A doubly base‐stabilised diborane based on a benzylphosphine linker was prepared by a salt elimination reaction between 2‐LiC₆H₄CH₂PCy₂⋅Et₂O and B₂Br₄. This compound was reduced with KC₈ to its corresponding diborene, with the benzylphosphine forming a five‐membered chelate. The diborene reacts with butadiene, 2‐trimethylsiloxy‐1,3‐butadiene, and isoprene to form 4,5‐diboracyclohexenes, which interconvert between their 1,1‐ (geminal) and 1,2‐ (vicinal) chelated isomers. The 1,1‐chelated diborene undergoes a halide‐catalysed isomerisation into its thermodynamically favoured 1,2‐isomer, which undergoes Diels–Alder reactions more slowly than the kinetic product.

中文翻译：

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螯合二硼烷及其与二烯的反电子需求Diels-Alder反应

根据一个benzylphosphine接头甲双碱稳定的乙硼烷进行制备之间通过盐消除反应2-LIC ₆ ħ ₄ CH ₂ PCY ₂ ⋅Et ₂ O和乙₂溴₄。该化合物用KC ₈还原与其相应的二硼烯成键，然后苄基膦形成五元螯合物。二硼烯与丁二烯，2-三甲基甲硅烷氧基-1,3-丁二烯和异戊二烯反应形成4,5-二硼杂环戊烯，它们在1,1-（基团）和1,2-（邻位）螯合的异构体之间相互转化。1,1螯合的二硼烷经历卤化物催化的异构化，成为热力学上受支持的1,2-异构体，其经历Diels–Alder反应的速度比动力学产物慢。