Sigmatropic rearrangements of ‘onium’ ylids

Abstract

Rearrangement reactions occupy a special place within the canon of organic synthesis, by virtue of the inherently high efficiency of chemical processes which form and break bonds by redistribution of electrons around a retained atomic framework. Within the broader class, sigmatropic rearrangements are chemical processes defined by mechanisms involving unimolecular migration of sigma-bonds with concomitant redistribution of one or more pi-bonds. Sigmatropic processes may involve uncharged or charged species, with the charges located on carbon or heteroatoms; the latter reaction type is the subject of this tutorial review.

Toward a Symphony of Reactivity: Cascades Involving Catalysis and Sigmatropic Rearrangements

“…[125] These methods have provided a much milder alternative to stoichiometric base-promoted methodologies. Competing carbenoid reactions (e.g.…”

Intramolecular carbenoid ylide forming reactions of 2-diazo-3-keto-4-phthalimidocarboxylic esters derived from methionine and cysteine

“…In this case, the simultaneous formation of five-ring sulfonium ylide 12c and six-ring carbonyl ylide 14c is immediately followed by intramolecular pericyclic reactions with participation of the allylic π-system. Sulfonium ylide 12c rearranges by the expected [2,3]-sigmatropic rearrangement [3,10,16] to form tetrahydrothiophene 16 (31% yield, two diastereomers), and carbonyl ylide 14c is trapped by an intramolecular [3 + 2]-cycloaddition to give the pentacyclic compound 17 (35% yield). The regioselectivity of the latter reaction was established by NMR studies: after assignment of proton resonances from HMBC spectra, a NOESY NMR experiment indicated the correlation shown in Scheme 6.…”

Synthesis and X-ray Structural Studies of a Substituted 2,3,4,5-Tetrahydro-1H-3-benzazonine and a 1,2,3,5-Tetrahydro-4,3-benzoxazonine

“…In both the Stevens and Meisenheimer [2,3] rearrangements, the cis isomer of the respective intermediate N-ylide 4 or N-oxide 5 is involved, as a favourable concerted transition state geometry [19,21] can be accessed to give the nine-membered ring products. On the other hand, with the corresponding trans-isomeric ylide or N-oxide, this is not the case, and the diradical mediated [1,2] rearrangements to give seven-membered ring products can then proceed.…”

“…Synthetic approaches to these systems often involve rearrangement strategies incorporating a ring expansion [8][9][10][11], although ring formation [12][13][14] and ring cleavage approaches [5,15,16] can also be used. The Meisenheimer [1,2] and [2,3] sigmatropic rearrangements of amine N-oxides [17][18][19] and the analogous Stevens [2,3] sigmatropic rearrangements of ylides [20,21] afford good opportunities for medium ring synthesis. To further explore these synthetic prospects and to assess substituent effects (e.g., a phenyl group vs. a methyl group or hydrogen [17]) on configurational and conformational issues in the products, we have investigated the synthetic utility of the [2,3] versions of these rearrangements from the same starting amine precursor, the 1-(1-phenylethenyl) substituted tetrahydroisoquinoline derivative 3.…”