Cope cyclization, reverse

Nucleophilic addition of primary o.-R -allylamine to nitrone followed by a reverse Cope cyclization and Meisenheimer rearrangement gives the oxadiazi-nanes (426a-h) (Scheme 2.198). These reactions have found use for the preparation of oxadiazines, vicinal aminohydroxylamines, and diamines the latter are of particular interest as chiral ligands (683, 684). 

Allylthiols376 and unsaturated lithio sulfones377 have been found to react as nucleophiles with nitrones to yield intermediate hydroxylamines which undergo reverse-Cope cyclization to provide 1,3-thiazolidine N-oxides and pyrrolidine A-oxides, respectively. In the case of derivatives of C-phenyl nitrone (321 R2 = Ph), thermolysis was found to result in smooth Meisenheimer rearrangement leading to 1,5,2-oxathiazinane (322) (see Scheme 76). 

Cooper, N. J., Knight, D. W. The reverse Cope cyclization a classical reaction goes backwards. Tetrahedron 2004, 60, 243-269. 

Formation of pyrrolidines and related compounds via reverse Cope cyclization 04T243. 

Dioxolanone 33 is obtained when the unsaturated silyldiazoester 30 is decomposed by Rh2(pfb)4 in the presence of an aldehyde or of acetone (Scheme 11) [21]. The reaction sequence is likely to include formation and (probably reversible) 1,5-cyclization of carbonyl ylide 31, and Cope rearrangement of the allylvinylether 32. In analogy to carbonyl ylide 21, the SiMe3 should occupy the exo-position in 31, thereby bringing the ester carbonyl in a geometry that is favorable to the cyclization step. Again, the choice of catalyst determines the product pattern, since CuOTf catalysis affords not only 33, but also oxirane 22 and the intramolecular cyclopropanation product 34. 

Ent, H., De Koning, H., Speckamp, W. N. N-Acyliminium cyclizations via reversible 2-aza-Cope rearrangements. Tetrahedron Lett. 1985,... 

Gallagher, B. M., Pearson, W. H. Thermal cyclization of N-hydroxylamines with alkenes the reverse Cope elimination. Chemtracts Org. Chem. 1996, 9, 126-130. 

To minimize the undesirable reversibility of the 2-oxonia Cope rearrangement and preserve the optical purity of the cyclization products, many modified reaction... 

Mixed acetals (6), bearing allyl and silyl enolate moieties, are efficiently cyclized to tetrahydropyranones (7) in the presence of (la) and DTBMP [52]. A plausible mechanism is as follows (i) the treatment of (6) with (la) forms oxocarbenium ion (8), (ii) (8) is reversibly converted into another oxocarbenium ion (9) by the 2-oxonia Cope rearrangement, and (iii) intramolecular addition of the silyl enolate moiety to the carbenium ion center in (9) gives (7). The moderate stereoselectivity concerning the substituent R is attributable to competing cyclizations from chair and boat conformations in the last step (Scheme 9.11). 

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