σ 2 P,O‐Hybrid Ligands: Synthesis of the First 4‐Hydroxy‐1,3‐benzazaphospholes by ortho ‐Lithiation of m ‐Amidophenyl Diethyl Phosphates

The m ‐phosphorylanilides 2 are available from anilides 1 by the Atherton–Todd reaction; the selective ortho ‐lithiation of the o′ ‐methyl‐protected phosphorylpivalanilide 2b with t BuLi proceeded in high yield in the presence of ClSiMe 3 . The ortho ‐lithiation is followed by rapid 1,3‐migration of the PO 3 Et 2 group to yield the phosphonoanilide cis / trans ‐ 3b . This compound mainly reacts with excess LiAlH 4 by reductive cyclization to form the 4‐hydroxy‐1 H ‐1,3‐benzazaphosphole 6 . The lithiation of the o′ ‐unprotected phosphorylpivalanilide 2a with LDA was unselective and led to 3a and 4a in low yields, whereas additional ortho ‐lithiation of the benzoyl group occurred for the lithiation of the o′ ‐protected phosphonobenzanilide 2c with t BuLi/LDA to give 7 in rather low yield. The reduction of crude 7 led to (benzylamino)phenol 8 and the 4‐hydroxy‐1 H ‐1,3‐benzazaphosphole 9 as a minor product. The properties, NMR spectroscopy data, and crystal structures of 5b , 6 , and 8 are reported.