Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 15, Issue 8, Pages 1901-1908Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200802034
Keywords
allenes; cyclization; gold; heterocycles; palladium
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Funding
- DGI-MEC [CTQ2006-10292]
- Comunidad Autonoma de Madrid [CCG-07-UCM/PPQ-2308]
- Universidad Complutense de Madrid [GR74/07]
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We describe versatile regio-controlled metal-catalyzed heterocyclization reactions of gamma-allenol derivatives leading to a variety of fused enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines. Regioselectivity control in the O-C functionalization of gamma-allenols can be achieved through the choice of catalyst: use of AuCl3 exclusively affords tetrahydrofurans, use of La[N(SiMe3)(2)](3) usually favors the formation of dihydropyrans, whereas use of PdCl2 solely gives tetrahydrooxepines. In addition, it has been observed that for the Au-catalyzed cycloisomerization, the presence of a methoxymethyl protecting group not only masks a hydroxy functionality, but also exerts directing effects as a controlling unit in a regioselectivity reversal (7-endo versus 5-exo cyclization). In addition, the regioselectivity of the La-catalyzed cycloetherification can be tuned (5-exo versus 7-endo) simply through a subtle variation in the substitution pattern of the allene component (Ph versus Me). Thus, for the first time the regiocontrolled heterocyclization of gamma-allenol derivatives is both catalyst- and substrate-directable. These metal-catalyzed heterocyclization reactions have been developed experimentally (Part 1, this paper), and their mechanisms have additionally been investigated by a theoretical study (Part 2, accompanying paper).
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