Rearrangement acyloxy

Benzodiazepinone A-oxides 23 are converted into rearranged 3-(acyloxy)-l H-, 4-benzodiaze-pin-2(3//)-ones 24 by treatment with acid chlorides or anhydrides.236... 

The aryl radical thus formed attacks the substrate to give the intermediate 1 (p. 898), from which the radical 26 abstracts hydrogen to give the product. N-Nitroso amides probably rearrange to N-acyloxy compounds, which cleave to give aryl radicals ... 

Sulfonate esters and halides can also migrate in this reaction. a-Halo and a-acyloxy epoxides undergo ready rearrangement to a-halo and a-acyloxy ketones,... 

The question of rearrangement in acyloxy radicals is still unsettled. In the case of the decomposition of -methoxy- -nitrobenzoyl peroxide rearrangement is observed, but the other circumstances indicate a polar mechanism for the reaction.118... 

Since ditriptoyl peroxide is electrically symmetrical, and since benzene is not outstanding in its ability to solvate polar transition states, it seems probable that the inversion reaction in this case is due to the rearrangement of an acyloxy radical rather than cation. It may be that failure to isolate comparable products from other peroxides under free radical conditions is due to competition from very fast substitution... 

The role of steric effects is unclear but the anomeric effect could also contribute to an increase in electron density at nitrogen. X-ray data for the two TV-acyloxy-TV-alkoxyamides, a urea and a carbamate outlined above show clear evidence, both from bond lengths and conformations, of an anomeric interaction RO-N bonds are short when compared to alkoxyamines. This interaction is responsible for SN1, SN2, homolytic and rearrangement reactions of /V-acyloxy-TV-alkoxyamides (vide infra) and has also been supported computationally. Acyloxylation of the hydroxamic esters results in both pyramidalisation as well as anomeric donation from the... 

In parallel with the development of the heterolysis of b-substituted alkyl radicals, a rearrangement reaction was observed and extensively studied in organic solvents. This rearrangement was first noted for b-(acyloxy)alkyl radicals (Scheme 5) by Surzur et al. [48] and, later, for b-(phosphatoxy)alkyl radicals by the Crich and Giese groups [49,50]. 

The mechanisms of the (>-(acyloxy) alkyl, and later the (3-(phosphaloxy)alkyl rearrangements have been the subject of considerable effort by computational... 

The rearrangements of b-(acyloxy), (i-(phosphatoxy)alkyl, and related systems have been reviewed [51,52] and representative kinetic data are given in Table 2 above. As revealed by isotopic labeling experiments, the acyloxy... 

Ion pair collapse in the acyloxy migration is so rapid as to preclude nucleophilic trapping of the contact ion pair even by intramolecular nucleophiles, which essentially precludes the use of acetates as leaving groups in tandem rearrangement reactions of the types discussed below [111, 127]. 

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

An elegant ring expansion methodology has been developed by Paquette [699] (Figure 3.41). This synthetic sequence is based on the double methylenation of an a-(acyloxy)aldehyde to give an allyl vinyl ether, which undergoes (reductive) Claisen rearrangement when treated with trialkylalanes. 

The fate of A-alkoxy-Af-aminoamides from Af-methylaniline and Af-acyloxy-Af-alkoxy-amides has been modelled at semiempirical, ab initio and density functional levels of theory " . B3LYP/6-31G calculations predicted the HERON rearrangement of the model intermediate 214 to methyl formate (173) and l,l-dunethyldiazene (220) to be exothermic by 5.5 kcalmoG and have an activation energy of 21.4 kcalmoG in the gas phase (Scheme 32). 

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