Reaction of phospholes with acids; [1,5] proton shifts in 1H-λ5-phospholes

Abstract

Addition to phospholes of gaseous HCI at –90 °C or of an excess of trifluoromethanesulphonic acid at –70 °C, results in P-protonation. The triflate solutions are stable up to room temperature, but the 1H-phospholium chlorides form P^V adducts at –70 °C, which rapidly rearrange by a [1,5]sigmatropic H-shift. The observed product is a 1-chloro-2,5-dihydrophospholium chloride. Addition of a chloride ion source to the triflates produces the same result. Unprotonated 3,4-dimethyl-1-phenyl phosphole was found to react at a double bond of its 1H-phospholium ion, forming a crystalline 1,3′-biphospholium dimer.