Facile Ketene−Ketene and Ketene−Ketenimine Rearrangements:  A Study of the 1,3-Migration of α-Substituents Interconverting α-Imidoylketenes and α-Oxoketenimines, a Pseudopericyclic Reaction

Abstract

Theoretical calculations (B3LYP/6-311+G(3df,2p)//B3LYP/6-31G) of the 1,3 migration of NR(2) transforming alpha-oxoketenimines 1 to alpha-imidoylketenes 3 and vice versa indicate that this process is a pseudo-pericyclic reaction with a low activation energy (NH(2) 97 kJ mol(-1), N(CH3)(2) 62 kJ mol(-1)). The oxoketenimines were found to be more stable (by 18-35 kJ mol(-1)) which is in line with experimental observations. The hindered amine rotation in the amide and amidine moieties adjacent to the cumulenes are important in the migration of the NR(2) group, as one of the rotation transition states is close to the 1,3 migration pathway. This gives an interesting potential energy surface with a valley-ridge inflection (VRI) between the orthogonal hindered amine rotation and 1,3 migration transition states. The imidoylketene may also undergo ring closure to an azetinone 5; however, this is metastable, and under the conditions that allow the 1,3-migration, the oxoketenimine 1 will be favored. The imine NH E/Z-interconversion of the ketenimine group takes place by inversion and has a low activation barrier ( approximately 40 kJ mol(-1)). In all the amidines examined the E/Z-interconversion of the imine function was predicted to be by rotation with a high barrier (>80 kJ mol(-1)), in contrast to all other reported imine E/Z-interconversions which are by inversion.

Late‐Stage Direct o‐Alkenylation of Phenols by PdII‐Catalyzed C−H Functionalization

“…[19] Based on the above results and the previously reported ones, [20] we proposed the action mechanism driving the catalytic process, as shown in Scheme5.F irstly,i nt he presence of acetate, phenol coordinated with the palladium catalystt o form intermediate A. Then, 1,3-migrationo fp alladium via B generatedt he CÀHb ond metalatedi ntermediate C. [21] The insertion of alkene, followed by the b-H elimination, released the alkenylated product and the [Pd(acac)] species, which was oxidized to the Pd II speciest oc omplete the catalytic cycle. Eventually,t he intramolecular esterification generated the final product.…”

Silver‐Catalyzed Chemoselective [4+2] Annulation of Two Isocyanides: A General Route to Pyridone‐Fused Carbo‐ and Heterocycles

“…(1)]. [27] To test the possibility that our [4+ +2] annulation involved an amidoketenimine intermediate,w ea ttempted to generate an a-amidoketenimine from a-naphthyl isocyanate 10 and the salt 11 with the same substituents as isocyanides 1z and 2a [Scheme 5, Eq. [27] To test the possibility that our [4+ +2] annulation involved an amidoketenimine intermediate,w ea ttempted to generate an a-amidoketenimine from a-naphthyl isocyanate 10 and the salt 11 with the same substituents as isocyanides 1z and 2a [Scheme 5, Eq.…”

“…[26,27] Finally,the imidoylketene VI undergoes efficient 6 p electrocyclization and a1 ,3-proton shift to give aq uinolone 3. [26,27] Generally,t he coupling of carbenes with isocyanides produces ketenimines; [18] thus,isocyanides 2 can be viewed as stable a-amidocarbene precursors in this reaction.…”

Transition states for hydride-water (H–)(H2O)n clusters, n=2–6, 20

“…If the same result were found using IRC it would mean this is an example, or is very close to being an example, of an uncommon phenomenon called a valley-ridge inflection (VRI). A VRI is a PES feature where, after crossing a t-state, the intrinsic reaction pathway descends to a t-state between two other minima [48]. Fig.…”