3.20 Nitrogen- and Sulfur-Based Stevens and Related Rearrangements

Regiodivergent synthesis of pyrazino-indolines vs. triazocines via α-imino carbenes addition to imidazolidines

“…It is worth to mention that the process described from B to D′ corresponds to a formal [1,2]-Stevens rearrangement. 19 Finally, to proceed towards the formation of hexahydropyrazino[1,2- a ]indole 3 , intermediate D evolves through a Friedel–Crafts cyclization with the assistance of the Rh 2 (Piv) 4 catalyst (see details in Fig. S3 ‡ ).…”

[1,2]‐Shift in Chiral Ni(II) Schiff‐Base Derivatives: Conversion of α‐ Thiobenzylated Amino Acid into the Cysteine Derivative

“…After the S-alkylation of the starting complex and its deprotonation, the anionic [1,2]-sigmatropic shift occurs. The concerted four-electron process is forbidden under thermal activation [36] and the reaction, more likely, occurs as a stepwise process, via the Cα-S bond homolysis followed by recombination of thus formed species in the solvent cage, similarly to the other known examples of the anionic [1,2]-shifts (see [17] and references cited therein). The radical stepwise mechanism is the possible reason for low stereoselectivity of the observed rearrangement.…”

“…[14,15] Sulfur ylides are easily available carbanions which can be involved in various reactions with many electrophiles, as well as undergo skeletal rearrangements yielding the formation of new carbon-carbon bonds in a variety of fashions. [16] Rearrange-ments of sulfur ylides have attached much attention from synthetic and mechanistic view point (see, e. g., [17,18] and refs cited therein); however, to the best of our knowledge, sigmatropic shifts in ylides occurring in the metal coordination environment have not been reported yet.…”

Biocatalytic One-Carbon Ring Expansion of Aziridines to Azetidines via a Highly Enantioselective [1,2]-Stevens Rearrangement

“…12 However, we are unaware of any examples of a one-carbon ring expansion of aziridines through a [1,2]-Stevens rearrangement strategy. Secondly, the diradical mechanism of the [1,2]-Stevens rearrangement 13 has made it a challenging reaction class for asymmetric catalysis: few asymmetric variations have been reported. 14 Enantiopure quaternary ammonium salts can undergo [1,2]-Stevens rearrangements with N-to-C chirality transfer; 15 however, escape of the radical pair from the solvent cage is often competitive with radical recombination, 16 and erosion of enantiopurity is often observed.…”