Selective synthesis of unsymmetric dibenzo[a,e]pentalenes by a rhodium-catalysed stitching reaction† †Electronic supplementary information (ESI) available: General, experimental, spectral, and theoretical information. CCDC 1511836–1511838. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc04560j Click here for additional data file. Click here for additional data file.

Instrumentation: Nuclear magnetic resonance (NMR) spectra were recorded on a BRUKER Ascend500 spectrometer (1H: 500 MHz and 13C: 126 MHz) at ambient temperature unless otherwise noted. Chemical shift values for protons were referenced to the residual proton resonance of chloroform-d (δ: 7.26). Chemical shift values for carbons were referenced to the carbon resonance of chloroform-d (δ: 77.16). Elemental analyses were performed at One-stop Sharing Facility Center for Future Drug Discoveries, Graduate School of Pharmaceutical Sciences, The University of Tokyo or the Microanalytical Laboratory, Department of Chemistry, Graduate School of Science, The University of Tokyo. High resolution electrospray-ionisation (ESI) mass spectra were recorded on a JEOL JMS-T100LP AccuTOF LC-plus instrument. Infrared (IR) spectra were recorded on a Shimadzu FTIR-8400 spectrometer equipped with an attenuated total reflection (ATR) system. Melting points and decomposition points were recorded on an OptiMelt MPA-100 apparatus. Ultraviolet(UV)/visible absorption spectra were recorded on a Shimadzu UV-3150 spectrometer. Cyclic voltammograms were recorded on a BAS ALS electrochemical analyser 619Ep. Preparative gel permeation chromatography (GPC) was carried out with a JAI LC-9260 II NEXT system equipped with two JAIGEL-2HR column (Japan Analytical Industry Co., Ltd.; 20 mm i.d. × 600 mm). X-ray crystallographic analyses of single crystals were performed on a Rigaku VariMax with Saturn diffractometer. A single crystal was mounted with mineral oil on a loop-type mount and transferred to the goniometer. The radiation was performed with graphite-monochromated Mo Kα (α = 0.71075 Å) at 50 kV and 24 mA. The structures were solved by the direct method with (SHELXT 2014)1 and refined by full-matrix least-squares techniques against F2 (SHELXL 2014).1 The intensities were corrected for Lorentz and polarisation effects. The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed using AFIX instructions.