Synthesis of 5,9‐Diaza[5]helicenes

Abstract

A new method for the synthesis of 5,9‐diaza[5]helicenes is presented using 2,3‐bis(acylamino)‐substituted ortho‐terphenyls as precursors. Activation of the amide groups and electrophilic substitution at the ortho positions of the adjacent phenyl groups leads to the 5,9‐diaza[5]helicenes. A stepwise reaction including protection of the first amino group, amide formation at the second amino group with subsequent cyclization, followed by deprotection, amide formation and cyclization at the first amino group ensures that both electrophilic substitutions take place at sufficiently activated arenes and allows for the different substituents at the diaza[5]helicenes brought in with the amide groups. The terphenyl precursors are synthesized by two Suzuki couplings of suitably substituted building blocks. Three different 5,9‐diaza[5]helicenes with aliphatic, alkenyl and methoxycarbonylalkyl substituents were prepared; the latter would allow to attach further functionalities by ester or amide linkage.

Cyclopenta-fused polyaromatic hydrocarbons: synthesis and characterisation of a stable, carbon-centred helical radical

“…We recently developed a method in which the fusion of ortho,ortho'-substituted terphenyls yielded [5]helicene-type compounds 21 and we considered this strategy suitable for the construction of even larger helicenes by using similarly substituted quaterphenyls or even higher oligophenyls. We…”

Divergent Total Synthesis of Azalamellarins D and N

“…The conversion of 15 to 10 was performed using a modified procedure reported by Weiß and Podlech. 12 Thus, bromide 15 was treated with 1.1 equiv of bis(pinacolato)diboron The synthesis of pinacol borate 6a is shown in Scheme 4. The protection of the hydroxy group of 4-bromo-2-methoxyphenol (21) 14 by the MOM group afforded 22 in 92% yield.…”

Synthesis of Diaza[5]helicenes by ortho,ortho′-Fusion of ortho-Terphenyls

“…5, 17b, 17c, 21 We considered a double amidation of 2,3'-diamino-ortho-terphenyls and subsequent double intramolecular electrophilic aromatic substitution to be a suitable method for the preparation of 5,9-diaza [5]helicenes H. However, we had to realize that the first cyclization in bisamide F (between rings B and C) leads to a phenanthridine G, which is deactivated towards the second SEAr reaction (Scheme 2). 22…”

“…b) Synthesis of helicenes 35: as GP4a, but: Tf2O (6 equiv), Ph3PO (12 equiv) in CH2Cl2 (40 mL); diamide 34 (1 equiv ≙ 1 mmol) in CH2Cl2 (40 mL). Following a published protocol 23 197 (17), 183 (20), 180 (20), 169 (22), 168 (28), 167 (97), 166 (25), 152 (10), 140 (14), 139 (24), 115 (17).…”