Reductive Dimerization of Macrocycles Activated by BBr3

A macrocyclic motif composed of carbazole and pyridine subunits linked by a carbonyl bridge (C=O) forms a skeleton with a peripheral reactivity that leads to a pinacol-like coupling activated by BBr3, eventually entrapping a substantially elongated C–C bond. Slightly modified conditions lead to the efficient transformation of the C=O unit to a CH2 linker that, after exposure to air, gives a dimeric molecule with multiple bonds between two macrocyclic units, as documented in spectroscopy and X-ray analysis.

1. General information NMR Spectroscopy. 1 H NMR spectra were recorded on a high-field spectrometer ( 1 H 600.15 MHz and 500 MHz, 13 C 150 MHz and 125.75 MHz), equipped with a broadband inverse gradient probehead. Spectra were referenced to the residual solvent signal (chloroform-d, 7.24 ppm or acetone-d6 2.05 ppm). Two dimensional NMR spectra were recorded with 2048 data points in the t2 domain and up to 1024 points in the t1 domain, with a 1s recovery delay.
Mass Spectrometry. High resolution and Accurate Mass spectra were recorded on a Bruker apex ultra Apex-Qe 7T instrument (Bruker) spectrometer using the electrospray technique. The acetonitrile, dichloromethane or methanol were used as solvents for recording the mass spectra. The potential between the spray needle and the orifice was set to 4.5 kV.
LC-MS analysis. The LC-MS analysis was performed on Shimadzu LC IT-TOF. Separation was carried out on an RP-Zorbax (50×2.1 mm, 3.5 µm) column with a gradient elution of 0-80% B in A (A = 0.1% HCOOH in water; B = 0.1% HCOOH in MeCN) at room temperature over a period of 20 min (flow rate: 0.1 mL/min).

UV-Vis Spectroscopy.
Electronic spectra were recorded on a Varian Carry-50 Bio spectrophotometer.
Fluorescence. Steady state fluorescence spectra were recorded with a JASCO FP-8600 Spectrofluorometer apparatus.
X-Ray Analysis. X-Ray quality crystals were prepared by precipitation from DCM/MeOH (3), CDCl3 (4a, 6) and (CD3)2CO (5-Ac, 4-Ac, 8). Diffraction data were collected on a Rigaku Oxford Diffraction XtaLAB Synergy-R DW diffractometer equipped with a HyPix ARC 150° Hybrid Photon Counting (HPC) detector using CuKα (λ = 1.54184 Å) for 4-Ac, 5-Ac and 8 at 80, 100 and 100 K, respectively. Diffraction data for 3 were collected on a Kuma KM4 diffractometer equipped with Sapphire CCD detector at 100 K using MoKα (λ = 0.71073 Å). Diffraction data for 4a and 6 were collected on a Xcalibur Gemini Ultra diffractometer equipped with Ruby CCD detector at 100 K using CuKα (λ = 1.54184 Å). Data were processed using the CrystAlisPro software. The structures were solved by intrinsic phasing with SHELXT (2015 release) and refined by full-matrix least-squares methods based F 2 using SHELXL. For all structures, H atoms bound to C atoms were placed in the geometrically idealized positions and treated in riding mode, with C-H = 0.95Å and Uiso(H) = 1.2Ueq(C) for C-H groups, and C-H = 0.98Å and Uiso(H) = 1.5Ueq(C) for CH3 groups, while the O-and N-bound H atoms were refined freely.
The diffraction data for crystal of 5-Ac was insufficient for publication therefore only a model of structure is presented.
Theoretical calculations. Geometry optimization for 6 was carried out with the Gaussian 09 1 software package within unconstrained C1 symmetry, with starting coordinates derived from X-ray analysis. Becke's three-parameter exchange functional with the gradient-corrected correlation formula of Lee, Yang and Parr (DFT-B3LYP) 2 were used with the 6-31G(d,p) basis set. The polarizable continuum model of solvation was used (PCM, standard dichloromethane/chloroform/acetone parametrization) for all optimizations. Harmonic vibrational frequencies were calculated using analytical second derivatives as a verification of local minimum achievement with no negative frequencies observed. Wiberg indices were calculated with application of NBO analysis implemented into Gaussian package.

Experimental section
All solvents (MeOH, Ethyl Acetate, CHCl3, n-hexane, toluene, acetone, water) if not indicated differently were used without purification. CH2Cl2 was distilled over CaH2. Chloroform-d was prepared directly before using by passing through a basic alumina column. All reactions were performed under inert atmosphere.