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

Abstract

1,3‐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.

Arrays of Dipolar Molecular Rotors in Tris(o-phenylenedioxy)cyclotriphosphazene

“…The rods 16-18 were formed by Sonogashira cross-coupling of the bicyclo[1.1.1]pentane derivative 43 with the alkynes 44-46 (Scheme 10) in almost quantitative yields, but their low solubility reduced the isolated yields to 50-80%. Access to 43 requires six known steps from commercial precursors [73][74][75], starting with the conversion of the tetrahalide 36 to [1.1.1] propellane (47). Photochemical radical insertion of biacetyl afforded the diketone 48, which was transformed to the dichloro derivative 49 by treatment with hexachloroethane in molten PPh 3 .…”

“…The light sensitive iodo derivative 37 was obtained from 36 using a previously published procedure [72,73]. Lithiation of 37 followed by reaction with anhydrous acrolein yielded racemic alcohol 38, whose metathesis afforded a mixture of diastereomeric diols 39 and 40.…”

Molecular Rods: Facile Desymmetrization of 1,4‐Diethynylbicyclo[2.2.2]octane

“…Crystallographic data for all compounds were collected either with a Nonius Kappa CCD diffractometer equipped with Bruker APEX‐II CCD detector using monochromatized Mo‐ K α radiation ( λ = 0.71073 Å) (samples 7 and 13 ) or with a Bruker D8 VENTURE Kappa Duo PHOTON100 by IµS micro‐focus sealed tube Cu‐ K α radiation ( λ = 1.54178 Å) ( 2 and 6 ), or Mo‐ K α radiation ( 1 and 5 ) at 150(2) K (except 1 measured at 120 K). The structures were solved by direct methods (XT) and refined by full‐matrix least‐squares based on F 2 (SHELXL2018) …”

Bicyclo[1.1.1]pentane‐Derived Building Blocks for Click Chemistry

“…In turn, compound 2a was obtained by the reaction of propellane ( 1 ) with IN 3 , or via 1,3‐diiodopropellane ( 4 ), (Scheme ). A number of papers have described the synthesis and some selective reactions (e.g., Sonogashira coupling or silylation) of 1,3‐diethynyl[1.1.1]bicyclopentane ( 5 ); this compound was prepared in two steps from 1,3‐diacetylbicyclo[1.1.1]pentane ( 6 ) . Apart from this, alkynes 3 and 7 (R 1 = H, Cl) have also been prepared using a similar method …”

“…A number of papers have described the synthesis and some selective reac-tions (e.g., Sonogashira coupling or silylation) of 1,3-diethynyl[1.1.1]bicyclopentane (5); this compound was prepared in two steps from 1,3-diacetylbicyclo[1.1.1]pentane (6). [25][26][27][28][29][30] Apart from this, alkynes 3 and 7 (R 1 = H, Cl) have also been prepared using a similar method. [31]…”