Stereoselective Synthesis of (<i>E</i>)-α-Bromo- and (<i>E</i>)-α-Iodoacrylates from Readily Available <i>tert</i>-Butyl Diphenylphosphonoacetate

<i>tert</i>-Butyl (diphenylphosphono)bromoacetate <b>3d</b> was readily prepared by brominating <i>tert</i>-butyl diphenylphosphonoacetate <b>5d</b>. The HWE reaction of <b>3d</b> with various aldehydes gave (<i>E</i>)-α-bromoacrylates <b>1</b> with selectivity ranging from 89:11 to 99:1, typically in yields exceeding 90%. Additionally, the HWE reactions after treatment of <b>3d</b> with NaI or iodinating <b>5d</b> produced the corresponding (<i>E</i>)-α-iodoacrylates <b>7</b> in yields of 87-100%, with selectivities ranging from 91:9 to 99:1. The products were used to synthesize trisubstituted alkenes through Sonogashira coupling.