Halogenation of 1‐Ethoxy‐1‐oxophosphindolin‐3‐one, a Potential Phosphaindigo Precursor

Abstract

AbstractThe bromination of 1‐ethoxy‐1‐oxophosphindolin‐3‐one (1) with two equivalents oi bromine occurs with elimination of hydrogen bromide and ethyl bromide, providing 2,2‐di‐ bromo‐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. Triethylamine deprotonates 4, providing the solid triethylammonium salt 5. Silylation of 4 with chlorotrimethylsilane leads to the trimethylsilyl ester 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 analytically and spectroscopically (EI‐MS, 1H, 13C and 31P NMR). The crystal 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.