Synthesis of 2-Phospha[7]helicene, a Helicene with a Terminal Phosphinine Ring

Org Lett. 2022 Jul 8;24(26):4756-4761. doi: 10.1021/acs.orglett.2c01723. Epub 2022 Jun 24.

Abstract

A synthetic strategy toward phosphahelicenes containing a terminal phosphinine ring has been explored. The 4-phenyl-6-methyl-2-phospha[7]helicene was prepared from starting 2-bromobenzo[c]phenanthrene in 12% overall yield in 12 steps. The synthetic approach involves introduction of the phosphorus function prior to photocyclization forming the final helicene skeleton, followed by the formation of a phosphorus hexacycle. The structure of the first phosphahelicene with a terminal phosphinine ring was confirmed by X-ray crystallography.