10.1021/jo991651k.s001 Hao-Ming Chang Hao-Ming Chang Chien-Hong Cheng Chien-Hong Cheng Palladium-Catalyzed Synthesis of 1,3-Dienes from Allenes and Organic Halides American Chemical Society 2000 2 e PdCl 2 Various palladium systems aryl CRCH DMA regioisomers 3 v diene formation CH vinylic halides Z isomers 3 t diene products PPh K 2 CO 3 2000-02-24 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Palladium-Catalyzed_Synthesis_of_1_3-Dienes_from_Allenes_and_Organic_Halides/3720348 A wide range of aryl and vinylic halides react with 1,1-dimethylallene (<b>2a</b>) and potassium carbonate in the presence of Pd(dba)<sub>2</sub> (dba = dibenzylideneacetone) in <i>N</i>,<i>N</i>-dimethylacetamide (DMA) at temperature 100−120 °C to give the corresponding dienes CH<sub>2</sub>C(CH<sub>3</sub>)CRCH<sub>2</sub> (<b>3a</b>−<b>o</b>), where R is aryl or vinylic, in good to excellent yields. Higher yields of diene products were obtained for aryl bromides than for the corresponding aryl iodides and chlorides. Under similar reaction conditions, tetramethylallene (<b>2b</b>), 1-methyl-1-phenylallene (<b>2c</b>), 1-methyl-3-phenylallene (<b>2d</b>), and 1-cyclohexylallene (<b>2e</b>) also react with aryl and vinylic halides to give diene products (<b>3p</b>−<b>w</b>). For <b>2d</b>, both <i>E</i> and <i>Z</i> isomers <b>3t </b>and <b>3u </b>of the diene product were observed. For <b>2e</b>, two regioisomers <b>3v </b>and <b>3w</b> were isolated with <b>3w</b> likely from alkene isomerization of <b>3v</b>. Various palladium systems were tested for the catalytic activity of diene formation. In addition to Pd(dba)<sub>2</sub>/PPh<sub>3</sub>, Pd(OAc)<sub>2</sub>/PPh<sub>3</sub>, PdCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>, and PdCl<sub>2</sub>(dppe) are also very effective as catalysts for the reaction of <b>2a</b> with <i>p</i>-bromoacetophenone (<b>1a</b>) to give <b>3a</b>. Studies on the effect of solvents and bases show that DMA and K<sub>2</sub>CO<sub>3</sub> are the solvent and base that give the highest yield of diene <b>3a</b>. Possible mechanisms for this catalytic diene formation are proposed.