Unexpected Insertion of CO₂ into the Pentacoordinate P–N Bond: Atherton–Todd-Type Reaction of Hydrospirophosphorane with Amines

The Atherton–Todd-type reaction of pentacoordinate hydrospirophosphoranes with amines was investigated, and a novel CO2 insertion reaction into the pentacoordinate P–N bond under mild conditions was developed. The mechanism and stereochemistry of the CO2 insertion reaction between hydrospirophosphoranes and secondary amines were proposed via a carbon-13 labeling experiment, a 31P NMR tracing experiment, and X-ray diffraction analysis. The chlorinated spirophosphorane intermediate was first generated with stereoretention of the configuration at phosphorus and subsequently was attacked by a carbamate anion formed from CO2 and a secondary amine. It was found that rear attack of nucleophilic substitution with stereoinversion at pentacoordinate phosphorus was the preferred route, although front attack happened for sterically hindered reactants. The configuration of the CO2 insertion product depended mainly upon the original phosphorus configuration of the hydrospirophosphoranes.本研究针对五配位氢螺磷烷（pentacoordinate hydrospirophosphoranes）与胺类的阿瑟顿-托德型反应（Atherton–Todd-type reaction）展开探究，开发出一种可在温和条件下于五配位磷-氮键中发生的新型二氧化碳（CO₂）插入反应。通过碳13标记实验、磷31核磁共振追踪实验（31P NMR tracing experiment）以及X射线衍射分析（X-ray diffraction analysis），本研究提出了氢螺磷烷与二级胺之间二氧化碳插入反应的反应机理与立体化学过程。研究发现，反应首先生成保持磷原子构型的氯化螺磷烷中间体，随后该中间体被由二氧化碳与二级胺形成的氨基甲酸根阴离子进攻；尽管位阻较大的反应物会发生正面进攻，但五配位磷原子处伴随构型翻转的亲核取代背面进攻为更优反应路径。二氧化碳插入产物的构型主要取决于原料氢螺磷烷中原有的磷原子构型。