,4-naphthoquinone [69833-10-9], R = Br, yields 82% of 3-thiophenyl-5-methoxy-l,4-naphthoquinone [112740-62-2] R = SC H. ... 

The nitrogen substitution chemistry of 2,3-dichloro-l,4-naphthoquiaone (30) has been widely employed (101). Although the product mixtures are sometimes complex, many examples illustrate the excellent results possible ia specific iastances eg, 3-nitro-12JT-ben2o[b]phenoxa2iae-6,ll-dione... 

Nucleophilic substitution chemistry of the anions are not well understood. In the cases where n = 10,12, reactions can be described... 

The M(05H5)201 compounds, which are actually 01-bridged dimers, [(05H5)M(/l-01)2-M(05H5)], provide an extensive substitution chemistry in which /r-Ol can be replaced by a variety of ligands including H, ON, NH2, MeO and alkyl groups. 

The fourth chapter gives a comprehensive review about catalyzed hydroamina-tions of carbon carbon multiple bond systems from the beginning of this century to the state-of-the-art today. As was mentioned above, the direct - and whenever possible stereoselective - addition of amines to unsaturated hydrocarbons is one of the shortest routes to produce (chiral) amines. Provided that a catalyst of sufficient activity and stabihty can be found, this heterofunctionalization reaction could compete with classical substitution chemistry and is of high industrial interest. As the authors J. J. Bmnet and D. Neibecker show in their contribution, almost any transition metal salt has been subjected to this reaction and numerous reaction conditions were tested. However, although considerable progress has been made and enantios-electivites of 95% could be reached, all catalytic systems known to date suffer from low activity (TOP < 500 h ) or/and low stability. The most effective systems are represented by some iridium phosphine or cyclopentadienyl samarium complexes. 

The incorporation of a fluorine-18 label can also be achieved by standard aliphatic nucleophilic substitution chemistry, as exemplified in Scheme 6.171. Here, the widely used reagent [18F]-/f-fluoroethyl tosylate was utilized to prepare several important 18F-labeled compounds [323],... 

The substitution chemistry of the OsgCCOhg unit has not been extensively investigated. Amine oxide oxidation reactions carried out in the... 

A general approach to rhenium hydrazido complexes is the reaction of oxo or chloro compounds with organohydrazines as has been demonstrated in an early report with the synthesis of [Re NNC(Ph)0 Cl2(PPh3)2] (310), " the molecular structure of which was solved in 1988. A detailed study on [Re(NNR)Cl2(PPh3)2] complexes with R = COPh or phthalazine shows that the course of subsequent reactions is governed both by the nature of the donor group R responsible for chelate closure and by the type of donor ligand introduced. No simple substitution chemistry has been observed for R = phthalazine. The benzoyl compound... 

C-2 Chain extension via allylation (578->579) followed by oxidation to expose a latent aldehyde and cyclization constitutes another general route, in this case, leading to skimmianine (580) (Scheme 174) [73JCS(P1)94]. These routes, which overcome problems of poor 3-position reactivity by electrophilic substitution chemistry, were also applied to the furoquinoline... 

Nucleophilic substitution chemistry of the [closo-B HJ2- anions are not well understood. In the cases where n = 10,12, reactions can be described as acid-catalyzed nucleophilic substitution. Most acid-catalyzed nucleophilic substitutions of [B H ]2- with, for example, amides, ethers, and sulfones give products having equatorial substituents. 

The complexes exhibit reversible oxidations to the [Os2Xg] analogs and irreversible reductions (522, 523). Decomposition and substitution chemistry of the complexes has also been studied (302,523). The tetra-meric complex [I40s0sl2(/A-I)2l20s0sl4]2 contains two [Os2Is] units fused together via two bridging iodides, as shown by X-ray diffraction... 

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