SHERADSKY Rearrangement

The following is an example of the Sheradsky Rearrangement. It is an oxygenated analog of the Benzidine Rearrangement. 

Laronze, J.Y., Boukili, R.E., Cartier, D., Laronze, J, and Levy, J. (1989) The Sheradsky rearrangement of a,a-disubstituted cyclopentenone aryloximes a synthesis of the sesquiterpenes ( )-aplysin and ( )-filiformin. Tetrahedron Lett., 30, 2229-2232,... 

The [3,3]-sigmatropic rearrangement of O-aryl oximes was first described by Sheradsky and it has been used as an adequate route to benzofuran ring, a structural unit largely present in natural products. 

Sheradsky has found that the hydroxyl function of a ketoxime such as acetophenone oxime can be made to react with DMAD when the reaction is carried out in methanol with a basic catalyst, to give mixture of the fumarate and maleate isomers (164) in the ratio 2 1. This mixture on heating undergoes a hetero-Cope rearrangement followed by cyclization and dehydration to give dimethyl 5-phenylpyrrole-2,3-dicarboxylate (168) (Scheme 25). Similarly, Heindel and Chun have reported that vinyl ether adducts (171), obtained by the condensation of arylamide oximes with DMAD, get thermally converted into oxa-diazolines (172) or imidazolinones (174), depending on the reaction conditions. A similar reaction occurs with aromatic amidoxime-methyl propiolate adducts to give imidazoles (170) (Scheme 26). 1,2,4-Dioxazoles have been reported to be formed in the reaction of hydrox-amic acids with DMAD. - ... 

Thermal hetero Cope [3,3] - rearrangement of O-arylated oximes (Sheradsky) or acid catalyzed anionic hetero [3,3] and [3,5] - rearrangement of hydroxylamines with N-O bond cleavage.(see 1st edition). 

Sheradsky and Moshenberg attempted the preparation of (88) by electrocychc ring opening of the dione (89). Irradiation of (89) did indeed give the triazonine (M), but this was too reactive to be isolated. When the irradiation was conducted in dichloromethane solution, (88) rearranged to (90), but in methanol, transannular addition of the solvent to (88) occurred, leading ultimately to a mixture of (91) and (92) (Scheme 2) <84JOC587>. 

Sheradsky, T. 1970. The rearrangement of O-vinyloximes. A new synthesis of substituted pyrroles. Tetrahedron Lett 11 (l) 25-26. 

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