Stereoselective Synthesis of (2<i>e</i>)-2-Benzylidene-5-Hydroxy-5-Methylhex-3-Ynal
A stereoselective synthesis of (2E)-2-benzylidene-5-hydroxy-5-methylhex-3-ynal was carried out based on the Pd/Cu-catalyzed coupling of (2Z)-2-bromo-3-phenylprop-2-enal with 2-methylbut-3-yn-2-ol. The starting (2Z)-2-bromo-3-phenylprop-2-enal was obtained by bromination/dehydrobromination of available cinnamaldehyde with molecular bromine and triethylamine. Its cross-coupling with 2-methylbut-3-yn-2-ol in the presence of the Pd(PPh3)2Cl2/CuI catalytic system and diisopropylamine as a base in acetonitrile at room temperature gives the desired (2E)-2-benzylidene-5-hydroxy-5-methylhex-3-ynal with high yield (84%) and stereoselectivity (99%).