pi-Excess sigma P-2,O Hybrid Ligands: Synthesis of the First 4-Methoxy-1H-1,3-benzazaphospholes

The synthesis of the first 4-methoxy-substituted 1,3-benzazaphosphole was accomplished by using a C, O-dilithium intermediate generated from N-(3-methoxyphenyl)-2,2-dimethylpropanamide and butyllithium. This intermediate was subjected either to direct phosphonylation or to a bromination and phosphonylation sequence; subsequent reductive cyclization with excess lithium aluminum hydride led to the desired product. In addition, N-(2,2-dimethylpropyl)-3-methoxy-2-phosphinoaniline, formed in a side reaction, was cyclized with (dimethoxymethyl) dimethylamine to give 1-(2,2-dimethylpropyl)-4-methoxy-1H-1,3-benzazaphosphole. The behavior of these +M-substituted pi-excess aromatic sigma P-2-heterocycles towards moisture is reported, together with their H-1, C-13, and P-31 solution NMR spectra and a crystal-structure analysis. The new compounds represent potential sigma P-2, O hybrid or chelate ligands with a high pi-density at the phosphorus atom.