N-Aryl migration

The key step in the process is the thermal rearrangement of (2) to a 3-aryl-2-phenyl-4(3H)-quinazolinone (3). This 1,3-0 to N aryl migration was first observed by Tschitschi-babin and Jeletzky. This rearrangement proceeds at useful rates in the temperature range 275-325° it can be carried out neat, but the reaction is generally cleaner when run in heavy mineral oil. The final step consists of hydrolysis to the aniline and 2-phcnyl-4H-3,l-benzoxazine-4-one (4). This reaction can be carried out by alkaline... 

CHAPMAN Rearrangement O to N aryl migration in O-aryliminoethers (see 1st edition). 

Aminovinyl)tetrazoles from P-chloro-a,P-ethyleneazomethinium salts via C- N-aryl migration... 

Phenols can be successfully converted into ar. amines via O N-aryl migration in quinazoline derivatives... 

When we allowed pentafluorophenyl-lithium to decompose in ether in the presence of an excess of N, ZV-dimethy laniline we obtained the compounds (92) 70, X = F), (94), the latter as the major compound, and a product which was shown to be (97). That this latter compound did not arise by metallation of 2V,lV-dimethylaniline followed by addition to tetrafluorobenzyne was shown by quenching the reaction mixture with deuterium oxide. No deuterium incorporation was detected. The compound (97) provides a rare example of a product derived by a Stevens rearrangement in which aryl migration has occurred b>. 

The influence of steric effects on the rates of oxidative addition to Rh(I) and migratory CO insertion on Rh(III) was probed in a study of the reactivity of a series of [Rh(CO)(a-diimine)I] complexes with Mel (Scheme 9) [46]. For a-diimine ligands of low steric bulk (e.g. bpy, L1, L4, L5) fast oxidative addition of Mel was observed (103-104 times faster than [Rh(CO)2l2] ) and stable Rh(III) methyl complexes resulted. For more bulky a-diimine ligands (e.g. L2, L3, L6) containing ortho-alkyl groups on the N-aryl substituents, oxidative addition is inhibited but methyl migration is promoted, leading to Rh(III) acetyl products. The results obtained from this model system demonstrate that steric effects can be used to tune the relative rates of two key steps in the carbonylation cycle. 

From a study of his and van Alphen s results, Huttel identified three classes of rearrangement (Scheme 40).137 Type A involved migration of a group from C-3 to unsubstituted C-4 (e.g., 114 - 11564), Type B an acyl migration from C-4 or C-5 to N (e.g., 116 -> 11764or 118 - 117137), and Type C an aryl migration from C-3 to N (e.g., 118 - 119137) the latter two modes were observed when all carbon atoms were fully substituted. 

Reported a-elimination studies of vinyliodonium salts are limited to the substrates shown in Table 10. While aryl migrations might be expected, a-elimination reactions of (/2-arylvinyl)iodonium salts have not been described. Thus far, migrations of /2-hydrogen atoms (equations 230,233 and 234)128, /2-halogen atoms (Cl, Br)104, /2-ArS(0) groups (n = 0,1,2)32 and the methyl group128 have been reported. 

The photochemical behavior of aminocyclohexenones depends on the substituents on nitrogen. Cyclization of iV-arylketoenamines to 2-carbazolones is achieved photochemic-ally332 (equation 251). However JV-benzyl-jV-tosyl-a-ketoenamines yield stereospecific-ally on irradiation a-keto azetidinones. Branched N-alkyl substituents suffer desulphona-tion and intramolecular aryl migration to give 2-amino-3-aryl-2-cyclohexenones333 (equation 252). 

Isomerization of N-allyl amide to N-propenyl amide is a key step of the deprotection of an amino group. ( )-N-Aryl-N-(l-propenyl)ethanamides 35 are obtained via the double bond migration of N-aryl-N-allylamide 34 catalyzed by a ruthenium hydride complex [19]. The configuration of the N-propenyl moiety in the product is almost E, and the high E selectivity is probably due to the steric repulsion between the aryl group and the methyl substituent of the propenyl group (Eq. 12.13). 

The thermal and photochemical Smiles rearrangement (Section III.A.4.a) is most often employed for the transformation of O-substituted phenol derivatives 226 into N-substituted anilines 227 that occurred with aryl migration from oxygen to nitrogen317 (equation 88). 

An extensive screening of structure-activity relations revealed ( 1 ) the outstanding properties of N,N -disubstituted PD. It is generally accepted that the presence of N-sec.alkyls accounts for better antiozonant protection than that of N-prim. and N-tert.alkyls or N-aryls (21). This may be one of the clues to decipher the chemical pathways of the antiozonant mechanism. The final effect is moreover fully dependent on the composition of the vulcanizate. The structure of commercially used antiozonants is an optimum compromise of efficiency, physical properties and toxicity. N, N -Disec.alkyl-1-4-PD are used in the U.S.A., N-sec.alkyl-N -aryl-l,4-PD are preferred in Europe. N,N -Diaryl derivaties are not applied as antiozonants in NR, BR, IR, or SBR. One of the reasons may be their low solubility in rubber vulcanizates (22). It does not allow them to reach a concentration level in the rubber bulk which is able to act as a long-term operative store of a stabilizer ready to supply the rubber surface slowly but continuously with active compounds by migration and to maintain the protective effect without inefficient quick blooming of an incompatible PD. A chemical reason accounting for the minority antiozonant role of N,N -diaryl PD is discussed later. 

Rearrangement by nucleophilic aromatic substitution and aryl migration from one hetero atom to another (O to N or S to O) (see 1st edition). 

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