Quinamine rearrangement

Quinamines having no substituents at the para-position of the aniline ring gave 4-aminodiphenyl ethers 77 as the principal products in almost quantitative yields. The behavior of quinamines 76 and their geometric features as well as the kinetic characteristics of the reaction make this transformation very similar to the well-known benzidine rearrangement (Section III.B.l). Like the latter, the mechanism of the quinamine rearrangement involves a transition state that resembles a sandwich of two rings (jr-complex)129. 

In synthetic work towards tetracyclines the tricyclic dienone (99) was rearranged at 0 °C using boron trifluoride, to the anthraquinone (100 65%) apparently by a direct 1,5-shift. The quinamine (101) undergoes facile reorganization in hydrochloric acid to the biaryl (102) jn an aza-Claisen-like process. 

The last example in this section is the facile and quantitative learrangement of the quinamine (168) in lO M hydrochloric acid, to the aminoary 1 ether (169), with extracyclic shift of aryl to oxygen. A number of examples are known and the mechanism appears similar to the benzidine rearrangement. 

An interesting reaction that represents a half-way point between the quinamine and benzidine rearrangements can be also mentioned here129, namely the conversion of A-acetyl-0,A-diphenylhydroxylamine 78 into biphenyls 79 and 80 (equation 32) (see Section IILA.4.C about rearrangements of A-acylanilines and Section m.C.l concerning rearrangements of hydroxylamines). 

The arenesulfenanilide rearrangement is another member of an important class of rearrangements described above, such as the benzidine, quinamine and nitramine rearrangements. This rearrangement consists of the conversion of arenesulfenanilides 197 into ortho- and para-aminodiphenyl sulfides 198 and 199287.288 (equation 76). Substitution at the para-position generally predominates over ortho-substitution289. 

Analogously, photochemically induced rearrangement of 4-[acetyl(methyl)amino]-2,4,6-triphenylcyclohexa-2,5-dienone (13) provided a mixture of exo- and e (/o-6-[acetyl(meth-yl)amino]-l,3,6-triphenylbicyclo[3.1.0]hex-3-en-2-ones (14) in 37% yield, which in turn may be converted thermally or photochemically into the corresponding ort/ju-quinamine 15. 

Benzidine-like rearrangements are reported on acid treatment of suitable imidazoles , pyridine and thiazole hydrazocompounds , but not ferrocene derivatives. Related, probably intramolecular, rearrangements of/>-quinamines and 0,iV-diarylhydroxylamines , (reactions 106 and 107) have been arbitrarily assigned w-bond mechanisms, whereas reactions (108) and (109) are probably inter-molecular, although the observed formation of cross-over products counts for litde . ... 

When quinamine was refluxed in dilute acetic acid for a prolonged period it afforded the ketoamine, quinamicine, which may have been the result of a direct loss of water or more likely an allylic rearrangement of the tertiary hydroxyl group in the hydroxy-methyleneindoline form then elimination (the hydroxyl cannot be lost to form the iminium ion because of the bridgehead position of the quinuclidine nitrogen). The formulation of quinamicine is the only reaction of these compounds which has any parallel in... 

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