Ortho labeling

Tail-to-tail union of 3-carbon units resulting in ortho labeling... 

At still higher temperatures, 3,4-dimethylenecyclobutene gave both fulvene and benzene in a 2 1 ratio, respectively, in a flow system. Further, when the 1,2-dideuterio material was pyrolyzed, the fulvene appears to have deuterium on the 2 and 3 positions while the benzene is 93% ortho labeled with only 5% meta labeled and 2% para labeled. The proposed mechanism for these conversions invoked reversion to the bisallene follwed by recyclization in two different modes to produce biradicals whose resonance structures are carbenes which undergo insertion(s) into adjacent CH bonds (Scheme 7.17). 

Exchange of formyl hydrogens for tritium is observed to occur in both aryl aldehydes (with concurrent ortho labeling in appropriate cases) and aliphatic aldehydes using [(cod)Ir(PCy3)(py)]PF6. Partial reduction of aldehydes to alcohols may occur in some cases. Labeling by other iridium phosphine catalysts has not been reported but is likely to occur. This type of catalytic activity, which likely involves reversible oxidative addition of the iridium center into the formyl C—H bond, is different in outcome from that of organorhodium complexes, whose insertion into formyl C—H bonds proceeds instead to decarbonylation. 

Experiments with 14C-labelled substrates also demonstrated conclusively the intramolecularity of the rearrangement. The generally accepted scheme involves the formation of the dienone LXXXV which can lose a hydrogen atom if R = H, to form the ortho product or if R H further rearrangement to LXXXVI occurs with subsequent formation of the para product, viz. 

Patterns of excretion in rats differed among [14C]labeled tricresyl phosphate isomers administered by gavage at dosage levels ranging from 0.5 to 200 mg/kg (NTP 1988). Radioactivity from tn-ortho-cresy phosphate was excreted within 24 hours predominately in urine at all dosage levels ( 70% of applied doses). Radioactivity from trww-cresyl phosphate was excreted predominately in feces at all dosage levels. 

As mentioned above, methyl loss from ionized methoxymethyl derivatives of methyl benzoate is not restricted to the ortho-isomet 93. 2H labelling has shown that the mita and para compounds 96 also eliminate CH3 specifically from the methoxymethyl group. Interestingly, neither from the unsubstituted benzyl methyl ether 97 (X = H) nor from the X-substituted analogues 97 (X = CH2OH, NQ2) loss of CH3 is observed (21). Thus, the earbomethoxy function seems to play a decisive role in the dissociation process. 

OH elimination from ortho substituted aldoximes 179 (X = CH2, NH, O) may be at least partially the result of a hydrogen migration/cyclization/elimination process, whereby the heterocycles 182 are formed72 (46). A metastable peak shape analysis, the investigation of 2H-labelled derivatives and the study of positional isomers indicate that in addition to 182 the protonated isocyanide 183 is formed via a mechanism which is not fully understood. However, it is known that the generation of 183 occurs without any detectable interaction with the XH ortho substituent. 

Figure 70 The flourescein (Fl)-labeled nido-OPDs (119 and 120) and ortho-OPDs (121) boron delivery systems. (Adapted from ref. 146.)...

The alkene loss from ionized cycloalkyl-substituted nitrobenzenes has been studied by isotopic labelling and collision activation mass spectrometry77. The reaction path was found to depend highly on the placement of the nitro group. The ortho nitro-substituted phenylcyclopropane and its isotopomers were studied. 

Nitrogen, carbon-13 and carbon-14 kinetic isotope effects have been determined38 for the analogous acid-catalyzed ortho,ortho -rearrangement of the Af-2-naphthyl-Ar/-phenylhydrazine (equation 24). The labelled compounds required for this study were prepared by the sequence of reactions shown in Schemes 20-22. 

The photolysis of N-methylborazine in the presence of ammonia produced B-amino-N-methylborazine. The major isomer in this reaction, e., the ortho isomer, was identified by labeling the ring nitrogens of N-methylborazine with N and observing the H NMR spectrum of the photolysis product Both N-methylborazine and ammonia absorb 184.9 mn radiation (q jh, = 12101 mole cm eHjB3N3H2 (CH3)... 

F-Labelled 2-amino-2 -fluorobenzhydrol, intermediates in the synthesis of amino benzodiazepinones, has been synthesized in an elegant one-step procedure [168] based on the specific ortho coupling of an anilinodichloroborane with an aldehyde [169] (Scheme 32). 

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