C-Aryl migration

An intriguing advancement in the realm of diazonamide A chemistry has been made by the Magnus group which has observed a unique O-aiyl to C-aryl migration... 

Cheung CM, Goldberg FW, Magnus P, Ressell Cl, Turnbull R, Lynch V (2007) An expedient formal total synthesis of (-)-diazonamide A via a powerful, stereoselective 0-aryl to C-aryl migration to form the CIO quaternary cotter. J Am Chem Soc 129 12320-12327... 

Bromine/irradiation Dehydrogenation with C-aryl migration... 

The carbolithiation- N C aryl migration sequence was performed in TH F, with and without the addition of DMPU, followed by the carbamate cleavage leading to highly substituted propargyl alcohols 47. When the enyne 48 was treated with n-BuLi in toluene without the addition of DMPU, allene products were observed after the protonation step (Scheme 10.16). The addition of (—)-sparteine and carrying out the reaction at —78 °C led to the product 49 as a racemic mixture or at best with moderate enantiomeric excess. 

The value of such heteroatom-> C rearrangements has been expertly demonstrated by Clayden and coworkers when it was shown that substituted diaryhnethylamines could be prepared by a stereospecific intramolecular electrophilic arylation of hthiated ureas [17], This work was soon followed-up and developed further to produce a-arylated cyclic amines [18], a-arylated benzylic alcohols [19], an asymmetric synthesis of clemastine (Scheme 18.5) [20], a sequential double a-arylation of A -allylureas by asymmetric deprotonation and N C aryl migration [21], and a simple method for the synthesis of tertiary thiols and thioethers [22], and tertiary alcohols [23], all involving a Truce-Smiles rearrangement. 

Phosphorus oxide chloride/poly phosphoric acid Pictet-Gams isoquinoline ring closure with C-aryl migration... 

Silver hexafluoroantimonate Isoflavones from 3-bromoflavanones 2->-3-C-Aryl migration... 

Diaryloxaziridines are even less stable. With oxaziridines (66 Ar = Ph or 4-Me2NC6H4) acid amide formation at 25 °C proceeded in the course of 66 and 10 h respectively in the latter case there were equal amounts of H and aryl migration. Ethanol as solvent again accelerated the reaction, in the latter case by a factor of lO. ... 

Direct proof of an oxaziridine intermediate was achieved in photolysis experiments in an organic glass at 77 K (80JA5643). Oxaziridine (75), formed by photolysis of A/-oxide (74) and evidenced by UV spectroscopy under the above conditions, decomposed at higher temperature to form the imino ether (76) by N—O bond cleavage and C -> O migration of an aryl group. 

This rearrangement can be considered to occur via a transition state in which C(2)—C(4) bridging is accompanied by a 4 3 aryl migration ... 

Anthryl, 1-naphthyl, mesityl, and 4-quinolyl groups in 37h-k promote C/C aryl shift (see Table 2) their proclivity to migrate is far greater than expected from the electronic influence of the x-systems. This is presumably due to the intermediacy of spiro-linked benzenium betaines 30 31 , occurring in place of the carbenes otherwise encountered. The formation of phosphinic esters 42h-k is partly or completely suppressed 30). 

Diarylboron chelates C-(l-hydroxyalkyl)nitrones (238) on boiling in toluene tend to undergo 1,4-aryl migration and form heterocyclic arylboronates (239) (Scheme 2.82) (446). 

STEELE, C.L., GLJZEN, M., QUTOB, D., DIXON, R.A., Molecular characterization of the enzyme catalyzing the aryl migration reaction of isoflavonoid biosynthesis in soybean, Arch. of Biochem. and Biophys., 1999, 367, 146-150. 

The high-valent metal species required for activation of an alkyne has also been generated by the oxidative addition to an allylic or propargylic system. For example, with an allyl aryl ether as the substrate, this type of reaction achieves a cycloisomerization that occurs through an 0- to C-allyl migration (Equation (92)) 323,324 similarly, (9-propargyl derivatives lead to a mixture of allenyl and propargyl products (Equation (93)).325,326... 

D.F. (1980) Activation of coordinated carbon monoxide toward alkyl and aryl migration (CO insertion) by molecular Lewis acids and X-ray structure of the reactive intermediate Mn(C(OAlBrBr2) CH3)(CO)4. J. Am. Chem. Soc., 102, 5093-5100. 

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. 

---