C,C-Diacetylenic phosphaalkenes in palladium-catalyzed cross-coupling reactions

Abstract

The reactivity of bis-TMS-substituted C,C-diacetylenic phosphaalkene (A₂PA) 1 in Sonogashira–Hagihara cross-coupling reactions has been examined. The selective and successive deprotection of the two silyl groups in 1 is enabled by the steric bulk of the Mes* group which renders the acetylenetrans to Mes* more reactive and thereby facilitates selective and consecutive couplings with iodoarenes. In situ transformation of the TMS-protected acetylenes into Cu(I)acetylides is the key step in the synthetic sequence and enables the preparation of the first dimeric A₂PA linked by a phenylene spacer. cis–transIsomerization across the PC bond is triggered by a tertiary amine and exclusively observed in the case of nitrophenyl-substituted A₂PAs. The introduced aryl groups are integral parts of the entire π-system as evidenced by spectroscopic and electrochemical studies.