Group Migration Reactions

Group Migration Reactions.—1,3-Fluorine migrations have been reported following the mercury-sensitized irradiation (7 days) of the perfluoroalkenes (17a) and (17b).The products from the reaction are the skeletally rearranged compounds (18). Direct irradiation of the natural product Mortonin C (19) in methanol yielded two photoproducts identified as (20a) and (20b). These 

Group Migration Reactions.- Direct irradiation of cyclooctene (la) in pentane brings about CIS -trans isomerization as well as the formation of the bicyclic products (2a) and (3). These are formed via the carbene intermediates (4) and (5). The latter carbene (5) also affords methylenecycloheptene. cis -trans -Isomerization also arises with the cycloalkenes (lb) and (Ic). Product (2b) is formed from cyclodecene (lb) and 

A detailed study of the photochemical formation of the cyclobutene (17) by irradiation of l,l -bicyclohexenyl has been carried out. The photo- reaction also affords 1,2- and 1,4- addition products involving the incorporation of methanol. Steady state and transient methods have shown that the intermediate involved in the formation of these products is a highly strained ground state cis - trans -compound (18). This compound is the only precursor to the cyclobutene (17) following triplet sensitization of 

Photoelectron transfer processes between styrenes and Cu(U) and Fe (III) species have been studied. The reactions encountered include the addition of methanol to the double bond of the styrene. Some styrene derivatives have been irradiated in the presence of CdS. The trans -cis isomerization still occurs but the authors suggest that electron transfer is involved forming a radical-cation.  

Interest is shown still in the isomerization of stilbene and its derivatives. A study of the pathways for the cis -trans isomerization of 4-nitro, 4,4-dinitro, and 4-nitro-4 -methoxy stilbenes has been reported. The dynamics of the photoisomerization of stilbenes in hydrocarbon solution has been studied and a comparison of the trans -cis isomerization of stilbene in low viscosity liquid alkanes and in the gas phase has been carried out. The photoisomerization of stilbene in straight chain alcohols has provided evidence for the existence of rotational relaxation in the excited and the ground states. An analysis of the isomerization rates of photoexcited stilbene has been made and the photobehaviour of poly deuteriated stilbene has been studied.  

De Mayo and Hasegawa have studied the cis -trans -isomerization of stilbenes (23) mediated by a CdS semiconductor.  

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Recent studies on the formation of diols such as 19 have shown that functional-group migration reactions are possible when very electron-rich aryl groups are used (Scheme 3.5). In the extreme case of 5-methoxythienyllithium, only the rearranged product 26 was isolated [31]. 

The mechanism of the Fries reaction is not known with certainty. One mechanism regards it as a true intramolecular rearrangement in which the acyl group migrates directly from the oxygen atom to the carbon atoms of the ring. Another scheme postulates that the ester is cleaved by the reagent... 

The reaction is stereospecific the alkyl group migrates with retention of configuration O O... 

Chemical reactions that the xylenes participate in include (/) migration of the methyl groups, (2) reaction of the methyl groups, (7) reaction of the aromatic ring, and (4) complex formation. 

The presence of water in the carbonylation mixture makes it possible to halt the reaction after the second group migration (step 2). Oxidation of the intermediate boraglycol yields the corresponding ketone, and alkaline hydrolysis affords the secondary alcohol, R HOH. A blocking group of low... 

Bake sulfonation is an important variant of the normal sulfonation procedure. The reaction is restricted to aromatic amines, the sulfate salts of which ate prepared and heated (dry) at a temperature of approximately 200°C in vacuo. The sulfonic acid group migrates to the ortho or para positions of the amine to give a mixture of orthanilic acid [88-21-1] and sulfanilic acid [121 -57-3] respectively. This tendency is also apparent in polynuclear systems so that 1-naphthylamine gives 1-naphthy1amine-4-su1fonic acid. 

The reaction of 3-amino-1,2,4-triazine 1-oxide 1 with methyl iodide in the presence of sodium bicarbonate leads to the methylation of the amino group to afford 3-methylamino-l,2,4-tiiazine 1-oxide 123. This iV-oxide 123, under neutral conditions in the presence of Mel, undergoes methyl group migration to the N(2) atom of the 1,2,4-triazine ring, yielding 3-imino-2-methyl-1,2,4-triazine 1-oxide 124. The same product 124 was obtained by direct methylation of compound 1 under neutral conditions (84TL1677). 

That the postulated phosphate group migration did in fact, occur, was eventually proved (58) in the following way. During the many experiments done to find conditions in which the phosphate group migration could be demonstrated by periodate oxidation, the conclusion was reached that one of the difficulties in the interpretation of the results was because of the fact that the reaction between the phosphorylated... 

The Curtius rearrangement, like the Hofmann rearrangement, involve migration of an -R group from the G-O carbon atom to the neighboring nitro gen with simultaneous loss of a leaving group. The reaction takes place on heat ing an acyl azide that is itself prepared by nucleophilic acyl substitution of m acid chloride. 

The effect of substrate structure on product profile is further illustrated by the reactions of cis- and trons-stilbene oxides 79 and 83 with lithium diethylamide (Scheme 5.17) [32]. Lithiated cis-stilbene oxide 80 rearranges to enolate 81, which gives ketone 82 after protic workup, whereas with lithiated trans-stilbene oxide 84, phenyl group migration results in enolate 85 and hence aldehyde 86 on workup. Triphenylethylene oxide 87 underwent efficient isomerization to ketone 90 [32]. 

The use of boron trifluoride-diethyl ether complex as the Lewis acid in these reactions promotes silyl group migration and gives rise to the formation of tetrahydrofurans with excellent stereoselectivity82. 

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