Reaction intermediate analogs

The reaction of 1,2,3-diazaphospholes 110 with diazodiphenylmethane leads directly to bicyclic phosphiranes 117 (184). The analogous product 118 was obtained using a 1,3,4-thiaazaphosphole (185). It is reasonable to assume that these phosphiranes result from a 47i-electrocyclization of the bis(methylene)phos-phorane unit of a reaction intermediate analogous to 115. 

LThDP) was among the first examples of a covalently bound predecarboxylation reaction intermediate analog in any ThDP-dependent enzyme. ... 

Irreversible covalent inactivation has previously been suggested as a prerequisite for consideration of a compound as a mechanism-based enzyme inactivator (Abeles and Maycock, 1976 Walsh, 1977). Silverman and Hoffman (1984) have argued, however, that rearrangement of the enzyme-inactivator adduct to release the inhibitor and restore activity is independent of the inactivation reaction and should not reflect on its classification as a mechanism-based process. Inactivation which is apparently irreversible is not a property unique to mechanism-based inactivation. Transition state or reaction intermediate analogs, which are stable mimics of unstable reaction intermediates, often bind with such slow dissociation rates that they are effectivley irreversibly bound under normal experimental time scales. Reaction intermediate analogs have been recently reviewed (Morrison and Walsh, 1987 Schloss, 1988) and are not covered here. 

Bhaird, N., Kumaravel, G., Gandour, R, Krueger, M. Ramsay, R. (1993) Biochem. J. 294, 645-651. Comparison of the active-sites of the purified carnitine acyltransferases from peroxisomes and mitochondria by using a reaction-intermediate analog. 

Alberg, D.G. and Bartlett, P.A. (1989) Potent Inhibition of 5-Enolpyruvylshikimate-3-phosphate Synthase by a Reaction Intermediate Analog, J. Am. Chem. Soc., Ill, 2337-2338. 

Alkynes react when heated with trifluoroacetic acid to give addition products. Mixtures of syn and anti addition products are obtained. Similar addition reactions occur with trifluoromethanesulfonic acid. These reactions are analogous to acid-catalyzed hydration and proceed through a vinyl cation intermediate. 

In a similar process, tertiary enaminones react with alkynylcarbene complexes to give the corresponding pyranylidene complexes following a reaction pathway analogous to that described above. First, a [2+2] cycloaddition reaction between the alkynyl moiety of the carbene complex and the C=C double bond of the enamine generates a cyclobutene intermediate, which evolves by a conrotatory cyclobutene ring opening followed by a cyclisation process [94] (Scheme 49). 

The reaction product 136 is not an appropriate hapten for generating catalytic antibody as it does not closely resemble the reaction intermediate 135. Antibody 1E9 was prepared against hapten 137, a stable analog of 135, and the catalyst promoted the Diels-Alder reaction with multiple (> 50) turnovers. 

Formally, the reaction can be regarded as if it were analogous to the Grignard reaction (16-27), with as an intermediate analogous to RMgX. There is an... 

Yamamoto and Yamazaki 171) carried out reactions of Pt(PEt3)2CHjI and Pt(PPhMe2)(CH2CjH5)I with tert-butyl and cyclohexyl isocyanides. These reactions gave small yields of the ionic intermediate species, which readily reverted to the appropriate iminoacyl complexes. In reactions of analogous chloride complexes the intermediate species was not isolated. It is suggested on the basis of PMR data that these iminoacyl complexes are five-coordinate (see above). 

Unlike chlorine and fluorine, the free bromine and iodine are produced by chemical methods (reaction of chlorine with bromide or iodide solutions). Electrochemical methods are used to produce the salts of their oxygen-containing acids, the bromates and iodates, from the corresponding bromide and iodide solutions. These reactions are analogous to those in chlorate production [Eqs. (15.31) to (15.34)] and involve the intermediate formation of hypobromites and hypoiodites. 

The triplet state is usually the ground state for non-conjugated structures, but either species can be involved in reactions. The most common method for generating nitrene intermediates, analogous to formation of carbenes from diazo compounds, is by thermolysis or photolysis of azides.246... 

There are a group of reactions very closely related to that of Hofmann, all of which involve the formation of an isocyanate (61) by rearrangement of an intermediate analogous to (60) ... 

Clark and co-workers have reported reactions of Ir(III) cations with terminal alkynes in methanol in which alkoxycarbene complexes are formed (60). By analogy with a more extensively studied Pt(II) system (61), it has been concluded that cationic vinylidene complexes, e.g., 35, are reaction intermediates, e.g.,... 

Lastly, it is appropriate to comment on the relationships between the intermediates seen in photochemical studies and possible reactive intermediates along the reaction coordinates of related thermal transformations. Earlier kinetics studies (] 3) of the reactions of Ru3(CO)i2 with various phosphorous ligands PR3 have found evidence for both first order and second order pathways leading to substitution plus some cluster fragmentation. The first order path was proposed to proceed via reversible CO dissociation to give an intermediate analogous to II. 

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