ChemInform Abstract: 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.

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 H2PtCl6 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 σ2P‐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.

Phospha-Mannich reactions of RPH2, R2PH, and R3P

“…Cyclo-P(O),N-acetals, obtained by Pd-catalyzed P-arylation of N-neopentyl-1,3benzazaphosphole. [191,192] Entry R Yield, % Table S33. P,NH-acetals, obtained by hydrophosphination of imines with secondary phosphines.…”