ORGANIC
LETTERS
2012
Vol. 14, No. 1
280–283
Synthesis of Propargylic and Allenic
Carbamates via the CꢀH Amination of
Alkynes
R. David Grigg,† Jared W. Rigoli,† Simon D. Pearce, and Jennifer M. Schomaker*
Department of Chemistry, University of Wisconsin;Madison, Madison, Wisconsin
53706, United States
*schomakerj@chem.wisc.edu
Received November 12, 2011
ABSTRACT
Propargylic amines are important intermediates for the synthesis of nitrogen-containing heterocycles. The insertion of a nitrene into a propargylic
CꢀH bond has not been explored, despite the attention directed toward the Rh-catalyzed amination of other types of CꢀH bonds. In this
communication, the conversion of a series of homopropargylic carbamates to propargylic carbamates and aminated allenes is described.
Propargyl amines are versatile synthetic building blocks
for the construction of diverse heterocycles, including ox-
azoles, indolizines, pyrroles, quinolines, and pyrrolidines.1
The most common approaches to synthesize propargyl
amines involve either the addition of an acetylide to an
imine or ketimine or the transition-metal-catalyzed cou-
pling of an aldehyde, amine, and alkyne. In many of these
cases, the use of an aromatic aldehyde or a secondary
amine is required, limiting the scope of the reaction.2,3 In
the context of other studies ongoing in our group, we were
interested in the synthesis of allenic amines of the form 2b
(Scheme 1), where the nitrogen could be either readily
deprotected or further functionalized.
Since the preparation of vicinal and 1,3-aminoalcohols
via the Rh-catalyzed insertion of carbamate and sulfa-
mate-derived nitrenes into benzylic, allylic, allenic, and
methylene CꢀH bonds is so well-established, we at-
tempted to prepare 2b by employing allenic carbamate 1
as the substrate (Scheme 1).4 However, allene aziridination
to the bicyclic methylene aziridine 2a was always a major
competing reaction (Scheme 1, top) and, in fact, was the
exclusive product obtained when sulfamate nitrene precur-
sors were employed.5 The desired CꢀH amination product
2b could be obtained selectively only through substrate
control; thus, we sought to gain exclusive access to allenic
amines by an alternative approach.5b
† These authors contributed equally.
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r
10.1021/ol203055v
Published on Web 12/19/2011
2011 American Chemical Society