C O M M U N I C A T I O N S
9). The reactions of propargylic amines 3fd and 3gd also gave
4f and 4g in 75% and 66% yields, respectively (entries 10 and
11).
A representative procedure for the palladium-catalyzed hydrogen
migration reaction is as follows. To a solution of 3cd (0.4 mmol)
in dry dioxane (1 mL) were added Pd2dba3‚CHCl3 (0.01 mmol)
and (C6F5)3P (0.08 mmol). The mixture was stirred at 100 °C for
24 h. The reaction progress was monitored by GC. The solvent
was removed under reduced pressure, and the residue was purified
by silica gel column chromatography with hexane to give 4c
quantitatively.
We developed a novel transformation of allenes using propargylic
amines as an allenyl anion equivalent. The use of (C6F5)3P is
essential for the palladium-catalyzed hydrogen-transfer reaction.
Although mechanisms based upon either Pd(0)20 or Pd(II) could
be envisaged (details are discussed in the Supporting Information),
hydrogen transfer from a C-H bond adjacent to nitrogen to an
alkyne moiety via a hydride-palladium would give the allenes 4.
Further extension of the catalytic allene transformation using
propargylic amines as an allene equivalent is now in progress.
Propargyl diisopropylamines, as an allenyl anion equivalent, can
be introduced into carbonyl compounds. Various propargylic
alcohols and the benzyl ether (5a-f) containing a diisopropyl-
aminomethyl group were synthesized by the addition of a lithium
acetylide of 2d to aldehydes and a ketone. The results are
summarized in Table 2. The allene transformation reaction of 5a,
which was prepared from benzaldehyde and 2d, proceeded in
the presence of Pd2dba3‚CHCl3/(C6F5)3P at 80 °C in dioxane for
13 h, giving the corresponding allene 6a in 64% yield (entry 1).
The benzyl ether 5b, however, afforded 6b in a higher yield (91%;
entry 2). The propargylic alcohols 5c-e, derived from 4-anisalde-
hydes, 3,5-dimethoxybenzaldehyde, and hexanal, respectively,
underwent the transformation reaction to give the corresponding
allenes 6c-e in 56-92% yields (entries 3-5). The reaction of 5f,
derived from cyclohexanone, also proceeded to give 6f in 86% yield
(entry 6).
Supporting Information Available: Experimental details, mech-
anisms, and characterization data for compounds 3, 4b-g, and 6a-f
(PDF). This material is available free of charge via the Internet at http://
pubs.acs.org.
Table 2. Palladium-Catalyzed Hydrogen-Transfer Reaction of 5
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a The reactions were carried out in the presence of Pd2dba3‚CHCl3 catalyst
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b Isolated yields.
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