Isomerization thermally promoted

Since complexes 70 and 71 have been sho vn to be thermally stable in contrast to 69 [39], and hence their thermal degradation vas negligible. Although reaction of 70 with 1-octene performed at room temperature in ADMET conditions afforded mainly Ci4-olefin, significant amounts of Cy and C9-C13 olefins were observed in the reaction performed at 60 °C [40]. This result suggests that olefin isomerization is promoted to some extent at a higher temperature. 

The rearrangement of an Af-arylsulphonamide, or an JV-arylsulphamide, to the isomeric aminoaryl sulphonyl compound (equation 43) is now a well-known reaction. The reaction is the nitrogen analogue of the Fries rearrangement (Section III.A.). For sulphonamides, acid-catalysed, base-catalysed, thermally promoted and photochemically promoted rearrangements have been observed for sulphamides, only the thermal and base-catalysed processes have been reported. 

Diels-Alder reaction of pyran-2-ones. Diels-Alder reaction of 2-pyrones, if successful, can provide unusual cyclohexenecarboxylic acids, but thermally promoted cycloadditions with these electron-deficient dienes usually result in decarboxylation and aromatization of the adducts as a result of the required high temperatures (6,291-292). Successful Diels-Alder reactions of 3-bromo-2-pyrone (1) with the electron-rich dioxole 2 can be effected with a catalytic amount of ethyldiisopropylamine at 90° (4 days) to give the major adduct (endo-3) in 63% yield. The adduct is hydrolyzed by p-toluenesulfonic acid in methanol to 4 as the only diastereomer. The trisilyl ether of 4 was transformed to the a,/8-unsaturated ester 5 by radical debromination and DBU isomerization. ... 

In 1987, Nitta reported the formation of an unexpected vinylketene complex from the reaction of an azido-substituted cyclopropene with diiron nonacarbonyl.104 They had previously investigated the chemical behavior of the complexed nitrene intermediates that result from the reaction of organic azides and iron carbonyls113 and were interested in replicating the thermal isomerization of 3-azido-l,2,3-triphenylcyclopropene (163) into 4,5,6-triphenyl-l,2,3-triazine using a metal carbonyl-promoted re-... 

UV irradiation of the naphthalen-l,4-imines 104 and 105 promotes their isomerization to 3-benzazepine derivatives 139 and 140. Although no direct evidence was obtained to confirm the formation of azaquad-ricyclanes (138) as intermediates (see Section II,F), the extra strain associated with structure 138 and the extra benzenoid stabilization of the products 139 and 140 make it understandable that the thermal rearrangement of 138 should occur faster than that of 76 or 78. Analogous photochemical transformations are those of compound 106 to trimethyl 3-benzazepin-l,3,5-tricarboxylate, and of 1,4-epoxynaphthalenes to benzoxepin derivatives. ... 

The isomerization of methylsilene and dimethylsilylene is now a well-known reaction in low-temperature matrices. It is a photochromic process that may be reversed upon irradiation of the matrix at selected wavelengths. Warming to temperatures as low as 100 K promotes the formation of the more thermally stable silylene (equation 39). 

Thermal or photochemical treatment of isoxazoies 851 has been found to result in a ring-contraction reaction to produce acyl 277-azirines 852, which sometimes rearrange to form other heterocycles like oxazoles 853. This ring-contraction reaction can also be promoted by iron(ii) catalysts. Thus, 5-alkoxy- and 5-aminoisoxazoles isomerize to 27/-azirine-2-carboxylic esters and 2/7-azirine-2-carboxamides, respectively, in nearly quantitative yield by reaction with catalytic FeCb (Scheme 212) <1997T10911>. 

In another example, a mixed monolayer composed of a photoisomerizable component and an electrochemical catalyst was applied to switch the electrocatalytic properties of a modified electrode between ON - and OFF -states. A gold electrode surface functionalized with a spiropyran-monolayer and pyrroloquinoline quinone (PQQ) moieties incorporated into the mono-layer was applied to control the electrocatalytic oxidation of NADH by light [92]. The positively charged merocyanine-state interface resulted in the repulsion of Ca2+ cations (promoters for the NADH oxidation by the PQQ), thus resulting in the inhibition of the electrocatalytic process. In the nitrospiropyran-state the monolayer does not prevent association of the PQQ-catalyst and Ca2+-promoter, so provides efficient electrocatalytic oxidation of NADH. Similar results have been achieved by a combination of the photo- and thermal effects resulting in the isomerization of the spiropyran-monolayer with the incorporated PQQ-catalyst [93], Other photoisomerizable materials such as an azobenzenealkanethiol derivative mixed with a ferrocene-redox component have also been used to control the electrocatalyzed electron transfer process between a command interface and a dissolved redox probe [94]. 

FeC C 0)4 ( C 0). It was found that irradiation of the matrix with the output of a tunable IR laser at a frequency corresponding to one particular isotopomer promoted a selective rearrangement as shown in Scheme 2. These interconversions may clearly be described as pseudorotations but the results show that the permutational mode is not that expected for the normal Berry Pseudorotation seen, for example, in the thermal rearrangement of SF4. Thus the isomerization of Fe(CO)4 was the first reported example of a non-Berry pseudorotation. 

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