C–Me Bond Formation at All Methylene Bridges of the Calix[4]arene Scaffold

Abstract

A reaction of a distal dibromo diketocalix[4]arene with excess MeLi, followed by acid-catalyzed dehydration, yields a derivative with a pair of opposite exocyclic double bonds, and a pair of trans methyl groups at the bridges. A reaction of a tetrabromo calix[4]arene derivative with excess MeLi yields a calix[4]arene derivative with all methylene bridges monomethylated in all- cis fashion.

Calixrotanes: Calixarenes Incorporating Spiro‐Linked Cyclopropyl Groups

“…Calix[4]arene 10 was previously characterized as the trans isomer based on its 1 H NMR spectrum in the presence of a chiral solvating agent. Two separate singlets were observed for the vinyl protons, and the absence of mutual coupling was consistent only with a trans disposition of the methyl groups . To corroborate this structural assignment, we grew a single crystal of 10 from CHCl 3 and submitted it to X‐ray diffraction analysis (Figure ).…”

“…(1)]. In the first synthetic step, both addition to the carbonyl groups and C−Me bond formation at the brominated bridges take place …”

“…The starting material dimethyl‐dimethylenecalix[4]arene 10 was prepared as described previously . X‐ray crystallographic data for 10 : C 52 H 70 O 5 , M =775.08 g mol −1 , crystal size 0.60×0.25×0.20 mm 3 , triclinic, space group P , a =9.297(3), b =11.159(4), c =19.471(4) Å, α =66.252(5), β =86.352(6), γ =80.271(6)°, V =1213.0(7) Å 3 , Z =1, ρ calcd =1.061 Mg m −3 , μ =0.066 mm −1 , λ =0.71073 Å, T =294(1) K, θ range=1.72–27.00°, reflections collected 11 900, independent reflections 5098 ( R (int)=0.0411), 331 parameters.…”

Enantiomerization Barrier of all‐cis C‐Me‐tetrahydroxy p‐tert‐butylcalix[4]arene and Atropisomeric Equilibrium of its Tetraacetoxy Derivatives

“…All‐cis C‐Me‐tetrahydroxy p‐tert ‐butylcalix[4]arene (5) . All‐cis C‐Me‐tetramethoxy p‐tert ‐butylcalix[4]arene 4 (200 mg, 0.26 mmol) was dissolved in 22 mL anhydrous DMF (99.8 %). The round‐bottomed flask was equipped with a reflux condenser and a drying‐tube containing CaCl 2 .…”

“…The reaction is stereoselective and the all‐cis isomer is formed preferentially. In contrast to 3 which exist in solution as a conformational mixture where the partial‐cone form is the predominant conformer, 4 exists exclusively in a pinched‐cone conformation . This conformational shift was rationalized by the conformational preferences of the methyl group at the bridges.…”