Intramolecular transformations

It is prepared by an intramolecular transformation of diazoaminobenzene in the presence of aniline hydrochloride, or in one stage by diazotizing a solution of aniline and aniline hydrochloride with an insufficient amount of nitrous acid. 

Stereochemical aspects of epoxidation of substituted norbomenes and accompanying intramolecular transformations 98UK299. 

There is mounting evidence that the intramolecular transformation of a hydridocarbonyl, M(H)CO, into a 1T]-formyl, MC(0)H, is not thermodynamically favorable (1 ). This has directed attention towards reactions which provide exceptional stability to the formyl species. 

The ether-catalyst complex (II) splits into a complex anion (III) and a carbonium ion (IV), which rearranges to the configuration of maximum stability (V). This carbonium ion (V) could itself initiate polymerisation, but it is more likely that it attacks the double bond of the closely associated anion (III), giving the double ion (VI) in equilibrium with the aldehyde (VII). Rearrangements of the type (I)-(VII) have been observed for vinyl ethers [7], and a closely parallel isomerisation is that of isobutyl phenyl ether into para-tertiary butyl phenol under the influence of A1C13 [8]. It is unlikely that the steps from (II) to (VI) take place in a well defined succession. The process probably proceeds by a single intramolecular transformation. 

Internal DCR of Nitroaldol Libraries (Scheme 6.10) [5,6] iDCR was demonstrated by using a conceptual nitroaldol library including five benzaldehyde derivatives (24,36, and 47-49) and one nitroalkane (50, DCL-F, Scheme 6.11). The benzaldehydes, all with a unique substitution pattern, were selected in order to make analysis clear and simple. However, one of the henzaldehydes contained a cyano functionality in the 2-position (49), deliberately making it a candidate for subsequent tandem cyclization following nitroalcohol formation. 5-exo-dig type cyclizations of hydrox-ynitriles to the corresponding iminolactones are expected [40,41], albeit unexplored [42 5], intramolecular transformations, which in this case could lead to possible kinetic resolution of the library. 

In another approach, 2-(alkylamino)alcohol is employed as starting material for aziridine syntheses with the aid of dihalogenophosphoranes (70BCJ1185). Intramolecular transformation of 3-azidopropyloxirane 73 results in a simultaneous formation of a condensed aziridino[l,2-a]pyrrol-idine system (Scheme 39). The azide group is first transformed into imino-phosphorane 74, the nucleophilic N atom cleaves the oxirane to form betaine 75 [as in the Mitsunobu reaction (81S1)], and the phosphorus is shifted from N to O and then eliminated as phosphane oxide under simultaneous cyclization to bicyclic 76 (89JA7500). 

The Michael additions to 1 - 3 of a large variety of carbon, nitrogen, oxygen, sulfur and selenium nucleophiles, as well as hydride, followed by inter- or intramolecular transformations of the chlorine substituent or/and the methoxy-carbonyl fragment, offer versatile synthetic approaches to a large variety of synthetically useful and important organic molecules. 

Intramolecular lactonization can also be carried out with DCC and DMAP. As with other macrolactonizations, the reactions must be carried out in rather dilute solution to promote the intramolecular transformation in competition with intermolecular reaction, which leads to dimers or higher oligomers. A study with 15-hydroxypentadecanoic acid has demonstrated that a proton source is beneficial under these conditions and found the hydrochloride of DMAP to be convenient.121... 

This carbyne was shown not to be the RCM active species. At —20 °C it rearranged spontaneously into the indenylidene complex XV with release of TfOH. This intramolecular transformation corresponds to the electrophilic ortho-substitution of one phenyl group by the electrophilic carbyne carbon of XIV. The carbene complex XV was identified as the species thermally formed in situ from the catalyst precursors Ia,b in the range 25-80 °C. 

One of the rare examples, where the palladium catalyzed closure of a six membered ring leads to an aromatic heterocycle is presented in 4.18. Intramolecular transformation of the 2-bromoindole derivative in the presence of a palladium-BINAP catalyst led to the formation of the a-carboline (pyrido[2,3- ]indole) skeleton. The ring closure was accompanied by the oxidation of the intermediate dihydrocarboline derivative.21... 

The participation of halopyrroles in Heck coupling is mostly limited to intramolecular transformations. In a recent example of intermolecular Heck reaction different A-protcctcd 3-iodo-4-trimethylsilyl-pyrroles were coupled... 

Metal(V) species derived from the complexes in Table I are rare. In fact, only one such species, L1Cr(V) (presumably a dioxo or hydro-oxo species), has been observed and characterized by ESR and UV-visible spectroscopies (45,69), Figs. 5 and 6. This Cr(V) species, which has a lifetime of several seconds at room temperature, was generated from a hydroperoxo precursor by an intramolecular transformation that closely resembles the proposed, but so far unobserved step in the chemistry of cytochrome P450, whereby the hydroperoxoiron(III) is transformed to the FeIV(P + ) form also known as oxene (P += porphyrin radical cation). All the steps in Scheme 1 for the L1Cr(H20)2+/02 reaction have been observed directly (45,69). 

The fundamental types of thermally and photochemically induced intramolecular transformations are summarized in Scheme 1. All reactions of this class involve intermediates in which aromaticity is lost hence they are most common in the classes of less aromaticity, i.e. polyhetero rings, cationic rings, rings containing carbonyl groups. However, polysubstitution, especially by bulky groups, can also induce reactions by strain relief in transition states. Most of the reactions known are photochemical. 

Thermolysis of the formamidrazone 590, obtained from the reaction of hydrazine 488 with Vilsmeier salt 589, at 200°C or on boiling in nitrobenzene led, by intramolecular transformation, to the triazolo[4,3-c]pyrimidine 591 (90T3897). Aryl isocyanide dichlorides reacted with 488 in the presence of Et2N to give 3-anilinotriazolopyrimidines (592) (Scheme 117). 

As indicated in a preliminary study (ref. 6) compounds IV and V are probably formed through the intramolecular transformation of ortho-acetoxyacetophenone. The formation of IV and V implies the enolization of the acetyl and of the acetoxy groups respectively. On HY ortho-acetoxyacetophenone would be transformed quantitatively into IV and V. The fact that these compounds are not formed on HZSM5 means that ortho-acetoxyacetophenone is not either, or that the products cannot desorb because of steric constraints. 

Sequences that involve all intramolecular transformations are by far the easiest to conduct, yet they are among the most powerful. The requirements for success are similar to those for standard radical cycliza-tions. In general, the slowest intramolecular reaction must still be more rapid than the reaction that converts that radical to a nonradical product (this ensures that the initial and intermediate radicals are not intercepted prior to intramolecular reaction). The differentiation of the intermediate radicals is provided by the structure of the substrate itself radicals A- and B- should have only one reasonably rapid intramolecular option, and radical C- should have none. 

Sometimes, aldehydes obtained by TPAP oxidations suffer in situ intramolecular transformations in substrates with a great predisposition to do so. Examples found in the literature include retro-Claisen rearrangements,108 dipolar additions on enals,106a and attack of malonates109 and indole rings11 on aldehydes. 

A similar type of dimerization is known for quinolinium (82KGS291) and 1-benzopyrylium (69TL2047) salts, but dimers thus formed are unable to undergo further intramolecular transformations. Contrary to these results, dimer 269, which may be considered as a C-adduct between the initial... 

Carbon monoxide has been used to scavenge OH fonned from the ozonolysis of alkenes. The CO2 tints generated was detected by FTIR spectroscopy and the "OH yields for individual reactions were calculated.239 The significance of the OH-induced intramolecular transformation of glutathione thiyl radicals to a-aminoalkyl radicals has been discussed with respect to its biological implications.240 The kinetics and mechanism of the process indicated that it could be a significant pathway for the selfremoval of glutathione thiyl radicals in vivo. 

Various intramolecular transformations are conceivable for dicarbene 127, which would result from twofold elimination of molecular nitrogen from bis(diazomethyl)silane 126. HF energies, calculated by ab initio methods, for the possible rearrangement products 128-134 are given in Scheme 665. 

Frequently the basic conditions used cause the initial Michael adduct to undergo intramolecular transformations, as for example in the synthesis of dimedone (Expt 7.11). This involves a Michael reaction between mesityl oxide and diethyl malonate followed by an internal Claisen ester condensation. 

Grierson L, Hildenbrand K, Bothe E (1992) Intramolecular transformation reaction of the glutathione thiyl radical into a non-sulphur-centered radical a pulse radiolysis and EPR study. Int J Radiat Biol 62 265-277... 

Zhao R, Lind J,Merenyi G, EriksonTE(1997) Significance of the intramolecular transformation of glutathione thiyl radicals to a-aminoalkyl radicals. Thermochemical and biological implications. J Chem Soc Perkin Trans 2 569-574... 

The model we have used for the description of the transition states implies that also the corresponding n-olefin complexes contain an asymmetric metal atom and that changes of configuration at the metal occur more slowly than the intramolecular transformation of the 7i-complex into the metal-alkyl complex. 

In another example of consecutive kinetics, a macrocyclic hydroperoxochromium complex L1(H20)Cr00H2+ undergoes an enzyme-like intramolecular transformation to yield a chromium( V) intermediate that subsequently decays by oxidation of the macrocycle.37 38 In acidic solutions, these reactions are described by Equation 8.67. 

The scheme (Figure 3.5) of the transformation of this P - acetic acid mixture over HMFI at 553 K was established from the effect of conversion (or of contact time) on product distribution.[69] At short contact times (i.e. at low conversions), PA was practically the only reaction product. However, there was also formation of a very small amount of o-HAP (Figure 3.6). This means that O acetylation is much faster than C acetylation (ca. 20 times) and that the latter reaction leads to the ortho isomer only. Because of the high rate of O acetylation, thermodynamic equilibrium between P, acetic acid and PA was established at relatively short contact times. At high conversions, the formation of o-HAP involved the participation of PA as demonstrated by the decrease in PA yield and the apparent secondary mode of o-HAP formation (Figure 3.6). This mode of o-HAP formation from PA is mainly intermolecular involving the acetylation of P by PA. The intramolecular transformation of PA into o-HAP is much slower as shown by comparing the transformations of pure PA and of an equimolar mixture of PA and P.[69] The formation of small amounts of p-HAP would result mainly from the hydrolysis of... 

An analogous intramolecular transformation was also successful, as illustrated in the following cyclization [34] ... 

The fundamental types of thermally and photochemically induced inter- and intramolecular transformations proceed, in general, with loss of heteroaromaticity. This leads mostly to metastable intermediates prone to further interconversions. 

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