Walk rearrangement

Dimethyl-5-phenyl-l,4-oxazepine isomerizes to 6,7-dimethyl-4-phenyl-l,3-oxazepine in boiling benzene.30 The process involves successive valence isomerization, a walk rearrangement and a second valence isomerization. 

The Diels-Alder reaction of cyclopropenes with 1,2,4,5-tetrazines (see Vol.E9c, p 904), a reaction with inverse electron demand, gives isolable 3,4-diazanorcaradienes 1, which are converted into 4H-1,2-diazepines 2 on heating. The transformation involves a symmetry allowed [1,5] sigmatropic shift of one of the bonds of the three-membered ring, a so-called walk rearrangement , followed by valence isomerization.106,107... 

A mixture of ethyl 3,5-dimethyl-l/f-thieno[2,3-c]-1,2-diazepine-l-carboxylate (6) (10-15%) and the isomeric ethyl 2,5-dimethyl-3//-thieno[2,3-t/]-l, 3-diazepine-3-carboxylate (8) (50-60%) is obtained when a solution of the thienopyridine A-iminc 4 in benzene is irradiated with a 400-W high-pressure mercury lamp for 2-3 hours at 20rC. It has been suggested that product 6 is formed from the intermediate 5. The isomeric intermediate 7 undergoes two consecutive walk rearrangements, followed by valence tautomerization, to give the major product 8.168... 

Irradiation of a benzene solution of 7-benzyl-2,5-diphenyl-3,4,7-triazanorcara-2,4-diene (15) with a high-pressure mercury lamp (Pyrex filter) results in a photochemical walk rearrangement to give 4-benzyl-3,7-diphenyl-477-l, 2,4-triazepine (16) in 53 % yield, accompanied by A-benzyl-3,6-diphenylpyridazin-4-amine (6%), 1-benzyl-2,3-diphenylpyrrole (1%) and... 

The principal products of irradiation of 2-cyano-l-methylpyrrole (166) in methanol, however, are the corresponding 3-cyanopyrrole 167 and the methanol adduct 168.129 These products appear to arise by a 2,5-bonding process followed by a thermal walk rearrangement as shown in Scheme 5. 

SCHEME 10. Bicycle and pivot alternatives for a walk rearrangement... 

Formation of 648 from 647 was experimentally discarded. Since the most basic site of 646 is the carbonyl group, both Bronsted and Lewis acids should first coordinate to this position. In the case of Bronsted acid, protonation could occur at the electron-rich 9-position, and this was followed by deprotonation at the 1 la-position, which is promoted by the carbonyl protonation. In contrast, the Lewis acid cannot add to the 9-position and thus the skeletal rearrangement to give 648 took place. This kind of rearrangement through norcaradiene tautomers, shown in Scheme 128, is called walk rearrangement in thermal reaction of cycloheptatrienes <2002CL260>. 

Thus it may be that 14 actually results from a walk rearrangement (vide infra) with a very low activation energy, due to the alkoxycarbonyl group. 

Table 9. Configuration at the Migrating Carbon of [n. 1.0] Bicycles of Formula 1 in Thermally or Photo-chemically Induced Walk Rearrangements...

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