Angewandte
Communications
Chemie
[
a]
Table 1: Effect of substituents at the diyne termini.
1
2
[b]
[b]
Entry
1 (R , R )
3
Yield [%] (E/Z)
4
Yield [%]
1
2
3
1a (Me, Me)
1b (Me, Ph)
1c (Ph, Ph)
3aa
3ba
3ca
16
4aa
4ba
4ca
34
8
<5
43 (75:25)
70
[
a] [Rh(cod) ]BF (0.010 mmol), H -binap (0.010 mmol), 1 (0.10 mmol),
2
4
8
2
a (0.11 mmol), and CH Cl (2.0 mL) were used. [b] Yield of the isolated
2 2
product. cod=1,5-cyclooctadiene, H -binap=2,2’-bis(diphenylphos-
8
phino)-5,5’,6,6’,7,7’,8,8’-octahydro-1,1’-binaphthyl.
Table S1 in the Supporting Information). The scope of this
fulvene synthesis was then explored as shown in Scheme 2.
With respect to the cyclopropylideneacetamide, not only
tertiary amides (substrates 2a and 2b) but also secondary
(
substrates 2c and 2d) and primary amides (substrate 2e)
reacted with 1c to give fulvenes 3ca–ce in good yields. With
respect to the linker (Z, X) of the 1,6-diyne, not only oxygen-
(
(
substrate 1c) but also tosylamide- (substrate 1d), ester-
substrate 1e), and malonate-linked 1,6-diynes (substrate 1 f)
reacted with 2a to give fulvenes 3da–fa in good yields. With
respect to the substituents R and R of the 1,6-diyne,
electron-rich and electron-poor phenyl-substituted diynes
Scheme 2. Scope of the synthesis of fulvenes 3. [Rh(cod) ]BF
4
1
2
2
(0.020 mmol), segphos (0.020 mmol), 1 (0.20–0.24 mmol), 2 (0.20–
0
.22 mmol), and (CH Cl) (2.0 mL) were used. Cited yields are for the
2 2
1
g–i were suitable substrates, although the reaction of
isolated products. [a] Reaction time: 40 h. [b] A solution of
1 (1.2 equiv) was added to a solution of 2 (1.0 equiv) and the Rh
catalyst over 5 h, and the mixture was stirred for 1 h. [c] The reaction
was carried out at room temperature. A solution of 1 (1.2 equiv) was
added to a solution of 2 (1.0 equiv) and the Rh catalyst over 9 h, and
the resulting mixture was stirred for 9 h. Bn=benzyl.
sterically bulky 1i required a prolonged reaction time. Not
only diaryl- but also phenyl/methyl- (substrate 1b), dimethyl-
(
(
substrate 1a), and methoxycarbonyl-substituted 1,6-diynes
substrates 1j and 1k) reacted with 2a and 2b to give the
corresponding fulvenes 3ba, 3bb, 3aa, 3ja, and 3ka. For the
preparation of 3ba, 3aa, and 3ka, the slow addition of 1 to 2a
and the Rh catalyst was preferable to suppress the undesired
tigation with 3ca–ce, which were obtained in high yields as
air-stable solids (except 3cb; Scheme 4). The complexation of
3ca–ce bearing various amide moieties with RhCl ·nH O in
[
3+2+2] cycloaddition of 1 with 2a and/or [2+2+2] dimeri-
zation of 1.
A plausible reaction mechanism for the formation of 3 is
shown in Scheme 3a. Thus, oxidative addition of 2 to rhodium
3
2
EtOH proceeded almost quantitatively to give the corre-
A
III
sponding Cp Rh complexes 5ca–ce, which were isolated in
[
15]
generates rhodacyclobutane A, which undergoes b-carbon
elimination to give the ethylene-coordinated rhodium vinyl-
idene species B.
moiety of 1 affords the alkyne-coordinated rhodacyclobutene
C through the release of ethylene. Insertion of the pendant
alkyne generates rhodacyclohexadiene D, which undergoes
high yields as air-stable red solids by precipitation.
A
III
Gratifyingly, the Cp Rh complex 5cd with pendant
[13]
The [2+2] cycloaddition of the alkyne
amides was a highly active catalyst for oxidative annulation
2
3
and cyclization reactions through C(sp )ꢀH and C(sp )ꢀH
[16]
functionalization (Scheme 5). Complex 5cd catalyzed the
oxidative [3+2] annulation of acetanilide (6) with diphenyl-
acetylene (7) to give N-acetylindole 8. In this reaction, the
catalytic activity of 5cd was higher than that of Cp*Rh and
comparable to that of Cp Rh catalysts.
I+
reductive elimination to afford 3 and regenerate the Rh
III
catalyst. As the generation of rhodacyclopentadiene E, which
affords 4 via rhodacycles F and G, might compete with the
formation of rhodacyclobutane A, a higher concentration of 2
relative to that of 1 is preferable for the selective synthesis of
E
III
[3c,17]
Furthermore,
complex 5cd catalyzed the intramolecular allylic amidation of
alkenyl tosylamide 9 to give vinylpyrrolidine 10 with higher
III
E
III
[3f,18]
3. Consistent with this proposed mechanism, ethylene gen-
activity than both Cp*Rh and Cp Rh catalysts.
Thus,
[
13,14]
1
eration
was confirmed by H NMR analysis of the crude
the pendant amide moiety may play an important role in both
2
3
reaction mixture (Scheme 3b).
C(sp )ꢀH and C(sp )ꢀH functionalization, although the
mechanism is not clear at the present stage. As the reductive
complexation of fulvenes 3 with RhCl ·nH O in EtOH
We anticipated that fulvenes 3 would be useful precursors
III
[3a]
of CpRh complexes. We conducted a preliminary inves-
3
2
2
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2017, 56, 1 – 5
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