Mechanistic study of the manganese-catalyzed [2 + 2 + 2] annulation of 1,3-dicarbonyl compounds and terminal alkynes

Naohiko Yoshikai, Song Lin Zhang, Ken Ichi Yamagata, Hayato Tsuji, Eiichi Nakamura

Research output: Contribution to journalArticlepeer-review

43 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)4099-4109
Number of pages11
JournalJournal of the American Chemical Society
Volume131
Issue number11
DOIs
Publication statusPublished - 2009 Mar 25
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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