Aryl rearrangements

H,3H- Pyrrolo[l, 2-c]oxazole-l, 3-dione, 5,6,7,8-tetrahydro-IR spectra, 6, 978 [2.2](2,5)Pyrrolophane, N-aryl-rearrangements, 4, 209 Pyrrolophanes natural products, 7, 764 synthesis, 7, 771 Pyrrolophanes, N-aryl-synthesis, 7, 774 (2,4)Pyrrolophanes synthesis, 7, 771 Pyrrolo[3,4-c]pyran-4-ones synthesis, 4, 288 Pyrrolopyrans synthesis, 4, 525, 526 Pyrrolopyrazines synthesis, 4, 526 Pyrrolo[l, 2-a]pyrazines synthesis, 4, 516 Pyrrolo[2,3-6]pyrazines Mannich reaction, 4, 504 Vilsmeier reaction, 4, 505 Pyrrolo[3,4-c]pyrazole, 1,3a,6,6a-tetrahydro-structure, 6, 976 synthesis, 6, 1019 Pyrrolopyrazoles synthesis, 5, 164 Pyrrolo[l,2-6]pyrazoles synthesis, 6, 1002, 1006 Pyrrolo[3,4-c]pyrazoles reactions, 6, 1034 synthesis, 6, 989, 1043 Pyrrolo[3,4-c]pyrazolones synthesis, 6, 989 Pyrfolopyridazines synthesis, 4, 517 Pyrrolo[l, 2-6]pyridazines synthesis, 4, 297 6/7-Pyrrolo[2,3-d]pyridazines synthesis, 4, 291 2/f-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291 6/7-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291... 

Table 5.21. Extent of Aryl Rearrangement in 2-PhenyIetiiy1 Tosylate Solvolysis"...

A C N 1,2-aryl rearrangement was observed when alkyl azides were treated with n-Bu3SnH, proceeding via an C—N —SnBu3 species to give an imine. ... 

The thermodynamic stabilities of phenonium ions have been determined based on bromide-transfer equilibria in the gas phase and, depending on the substituents, the bridged species (1) has been proposed as an intermediate or transition state on the potential-energy surface for the 1,2-aryl rearrangement of triarylvinyl cations (see Scheme 1). Phenonium ion (3) has been presented as an intermediate to account for the fact that lactonization of methyl 4-aryl-5-tosyloxy hexanoate (2) produces y-lactone (4) selectively under thermodynamic conditions, but affords 5-lactone (5) preferentially under kinetic conditions. It has been shown that anodic oxidation of frany-stilbene in alcohols in the presence of KF or BU4NBF4 is accompanied by its electro-oxidative rearrangement into diphenylacetaldehyde acetals. The mechanism outlined in Scheme 2 has been proposed" for the transformation. 

In suitable vinylic halides, nucleophilic photosubstitution occurs intramolecular- 295-297,324,330-332 por jnstance irradiation of 113 in methanol only yields benzofuran 114, and no vinyl ether product or 1,2-aryl rearrangement products are formed (equation 84a)296. Apparently, the reaction with an internal nucleophile is faster than the 1,2-aryl shift and also faster than the reaction with an external nucleophile. With the less stabilized vinyl cations derived from the a-methyl- and a-H-analogues of 113-OMe, 1,2-aryl shifts do... 

C. Villiers and M. Ephritikhine, J. Chem. Soc., Dalton Trans. 1994, 3397 (mechanism and aryl rearrangements). 

Further examples of the four-centre scheme may be seen in the mass-spectral fragmentations (86)-(88) in which aryl rearrangement is prominent. 

A conceivable multistep mechanism of /3-aryl-assisted solvolysis is one involving a pre-equilibrium ionization to the initially formed non-conjugative cation (referred to as the o" step) followed by a rate-determining aryl-rearrangement step (referred to as the a"" step) as shown in (13). By the use of equation (12), the pi and p2 values are unambiguously assigned for both steps irrespective of any assumption regarding the nature of the steps. 

There is a report on the synthesis of ( )-mesembrine (387) by a reaction involving aryl rearrangement and Robinson annulation through an enamine (191) (Scheme 46). Reaction of 3-bromo-N-methoxycarbonyl-... 

Other aspects of nucleophilicity toward vinyl cations are the site of capture of ambident ions and the easy intramolecular cyclization by o-methoxy and o-thiomethyl substituents on a P ring. The extensively studied P-aryl rearrangement across the double bond could be regarded as intramolecular substitution by the aryl ring, and data are available on the relative rate of rearrangement and capture by the solvent (69, 70). These topics are not discussed here for lack of space but should be addressed in a more complete discussion of the nucleophilicity. 

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