Steric control of the in/out sense of bridgehead substituents in macrobicyclic compounds: isolation of new “crossed chain” variants of in/out isomers

Abstract

Isomers of the cage like dibridgehead diphosphine P((CH₂)₁₄)₃P (1) are treated with Ph₃PAu(2,6-C₆H₃(Trip)₂) (2 equiv.; Trip = 2,4,6-C₆H₂(iPr)₃). With out,out-1, workup gives out,out-1·(Au(2,6-C₆H₃(Trip)₂))₂ (46%), as confirmed by a crystal structure. With in,out-1, crystallization affords not in,out-1·(Au(2,6-C₆H₃(Trip)₂))₂, but rather an out,out isomer in which one of the (CH₂)₁₄ segments threads through the macrocycle formed by the other two. Implications for mechanisms of interconversion of in,out isomers are analyzed.