Palladium‐Catalyzed Cyclization of a Pyryne Precursor to Higher Pyrenylenes

Abstract

The palladium catalyzed cyclotrimerization of ortho-silylaryl triflates as aryne precursors is meanwhile an established method to synthesize polycyclic aromatic hydrocarbons (PAHs) with triphenylene cores. During the palladium-catalyzed reaction of a pyrene with an osilylaryl triflate moiety in the K-region higher homologues with central eight-and ten-membered rings (the pyrenylenes) were found, besides the expected trimer and a protocol was developed to isolate all members of this series. This unprecedented new class of PAHs was fully investigated by all means, including X-ray diffraction of single-crystals, UV/Vis and fluorescence spectroscopy and theoretical calculations. Supported by density-functional theory (DFT) calculations, a mechanism of all higher cyclooligomers is proposed.

Thermolysis of Biphenylene toward Cyclo‐ortho‐phenylenes

“… Examples of small [n]COPs in literature: bisacene‐fused tetrabenzocyclooctatetraene A , [16] [5]pyrenylene B [17] and [8]cyclo‐ ortho ‐phenylene C [9] …”

“…At lower temperatures and longer reaction times oligomerization proceeds as a consequence of low biphenyl diradical concentration and, after addition, unfavorable conformations preclude immediate ring closure (see SI, Scheme S1 for a mechanistic proposal). [24] Control experiments rule out the [16] [5]pyrenylene B [17] and [8]cycloortho-phenylene C. [9] homolysis of higher COPs to reparticipate again in the growth of the macrocycles (see below). Importantly, oligophenyl formation by hydrogen abstraction was not observed.…”

“…[14] To avoid triphenylenes, [15] sterically demanding substituents at the monomers have been introduced giving higher oligomers due to steric repulsion. Acene-or pyrene-based [n]COPs A [16] and B [17] (n = 4-5, yields: 1-14 %) were obtained (Figure 1) in low yields after extensive purification. Biphenyl-derived monomers avoid triphenylene formation, although transition-metal mediated tetraphenylene synthesis [18] is accompanied by polymer formation.…”

New advances in chiral nanographene chemistry

“…This group has made a variety of other contorted and chiral compounds based around irregular nanographene structures. 112–114…”