Rearrangement, acyl migration, acidic

In the Lossen reaction a hydroxamic acid derivative (usually an 0-acyl derivative) is deprotonated by base, and rearranges via migration of the group R to give an isocyanate 2. Under the usual reaction conditions—i.e. aqueous alkaline solution—the isocyanate reacts further to yield the amine 3. The Lossen reaction is closely related to the Hofmann rearrangement and the Curtins reaction. 

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. 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Acid catalyzed the rearrangement of the 2-alkyl-2-vinylcyclobutanones (244) to yield either cyclopentenones (245), (246) or cyclohexenones (247) via 1,2-acyl migration or 1,3-acyl migration respectively (Table 15)82). 

The formation of tluorinated Q -hydroxy-jS-imino esters (180) by treatment of fluorinated imino ethers (179) with lithium 2,2,6,6-tetramethylpiperidide has been reported. A possible explanation for this interesting intramolecular rearrangement is proposed in Scheme 64. Acyclic imides derived from primary benzylic amines and amino acid esters have been found to undergo a novel nitrogen to carbon acyl migration via a base-generated carbanion to yield the corresponding a-amino... 

Section IV,A,1 Attempts to prepare spiro-3i/-pyrazoIes from esters of 6-diazopenicillinic acid and l-phenyI-2-propyn-l-one resulted in spontaneous rearrangement to the isomeric l//-pyrazoIes via a unique migration of the 0-Iactam 6-7 bond.174 A similar spontaneous acyl migration was observed in the reaction between a 3-diazothiolan-4-one and DMAD.175... 

The second major metabolite from T. inflation is structurally closely related to cyclosporin A, as can be deduced by elemental analysis, mass spectrum (m/z 1217), IR and NMR spectra. Furthermore, the presence of the double bond and OH group of the unusual MeBmt was established. Sulphonic acids in methanol or dioxane effected the typical rearrangement reaction by N, O-acyl migration to the iso-compound (13). Hydrolysis furnished the same amino acids as cyclosporin A with the exception of L-a-aminobutyric acid, which is replaced in cyclosporin C (12) by L-threonine. The amino-acid sequence could be deduced by conversion of cyclosporin C into cyclosporin A via the corresponding tosylate (14) and iodo derivatives (15) [7]. Position 2 for L-threonine as well as the assumed twisted -pleated sheet conformation of the molecule were confirmed by 13C-NMR spectra. 

Figure I The pH-dependence of the acyl migration of lysophospholipids is shown. The log of the pseudo first-order rate constant it if or the rearrangement of 2-palmitoyl- n-glveero-3-phosphorYlchotine into l-palmitoyl-sn-glycero-3-phosphorylcholine is plotted against the pH buffered with 50mM iris HCl ( ). 50m M citrate (O), or 0.1 M HCI and 160m M Triton X-100 (A) to solubilize the reaction products at acidic pH.

Carboxylic acids react with phenyliminovinylidenetriphenylphosphorane (equation 106) via the intermediates (1) with formation of the alkylidenephosphoranes (2), which, on heating, rearrange in an intramolecular acyl migration to ylides (3). By heating (2) in the presence of an alcohol the acyl ylides (4) and N-phenylurethanes are formed. - The reaction sequence allows the replacement of the OH group in carboxylic acids by the ylide function. 

Acyl migration N -> O accelerates greatly the p-nitrobenzoylation of the 3j8-tropanol tertiary base, in contrast with that of the 3a-tropanol (24). The acid chloride gives an iV-aroyltropanium chloride which rearranges spontaneously into the 0-aroyltropanium hydrochloride if a cfs-hydroxyl is present, as is the case with pseudotropine. Here again the boat form must be present in the transition state to account for that marked stereospecificity JV-aroyltropanium chloride with an axial hydroxyl can be converted to the ester only by an intermolecular mechanism, consequently at a much lower rate. 

The photoisomerisation kinetics and other properties of the 1 1 inclusion complexes formed between aromatic derivatives of norbomadiene and P-cyclo-dextrin have been measured." (S)- or (R)-2-Chloropropiophenone affords partially racemised (S)- or (R)-2-phenylpropionic acid respectively by a photo-induced rearrangement via what is probably an ion or radieal intermediate," and (Z)-N-substituted benzoyl-a-dehydrophenylalanines such as (7) are photo-isomerised to 1-azetidine derivatives (8) by a 1,3-acyl migration. Irradiation of 9,9 -bifluorene-9,9 -diol (9) gives a mixture of fluoren-9-one and spiro[9H-fluorene-9,9 (10 -H)-phenanthren]-10 -one (10) whose composition is solvent dependent with the more polar solvents favouring (10). Laser flash photolysis shows the presence of two transients, one of which can be identified with the 9-fluorenyl cation (11), and which originates from photoheterolysis of the diol (9). There is also evidence to support the view that unimolecular rearrange-... 

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