The Synthesis and Chemoselective Reactivity of 3-Aminocyclopentadienones

Article abstract of DOI:10.1021/jo001044t

Iron and cobalt complexes of 3-aminocyclopentadienones have been synthesized from the [2 + 2 + 1] cycloadditions of nitrogen acetylenes and pendant alkynes. Following decomplexation, the resulting 3-aminocyclopentadienones have been subjected to chemo- and regioselective cycloadditions with dienophiles and heterodienes.

Full text of DOI:10.1021/jo001044t

7272
J . Org. Chem. 2000, 65, 7272-7276
Th e Syn th esis a n d Ch em oselective Rea ctivity of
3-Am in ocyclop en ta d ien on es
J on D. Rainier* and J ason E. Imbriglio
Department of Chemistry, The University of Arizona, Tucson, Arizona 85721
rainier@u.arizona.edu
Received J uly 12, 2000
Iron and cobalt complexes of 3-aminocyclopentadienones have been synthesized from the [2 + 2 +
1] cycloadditions of nitrogen acetylenes and pendant alkynes. Following decomplexation, the
resulting 3-aminocyclopentadienones have been subjected to chemo- and regioselective cycloadditions
with dienophiles and heterodienes.
In tr od u ction
Although cyclopentadienones are widely recognized as
having a high degree of synthetic potential, their relative
instability has limited their use in organic synthesis.1
Because of this, a significant amount of effort has
targeted the synthesis and use of masked cyclopentadi-
enones. A few of these are illustrated in Figure 1 and
include the following: (a) cyclopentadienone-cyclopenta-
diene Diels-Alder adducts (e.g., 1);2 (b) 4-alkoxycyclo-
pentenones (e.g., 2);3 (c) oxime adducts (e.g., 3);4 (d)
cyclopentadienone-transition metal complexes (e.g., 4).5
While the masking strategies depicted in Figure 1 are
cleverly designed and clearly of utility, from our perspec-
tive a better synthetic strategy would be one that used
cyclopentadienones directly. With this as one of our goals,
we have recently targeted and communicated the genera-
tion and use of 3-aminocyclopentadienones (e.g., 5, Figure
2).6,7 This came out of the notion that the divergent
electronic properties of the two enones (one being a
vinylogous amide) might enable us to use them in chemo-
and regioselective reactions and ultimately in the syn-
thesis of interesting alkaloids. As we are aware of very
few examples of the use of cyclopentadienones in complex
molecule synthesis,8,9 the success of these ventures would
demonstrate that strategies incorporating cyclopentadi-
enones are of merit.
F igu r e 1.
F igu r e 2.
well documented that substitution about the cyclopen-
tadienone leads to its stabilization.1 As our ultimate
interests included the use of 5 in the synthesis of
interesting alkaloids, we placed the additional constraint
on 5 that R, R′, and P be of general synthetical utility.
With regard to their synthesis, we became fascinated
with the generation of 3-aminocyclopentadienones from
cobalt- and iron-mediated [2 + 2 + 1] cycloaddition
reactions of nitrogen acetylenes (ynamines) and pendant
alkynes. While ynamines had not been utilized in this
context prior to our work,10,11 they had been used by
Witulski in cobalt-mediated Pauson-Khand reactions12
and in independent studies by Ficini13 and Witulski14 in
Ni- and Rh-mediated cycloaromatization reactions, re-
spectively. In addition to efficiency of synthesis, we were
Clearly, the aforementioned goals required that (a) we
have an efficient entry into 3-aminocyclopentadienones
(e.g., 5) and (b) that 5 be stable enough to isolate or to
trap. With respect to the latter requirement, it has been
(1) Ogliaruso, M. A.; Romanelli, M. G.; Becker, E. I. Chem. Rev.
1965, 65, 261.
(2) Dols, P. P. M. A.; Lacroix, L.; Klunder, A. J . H.; Zwanenburg, B.
Tetrahedron Lett. 1991, 32, 3739.
(3) Harre, M.; Raddatz, P.; Walenta, R.; Winterfeldt, E. Angew.
Chem., Int. Ed. Engl. 1982, 21, 480.
(4) Mackay, D.; Papadopoulos, D.; Taylor, N. J . J . Chem. Soc., Chem.
Commun. 1992, 325.
(10) For reviews on the chemistry of nitrogen acetylenes, see: (a)
Ficini, J . Tetrahedron 1976, 32, 1448. (b) Himbert, G. Methoden der
Organischen Chie (Houben-Weyl); Kropf, H., Schaumann, E., Eds.;
Georg Thieme Verlag: Stuttgart, 1993; p 3267.
(5) For
a review of metal cyclopentadienone complexes, see:
Kno¨lker, H.-J . Chem. Soc. Rev. 1999, 28, 151.
(11) For recent examples of the use of nitrogen acetylenes in
cycloaddition chemistry, see refs 12, 14, and: Hsung, R. P.; Zificsak,
C. A.; Wei, L.-L.; Douglas, C. J .; Xiong, H.; Mulder, J . A. Org. Lett.
1999, 1, 1237.
(12) (a) Witulski, B.; Stengel, T. Angew. Chem., Int. Ed. Engl. 1998,
37, 489. (b) Witulski, B.; Go¨âmann, M. J . Chem. Soc., Chem. Commun.
1999, 1879.
(6) Rainier, J . D.; Imbriglio, J . E. Org. Lett. 1999, 1, 2037.
(7) We are aware of one other aminocyclopentadienone. See:
LePage, T.; Nakasuji, K.; Breslow, R. Tetrahedron Lett. 1985, 48, 5919.
(8) Kno¨lker has utilized a cyclopentadienone in the synthesis of
corranulene. See: Kno¨lker, H.-J .; Braier, A.; Bro¨cher, D. J .; J ones, P.
G.; Piotrowski, H. Tetrahedron Lett. 1999, 40, 8075.
(9) Herndon has utilized reduced cyclopentadienones in synthesis,
see: Herndon, J . W.; Zhu, J . Org. Lett. 1999, 1, 15 and references
contained therein.
(13) Ficini, J .; d'Angelo, J .; Falou, S. Tetrahedron Lett. 1977, 1645.
(14) Witulski, B.; Stengel, T. Angew. Chem., Int. Ed. Engl. 1999,
38, 2426.
10.1021/jo001044t CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/03/2000

Synthesis and Reactivity of 3-Aminocyclopentadienones
J . Org. Chem., Vol. 65, No. 22, 2000 7273
Ta ble 1.
Sch em e 1
entry
product
M
R
yield (%)
1
2
14
15
CoCpa
Fe(CO)3
TMS
TMS
57
84
b
a
b
CpCo(CO2, hν, -20 °C f rt. Fe(CO)5, PhCH3, 110 °C.
Sch em e 2
attracted to the use of metal-mediated [2 + 2 + 1]
cycloadditions because the cyclopentadienones would be
generated as isolable metal complexes that might be
interesting in their own right.15,16
Outlined herein is a full report of our investiga-
tions demonstrating that cobalt and iron complexes of
[3.3.0]-, [4.3.0]-, and [5.3.0]aminocyclopentadienones can
be synthesized from yne-ynamine cycloaddition reac-
tions.6 Also described is the decomplexation of the cyclo-
pentadienones and their capture with dienophiles as well
as dienes in chemo- and regioselective cycloaddition
reactions.
amino alkynes 6 and 7, respectively. Conversion of 6 and
7 into the corresponding ynamine precursors 8 and 9
involved TMS-alkyne formation and selective thermal
removal of the Boc group.18 Ynamine formation provided
12 and 13, respectively.
Yn e-Yn a m in e Cycloa d d ition s to Cyclop en ta d i-
en on e Com p lexes. With access to yne-ynamine cy-
cloaddition precursors, we investigated their conversion
into the corresponding cobalt and iron cyclopentadienone
complexes via [2 + 2 + 1] cycloaddition reactions. To our
delight, when 11 was subjected to Vollhardt’s conditions
for the corresponding all-carbon cycloaddition (CpCo(CO)2
and photolysis at low temperature)15b we isolated cobalt
cyclopentadienone complex 146 as a dark red solid in 57%
yield (Table 1). Yne-ynamine 11 also proved amenable
to iron-mediated cycloaddition. Yellow cyclopentadienone
complex 15 was generated in 84% yield upon exposure
of 11 to Fe(CO)5 and elevated temperatures (Table 1).
Having generated iron and cobalt [3.3.0] complexes 14
and 15, we targeted the corresponding [4.3.0]- and [5.3.0]-
cyclopentadienone complexes. Thus far, all of our at-
tempts to generate [4.3.0]cobalt complex 16 from 12 using
the conditions that were successful for the synthesis of
14 have resulted in the formation of cyclobutadiene
complex 17 (Scheme 2).
Resu lts a n d Discu ssion
Yn e-Yn a m in e Syn th esis. We have synthesized yne-
ynamine cycloaddition precursors having 2-, 3-, and
4-carbon tethers between the alkyne and ynamine as
depicted in Scheme 1. Yne-ynamine cyclization precur-
sor 11 was synthesized in two steps from N-tosylaziri-
dine. Namely, ring opening of N-tosylaziridine with
lithium trimethysilylacetylide followed by ynamine for-
mation using Stang’s iodoacetylene salt 10 provided yne-
ynamine 11 in synthetically useful yields.17 The homolo-
gous yne-ynamines 12 and 13 were synthesized from the
corresponding alkynols. Mitsunobu coupling of (BOC)-
NH(Ts) with 4-pentyn-1-ol and 5-hexyn-1-ol provided
In contrast, the corresponding iron-mediated [2 + 2 +
1] cycloadditions provided iron [4.3.0]- and [5.3.0]cyclo-
pentadienone complexes in respectable yields (Table 2).
When yne-ynamine 12 was subjected to Fe(CO)5 and
heat, we isolated mono- and bis-TMS cobalt [4.3.0]
complexes in a 2.2:1 ratio in 96% overall yield.19 Simi-
larly, the 3-amino[5.3.0]cyclopentadienone iron complex
20 was obtained in 54% yield from the cycloaddition of
yne-ynamine 13.
These cycloadditions compare favorably with the cor-
responding all-carbon variants. In independent studies,
both Pearson and Kno¨lker have generated the all-carbon
[4.3.0]- and [5.3.0]cyclopentadienone-iron complexes but
in 57% and 50-59% yield (Pearson)20 and 82% and 15%
(15) Co-cyclopentadienone complexes: (a) McDonnell Bushnell, L.
P.; Evitt, E. R.; Bergman, R. G. J . Organometallic Chem. 1978 157,
445. (b) Gesing, E. R. F.; Tane, J . P.; Vollhardt, K. P. C. Angew. Chem.,
Int. Ed. Engl. 1980, 19, 1023. (c) For a Co-mediated [2 + 2 + 1]
cycloaddition of bis-alkynes where decomplexation occurs in situ, see:
Shibata, T.; Ohta, T.; Soai, K. Tetrahedron Lett. 1998, 39, 5785. (c)
Fe-cyclopentadienone complexes: (b) Pearson, A. J .; Dubbert, R. A. J .
Chem. Soc., Chem. Commun. 1991, 371. (c) Kno¨lker, H.-J .; Heber, J .;
Mahler, C. H. Synlett. 1992, 1002. (b) Pearson, A. J .; Shively, R. J .,
J r.; Dubbert, R. A. Organometallics 1992, 11, 4096. (c) Pearson, A. J .;
Shively, R. J ., J r. Organometallics 1994, 13, 578. (d) Brookhart, M.;
Chandler, W. A.; Pfister, A. C.; Santini, C. C.; White, P. S. Organo-
metallics 1992, 11, 1263. Ru-cyclopentadienone complexes: (d) Mauth-
ner, K.; Mereiter, K.; Schmid, R.; Kirchner, K. Organometallics 1994,
13, 5054. (e) Mo- and W-cyclopentadienone complexes: Slugovc, C.;
Mauthner, K. Mereiter, K.; Schmid, R.; Kirchner, K. Organometallics
1996, 15, 2954. Ox-cyclopentadienone complexes: Washington, J .;
McDonald, R.; Takats, J .; Menashe, N.; Reshef, D.; Shvo, Y. Organo-
metallics 1995, 14, 3996. Ni-cyclopentadienone complexes: (e) Tamao,
K.; Kobayashi, K.; Ito, Y. Synlett 1992, 539.
(18) (a) Henry, J . R.; Marcin, L. R.; McIntosh, M. C.; Scola, P. M.;
Harris, G. D., J r.; Weinreb, S. M. Tetrahedron Lett. 1989, 30, 5709.
(b) Downham, R.; Ng, F. W.; Overman, L. E. J . Org. Chem. 1998, 63,
8096.
(19) It is not clear at the present time whether mono-TMS adduct
19 results from an acid mediated desilylation reaction of 18 or one of
the intermediates leading to 18.
(16) Metal cyclopentadienone complexes have been shown to be
amenable to reactions on the cyclopentadienone. (a) Tane, J . P.;
Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1982, 21, 617. (b)
Pearson, A. J .; Shively, R. J ., J r.; Dubbert, R. A. Organometallics 1992,
11, 4096.
(17) Modern Acetylene Chemistry; Stang, P. J ., Diederich, F., Eds.;
VCH: Weinheim, 1995.
(20) Pearson, A. J .; Yao, X. Synlett 1997, 1281.

7274 J . Org. Chem., Vol. 65, No. 22, 2000
Rainier and Imbriglio
Ta ble 2.
late resulted in the formation of dihydroindolene 23 as a
single regioisomer in 67% yield from 14 (Scheme 3).22 As
it is widely accepted that C-5 substitution greatly stabi-
lizes cyclopentadienones,23 the efficient entry into 23 is
made all the more remarkable by the lack of vinylogous
amide substitution in 22.
Similarly, when a solution of cyclopentadienone 22 was
exposed to DMAD and heat indolene 24 was isolated in
78% yield from complex 14 (Table 3).24 Presumably,
decarbonylation was occurring in the course of the
synthesis of both 23 and 24 as we have not been able to
isolate the adduct prior to loss of CO.
entry
1
product
n
R
yield (%)
96a
18
19
20
2
2
3
TMS
H
TMS
2
54
a
Ca. 2.1:1 ratio of 18:19 was isolated from the cycloaddition of
Having successfully carried out the decomplexation of
cobalt complex 14 and subsequent cycloaddition of the
corresponding cyclopentadienone we then took aim at
iron cyclopentadienones 15, 18, and 20. As has been the
experience of others,25 we have found the decomplexation
of the iron complexes to be somewhat more problematic
in comparison to cobalt complex 14 and have investigated
a number of decomplexation protocols. Thus far, we have
examined the oxidative decomplexation using trimethyl-
amine N-oxide (TMANO) and morpholine N-oxide (NMO)
along with the base-induced decomplexation using NaOH.
In reactions that nicely complement the decomplexation
of 14, the decomplexation of bis-TMS cyclopentadienone
complex 15 with TMANO, NMO, or NaOH provided a
solution of bis-TMS cyclopentadienone 21. As was the
case in the cobalt decomplexation reaction, we did not
isolate 21 but instead immediately subjected it to cy-
cloaddition reactions with DMAD (Table 3) or unsatur-
ated carbonyl compounds (Table 4). In a fashion similar
to 22, the cycloaddition of 21 with DMAD resulted in the
formation of indolene 25 in moderate yield. Higher yields
were obtained when [3.3.0]- and [4.3.0]cyclopentadi-
enones 18 and 20 were carried through the decomplex-
ation and cyclization sequence with DMAD. Cycloaddi-
tion of [3.3.0]cyclopentadienone 26 gave a 54% overall
yield of cycloadduct 27 while [4.3.0]cyclopentadienone 28
gave a 70% overall yield of adduct 29.
12.
Sch em e 3
yield (Kno¨lker), respectively.21
Decom p lexa tion a n d Cycloa d d ition s of 3-Am i-
n ocyclop en ta d ien on es. With relatively efficient syn-
theses of metal cyclopentadienone complexes in hand, we
were prepared to test our hypothesis that 3-aminocyclo-
pentadienones might be valuable intermediates in com-
plex molecule synthesis. We initially targeted cycload-
dition reactions of metal-free 3-aminocyclopentadienones
because of the possibility that the divergent electronic
properties of the two enone alkenes would enable us to
carry these out chemo- and regioselectively.
Before examining the properties of 3-aminocyclopen-
tadienones, it was necessary to find conditions to effect
the decomplexation of 14, 15, 18, and 20. Upon exposure
of cobalt complex 14 to ceric ammonium nitrate (CAN)
at 0 °C for 1 h, we were able to generate a bright yellow
solution of cyclopentadienone 22 (Scheme 3).6 We sub-
sequently discovered that CAN had not only decomplexed
the cobalt but that it had also chemoselectively protode-
silylated the vinylogous amide. While we have been able
to access mixtures of mono-TMS cyclopentadienone 22
and bis-TMS cyclopentadienone 21 by subjecting 14 to
CAN for shorter periods of times, we have not been able
to selectively generate bis-TMS cyclopentadienone 21
from the CAN oxidative decomplexation of 14. In subse-
quent studies, we were able to isolate 21 from the
decomplexation of iron cyclopentadienone 15 (vide infra).
Due to our lack of success in our early attempts to
isolate 22 and its presumed instability to concentration,
we chose to immediately subject 22 to cycloaddition
reactions with dienophiles (Scheme 3 and Table 3) or
heterodienes (eq 2). Aqueous workup and dilution of the
yellow solution from decomplexation with an equal
volume of benzene followed by exposure to methyl acry-
We believe that the facility with which the highly
substituted aromatic heterocycles 24, 25, 27, and 29 have
been generated will be of significance for the synthesis
of these ring systems. Of interest is the observation that
1
the methylene protons in the H NMR spectra of 25, 27,
and 29 are magnetically inequivalent, implying a high
inversion barrier at the nitrogen atom when the ortho
position of the aryl ring is substituted with TMS.26
Interestingly, the decomplexation of 18 using TMANO
in acetone instead of CH2Cl2 provided dienone 30 as the
only product in 82% yield (eq 1). Kno¨lker and Pearson
have observed a similar phenomenon in the decomplex-
ation of the all carbon variant of 18.27
Having utilized 3-aminocyclopentadienones as the 4π
component in cycloadditions, we turned to their use as
(22) For the use of cyclopentadienones as dienes in cycloaddition
reactions see ref 1 and: (a) Kno¨lker, H.-J .; Baum, E.; Heber, J .
Tetrahedron Lett. 1994, 35, 578. (b) Baraldi, P. G.; Barco, A.; Benetti,
S.; Pollini, G. P.; Polo, E.; Simoni, D. J . Chem. Soc., Chem. Commun.
1984, 1049.
(21) Kno¨lker, H.-J .; Heber, J . Synlett 1993, 924.

Synthesis and Reactivity of 3-Aminocyclopentadienones
J . Org. Chem., Vol. 65, No. 22, 2000 7275
Ta ble 3.
cyclopenta-
dienone
yield
(%)
entry
1
M
conditionsa
n
R
product
CoCp
A
B
D
B
C
C
D
1
1
1
2
2
3
3
22
21
21
26
26
28
28
H
24
25
25
27
27
29
29
78
36
28
57
48
70
36
Fe(CO)3
Fe(CO)3
Fe(CO)3
Fe(CO)3
Fe(CO)3
Fe(CO)3
TMS
TMS
TMS
TMS
TMS
TMS
2
4
5
6
7
a
Key: A, CAN, B, TMANO; C, NMO; D, NaOH.
Ta ble 4.
entry
heterodiene
M
n
X
R
R′
R′′
adduct
yieldd (%)
a
1
2
3
4
5
6
acrolein
Fe(CO)3b
Fe(CO)3b
Fe(CO)3
CoCpc
1
1
2
1
1
1
TMS
21
21
H
H
H
H
32
32
33
34
35
36
54e
44e
66
acrolein
TMS
TMS
CH3
H
H
H
acrolein
H
H
H
CH3
H
methylvinyl ketone
crotonaldehyde
methacrolein
H
74
CoCpc
H
H
36
66
CoCpc
H
H
CH3
a
b
d
Decomplexed with NMO. Decomplexed with TMANO. c Decomplexed with CAN. Yield over two steps. e 4:1 mixture with the
corresponding enone adduct.
dienophiles in hetero-Diels-Alder cycloadditions with
unsaturated aldehydes and ketones.28,29 We were thrilled
to isolate adduct 31 in 82% yield from cobalt complex 14
when cyclopentadienone 22 was condensed with acrolein
(eq 2). This experiment truly demonstrates the utility of
3-aminocyclopentadienones as we have utilized them
chemo- and regioselectively as both dienes and dieno-
philes.
acrolein. In a fashion similar to 22, cyclopentadienone
26 reacted exclusively at the vinylogous amide to give
33 in 66% yield for the two steps (Table 4, entry 3). The
reaction of cyclopentadienone 21 was not as selective.
While its reaction with acrolein resulted in the formation
of vinylogous amide adduct 32 as the major product, it
also gave a small amount of a byproduct whose structure
we have tentatively assigned to the corresponding iso-
lated enone adduct (Table 4, entries 1 and 2).30 While
the enhanced selectivity of 22 relative to 21 can be
rationalized as being due to the presence of the vinylo-
gous amide TMS group in 21, at the present time it is
not clear why 26 is more selective than 21. The reaction
of 22 with heterodienes at the vinylogous amide appears
to be general. Aminocyclopentadienone 22 reacts with
methyl vinyl ketone (entry 4), crotonaldehyde (entry 5),
and methacrolein (entry 6) to give adducts 34, 35, and
36, respectively in reasonable yields for the two-step
process.
Both bis-TMS-substituted cyclopentadienones 21 and
26 also acted as 2π components in their reaction with
Surprisingly, 3-amino[5.3.0]cyclopentadienone 28 un-
derwent cycloaddition with acrolein at the isolated enone
instead of at the vinylogous amide to give 37 in 52% yield
(eq 3).31
(23) See ref 1 and Maier, G.; Lage, H. W.; Reisenauer, H. P. Angew.
Chem., Int. Ed. Engl. 1981, 20, 976.
(24) A similar vinylogous ester was unreactive in analogous cy-
cloaddition reactions. See: Herndon, J . W.; Patel, P. P. Tetrahedron
Lett. 1997, 38, 59.
(25) (a) Kno¨lker, H.-J .; Goesmann, H.; Klauss, R. Angew. Chem.,
Int. Ed. 1999, 38, 702. (b) Kno¨lker, H.-J .; Baum, I.; Goesmann, G.;
Klauss, R. Angew. Chem., Int. Ed. Engl. 1999, 38, 2064.
(26) The methylene signals did not coalesce at 80 °C.
(27) See ref 21 and: Pearson, A. J . Perosa, A. Organometallics 1995,
14, 5178.
(28) For an example of the use of an enamine in a hetero-Diels-
Alder cycloaddition reaction see: Stork, G.; Landesman, H. K. J . Am.
Chem. Soc. 1956, 78, 5128.
(29) For the use of cyclopentadienones as 2π components in cycload-
dition chemistry, see ref 1 and (a) Gavina, F.; Costero, A. M.; Gil, P.;
Palazon, B.; Luis, S. V. J . Am. Chem. Soc. 1981, 103, 1797. (b) Depuy,
C. H.; Isaks, M.; Eilers, K. L.; Morris, G. F. J . Org. Chem. 1964, 29,
3503.
(30) Thus far, we have been unable to separate vinylogous amide
adduct 32 from the corresponding enone adduct without selectively
destroying the enone adduct. The structure of the enone adduct was
assigned based upon the similarity of its 1H and 13C NMR spectra to
37.

7276 J . Org. Chem., Vol. 65, No. 22, 2000
Rainier and Imbriglio
metal mediated yne-ynamine [2 + 2 + 1] cycloaddition
reactions. In addition, we have shown that metal free
3-aminocyclopentadienones can serve as both the 4π and
2π component in chemoselective cycloaddition reactions.
We are currently focused on the optimization of the
reactions that have been discovered, the use of iron and
cobalt complexed cyclopentadienones in addition reac-
tions, and the use of the substrates from these reactions
in the synthesis of interesting targets.
In addition to the heterodiene investigations described
above, we have examined the cycloaddition of cyclopen-
tadienone 21 with cyclopentadiene. To our delight, endo-
adduct 38 was isolated in 57% yield when 21 was exposed
to cyclopentadiene (eq 4). In contrast to our heterodiene
results with 21, cyclopentadiene had reacted exclusively
at the isolated enone of 21.
Ack n ow led gm en t. We gratefully acknowledge the
American Cancer Society (IRG-110T) and the University
of Arizona for support of this work. We are grateful to
Dr. Arpad Somogyi for help with mass spectra analysis,
Dr. Neil J acobsen for help with NMR experiments, and
Dr. Mike Carducci for obtaining the X-ray crystal
structures of 14, 32, 37, and 38.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
1
cedures and characterization data, along with H and 13C NMR
Con clu sion s
spectra for compounds 6-9, 12, 13, 15, 17, 18, 20, 25, 27, 29,
30, 32, 33, and 37. ORTEP figures, atomic coordinates, thermal
parameters, bond lengths, and bond angles for 14, 37, and 38.
This material is available free of charge via the Internet at
http://pubs.acs.org.
To conclude, we have demonstrated that 3-aminocy-
clopentadienones can be efficiently synthesized from
(31) We also isolated an additional 30% of unrecognizable material
from this reaction. The reason for the disparate reactivity of 28 with
acrolein is not apparent to us at the present time.
J O001044T