Reactions with Organic Substrates

Thionation reactions have been widely used in organic syntheses, in particular for the transformation of carbonyl groups into the corresponding thiocarbonyl 

Dithiophosphoric acids, (RO)2PS2H, have been used for the thionation of carbonyl groups in certain aldehydes, ketones, amides, esters, thio-carboxylates and other organics.163 The mechanism for this reaction proceeds via a reversible nucleophilic attack of the thioacid on the carbonyl compound, which can then rearrange by way of a four-membered PSCO cyclic intermediate into the desired C=S containing molecule and thiophosphoric acid (Equation 81).163 

Dithiophosphoric and dithiophosphinic acids can also react with organic compounds containing multiple carbon-nitrogen bonds, often under very mild conditions, to give thioamides and other related compounds (e.g., Equation 82).163 

Recent advances in the use of Lawesson s reagent include its application in microwave assisted solvent-free syntheses, solid-phase synthesis and combinatorial chemistry.165 Despite the ubiquity of Lawesson s reagent for organic thionation reactions, there are still some classes of compounds that it does not 

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INORGANIC ION-RADICALS IN REACTIONS WITH ORGANIC SUBSTRATES... 

In reactions with organic substrates, the 0 anion-radical is usually bad at electron transfer, but good at hydrogen atom abstraction. Because of the O spherical symmetry, its reactions are vulnerable by steric factors. Because of the O charged nature, its reactions with organic ions are of course susceptible to the effects of coulombic interaction also. Armstrong et al. (2004) showed that the predominant reactions with the anions of alanine and methylalanine proceed as follows ... 

The transition metal nature is not essential for this redox reaction. However, one of the reaction products, namely, the anion-radical 8O4 , can be complexed by a transition metal in a higher oxidation state. This leads to some stabilization of 8O4 and increases its reactive concentration. In other words, further reactions with organic substrates are facilitated (Fristad and Peterson 1984). 

Every organic reaction proceeds with the participation of inorganic reagents. Ion-radical organic reactions also have inorganic participants. The chapter discusses inorganic ion-radicals in their reactions with organic substrates. The main aim of this chapter is to lay the basis for all the subsequent chapters. 

The facile activation of dioxygen by these simple organometalHc complexes generates high-valent (V(V), Cr(V)) metal 0x0 complexes, which may undergo oxygen atom transfer reaction with organic substrates, and thus serve as catalysts for aerobic oxidations (Sect. 3.3). 

Thermally stable tetraphenylphosphonium hydrogen difluoride can act as a powerful in situ source of F" in various reactions with organic substrates as a nucleophile in... 

Metal-bound isocyanates give similar results to nitrosyl compounds.363,367 Starting with [Ru4(NCO)(CO)13] , one can obtain [Ru4(CO)i2N] in 78% yield upon thermolysis. Treatment of [Ru2(CO)r(NCO)] (x = 10,11) with Ru3(CO),2 leads to the hexanuclear nitride [Ru6(CO)i6N] in 82% yield. Organic nitroso and nitro can be similarly reduced by metal carbonyls or carbonylate anions. These reactions are discussed in the later section on reactions with organic substrates. 

A. T. Pudzianowski and G. H. Loew, Int. J. Quantum Chem., 23, 1257 (1983). Mechanistic Studies of Oxene Reactions with Organic Substrates Reaction Paths on MNDO Enthalpy Surfaces—Models for Cytochrome P450 Oxidations. 

Biological systems overcome the inherent unreactive character of 02 by means of metalloproteins (enzymes) that activate dioxygen for selective reaction with organic substrates. For example, the cytochrome P-450 proteins (thiolated protoporphyrin IX catalytic centers) facihtate the epoxidation of alkenes, the demethylation of Al-methylamines (via formation of formaldehyde), the oxidative cleavage of a-diols to aldehydes and ketones, and the monooxygenation of aliphatic and aromatic hydrocarbons (RH) (equation 104). The methane monooxygenase proteins (MMO, dinuclear nonheme iron centers) catalyze similar oxygenation of saturated hydrocarbons (equation 105). ... 

Reaction with distannanes 1.6.2.4 Reaction with esters 1.6.6.1 Reaction with imine I.5.2.1.2 Reaction with organic substrates in presence of catalysts 1.6.2.1.2 Reaction with oxime 1.5.2.1.2 Reaction with selenophosphinic acid ... 

As RS" is a much better electrophile and is considered to be the active species in reactions with organic substrates, better product yields are expected in CH2CI2 solutions. This was observed when disulfides were electrolyzed in the presence of terminal alkynes, in solutions containing nucleophiles, as H2O, MeOH, EtOH, and a-oxo-thioesters were obtained as major products ... 

Alkylations ofNonstabilized Carbanions 1. 2.4 Reactions With Organic Substrates... 

Cytochrome P-450 is a unique agent for the stimulated activation of dioxygen to the peroxide state with subsequent reaction with organic substrates. Three model substrate reactions often are used to characterize this important enzyme system. 

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