Chemistry of the sulfur-nitrogen bond. X. Barriers to planar inversion in N-(4,4'-dimethylbenzophenylidene)arenesulfenamides and -selenenamides

Stereodefined acyclic trisubstituted metal enolates towards the asymmetric formation of quaternary carbon stereocentres

“…65,76 The absolute configuration of the Mannich adducts was determined by X-ray crystallographic analysis and was consistent with a Zimmerman-Traxler transition state 79 with approach of the electrophilic imine from the stereoface opposite of the benzyl group of oxazolidinone. However, in this case the barrier of planar E to Z inversion of N-sulphonyl imines is low, 81 and steric factors most probably account for the favorable formation of the Z-isomer (the E-isomer of N-sulphonyl imine would generate 1,4-diaxial steric interactions with the chiral unit) in the sixmembered transition state (Scheme 28).…”

N-derivatives of formaldimines: the reason for the high nitrogen inversion barriers in N-methyl- and N-chloroimines

“…The values of ∆∑Е5 correlate completely with the values of ∆Еі ≠ of the imines II-IV and V-VII (Table 3, Eqns. 20,21). In this case, the increase in electronegativity of the X atom in subgroup A contributes to the increase in the inversion barriers as a result of decreasing stabilization of the inversion TS, while in subgroup B it decreases the values of ∆Еі ≠ due to the increasing stabilization of the TS.…”

“…18,19) and even more of the imines I-IV and V-VIII (Table 3, Eqns. 20,21). This indicates a minor participation of these interactions in increasing the inversion barriers of N-methyl-(I) and Nchloroformaldimines (VIII) and reducing the energies ∑∆∑Е1-5(i) for them.…”

“…For example, it was pointed out that these interactions underlie the low inversion barriers of the sulfenyl-, sulfinyl-, and sulfonylimines. [20][21][22][23] The analysis of the interactions between the nitrogen LP and the Rydberg orbitals of the atoms of C=N-X group ( Table 2, Group 3) shows that with an increase in electronegativity of X atoms in subgroup A, they contribute to a slight increase in the inversion barriers and their slight decrease in subgroup B (Table 3, Eqns. 14,15).…”

1,1,1-Trifluoropropan-2-ammonium triflate enantiomers: stereoselective synthesis and direct use in reaction with epoxides

“…N-sulfinylimines are known to undergo rapid E/Z isomerization (but with a high enough isomerization barrier as to be able to observe the individual isomers by NMR at rt), 24,25 and was reported for a number of other N-sulfinylimine reactions. [26][27][28][29][30][31][32] This was typically explained by invoking chelation, or through prior coordination with a Lewis acid before reaction.…”