Interconversions with

With some special diazirines interconversion with diazoalkanes was observed on illumination (79AHC(24)63), e.g. with diazirinecarboxylic acid piperidide (194), spirodiazirine (195) and the tetracyclic ketodiazirine (196) (78CC442). 

The stereochemistiy of reactions involving substituted alkenyl free radicals indicates that radicals formed at trigonal centers rapidly undergo interconversion with the geometric isomer. Reactions proceeding through alkenyl radical intermediates usually give rise to the same mixture from both the E- and the Z-precursor ... 

The interconversion with di- and tri-bromothiophenes is very selective. Thus 2,3,5-tribromothiophene gives exclusively 3,5-dibromo-2-thienyllithium, the hydrolysis of which affords a very convenient synthesis of 2,4-dibromothiophene. Similarly, 2,4- and 2,3-di-bromothiophene give interconversion selectively with the a-bromine. 

Calixarenes are cyclophane-type molecules, in which at least four aromatic units are joined via methylene or related groups [9]. It is known that calix[4]arenes with hydroxy groups in the 2-position normally prefer a conelike conformation, however, depending on the substituents a more or less rapid dynamic interconversion with three possible partial cone conformations is possible (Fig. 1) [9, 10]. 

Scheme 10.4 Reversible photochromism of spirooxazine 247 involving interconversion with...

The fusion of the benzene ring at the 3-4 bond of the furoxan system dramatically decreases the energy barrier of thermal interconversion, with the consequence that, in benzofuroxan derivatives 10a and 10c, the equilibrium is active at room temperature [6, 7, 10] (Scheme 6.2). 

Such interconversions with monosubstituted cyclohexanes and also with disubstituted ones do not involve any rearrangement i.e., no chemical bonds are broken nor reformed, only their conformation changes and this has been confirmed by NMR studies e.g., methyl cyclohexane at -110°C gives separate signals for equatorially or axially oriented methyl groups. 

C NMR spectroscopy (29). Carbocation 6 was found to be involved in a rapid interconversion with cations 7 and 8 (Scheme 7). 

Similar to irreversible reactions, biochemical interconversions with only one substrate and product are mathematically simple to evaluate however, the majority of enzymes correspond to bi- or multisubstrate reactions. In this case, the overall rate equations can be derived using similar techniques as described above. However, there is a large variety of ways to bind and dissociate multiple substrates and products from an enzyme, resulting in a combinatorial number of possible rate equations, additionally complicated by a rather diverse notation employed within the literature. We also note that the derivation of explicit overall rate equation for multisubstrate reactions by means of the steady-state approximation is a tedious procedure, involving lengthy (and sometimes unintelligible) expressions in terms of elementary rate constants. See Ref. [139] for a more detailed discussion. Nonetheless, as the functional form of typical rate equations will be of importance for the parameterization of metabolic networks in Section VIII, we briefly touch upon the most common mechanisms. 

More recent work on the chemistry of gaseous 1,3,5-cycloheptatriene radical cations concerns the energetics and dynamics of the interconversion with ionized toluene and the competing losses of H from both isomers. Lifshitz and coworkers22,143 have reported on the details of the energy surface of the ions. Most importantly, the critical energies... 

Four new stable digermenes 66-69 were synthesized from dichlorogermanes and sodium in toluene or lithium naphthalenide (Scheme 10). 66 and 68 have been characterized by X-ray61 (see Section III,B,1). 66-6851 keep their digermene structure in solution, in contrast to 6960 (probably the E isomer due to the steric hindrance in the Z isomer), for which an interconversion with the corresponding germylene was observed. 

As a substrate for chemical modification, vincristine (2) represents much more challenge. The extracted yield of 2 from Catharanthus is approximately 10% that of 1, making this compound a much scarcer substrate (42). Furthermore, the chemical lability of the N-1 formyl bond is extreme under a variety of conditions. The preparation of compounds in this series is usually accomplished by performing the requisite functional group interconversions with compounds bearing an N-1 methyl and reserving the oxidation of this methyl for the last step. 

D-Fructose 6-phosphate, interconversion with D-glucose 6-phosphate,... 

The Lee group originated rhodium alkenylidene-mediated catalysis by combining acetylide/alkenylidene interconversion with known metal vinylidene functionalization reactions [31], Thus, the first all-intramolecular three-component coupling between alkyl iodides, alkynes, and olefins was realized (Scheme 9.17). Prior to their work, such tandem reaction sequences required several distinct chemical operations. The optimized reaction conditions are identical to those of their original two-component cycloisomerization of enynes (see Section 9.2.2, Equation 9.1) except for the addition of an external base (Et3N). Various substituted [4.3.0]-bicyclononene derivatives were synthesized under mild conditions. Oxacycles and azacycles were also formed. The use of DMF as a solvent proved essential reactions in THF afforded only enyne cycloisomerization products, leaving the alkyl iodide moiety intact. 

The oral bioavailability of spironolactone is about 70%. It is extensively bound to plasma proteins and is completely metabolized in liver. Canrenone is a major active metabolite of spironolactone, which can be converted enzymatically into canrenoate (hydrolytic product). Canrenoate has no intrinsic activity, but it can exert their effects by virtue of its interconversion with canrenone. 

Halogen-Metal Interconversions with Halo-geneted Anilines. A highly explosive compound which appears to be p-N,N-Trilithioani-line is formed as a by-product in the reaction of BuLi and p-Br-aniline but not o-Br-aniline (Ref 1). More recently this reaction was repeated but no by-product is mentioned (Ref... 

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