Photolysis of 3-chlorodiazirine in the presence of alkenes. Kinetic evidence for intervention of a carbene-alkene intermediate in addition of chlorocarbene to alkene

Abstract

During the course of the studies on the competition between intramolecular 1,2-H shift and intermolecular addition of benzylchlorocarbene to alkene, we obtained chemical evidence for

Distortion/interaction analysis of the reactivities and selectivities of halo– and methoxy–substituted carbenes with alkenes

“…We found that favorable interaction energy contributes to negative ∆E at intermediate separation of the carbenes and alkenes studied here and suggests the formation of carbene-alkene precursor complexes, although the existence of these has been debated in the literature. [20][21][22][23][24][25][26][27][28][29] We have confirmed π-complexes for cycloadditions to 2a, 2b, and 2d that are stabilized by 0-5 kcal mol…”

Carbene Complexes of Nonmetals

“…If 56 was the only intermediate, the ratio 59/ 58 would increase linearly with the concentration of alkene. However, curved plots were obtained on photolysis of 54, [80] as shown for 54a Ϫ TME in Figure 1. The curvature Scheme 13.…”

“…Liu and Bonneau assigned this role to CAC 57, [80][81] while rearrangement in the excited state (RIES) of the diazirine (1,2-H shift in concert with extrusion of nitrogen) was advocated by Goodman, [82] Platz, [83] and Moss.…”

Modulation of Carbenic Reactivity by π-Complexation to Aromatics

“…Even more difficult, because the interaction energies should be smaller, is the modulation of carbenic reactivity by intermediate carbene−π electron complexation. Liu and Bonneau maintain that the transient formation of carbene−alkene π-complexes is integral to the competition between intramolecular rearrangement (Re) and intermolecular addition (Ad) when alkylhalocarbenes are generated in the presence of alkenes. , However, Houk's calculations suggest that additions of chlorocarbenes to ethylene or tetramethylethylene (TME) proceed to cyclopropanes without transiting bound carbene−alkene complexes. 7a-c Alternatively, broad shallow wells for complexes might occur in the reaction enthalpy profile, but would not constitute minima on the free energy surface 7d. Additionally, Platz and Goodman offer alternative explanations, based on the intervention of excited state carbene precursors, for the kinetic anomalies that originally triggered the suggestion of carbene−alkene complex participation. , …”