TY - JOUR
T1 - Mechanistic study of the manganese-catalyzed [2 + 2 + 2] annulation of 1,3-dicarbonyl compounds and terminal alkynes
AU - Yoshikai, Naohiko
AU - Zhang, Song Lin
AU - Yamagata, Ken Ichi
AU - Tsuji, Hayato
AU - Nakamura, Eiichi
PY - 2009/3/25
Y1 - 2009/3/25
N2 - The manganese-catalyzed dehydrative [2 + 2 + 2] annulation reaction of a 1,3-dicarbonyl compound and a terminal alkyne provides an efficient and regioselective synthesis of a substituted benzene derivative, highlighted by the exclusive formation of a p-terphenyl derivative from an aryl acetylene. The mechanism and the origin of the regioselectivity of the reaction were explored by experiments and density functional theory (DFT) calculations. Experimental data revealed the cis stereochemistry of a cyclohexadienol precursor to the benzene product and suggested that two reaction pathways may operate competitively-sequential carbometalation reactions of a manganese enolate and formation of a manganacyclopentadiene intermediate. The DFT study supported the first possibility, namely that the reaction involves three steps: (1) addition of a manganese enolate of a 1,3-dicarbonyl compound to a terminal alkyne to give a vinylmanganese complex, (2) insertion of a second alkyne into the vinyl-Mn bond to give a dienylmanganese complex, and (3) intramolecular nucleophilic addition of the dienylmanganese to the carbonyl group. This mechanism is consistent with the experimental facts such as the perfect regioselectivity of the reaction of an aryl acetylene, the moderate regioselectivity of the reaction of an alkyl acetylene, and the stereochemistry of the annulation product. An alternative mechanism involving a manganacyclopentadiene intermediate failed to account for the experimental regioselectivity, although it may be occurring as a very minor competitive pathway.
AB - The manganese-catalyzed dehydrative [2 + 2 + 2] annulation reaction of a 1,3-dicarbonyl compound and a terminal alkyne provides an efficient and regioselective synthesis of a substituted benzene derivative, highlighted by the exclusive formation of a p-terphenyl derivative from an aryl acetylene. The mechanism and the origin of the regioselectivity of the reaction were explored by experiments and density functional theory (DFT) calculations. Experimental data revealed the cis stereochemistry of a cyclohexadienol precursor to the benzene product and suggested that two reaction pathways may operate competitively-sequential carbometalation reactions of a manganese enolate and formation of a manganacyclopentadiene intermediate. The DFT study supported the first possibility, namely that the reaction involves three steps: (1) addition of a manganese enolate of a 1,3-dicarbonyl compound to a terminal alkyne to give a vinylmanganese complex, (2) insertion of a second alkyne into the vinyl-Mn bond to give a dienylmanganese complex, and (3) intramolecular nucleophilic addition of the dienylmanganese to the carbonyl group. This mechanism is consistent with the experimental facts such as the perfect regioselectivity of the reaction of an aryl acetylene, the moderate regioselectivity of the reaction of an alkyl acetylene, and the stereochemistry of the annulation product. An alternative mechanism involving a manganacyclopentadiene intermediate failed to account for the experimental regioselectivity, although it may be occurring as a very minor competitive pathway.
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U2 - 10.1021/ja809202y
DO - 10.1021/ja809202y
M3 - Article
C2 - 19254030
AN - SCOPUS:67849111871
VL - 131
SP - 4099
EP - 4109
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 11
ER -