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π‐Excess σ 2 P=C–N–Heterocycles: Catalytic P ‐Arylation and Alkylation of N ‐Alkyl‐1,3‐benzazaphospholes and Isolation of P , N ‐Disubstituted Dihydrobenzazaphosphole P ‐Oxides
Author(s) -
Niaz Basit,
Aluri Bhaskar R.,
Jones Peter G.,
Heinicke Joachim W.
Publication year - 2015
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201500532
Subject(s) - chemistry , aryl , alkylation , alkyl , iodide , medicinal chemistry , halide , electrophile , oxidative addition , catalysis , nuclear magnetic resonance spectroscopy , crystal structure , organic chemistry
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 PdCl 2 or H 2 PtCl 6 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.