Possible Intermediates in

Pyrrolealdehyde has been prepared from pyrrole, chloroform, and potassium hydroxide from pyrrolemagnesium iodide and ethyl, propyl, or isoamyl formate and, by the method here described, from pyrrole, phosphorus oxychloride, and dimethylformamide. Smith has suggested a possible intermediate in this process. The method has also been applied to substituted pyrroles and is similar to that described in this series for the preparation of -dimethylaminobenzaldehyde from di-methylaniline. ... 

The bridged radical A has been suggested as a possible intermediate in the photochemical decarbonylation of 3-phenylpropanal. Suggest an experiment to test this hypothesis. 

Structural subgoals may be useful in the application of transform-based strategies. This is especially so with structurally complex retrons which can be mapped onto a target in only one or two ways. It is often possible in such cases quickly to derive the structure of a possible intermediate in a trial retrosynthetic sequence. For instance, with 109 as TGT the quinone-Diels-Alder transform is an obvious T-goal. The retron for that transform can readily be mapped... 

Thebainone methyl enolate. CuHjjOjN. This possible intermediate in the hydrogenation of thebaine to dihydrothebainone-J-5 6-methyl enolate (see above) has m.p. 154-6°, [a] ° -f 9-6° (EtOH). ... 

The N-Lim classification does not eliminate the possibility of borderline cases between these two categories, but it leads to the suggestion that no sharp distinction can be made between the possible intermediates in these mechanisms and that perhaps all solvolyses proceed via an intermediate. The mechanistic category of a particular solvolysis then depends upon the relative weights of the canonical structures 3, 4, and 5 to the transition state resonance hybrid. 

In the literature tetrathiosulfuranes have been discussed as possible intermediates in the thermal decomposition of sulfanes and other polysulfur compounds. High-level ab initio MO calculations have in fact revealed that such species are local minima on the potential energy hypersurface [34]. However, recent results show that both the Gibbs reaction energies as well as the activation enthalpies for reactions of the type... 

To rationally govern the selectivity of a catalytic process, the elementary reaction steps on real catalyst surfaces must be identified. The use of well-defined organometallic compounds (possible intermediates in surface reactions) can be very useful in the determination of these steps. The use of kinetic modelling techniques combined with statistical analysis of kinetic... 

Scheme 4-7 Possible intermediates in the reaction of acetylene and N Hj leading to acetonitrile...

In the case of neutral systems the geometry corresponds to a bicapped tetrahedron or, in other words, to a tetrahedron which undergoes two nucleophilic coordinations. They have been observed [5] to be stable in solution. A careful H variable temperature NMR study shows that these compounds undergo an intramolecular isomerization which takes place without cleavage of Si-N bonds. The AGt of this so-called "Baylar Twist" isomerization has been estimated at between 12 and 18 kcal/mole depending on the substituents at the silicon. We can conclude that this work supports strongly hexacoordinated silicon structures as possible intermediates in the usual course of nucleophilic reactions at silicon. 

From these results we can conclude that heptacoordination at silicon cannot be excluded a priori as a possible intermediate in the course of reactions at silicon. 

Nagels, L. and Parmentier, F. (1976). Kinetic study of possible intermediates in the biosynthesis of chlorogenic acid in Cestrum poeppigii. Phytochemistry 15 703-706. 

Regarding mechanism 2 which involves H as an intermediate reducing agent, the author is unaware of reports of H as a possible intermediate in the mechanisms proposed for reactions for the hydrogen electrode. As in the case of mechanism 1, the supposed active intermediate is consumed in two reactions (equations (8) and (9)), an unlikely event for an unlikely intermediate. In his review of the H2 electrode reaction, Enyo [46] concluded that involvement of H intermediates in H2 electrode reactions had not gained sufficient experimental evidence to warrant serious consideration. Nevertheless, the mechanism has been occasionally invoked, as for example, recently by Gemmler et al. for electroless Ni-P deposition [47]. 

Fig. 9.—Possible Intermediates in the Metabolism and Intereonversion of d-G1u-cosamine and D-Galactosamine.

Organometallic betaines of type I can be considered as the closest structural analogs of carbon betaines of the (+ )P-C-C-X( ) type (IV), which were regarded for a long time as possible intermediates in classical reactions of carbonyl and thiocarbonyl compounds with phosphorus ylides (Wittig and Corey-Chaykovsky reactions and related processes,5,6 Scheme 1). Vedejs and coworkers7,8 proved unambiguously that oxapho-sphetanes (III) are true intermediates in the reactions of nonstabilized phosphorus ylides with carbonyl compounds. The formation of oxabetaines (+)p-c-c-o(-> was detected only in the form of their adducts with lithium salts.9,10... 

In addition to mono and diradicals, the conjugate base of a nitrogen positive ion is a possible intermediate in the above reactions. 

Many researchers have considered models for possible intermediates in the nitrogenase reaction. Two possible dinitrogen attachments to the FeMoco factor of MoFe-protein have been put forward. Symmetric, edge- or side-on modes discussed by Dance48 would lead to a reaction sequence such as is shown in reaction 6.11. In contrast, the asymmetric end-on terminal mode discussed in the work of Nicolai Lehnert50 may be favored thermodynamically and by molecular orbital calculations. Reaction sequence 6.13 below illustrates one scenario for the asymmetric model. 

A large number of (mostly zero-valent) nickel-alkene complexes has been reported. Although these complexes have not been recently reviewed, their general properties and structures were expertly described in 1982 [21]. A complete overview of the reported nickel-alkene and nickel-alkyl complexes is beyond the scope of this section, in which a selection of nickel-alkene and nickel-alkyl complexes is described, mostly related to possible intermediates in hydrogenation catalysis. 

Mico BA, Pohl LR. 1983. Reductive oxygenation of carbon tetrachloride trichloromethylperoxyl radical as a possible intermediate in the conversion of carbon tetrachloride to electrophilic chlorine. Arch Biochem Biophys 225 596-609. 

Diaza-OTdo-hexaboranes [N2B4R4R 2] are the products of the fusion of rings NB2R2R. The mechanism of this cluster formation was investigated and in the case of the neopentyl substituent (R = CH2/Bu, R = /Bu) a tetracyclic molecule was identified as a possible intermediate in the ring fusion reaction.81,8111... 

Scheme 6.62 The 3<52-pyran derivative 288 as a possible intermediate in the thermal cyclization of undeca-3,8-diyne-2,10-dione (287).

B Liberek. Tertiary butyl esters of protected (S-cyano-L-alanine peptides as possible intermediates in the preparation of L-asparaginyl peptides, (peroxide for oxidation) Chem Ind 987, 1961. 

Considering the success of the condensation route to carboranes in the hydride bath (vide supra), other alkynylboranes than diethyl(propyn-l-yl)borane might be equally suitable. By heating a mixture of bis(diethylboryl) ethyne (65) and excess of (Et2BH)2 ( hydride bath ) at 110-120 °C, l,2,3,4-tetraethyl-5,6,7,8-tetracarba-mdo-octaborane(8) 64c was obtained by distillation in ca. 20% yield as a colorless liquid, stable to air and H2O (Scheme 3.2-35) [87]. Possible intermediates in this reaction can be proposed as 67 and 68, where 67 results from double hydroboration of bis(diethylboryl)ethyne (65), which dimerizes to 68 and finally yields the carbo-rane 64c by elimination of Et3B. 

Identification of possible intermediates in the cyclization was attempted by adapting the isotope dilution method which had been... 

Transient digermene 86 was postulated as possible intermediate in the reaction of 1,2-dichlorodigermacyclobutane 87 with Mg/MgBr2 in the presence of an alkene, leading to the bicyclic compound 8878 [Eq. (17)]. However, an electron transfer reaction with the intermediate formation of a germyl radical is also a possibility.78 Similarly, transient 1,2-digermacyclobu-... 

In M14 = Mi4 compounds (M, M = Si, Ge, Sn), only >Si = Sn< derivatives have not yet been physicochemically characterized (a transient compound of this type has been postulated by Lappert et al. as possible intermediate in the reaction between a silylene and a stannylene leading to a silylstannylene118). 

A. Polarization and Electrophilic Svhstitidion From the various accounts that have been given of the role of 77-complexes and <7-complexes as possible intermediates in reaction mechanisms, that described by Olah e al.(1961)is selected for special attention, since it... 

Thymine derivatives - 5-[7V-(2-Amino-4-hydroxy-6-methyl-5-pyrimidinyl-propyl)-p-carboxyanilinomethyl] uracil (XXXIII) was synthesized for study as a possible intermediate in the enzymatic synthesis of thymidylate. It is active as an enzyme inhibitor against thymidylate synthetase isolated from E. coli [298]. Certain thymine derivatives containing a 2-thioimidazole moiety (XXXIV, R = alkyl) inhibit growth of Ehrlich ascites carcinoma (fluid form) in mice [299]. 

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