1,3‐Diethynylbicyclo[1.1.1]pentane, a Useful Molecular Building Block

Abstract

Abstract1,3‐Diethynylbicyclo[1.1.1]pentane (DEBCP) has been found to be a valuable molecular building block mostly for the synthesis of extended, rigid, rod‐like molecules. With its straightforward linear geometry, DEBCP can be used as a nonconjugated alternative to more frequently used π‐conjugated, rod‐like building blocks. Examples of reactions that introduce DEBCP into larger structures are (1) the reaction of DEBCP lithium acetylides with electrophiles such as TMSCl, CO2, and Ph2PCl, (2) Sonogashira–Hagihara cross‐coupling reactions with aryl or heteroaryl iodides or bromides, and (3) umpolung reactions that afford the corresponding dibromo and diiodo derivatives of DEBCP, which then successfully react with tert‐C‐cuprates derived from p‐ and m‐dicarbadodecaboranes or bicyclopentanes. These umpolung reactions afforded a new class of molecular rods that combine carborane or bicyclo[1.1.1]pentane cages with ethynylene linkers. Many of the DEBCP derivatives were studied by single‐crystal X‐ray diffraction. They form well‐organized arrays of molecular rotors, the DEBCP units, and so can be considered as examples of artificial molecular‐size machines.