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.
Highlights
A new method for the synthesis of 5,9-diaza[5]helicenes is presented using 2,3-bis(acylamino)-substituted ortho-terphenyls as precursors
Seven aza[5]helicenes and 91 diaza[5]helicenes can be constructed, where a small fraction of these compounds have been realized in prior syntheses.[1,7,8]
These and other azahelicenes have been used as chiral organocatalysts in asymmetric synthesis[9,10,11,12] and in kinetic resolutions,[13] as proton sponges,[14,15,16] and for the synthesis of helicene-based transition metal complexes.[17]
Summary
A new method for the synthesis of 5,9-diaza[5]helicenes is presented using 2,3-bis(acylamino)-substituted ortho-terphenyls as precursors. We planned to build the western amide function, where the other amino group is still suitably protected (I); electrophilic acylation towards phenanthridine H would proceed at an Scheme 2.
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