HALOGENATION OF 1-ETHOXY-1-OXOPHOSPHINDOLIN-3-ONE, A POTENTIAL PHOSPHAINDIGO PRECURSOR

The bromination of 1-ethoxy-1-oxophosphindolin-3-one (1) with two equi valents of bromine occurs with elimination of hydrogen bromide and eth yl bromide, providing 2,2-dibromo-1-hydroxy-1-oxophosphindolin-3-one ( 4) in high yield. In the presence of triethylamine this process leads to 2,2-dibromo-1-ethoxy-1-oxophosphindolin-3-one (3) instead. Triethyl amine deprotonates 4, providing the solid triethylammonium salt 5. Sil ylation of 4 with chlorotrimethylsilane leads to the trimethylsilyl es ter 6. Monobromination in a two-phase reaction allows the isolation of a mixture of isomers of 2-bromo-1-ethoxy-1-oxophosphindolin-3-one (2a , b). Chlorination with chlorine furnishes 2,2-dichloro-1-ethoxy-1-oxo phosphindolin-3-one (7). The new compounds 2-7 were characterized anal ytically and spectroscopically (EI-MS; H-1, C-13 and P-31 NMR). The cr ystal structure of acid 4 was determined by:X-ray diffraction. Solid 4 consists of aryl stacks connected by chains of P-OH ... O=P hydrogen bonds and secondary Br ... Br contacts.