Nucleophilic β-Oniovinylation: Concept, Mechanism, Scope, and Applications

Insertion of an electron-deficient alkyne A−C⋮C−A (A = CO2Me) into the C−L+ bond of an
acyl-onio salt R−C(O)−L+ (R = Ar, OAlk; L = 4-dimethylaminopyridine, PPh3) has for the first time been
achieved in the presence of catalytic amounts of the nucleophile L. For R = OMe, a second insertion of
the alkyne was observed. X-ray structures were obtained for a number of such β-oniovinylation products.
Depending on reaction conditions, preferentially E- or Z-stereochemistry was observed, the Z-isomer being
the thermodynamically more stable. A mechanism for this novel insertion reaction is presented which
accounts for the topology of the products and rationalizes the observed stereochemistry. The β-onio-activated
Michael systems thus generated represent a virtually unexplored class of compounds. The onio substituent
in such compounds can be selectively replaced by a number of nucleophiles. Thus a series of Michael
systems with donor functions in the β-position is easily synthesized. These compounds represent a source
for useful further transformations, for example, cyclizations to quinolones, thiochromones, and pyrazoles.

本研究首次在亲核试剂L催化量存在下，实现了缺电子炔烃A−C≡C−A（A=甲氧羰基，CO2Me）对酰基鎓盐R−C(O)−L+（R=芳基（Ar）、烷氧基（OAlk）；L=4-二甲氨基吡啶、三苯基膦（PPh3））的C−L+键插入反应。当R为甲氧基（OMe）时，可观察到该炔烃的第二次插入反应。针对多例此类β-鎓乙烯基化产物，我们成功获取了其X射线晶体结构。根据反应条件不同，产物可优先生成E型或Z型立体异构体，其中Z型异构体的热力学稳定性更优。本文提出了该新型插入反应的反应机理，该机理可合理解释产物的立体拓扑结构以及实验观测到的立体化学选择性。由此生成的β-鎓活化Michael加成体系，几乎属于尚未被充分探索的化合物类别。此类化合物中的鎓取代基可被多种亲核试剂选择性取代，借此可便捷合成一系列β位带有给电子官能团的Michael加成体系。此类化合物可作为后续有价值转化的反应底物，例如通过环化反应合成喹诺酮、硫色酮及吡唑类化合物。