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Synfacts 2012; 8(4): 0439
DOI: 10.1055/s-0031-1290542
Metal-Mediated Synthesis
© Georg Thieme Verlag Stuttgart · New York

n-BuLi-Initiated Ring-Opening Cyclization of Cyclopropene Derivatives

Contributor(s):
Paul Knochel
,
Andreas K. Steib
Liu Y, Ma S * Shanghai Institute of Organic Chemistry and East China Normal University, Shanghai, P. R. of China
Benzofurans or Isochromenes via the Ring-Opening Cyclization of Cyclopropene Derivatives with Organolithiums.

Org. Lett. 2012;
14: 720-723
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Publication History

Publication Date:
20 March 2012 (online)

 
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Key words

lithium - ring-opening cyclization - cyclopropenes

Significance

The authors report a new access to benzocycles from cyclopropene derivatives. Treatment of 2-acetyl or 2-acetoxymethyl cyclopropenes with n-BuLi leads to deprotection and subsequent ring-opening cyclization to yield benzofurans and isochromenes in a one-pot procedure.


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Comment

Based on deuterium experiments a plausible mechanism is proposed: The reaction of A with n-BuLi forms B and the oxygen anion in B attacks the cyclopropene moiety to give D. Alternatively, an excess of n-BuLi may further deprotonate the olefinic proton to generate dianion C, which may also undergo ring-opening cyclization to give E.


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