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.