Carbonyl- and Carboxyl-Substituted Enediynes: Synthesis, Computations, and Thermal Reactivity
摘要:
The influence of electron-withdrawing groups (carbonyl and carboxyl) at the alkyne termini on the reactivity of enediynes was investigated by a combination of experimental and computational techniques. While the general chemical reactivity of such enediynes, especially if non-benzannelated, is increased markedly, the thermal cyclization, giving rise to Bergman cyclization products, is changed little relative to the parent enediyne system. This is evident from kinetic measurements and from density functional theory (DFT, BLYP/6-31G* + thermal corrections) computations of the experimental systems which show that the Bergman cyclization barriers slightly (3-4 kcal/mol) increase, in contrast to earlier theoretical predictions. The effect on the endothermicities is large (Delta DeltaH(r) = 7-12 kcal/mol). Hence, the increased reactivity of the substituted enediynes is entirely due to nucleophiles or radicals present in solution. This was demonstrated by quantitative experiments with diethylamine and tetramethyl piperidyl oxide (TEMPO) which both give fulvenes through 5-exo-dig cyclizations.
Cu-Catalyzed oxidative 1 : 2 couplings of arynes with nucleophilic terminalalkynesunderaerobicconditions are described herein. A mechanistic investigation revealed a plausible involvement of an aryl-Cu(III)-generating pathway. By this method, ubiquitous arenediynes can be efficiently assembled in a single step under mild conditions.
Hypervalent Iodine(III) Compounds as Biaxial Halogen Bond Donors
作者:Flemming Heinen、Elric Engelage、Christopher J. Cramer、Stefan M. Huber
DOI:10.1021/jacs.9b13309
日期:2020.5.13
“Hypervalent” iodine(III) derivatives have been established as powerful reagents in organic transformations, but so far only a handful of studies have addressed their potential use as halogen-bonding noncovalent Lewis acids. In contrast to “classical” halogen-bond donors based on iodine(I) compounds, iodine(III) salts feature two directional electrophilic axes perpendicular to each other. Herein we