(Triphenylphosphoranylidene)ketene (1), also known as the Bestmann ylide, is a reagent with intriguing properties and proven synthetic utility.[¹] After early reports of this compound by others,[²] H. J. Bestmann popularized the use of 1 in the formation of a wide range of (triphenyl­phosphoranylidene)acyl derivatives.[³] The Bestmann ylide (1) is now commercially available and used in a wide range of reactions. Alternatively, 1 can be prepared by the deprotonation of methyl (triphenylphosphoranylidene)acetate (2, Scheme [1)] [⁴] A variety of strong bases have been used to perform this transformation,[⁵] with NaHMDS being particularly efficient and convenient.

Interestingly, the X-ray crystal structure of 1 shows a 145.5° P=C=C bond angle and a remarkably short C=C bond length (1.21 Å).[⁶] These properties are derived from the combination of three resonance structures (Scheme [2]), which highlight the two overlapping, orthogonal π-systems that stabilize the molecule. This makes the reactivity of the Bestmann ylide significantly different from typical ketenes and phosphorus ylides. The Bestmann ylide is surprisingly stable and can be stored under inert atmosphere at ambient temperature for months.[⁴]

（三苯基亚正膦）乙烯酮（1），也被称为Bestmann叶立德，是与耐人寻味性质和证明合成的效用的试剂。[ ¹ ]由他人该化合物的早期报告后，[ ² ] HJ Bestmann普及使用1在[ ³ ] Bestmann ylide（1）现在可以从市场上买到，并用于各种反应中。可选地，1可以是甲基的脱质子化（三苯基亚正膦）乙酸甲酯（制备2，方案〔1）] [ ⁴ ]各种强碱已经被用于执行此变换，[⁵ ] NaHMDS特别有效和方便。

有趣的是，X射线晶体结构1示出了145.5°，P = C = C键角和非常短的C = C键长（1.21埃）。[ ⁶ ]这些属性是从三个谐振结构的组合（派生方案[2]），其突出了使分子稳定的两个重叠的正交π系统。这使得Bestmann ylide的反应性与典型的烯酮和磷化磷明显不同。Bestmann叶立德令人惊讶地稳定，可以在惰性气氛中于环境温度下保存数月。[ ⁴ ]