Synlett 1998; 1998(7): 741-745
DOI: 10.1055/s-1998-1758
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Palladium-Catalyzed Cyclization of o-Alkynylphenols with Allyl Carbonates. A Regioselective Synthesis of 2-Substituted-3-allylbenzo[b]furans

Sandro Cacchi* , Giancarlo Fabrizi, Leonardo Moro
  • *Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Università "La sapienza", P.le A. Moro 5, 00185 Roma, Italy; Fax + 39 (6) 4991.2780; E-mail: cacchi@axrma.uniroma1.it
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Publikationsdatum:
31. Dezember 2000 (online)

2-Substituted-3-allylbenzo[b]furans 3 can be prepared from o-alkynylphenols 1 and allyl carbonates 2 through a palladium-catalyzed O-allylation/cyclization sequence. Two basic procedures have been developed: a stepwise method based on the isolation of O-allyl derivatives 4 and their subsequent cyclization to 3 (procedure A) and a one-pot reaction omitting the isolation of 4 (procedure B). The cyclization of 4 in the presence of the electron-rich sterically-encumbered ligand tris(2,4,6-trimethoxyphenyl)phosphine (ttmpp)exhibits remarkable regioselectivity in that 3-allylbenzofurans in which the benzofuryl unit is bound to the less substituted allyl terminus are formed almost exclusively. Some loss of the stereochemistry of the carbon-carbon double bond is observed.