Ketyl-Allene Cyclizations Promoted by Samarium(II) Iodide†
Gary A. Molander* and Elizabeth Pollina Cormier
Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania,
Philadelphia, Pennsylvania 19104-6323
Received November 29, 2004
Samarium(II) iodide has proven to be an effective reagent for intramolecular reductive coupling
reactions. Previous investigations of intramolecular ketyl-olefin coupling reactions provided
carbocycles in excellent yield and good diastereoselectivity. This method has been extended to ketyl
cyclizations with allenes. Substrates leading to both carbocycles and heterocycles in a selective
manner are explored.
Introduction
Recently, an influx of research concerning the forma-
tion of homoallylic alcohols via palladium-, rhodium-, and
nickel-catalyzed carbonyl-allene cyclizations has ap-
peared in the literature.5 Allenyl ketone and aldehyde
cyclizations utilizing electrolysis,6 photochemistry,7 and
dissolving metals8 were reported nearly two decades ago,
proceeding through a ketyl radical intermediate. The
reaction of allenes with ketyl radicals generated from
SmI2 was first reported by Gillmann some years ago on
a single intramolecular ketyl-allene system.9 More re-
cently, Reissig communicated his results of the intermo-
lecular reaction of aldehydes and ketones with methoxy-
allene as an acrolein equivalent.10 To expand upon the
aforementioned chemistry, intramolecular cyclizations
onto allenes were investigated. A thorough investigation
Carbon radicals are reliable and efficient intermediates
for the selective construction of carbon-carbon bonds. As
a result of their demonstrated synthetic utility, the use
of carbon radicals in contemporary organic chemistry has
received much attention. Our group has focused upon the
samarium diiodide (SmI2)1 promoted intramolecular re-
ductive coupling reactions of ketyl radicals with unsatur-
ated systems, such as alkenes,2 alkynes,3 and nitriles.4
These reductive cyclizations generate functionalized car-
bocycles containing tertiary alcohols.
† Dedicated to Professor Iwao Ojima on the occasion of his 60th
birthday.
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10.1021/jo047887s CCC: $30.25 © 2005 American Chemical Society
Published on Web 03/01/2005
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