Synthesis of Highly Distorted π‐Extended [2.2]Metacyclophanes by Intermolecular Double Oxidative Coupling

One-Pot Iridium Catalyzed C–H Borylation/Sonogashira Cross-Coupling: Access to Borylated Aryl Alkynes

“…These results suggest that the alkynyl group binds tightly to the active borylation catalyst at 25 °C, but at elevated temperatures the alkynyl group becomes a reactive partner. [33][34][35][36] a) Alkyne reactivity under iridium CHB conditions [28][29][30][31][32] Unwanted alkyne reactivity can be viewed as a CHB limitation, since borylated aromatic alkynes have found use in the synthesis of extensively conjugated polymeric materials [37] and in crystal engineering, biological inhibition, molecular sensing, chirality, and structural assignment, etc., [38][39][40][41]. The preparation of borylated aromatic alkynes usually involves introduction of the boronic ester/acid functionality on an aromatic alkyne by metalation/borylation [42,43] or Pd-catalyzed borylation of aromatic halides [44].…”

“…with R 1 = Bpin, R 2 = H b) Alkyne tolerance in iridium CHB of arenes and heteroarenes [33][34][35][36] a) Alkyne reactivity under iridium CHB conditions [28][29][30][31][32] Scheme 3. One-pot CHB of aryl halides followed by selective reaction of the C-Halogen bond [23,27].…”

“…In fact, addition of hydroborane or diboron reagents across triple bonds can occur with catalytic systems similar to the traditional conditions used for CHB (Scheme 1a) [28][29][30][31][32]. However, there are reports in which CHB of arenes or heteroarenes bearing an alkyne functionality have been successful (Scheme 1b) [33][34][35][36]. It is likely that in these examples the presence of two bulky substituents on the alkyne hinder its reactivity, allowing for chemoselective borylation of the porphyrin moiety (1,2) or the polyarene skeleton (3,4).…”

Selective Borylation of [4]Helicene

“…Based on preceding studies on the iridium-catalyzed borylation of arenes [10][11][12][13][14][15] and fused polyarenes, [9,[16][17][18][19][20][21][22][23][24][25][26] we subjected [4]helicene 1 to mild borylation conditions. Equimolar quantities of the substrate and B 2 pin 2 (pin = pinacolato) and a catalytic amount of [Ir(OMe)(cod)] 2 (5 mol-% Ir) (cod = 1,5-cyclooctadiene) and 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy) (10 mol-%) were reacted in cyclohexane at 23°C for 18 h. Removal of the volatiles and subsequent column chromatography on silica gel (hexane/DCM from 100:0 to 0:100) resulted in three colorless fractions: unreacted 1 (39 %), a mixture of monoborylated [4]helicenes (51 %), and the last small fraction containing a mixture of bisborylated [4]helicenes (< 8 %).…”

Isolation of a 1,4-diketone intermediate in oxidative dimerization of 2-hydroxyanthracene and its conversion to oxahelicene

“…During the course of our study on oxidation of aromatic alcohols, 4 we unexpectedly isolated such metastable 1,4-diketone intermediates 2 by oxidation of 2-hydroxyanthracenes 1. Although oxidative dimerization of 2-hydroxyanthracenes to BINOL-like axially chiral diols has been reported, dearomatized 1,4-diketone species have never been isolated.…”