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Ti‐Catalyzed Straightforward Synthesis of Exocyclic Allenes
Author(s) -
MuñozBascón Juan,
HernándezCervantes Carmen,
Padial Natalia M.,
ÁlvarezCorral Míriam,
Rosales Antonio,
RodríguezGarcía Ignacio,
Oltra J. Enrique
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201304033
Subject(s) - allene , enantioselective synthesis , chemistry , catalysis , propargyl , combinatorial chemistry , functional group , halide , organic chemistry , stereochemistry , polymer
Exocyclic allenes constitute useful building blocks in organic synthesis and have recently been identified as key intermediates in the synthesis of natural products. Here the first general method for the most straightforward synthesis of exocyclic allenes reported to date is presented. This method is based on the Barbier‐type cyclization of propargyl halides catalyzed by titanium; a safe, abundant, and ecofriendly metal. The reaction proceeds under mild conditions compatible with different functional groups and provides good yields of five‐, six‐, and seven‐membered carbocycles and nitrogen‐containing heterocycles bearing an exocyclic allene group. Experimental evidence supporting the proposed reaction mechanism is also provided. Moreover, this procedure can be carried out in an enantioselective manner by using chiral titanocene(III) catalysts. The utility of this method has been proved in the synthesis of the natural alkaloid stemoamide.