Π‐Excess σ2P=C–N–Heterocycles: Catalytic P‐Arylation and Alkylation of N‐Alkyl‐1, 3‐benzazaphospholes and Isolation of P, N‐Disubstituted Dihydrobenzaza­phosphole P‐Oxides. Issue 24 (17th July 2015)

• Record Type: Journal Article
• Authors: Niaz, Basit; Aluri, Bhaskar R.; Jones, Peter G.; Heinicke, Joachim W.
• Is Part Of: European journal of inorganic chemistry. Issue 24(2015)
• Page Start: 3995
• Page End: 4005
• Publication Date: 2015-07-17
• Subjects: Homogeneous catalysis -- Arylation -- Palladium -- Phosphorus heterocycles; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201500532
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract: 2‐Unsubstituted N ‐alkyl‐1, 3‐benzazaphospholes, diagonally P–C related to 2, 3‐unsubstituted indoles, were successfully arylated by aryl iodides and bromides or alkylated by neopentyl iodide by heating in DMF in the presence of a catalytic amount of PdCl2 or H2 PtCl6 and a suitable base. In contrast to the known 2‐arylations of indoles under these conditions, the reactions led to arylation in the 3‐position and proceeded via highly moisture‐sensitive intermediates to P ‐substituted 1, 3‐benzazaphosphole P ‐oxides. Thus, we present a novel route for the direct P ‐substitution of aromatic σ 2 P‐heterocycles with electrophilic aryl/alkyl halides. Characteristic NMR spectroscopic data of the intermediates are consistent with –P(aryl)–C(Br/Cl)–N– species formed by metal‐mediated addition of the aryl halides at the P=C bond rather than by oxidative addition to ylidic intermediates. Benzazaphospholium salts, accessible by using triethyloxonium tetrafluoroborate at room temperature and also very sensitive to hydrolysis, display distinct NMR spectroscopic data. The structures of the products were elucidated by conclusive NMR spectroscopy and HRMS data and crystal‐structure analysis. Minor amounts of a bis(arylation) product could likewise be identified by crystal‐structure analysis. Abstract : Aromatic σ 2 P‐heterocycles are unreactive to aryl/alkyl halides. Heating in the presence of Pd or Pt catalysts and a suitable base, however, allows direct P ‐arylation or P ‐alkylation. The intermediate products are extremely moisture‐sensitive and are transformed into phosphine oxides. Et3 OBF4 provides benzazaphospholium salts without a catalyst, but these also tend to hydrolyze to phosphine oxides.