Oxygen-Containing Nucleophiles

The reaction of a hydroperoxide with 2-methylaziridine [75-55-8] has been described (94). The reaction of ethyleneknine with phenols (95) and carboxyHc acids (96,97) produces ethylamine ethers and esters, respectively. However, these reactions frequentiy yield product mixtures which contain polyaminoalkylated oxygen nucleophiles and polymers, in addition to the desked products (1). The selectivity of the reaction can often be improved by using less than the stoichiometric amount of the aziridine component (98,99). 

Nucleophilic substitution of the chlorine atom in 2-chloropyrazine and 2-chloroquinoxa-lines has been effected with a variety of nucleophiles, including ammonia and amines, oxygen nucleophiles such as alkoxides, sodium azide, hydrazine, sulfur containing nucleophiles, cyanide, etc., and reactions of this type are typical of the group (see Chapter 2.02). 

The simplest of the reactions of N3P3C16 with nucleophiles containing oxygen involves hydrolysis. Complete replacement of all the chlorine atoms by hydroxyl groups should give rise to N3P3(OH)6. However, the... 

A wide range of carbon, nitrogen, and oxygen nucleophiles react with allylic esters in the presence of iridium catalysts to form branched allylic substitution products. The bulk of the recent literature on iridium-catalyzed allylic substitution has focused on catalysts derived from [Ir(COD)Cl]2 and phosphoramidite ligands. These complexes catalyze the formation of enantiomerically enriched allylic amines, allylic ethers, and (3-branched y-8 unsaturated carbonyl compounds. The latest generation and most commonly used of these catalysts (Scheme 1) consists of a cyclometalated iridium-phosphoramidite core chelated by 1,5-cyclooctadiene. A fifth coordination site is occupied in catalyst precursors by an additional -phosphoramidite or ethylene. The phosphoramidite that is used to generate the metalacyclic core typically contains one BlNOLate and one bis-arylethylamino group on phosphorus. 

Cathodic reduction of oxygen is the most convenient method of production of the superoxide radical-anion,. The properties of this important species have been well reviewed and key references to the extensive work on the electrochemistry of oxygen are contained therein. Of immediate significance is the large cathodic shift in E° for the 0 /0 couple which accompanies a change from aqueous to aprotic solvent (e.g. DMF, DMSO, and MeCN) this is interpreted in terms of relatively weak solvation in aprotic media which enhances the nucleophilicity of the superoxide anion. However, in the presence of acids the chemistry of superoxide is dominated by the disproportionation shown in equation 1. 

In that the charge relay tem is composed of the oxygen nucleophile and imidazole, polymer catalysts which contain hydroxamate and imidazole hmctions ould be particularly attractive as a serine en me model. 

The glutathione 5-transferases catalyze numerous reactions in which the glutathione thiolate anion (GS ) serves as a nucleophile (A20, G11, J2). Thus the fundamental catalytic action of GST is to facilitate the formation or stabilization of GS , which can, in turn, attack electrophilic carbon, nitrogen, sulfur, or oxygen atoms contained in any xenobiotic. Literally hundreds of different compounds exist that contain a carbon atom sufficiently electrophilic to be able to react with GS" and form thioether conjugates. Thioether formation has been widely studied since the earliest convenient spectrophotmetric assays represented this type of reaction for example, the conjugation of GSH with l-chloro-2,4-dinitrobenzene, 1,2-dichloro-... 

This type of reaction has been developed by employing aryl and alkenyl halides or triflates containing proximate nitrogen or oxygen nucleophiles and internal acetylenes. 

Metal-catalyzed epoxide ring-opening by oxygen nucleophiles is one of the most popular methods to synthesize oxygen-containing medium-ring... 

The second set of examples involves the use of thionium ions as electrophiles in inter- and intramolecular processes to obtain a-substituted sulfides (see 24 25, Scheme 20.7T which is the most common type of Pummerer reaction. Applications of this classical Pummerer rearrangement are exemplified in the synthesis of trans-solamin, the synthesis of indolizidine alkaloids, and the synthesis of the CDE ring of erinacine E. The first exanple fScheme 20.10 uses Pummerer chemistry in the generation of a thionium ion, which reacts in an intermolecular tin-mediated ene reaction the second one fScheme 20.11 uses Pummerer chemistry to introduce a nitrogen-containing heterocycle by intramolecular addition to form the coniceine core and the third example fScheme 20.12 is an intramolecular silicon-induced Pummerer reaction with oxygenated nucleophiles applied to the synthesis of a precursor of erinacine. Details of these Pummerer-based strategies are discussed below. 

In all of the above monomers the vinyl group is attached to the cyclo-phosphazene ring by means of a P-C bond. A simpler way of preparing the cyclophosphazene containing vinyl monomers is to use oxygen nucleophiles. 

Much larger cyclic systems containing the diisopropylsilyl group have been obtained by alkyne metathesis. The example shown in eq 18 describes the formation of a molecular triangle (not shown) and the rhomboid 33 involving the reactions between i-Pr2SiCl2 and oxygen nucleophiles to form silyl diether 32, alkynylation of 32, and subsequent Mo(CO)6-catalyzed alkyne metathesis. ... 

Also with starting compounds containing two oxygen nucleophiles, both alkoxy/ amino carbonylation and cyclocarbonylation (carbonylative cydization to lactone) mechanisms can occur in sequence. Some bicydic y-lactones from parasitic wasps (Hymenoptera Braconidae) were synthesized by hydrolytic kinetic resolution of epoxides and palladium(II)-catalyzed hydroxycyclization-carbonylation-lactoniza-tion of enediols. For example, cis- and trans-5-n-hexyl-tetrahydrofuro[3,2-b]furan-2 (3H)-ones 75 and 76, with the (3aR,5R,6aR) and (3aS,5R,6aS) configurations, respectively, were acquired in six steps from the inexpensive, readily available ridnoleic add 74 (Scheme 13.48) (89). 

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