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DOI: 10.1055/s-2006-950305
Regioselective Couplings of Dibromopyrrole Esters
Publikationsverlauf
Publikationsdatum:
12. Oktober 2006 (online)
Abstract
The regioselectivity of the Suzuki couplings of several 4,5- and 3,4-dibromopyrrole-2-carboxylate esters has been studied. In general, regioselectivity can be achieved for initial coupling at the more electron-deficient site (C5 and C3, respectively). At the same time, conversions are often modest (40-60%) and attempts to force the reactions to higher conversions often lead to competitive dicoupling.
Key words
Suzuki cross-coupling - regioselectivity - electronic effects - pyrroles - palladium
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Handy ST.Zhang Y. Org. Prep. Proced. Int. 2005, 37: 411 - 3
Handy ST.Zhang Y.Bregman H. J. Org. Chem. 2004, 69: 2362 - 4
Hodge P.Richard R. J. Chem. Soc. 1965, 459 - 5 For a review, see:
Schröter S.Stock C.Bach T. Tetrahedron 2005, 61: 2245 - Recently, two reports of regioselective couplings of pyrroles have appeared:
-
6a
Handy ST.Sabatini JJ. Org. Lett. 2006, 8: 1537 -
6b
Schröter S.Bach T. Synlett 2005, 1957 - 8
Handy ST.Bregman H.Lewis J.Zhang Y. Tetrahedron Lett. 2003, 44: 427 - 9
Bray B.Mathies P.Naef R.Solas D.Tidwell T.Artis D.Muchowski J. J. Org. Chem. 1990, 55: 6317 - 10
Handy ST.Sabatini JJ.Zhang Y.Vulfova I. Tetrahedron Lett. 2004, 45: 5057 - 11
Rawal VH.Jones RJ.Cava MP. J. Org. Chem. 1987, 51: 19 - 13
Fauvarque J.-F.Pfleuger F.Troupel M. J. Organomet. Chem. 1981, 208: 419 - 14
Handy ST.Zhang Y. Chem. Commun. 2006, 299 - 15
Harbuck JW.Rapoport H. J. Org. Chem. 1972, 37: 3618 - 16
Donohoe TJ.Guyo PM.Beddoes RL.Helliwell M. J. Chem. Soc., Perkin Trans. 1 1998, 667
References
Current address: Department of Chemistry, Middle Tennessee State University, Murfreesboro, TN 37132, USA.
7The one remaining isomeric dibromopyrrole ester (3,5-dibromo) has also been prepared. The regioselectivity of the Suzuki couplings of this substrate exhibit an unusual solvent dependency that remains under investigation.
12Bases tried include the following: Na2CO3, K2CO3, Cs2CO3, K3PO4, and Ba(OH)2. Solvents tried include the following: DMF, EtOH-toluene, acetone, and H2O.