FLP-type Alkenylation of a Phosphafluorene

Abstract

Phosphafluorenes, in which the chemically vulnerable C-9 position of the fluorene core has been replaced with phosphorus, demonstrate enhanced stability compared to conventional fluorene-based materials and belong to the general class of dibenzophospholes (DBPs). Phosphafluorene formation is commonly observed in the reductive functionalization of terphenyl-based dihalophosphanes. In here, we outline a high-yielding route towards phosphafluorene 1, starting from readily available DippTerPCl2 (DippTer = 2,6-Dipp-C6H3; Dipp = 2,6-iPr2-C6H3). Different functionalization strategies of 1 are outlined, including a complex with AuCl, its BH3 adduct, and its corresponding sulphide. Interestingly, facile alkenylation of 1 was achieved in the presence of B(C6F5)3 and various phenylacetylene derivatives. This FLP-type alkenylation is E-selective giving zwitterionic phosphonium borates.