Cobalt- and Silver-Promoted Methylenecyclopropane Rearrangements

Article abstract of DOI:10.1021/acs.joc.7b02477

The rate of the methylenecyclopropane rearrangement is enhanced by an alkyne-Co₂(CO)₆ complex bonded to the para position of a benzene ring. This is explained by a stabilizing effect on the transition state leading to the biradical intermediate. Computational studies indicate that the benzylic-type biradical intermediate is stabilized by a delocalization mechanism, where spin is delocalized onto the two cobalt atoms. Silver cation also enhances the rate of the methylenecyclopropane rearrangement. Computational studies suggest that silver cation can also stabilize a benzylic radical by spin delocalization involving silver. In the case of the silver-promoted reactions, the rate enhancements in a series of aryl-substituted methylenecyclopropanes correlate with σ⁺ values. The question remains open as to whether the silver-catalyzed methylenecyclopropane rearrangement proceeds via an argento-stabilized biradical or whether the reaction involves an argento-substituted allylic cation.

Full text of DOI:10.1021/acs.joc.7b02477

Subscriber access provided by READING UNIV
Article
Cobalt and Silver Promoted Methylenecyclopropane Rearrangements
Xavier Creary
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b02477 • Publication Date (Web): 28 Nov 2017
Downloaded from http://pubs.acs.org on November 29, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Organic Chemistry is published by the American Chemical Society.
1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 31
The Journal of Organic Chemistry
1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Cobalt and Silver Promoted Methylenecyclopropane Rearrangements
Xavier Creary
Department of Chemistry and Biochemistry
University of Notre Dame, Notre Dame, Indiana 46556
creary.1@nd.edu
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 31
2
1
2
3
Abstract
4
5
6
7
H3C
CH3
CH2
H3C
CH3
CH2
H
H
C
8
9
CCCH3
(Co2(CO)6)
R =
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
CH3
CH3
CH3
C
Co(CO)3
H3C
H
H3C
Co(CO)3
H3C
H
CH2
Co(CO)3
Co(CO)3
Ag+
H3C
CH3
R
H3C
CH3
CH2
H3C
H
CH3
R
Ag
CH2
H
H
C
CH2
Ag
R
Ag
R
R
The rate of the methylenecyclopropane rearrangement is enhanced by an alkyne-Co2(CO)6
complex bonded to the para-position of a benzene ring. This is explained by a stabilizing effect on
the transition state leading to the biradical intermediate. Computational studies indicate that the
benzylic type biradical intermediate is stabilized by a delocalization mechanism, where spin is
delocalized onto the two cobalt atoms.
Silver cation also enhances the rate of the
methylenecyclopropane rearrangement. Computational studies suggest that silver cation can also
stabilize a benzylic radical by spin delocalization involving silver. In the case of the silver
promoted reactions, the rate enhancements in a series of aryl substituted methylenecyclopropanes
correlate with σ+ values. The question remains open as to whether the silver catalyzed
methylenecyclopropane rearrangement proceeds via an argento stabilized biradical or whether the
reaction involves an argento substituted allylic cation.
ACS Paragon Plus Environment

Page 3 of 31
The Journal of Organic Chemistry
3
1
2
3
Introduction
4
5
6
7
8
9
Alkynes react readily with dicobalt octacarbonyl, Co2(CO)8, to give stable complexes of
type 1.1 These complexes have been extensively studied and they contain a two cobalt atoms
bonded in a tetrahedrane like structure.2 Compounds of type 1 are likely intermediates in the
Pauson-Khand reaction.3 The carbocation stabilizing properties of these cobalt complexes have also
been investigated and many carbocations of type 2 have been generated as stable molecules.4
Alkynes can be regenerated from complexes 1 by oxidative methods, and hence the cobalt can serve
as a protecting group for alkynes.4d,e Certain transition metal cations are also well known to
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
coordinate with alkynes, with the Ag+ complex 3 being a classic example.5
CH3
R
R
H3C
H
R
R
R
C
CH2
C
C
R
Co(CO)3
Ag
R
Co(CO)3
Co(CO)3
Co(CO)3
C
3
2
1
C
CH3
4
CH3
CH3
CH3
H3C
H3C
H
H3C
H
CH2
CH2
CH2
H
Co(CO)3
Co(CO)3
C
Co(CO)3
H3C
H3C
Ag
C
Co(CO)3
6
H3C
5
7
In view of the ability of cobalt-coordinated alkynes to stabilize carbocations, the effect of
cobalt on radicals was of interest. Also of interest was the interaction of other transition metals with
carbon-centered radicals. In order to investigate the effect of alkynes coordinated with cobalt on the
stability of radical intermediates, the methylenecyclopropanes 4, 5, and 6 were prepared. Also of
interest was the silver complex 7 that is potentially derived from reaction of 4 with silver cation.
These substrates of general structure 8 all undergo a thermal methylenecyclopropane rearrangement
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 31
4
1
to give 10 (Scheme 1).6 This type of thermal rearrangement has been the subject of numerous
investigations.7 The generally accepted mechanism involves the formation of a short lived singlet
biradical intermediate of type 9 that can close to form the product 10.8 This singlet biradical 9 is
distinct from the parent trimethylenemethane, which is a ground state triplet diradical that can be
observed by ESR spectroscopy.9 Reported here are the results of studies designed to evaluate the
effect of these transition metals on the stability of the biradical intermediates involved in the
methylenecyclopropane rearrangement.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1. Mechanism of the Thermal Methylenecyclopropane Rearrangement
CH3
CH3
H3C
C
CH2
H
CH3
H
Ar
Ar
10
8
H3C
CH3
H3C
CH3
CH2
=
H
H
H
H
Ar
Ar
9
9
Results and Discussion
Cobalt Complexes. The requisite methylenecyclopropane 4 was prepared (Scheme 2) using
our standard protocol involving arylcarbene addtion to 1,1-dimethylallene.10 Reaction of 4 with
dicobalt octacarbonyl gave the isolable complex 5. The meta-isomer 6 was prepared by a
completely analogous method. These substrates 4-6 thermally rearrange to the corresponding
1
isopropylidenecyclopropanes and rates can be readily monitored by H NMR spectroscopy. Rate
data for first order rearrangement processes are given in Table 1. For comparison purposes, data are
also given for the parent unsubstituted substrate 13.
ACS Paragon Plus Environment

Page 5 of 31
The Journal of Organic Chemistry
5
1
2
3
Scheme 2. Synthesis and Rearrangement of Cobalt Complex 5
4
5
6
7
8
9
CH3
CH3
CH3
CH3
CHN2
C
H3C
H
H3C
H
H3C
H3C
H
CH2
CH2
C
C
CH2
heat
Co2(CO)8
C
C
h!
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
C
Co(CO)3
H3C
Co(CO)3
Me
H3C
Co(CO)3
12
C
11
Co(CO)3
4
Me
5
Table 1. Rearrangement Rates for Substrates 4, 5, 6, and 13 in C6D6
Compound
T (°C)
k (s-1)
krel
CH3
H3C
80.0
65.0
55.0
45.0
3.86 x 10-4a
7.33 x 10-5
2.20 x 10-5
6.26 x 10-6
6.93
CH2
H
Co(CO)3
Co(CO)3
H3C
5
CH3
H3C
H
80.0
70.0
60.0
2.10 x 10-4
6.93 x 10-5
2.04 x 10-5
3.72
CH2
C
C
CH3
4
CH3
80.0
70.0
60.0
5.57 x 10-5b
1.72 x 10-5b
5.05 x 10-6b
1.00
1.01
H3C
CH2
H
13
CH3
5.63 x 10-5
5.47 x 10-6
H3C
H
80.0
60.0
CH2
Co(CO)3
Co(CO)3
H3C
6
a extrapolated from data at lower temperatures.
b reference 20.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 31
6
1
2
3
Scheme 3. Mechanism for Rearrangement of Cobalt Complex 5 to 12
4
H3C
CH3
5
6
7
H
CH2
8
9
heat
fast
5
12
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Co(CO)3
H3C
Co(CO)3
14
Immediately apparent is the fact that the rearrangement rate of the cobalt complex 5 is
enhanced relative to the parent methylencyclopropane 13 as well as the uncomplexed alkyne 4.
This rate enhancement of 6.93 is a significant factor relative to the effect of many previously
reported substituents.6 and suggests significant stabilization of the transition state leading to the
biradical intermediate 14 (Scheme 3) in the methylenecyclopropane rearrangement. This rate
enhancement is not seen when the cobalt containing substituent is placed in the meta-position. The
rate of the m-isomer 6 is essentially the same as that of the unsubstituted parent compound 13.
Scheme 4. Isodesmic Reactions of Cobalt Substituted Benzylic Radicals with Toluene
0.721
CH3
0.811
CH2
CH3
CH2
!E = 1.60 kcal/mol
+
+
B3LYP/LANL2DZ
H3C
Co(CO)3
Co(CO)3
17
15
H3C
Co(CO)3
Co(CO)3
16
18
0.820
CH2
!E = -0.68 kcal/mol
CH3
CH2
CH3
+
B3LYP/LANL2DZ
+
Co(CO)3
Co(CO)3
Co(CO)3
20
17
19
Co(CO)3
15
H3C
H3C
ACS Paragon Plus Environment

Page 7 of 31
The Journal of Organic Chemistry
7
1
2
3
4
5
6
7
8
9
In order to further understand the effect of the cobalt complex on the stability of biradical
14, the analogous substituted benzylic radicals 16 and 19 have been studied computationally11a at
the B3LYP/LANL2DZ level (a common density functional method and basis set that are useful for
organometallic compounds)11b using the isodesmic reactions shown in Scheme 4. Our previous
studies have shown that radical stabilization energies calculated by this process correlate well with
methylenecyclopropane rearrangement rates.6 The calculations in Scheme 4 suggest that 16 is
stabilized relative to the unsubstituted benzyl radical, 17. Further examination of the structure of 16
(Figure 1) reveals the origin of this stabilization. Calculated spin density at the benzylic carbon of
16 (0.721) is significantly reduced relative to the unsubstituted benzyl radical 17 (0.811). On the
other hand, the two cobalt atoms in 16 have accumulated some spin density (0.096). As expected,
this spin delocalization leads to stabilization in 16. Structures 16a and 16b (Scheme 5) display this
spin delocalization in terms of contributing resonance forms. Such forms 16a and 16b are
consistent with calculated bond lengths in 16, where the C1-C2 bond (1.408 Å) and the C7-C8 bond
(1.448 Å) are substantially shorter than the analogous bonds in the neutral molecule 18 (1.517 Å
and 1.462 Å respectively). This delocalization occurs when the cobalt substituent is in the para-
position. The meta-substituted benzylic radical 19 shows no such stabilization or spin
delocalization. In fact, the calculation suggests that the m-substituted radical 19 is slightly
destabilized relative to the unsubstituted benzyl radical 17.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 31
8
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. B3LYP/LANL2DZ calculated structures of cobalt complexes 16, 18, and 19.
Scheme 5. Resonance Forms of Cobalt Stabilized Benzylic Radical 16
CH2
CH2
CH2
Co(CO)3
Co(CO)3
H3C
H3C
Co(CO)3
H3C
Co(CO)3
Co(CO)3
Co(CO)3
16a
16
16b
Silver Ion Promoted Reactions. There is a very large volume of literature involving the
rearrangement of strained ring compounds promoted by transition metals.12 An early example is the
nickel-catalyzed rearrangement of methylenecyclopropane to butadiene.13 The rearrangement of
bicyclobutanes using silver, rhodium, and other transition metal catalysts has been one of the most
intensely studied processes.14 Transition metals are known to open methylenecyclopropane to form
stable complexes of trimethylenemethane.9,15 In light of these numerous studies, attention was next
turned to silver complexes of alkynes, in particular complexes of type 7. The question to be
answered involved the ability of silver ion to promote the simple methylenecyclopropane
rearrangement.
ACS Paragon Plus Environment

Page 9 of 31
The Journal of Organic Chemistry
9
1
2
3
4
5
6
7
8
9
Mixing silver triflate with solutions of 4 in C6D6, acetone-d6, or methanol-d4 led to solutions
of 4 in equilibrium with a silver complex. Complex formation was not complete even when four
equivalents of AgOTf were added as evidenced by the fact that NMR signals continued to shift
downfield even after the addition of excess AgOTf. The effect of silver triflate on the
methylenecyclopropane rearrangement of 4 was next investigated in a number of solvents. Table 2
shows the results of these studies. First order rate constants for the methylenecyclopropane
rearrangement are indeed enhanced when AgOTf is added to solutions of 4 in C6D6, acetone-d6, and
CD3OD. In CD3CN, there is a negligible rate enhancement. Silver perchlorate and silver
trifluoroacetate in C6D6 also lead to rate enhancements, with the effect being smaller for silver
trifluoroacetate.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 2. Rearrangement Rates of 4 with Added AgOTf at 60.0 °C
Solvent Equiv of AgOTf a
k (s-1)
C6D6
C6D6
C6D6
C6D6
0.00
0.94
2.03
4.20
2.04 x 10-5
3.64 x 10-5
5.35 x 10-5
7.75 x 10-5
Acetone-d6 0.00
Acetone-d6 1.79
Acetone-d6 3.00
1.84 x 10-5
3.83 x 10-5
5.00 x 10-5
CD3OD
CD3OD
0.00
1.64
1.59 x 10-5
6.62 x 10-5
CD3CN
CD3CN
0.00
1.65
1.92 x 10-5
2.01 x 10-5
a [4] = 0.025 M
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 31
10
1
Silver ion is known to coordinate with alkenes,5, 16 aromatics,17 as well as alkynes.5 It was
therefore necessary to evaluate the nature of the silver complex with 4, since all three functional
groups are present in 4. Five complexes of 4 with silver cation were located computationally at the
B3LYP/LANL2DZ level as shown in Figure 2. Two of these complexes (22 and 23) involve
coordination with the aromatic ring. Complex 24 has the silver complexed with the exocycic π-
bond and trans to the aromatic ring, while 7 is an alkyne complex. Finally, silver is coordinated
with both the alkene functional group and the cis-aromatic ring in 25. This complex 25 has the
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
B3LYP/LANL2DZ calculated lowest energy.
CH3
CH3
CH3
CH3
Ag
CH3
H3C
H
H3C
H
H3C
H
H3C
H
H3C
H
CH2
CH2
CH2
CH2
CH2
Ag
Ag
Ag
C
C
C
C
C
C
C
C
Ag
C
C
CH3
CH3
CH3
CH3
H3C
23
22
7
25
24
(7.8 kcal/mol)
(8.3 kcal/mol)
(7.9 kcal/mol)
(3.6 kcal/mol)
(0.00 kcal/mol)
Figure 2. Relative B3LYP/LANL2DZ calculated energies of Ag+ complexes of 4.
A number of mechanisms come to mind for the silver ion promoted methylencyclopropane
rearrangement of 4. The first involves a biradical intermediate 26 shown in Figure 3, where silver
cation is coordinated with the alkyne functional group. This biradical 26 has been modeled
computationally using the silver complexed benzylic radical 27. The isodesmic reaction shown in
Scheme 6 suggests that silver indeed lends stability to this benzylic radical. In addition to the
calculated radical stabilization energy of 2.86 kcal/mol, the spin density at the benzylic carbon is
reduced relative to the benzyl radical 17, and there is significant spin density on the silver atom in
27. In terms of resonance theory, form 27a makes a significant contribution to the structure of 27.
ACS Paragon Plus Environment

Page 11 of 31
The Journal of Organic Chemistry
11
1
2
3
4
CH2
H3C
H
CH3
CH2
CH2
5
6
7
C
C
8
9
Ag
C
Ag
C
C
C
H3C
H3C
27
27a
Ag
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
H3C
26
0.140
0.636
27
Figure 3. Structures of silver-alkyne complexed biradical and benzylic radical.
Scheme 6. Isodesmic Reaction of Silver-Alkyne Complexed Benzylic Radical with Toluene
CH3
Ag
+
H
H
C
C
C
CH3
27
15
!E = 2.86 kcal/mol
B3LYP/LANL2DZ
CH2
Ag
+
H3C
C
C
CH3
28
17
In view of the computational structures 22 and 23 in Figure 2 that suggests that silver ion
can also coordinate with the aromatic ring of 4, alternative mechanisms must be considered. Could
the rearrangement proceed via aromatic ring-coordinated biradicals such as 29? Indeed analogous
π-complexed benzylic radicals 30 and 31 (Figure 4) have been located at the B3LYP/LANL2DZ
level of theory. These radicals have decreased spin density at the benzylic carbon and significant
spin density is delocalized onto silver. They are presumably stabilized by silver. These
intermediates suggest that the alkyne functional group would not be necessary for the silver
promoted methylenecyclopropane rearrangement to occur.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 31
12
1
2
3
4
5
6
7
8
9
0.665
CH2
H3C
H
CH3
0.600
CH2
0.138
Ag
CH2
Ag
0.154
Ag
C
C
C
C
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
C
C
CH3
CH3
29
30
31
CH3
Figure 4. Structures of silver-arene complexed biradical and benzylic radical.
This hypothesis is verifiable and indeed, the substrates 13 and 32 have all been reacted
thermally in the presence of silver triflate where they all rearrange to 33 as shown in Scheme 7.
The rearrangements are not due to traces of triflic acid present in the reaction, since they still occur
in the presence of the base 2,6-lutidine. Table 3 shows that the magnitude of the rate enhancement
of the methylenecyclopropane rearrangement is substituent dependent. In fact the catalytic rate
enhancement due to silver in 13, 32b, and 32c is even greater than in the alkyne 4. A Hammett plot
(Figure 5) of the log of the rate enhancement versus σ+ gives a fairly good correlation (r = 0.99).
These results show that coordination of silver cation with an alkyne functional group is not a
necessary condition for the silver promoted methylenecyclopropane rearrangement. Some other
intermediate must be involved. Silver ion coordination with the aromatic system remains a distinct
possibility. The larger rate enhancements seen in the p-OCH3 and p-CH3 substrates 32b and 32c
and the smaller enhancement in the m-F and p-CF3 substrates 32d and 32e might be a reflection of
the increased ability of silver cation to coordinate with more electron-rich aromatic groups.
Scheme 7. Silver Ion Promoted Methylenecyclopropane Rearrangements
ACS Paragon Plus Environment

Page 13 of 31
The Journal of Organic Chemistry
13
1
2
3
4
CH3
CH3
CH3
CH3
C
H3C
AgOTf/C6D6
heat
AgOTf/C6D6
further reaction
H
CH2
CH3
H
5
6
7
8
R
R
R
9
33a (R = p-H)
13 (R = p-H)
34b (R = p-OCH3)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
33b (R = p-OCH3)
33c (R = p-CH3)
33d (R = m-F)
32b (R = p-OCH3)
32c (R = p-CH3)
32d (R = m-F)
32e (R = p-CF3)
33e (R = p-CF3)
Some of the rearrangement products (especially 33b) are not stable under the reaction
conditions, but undergo further reaction to give the diene 34b at longer times. The origin of this
further rearrangement is under active investigation.
Table 3. Rearrangement Rates of substrates in C6D6 with added AgOTf
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 31
14
1
2
3
4
5
6
7
8
9
Compound [AgOTf ] (M) T (°C)
k (s-1)
Enhancement
3.04
CH3
H3C
0.000
0.066
0.066a
70.0
70.0
70.0
1.72 x 10-5
5.23 x 10-5
4.44 x 10-5
CH2
H
13
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
CH3
H3C
0.000
0.066
60.0
60.0
1.01 x 10-5
1.48 x 10-4b
CH2
H
14.7
5.63
OCH3
32b
CH3
H3C
H
0.000
0.066
60.0
60.0
7.24 x 10-6
4.08 x 10-6
CH2
CH3
32c
CH3
H3C
H
0.000
0.066
70.0
70.0
1.68 x 10-5
2.99 x 10-5
CH2
1.78
1.40
F
32d
CH3
H3C
H
0.000
0.066
70.0
70.0
1.98 x 10-5
2.78 x 10-5
CH2
CF3
32e
CH3
0.000
0.066
60.0
60.0
2.04 x 10-5
5.74 x 10-5
H3C
H
CH2
2.81
C
C
4
CH3
a 0.022 M 2,6-lutidine added.
b rate over 40% reaction; product rearranges under reaction conditions.
ACS Paragon Plus Environment

Page 15 of 31
The Journal of Organic Chemistry
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. A plot of log [Enhancement] vs. σ+ for the AgOTf promoted methylenecyclopropane
rearrangements of 13 and 32.
These studies suggest that intermediates such as 35 (Figure 6) might well be involved in the
rearrangement of 32 as well as 4 and 13. Spin delocalization onto silver in the benzylic analog 36 is
implicated by the B3LYP/LANL2DZ calculated structure, where the spin density on silver is 0.153.
This is also reflected by resonance form 36c.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 31
16
1
2
0.711
3
4
5
6
H3C
H
CH3
CH2
0.153
7
8
Ag
Ag
9
35
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
R
36
CH2
CH2
CH2
Ag
36c
Ag
36a
Ag
36b
Figure 6. Structures of silver-arene complexed biradical and benzylic radical.
Scheme 8. Reactions of 4 and 13 with AgOTf in CH3OH
OCH3
CH3
CH3
CH3
H3C
CH3
CH2
C
H3C
H
CH2
AgOTf/CH3OH
heat
H
+
R
R
R
37 (R = CCCH3) (0.7 part)
37 (R = H) (1.7 parts)
33 (R = CCCH3) (1 part)
33 (R = H) (1 part)
4 (R = CCCH3)
13 (R = H)
The reactions of 4 and 13 with AgOTf in CD3OD or CH3OH followed a somewhat different
course as shown in Scheme 8. In addition to the normal methylenecyclopropane rearrangement
products 33, the methyl ethers 37 were also formed. What is the origin of the ethers 37? It is
tempting to suggest that the same silver complex is involved in the formation of both products 33
and 37. Indeed, a reasonable mechanism for formation of 37 is shown in Scheme 9. Coordination
of Ag+ with the aromatic ring, as emphasized by form 38a, might make the cyclopropyl ring prone
to fragment in a cationic process to give allylic cation 39. Solvent capture of this cation followed
by protonation of 40 at the benzylic position would generate the product 37.
ACS Paragon Plus Environment

Page 17 of 31
The Journal of Organic Chemistry
17
1
2
3
4
5
Scheme 9. Mechanism 1 for Formation of 37 in CH3OH
6
7
8
9
CH3
CH3
CH3
CH2
H3C
H3C
H
H3C
H
CH2
CH2
H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
open
R
Ag
38
R
Ag
38a
Ag
R
39
CH3OH
OCH3
OCH3
CH3
H3C
CH3
H3C
CH3O
H
H
CH2
CH2
- Ag+
Ag
R
R
37
40
Based on the ability of silver ion to coordinate with alkenes, an alternative mechanism
(Scheme 10) for formation of 37 in methanol comes to mind. The cyclopropyl carbon of silver
complex 41 should be electron-deficient as reflected in form 41a. Electrocyclic ring opening of 41
would generate the allylic cation 42, and methanol capture would give 43. Subsequent protonation
of 43 and loss of Ag+ would yield the observed product 37. Analogous ring opening of the related
complex 44, with silver coordinated to the exocyclic double bond as well as the cis-aryl group,
would give the same product 37 via the allylic cation 45.
Scheme 10. Mechanism 2 for Formation of 37 in CH3OH
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 31
18
1
2
3
4
CH3
CH3
Ag
H3C
CH3
Ag
H3C
H
H3C
H
Ag
CH2
H
5
disrotatory
opening
6
7
8
9
R
R
R
41
41a
42
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
CH3OH
OCH3
CH3
OCH3
CH3
H3C
H3C
Ag
H
CH3O
H
CH2
CH2
- Ag+
R
R
37
43
CH3
H3C
Ar
CH3
H3C
disrotatory
opening
H
Ag
CH2
Ag
H
45
R
44
Computational studies were used to gain insight into the viability of Mechanisms 1 and 2.
The relative energies of allylic cations 39, 42, and 45 were calculated at the B3LYP/LANL2DZ
level (Figure 7). Indeed, this study suggests that allylic cation 39 in Mechanism 1 lies 30.5
kcal/mol above allylic cation 42 in Mechanism 2 and 24.2 kcal above cation 45. This is reasonable
since Mechanism 2 avoids the loss of aromaticity required in the fragmentation step of Mechanism
1. In other words, Mechanism 2 is much preferred over Mechanism 1 for the formation of addition
product 37.
ACS Paragon Plus Environment

Page 19 of 31
The Journal of Organic Chemistry
19
1
2
3
4
5
6
7
8
CH3
CH2
H3C
H3C
H
CH3
H3C
Ph
CH3
Ag
CH2
H
CH2
Ag
H
45
Ag
H
42
0.0 kcal
relative energy (B3LYP/LANL2DZ)
9
39
30.5 kcal
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
6.3 kcal
Figure 7. Structures and relative energies of potential argento-allylic cations.
While silver stabilized biradical intermediates such as 35 may be involved in the
methylenecyclopropane rearrangement promoted by AgOTf, one should recall the old adage that
one never proves a reaction mechanism.18 There are other possibilities as shown in Scheme 11.
Could the same alkene complex 41 (or 44) proposed in formation of methyl ether 37 be involved in
the methylenecyclopropane rearrangement? Substituent effects in Table 3 and the Hammett plot in
Figure 5 are also consistent with ring opening of 41 to give an allylic cation 42.19 The cation 42
could cyclize with loss of silver cation to give the rearranged product 33. Alternatively, the alkene
complex 41, with a weakened cyclopropane bond, might homolytically fragment to give biradical
46. Could such a biradical convert to a silver coordinated trimethylenemethane 47 analogous to
other transition metal coordinated trimethylenemethanes?15 Loss of silver ion would also lead to
33. The possibility of a concerted rearrangement of 41 to 48 also cannot be ruled out. Further
studies are needed to shed more light on these silver promoted reactions.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 20 of 31
20
1
2
3
4
Scheme 11. Alternative Mechanisms for the Ag+ Promoted Methylenecyclopropane
Rearrangement.
5
6
7
8
9
CH3
H3C
CH3
H3C
H
CH3
Ag
H3C
H
-Ag+
?
Ag
CH2
H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Ar
Ar
33
42
41
R
?
H3C
CH3
Ag
H3C
H
CH3
H3C
H
CH3
Ag
?
?
Ag
CH2
H
CH2
Ph
Ph
Ph
46
48
47
Conclusions. A dicobalt hexacarbonyl-alkyne complex in the para-position of a benzene
ring enhances the rate of the methylenecyclopropane rearrangement. B3LYP/LANL2DZ
calculations indicate that the intermediate benzylic radical is stabilized by spin delocalization
involving the two cobalt atoms.
Addition of silver triflate to aryl-substituted
methylenecyclopropanes also leads to increased rearrangement rates that correlate with σ+ values.
In methanol solvent, a competing process involves formal addition of solvent to the strained
cyclopropane bond. Computational studies indicate that silver π-complexed benzylic radical
intermediates can also be stabilized by spin delocalization involving silver. The mechanism of the
silver catalyzed rearrangement remains uncertain. One potential mechanism involves complexation
of silver with the arene followed by fragmentation of the strained cyclopropane bond to give an
argento stabilized biradical. Fragmentation to an argento substituted allylic cation followed by re-
cyclization is an alternative process.
ACS Paragon Plus Environment

Page 21 of 31
The Journal of Organic Chemistry
21
1
2
3
Experimental Section
4
5
6
7
8
9
General. NMR spectra were recorded on a Varian DirectDrive 600 MHz spectrometer.
HRMS measurements were carried out using a Waters GCT Premier spectrometer (electron impact
ionization with time-of-flight mass analyzer). Samples were run in the gas chromatography mode
or using a direct insertion probe.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Preparation of 4-(prop-1-ynyl)benzaldehyde. 1-Bromo-4-(prop-1-ynyl)benzene20 (1.47 g)
was dissolved in 13 mL of anhydrous THF and the solution was cooled to -78 °C. n-BuLi in hexane
(5.0 mL of 1.6 M) was added slowly dropwise via syringe. After 30 min at -78 °C, a solution of
0.75 g of dry N,N-dimethylformamide in 3 mL of ether was added slowly dropwise using an
addition funnel. The mixture was then allowed to warm slowly to about -10 °C. The solution was
then quenched with water and transferred to a separatory funnel using ether. The ether extract was
then washed with two portions of water, saturated NaCl solution, and the dried over a mixture of
Na2SO4 and MgSO4. After solvent removal using a rotary evaporator, the residue was
chromatographed on 16 g of silica gel. The column was eluted with increasing amounts of ether in
pentane. The 4-(prop-1-ynyl)benzaldehyde21 (783 mg; 72% yield), mp 54-55 °C, eluted with 5-7%
ether in pentane. 1H NMR (600 MHz, CDCl3) δ 9.98 (s, 1 H), 7.80 (d, J = 8.3 Hz, 2 H), 7.52 (d, J =
8.3 Hz, 2 H), 2.09 (s, 3 H). 13C NMR (150 MHz, CDCl3) δ 191.5, 135.0, 132.0, 130.5, 129.5, 90.7,
79.3, 4.5.
Preparation of Methylenecyclopropane 4. Tosylhydrazine (780 mg) was suspended in 5
mL of methanol and 575 mg of 4-(prop-1-ynyl)benzaldehyde was added. The mixture was stirred
for 6 h at room temperature and then 9.1 mL of 0.510 M NaOCH3 in methanol was added. The
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 22 of 31
22
1
2
3
4
5
6
7
8
9
methanol solvent was then removed using a rotary evaporator. The solid that formed was evacuated
under aspirator pressure for an additional 8 h. Ethylene glycol (20 mL) was then added to the dry
salt and the mixture was heated to about 35 °C in an oil bath until the solid dissolved. The mixture
was then heated from 75-80 °C for about 10 min, cooled to room temperature, and then extracted
with a 50:50 ether:pentane mixture. This heating/extraction procedure was repeated a total of three
times. The combined ether/pentane extracts were washed with 2 portions of water, saturated NaCl
solution and dried over a mixture of Na2SO4 and MgSO4. The solvents were removed using a rotary
evaporator to give 459 mg (74% yield) of crude unstable 1-(diazomethyl)-4-(prop-1-ynyl)benzene,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
11, as an oil that was used in the next reaction without further purification. H NMR of 11 (600
MHz, CDCl3) δ 7.30 (d, J = 8 Hz, 2 H), 6.81 (d, J = 8 Hz, 2 H), 4.94 (s, 1 H), 2.04 (s, 3 H). 13C
NMR of 11 (150 MHz, CDCl3) δ 132.2, 129.2, 121.0, 119.2, 85.3, 79.7, 47.8, 4.4.
1-(Diazomethyl)-4-(prop-1-ynyl)benzene, 11, prepared above (423 mg) was dissolved in 28
mL of 3-methylbuta-1,2-diene and the solution was sealed in three Pyrex tubes under argon. Each
tube was individually irradiated with a Hanovia 450 watt lamp for a total of 50 min. The color
changed from red orange to light brown over the course of the irradiation. The tubes were then
opened and the excess 3-methylbuta-1,2-diene was removed using an aspirator vacuum. The
residue was chromatographed on 12 g of silica gel and the column was eluted with pentane. The
first fraction that eluted was an oil (95 mg) that contained 95% of 4 along with 5% of the isomeric
1-(prop-1-ynyl)-4-(2-(propan-2-ylidene)cyclopropyl)benzene. This was followed by fractions
containing mixtures of 4 and increasing amounts of the isomeric 1-(prop-1-ynyl)-4-(2-(propan-2-
1
ylidene)cyclopropyl)benzene. A total of 297 mg (56% yield) of products were obtained. H NMR
of 4 (600 MHz, CDCl3) δ 7.29 (d, J = 8.2 Hz, 2 H), 7.09 (d, J = 8.2 Hz, 2 H), 5.57 (m, 1 H), 5.52
(m, 1 H), 2.43 (t, J = 2.1 Hz, 1 H), 2.04 (s, 3 H), 1.33 (s, 3 H), 0.83 (s, 3 H). 13C NMR of 4 (150
ACS Paragon Plus Environment

Page 23 of 31
The Journal of Organic Chemistry
23
1
2
3
MHz, CDCl3) δ 145.4, 138.1, 131.1, 128.8, 121.3, 103.5, 85.4, 79.8, 32.1, 26.1, 24.1, 18.3, 4.4.
4
5
HRMS (EI) (M+) calculated for C15H16 196.1252, found 196.1235.
6
7
8
9
Preparation of Cobalt Complex 5. A sample of Co2(CO)8 (Strem Chemical Co.) was
purified by dissolving in pentane, decanting the pentane solution from the insoluble material, and
removing the pentane using a rotary evaporator. The resultant orange crystals are relatively pure
Co2(CO)8. A sample of Co2(CO)8 (44.8 mg; 0.131 mmol) was placed in a two mL vial and about
0.6 mL of C6D6 was added along with a micro stir bar. A solution of 24.2 mg (0.124 mmol) of the
methylenecyclopropane 4 in about 0.2 mL of C6D6 was then added. After 10 h at room temperature,
the solution was filtered through a small amount of silica gel in a pipette. Pentane was used to rinse
the silica gel and the solvents were then removed using a rotary evaporator to give 58.3 mg (98%
yield) of complex 5 as a thick dark red oil. This product was stored in pentane solution in the
freezer. Traces of paramagnetic impurities can lead to broadening of NMR spectra. Samples were
therefore filtered through silica gel using pentane before recording spectra. 1H NMR of 5 (600
MHz, C6D6) δ 7.45 (d, J = 8.2 Hz, 2 H), 7.05 (d, J = 8.2 Hz, 2 H), 5.54 (m, 1 H), 5.50 (m, 1 H), 2.43
(s, 3 H), 2.33 (t, J = 2.1 Hz, 1 H), 1.18, (s, 3 H), 0.79 (s, 3 H). 13C NMR of 5 (150 MHz, C6D6) δ
200.5, 146.0, 139.4, 136.0, 130.3, 129.5, 104.0, 94.7, 92.3, 33.0, 26.4, 24.8, 20.9, 18.7. HRMS (EI)
(M+) calculated for C21H16Co2O6 481.9611, found 481.9603.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Preparation of an Authentic Sample of Cobalt Complex 12. A sample of Co2(CO)8 (51.8
mg; 0.151 mmol) was placed in a vial and about 0.6 mL of C6H6 was added. A solution of 29.6 mg
(0.151 mmol) of the methylenecyclopropane 33 (R = CCCH3) in 0.2 mL of benzene was then
added. After 3 h at room temperature, analysis of a small sample showed about 7% unreacted
methylenecyclopropane. About 5 mg of additional Co2(CO)8 was then added and after an additional
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 24 of 31
24
1
2
3
4
5
6
7
8
9
5 h, the benzene was removed using a rotary evaporator. The residue was dissolved in 2 mL of
pentane and then filtered through 0.6 g of silica gel/pentane in a pipette. The pentane solvent was
removed using a rotary evaporator to give 66.2 mg (91% yield) of 12 as a thick dark red oil.
Samples of 12 were stored in pentane in the freezer. 1H NMR of 12 (600 MHz, C6D6) δ 7.46 (d, J
= 8.2 Hz, 2 H), 6.95 (d, J = 8.2 Hz, 2 H), 2.43 (s, 3 H), 2.38 (m, 1 H), 1.83, (m, 3 H), 1.67 (m, 3 H),
1.50 (m, 1 H), 0.98 (m, 1 H). 13C NMR of 12 (150 MHz, C6D6) δ 200.5, 144.1, 135.5, 129.9, 128.7,
127.5, 123.4, 120.6, 94.7, 92.5, 22.6, 22.5, 21.2, 20.9, 15.9. HRMS (EI) (M+) calculated for
C21H16Co2O6 481.9611, found 481.9584.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Preparation of Cobalt Complex 6. A sample of Co2(CO)8 (47.6 mg; 0.139 mmol) was
placed in a two mL vial and about 0.6 mL of C6D6 was added. A solution of 26.2 mg (0.134 mmol)
of the methylenecyclopropane 8 (Ar = m-CH3CCC6H4) 0.5 mL of C6D6 was then added. After 26 h
at room temperature, analysis of a small sample showed no unreacted methylenecyclopropane.
After 2 days the C6D6 was removed using a rotary evaporator and the residue was taken up into 2
mL of pentane. The pentane solution was filtered through 300 mg of silica gel and the solvent was
removed using a rotary evaporator to give 57 mg (79% yield) of 6 as a thick dark red oil. The
product 6 was stored in pentane solution. 1H NMR of 6 (600 MHz, C6D6) δ 7.56 (bs, 1 H), 7.34
(m, 1 H), 7.07-7.00 (m, 2 H), 5.60-5.57 (m, 2 H), 2.44 (s, 3 H), 2.39 (t, J = 2.1 Hz, 1 H), 1.18 (s, 3
H), 0.88 (s, 3 H). 13C NMR of 6 (150 MHz, C6D6) δ 200.5, 145.9, 140.0, 138.2, 130.4, 129.8,
129.4, 127.1, 104.0, 94.6, 92.7, 32.6, 26.3, 24.5, 20.8, 18.7. HRMS (EI) (M+) calculated for
C21H16Co2O6 481.9611, found 481.9591.
Reaction of 33b with Silver Triflate. The isopropylidenecyclopropane 33b (11.7 mg) was
dissolved in 906 mg of C6H6 that contained 16.1 mg of AgOTf. The solution was heated in a sealed
ACS Paragon Plus Environment

Page 25 of 31
The Journal of Organic Chemistry
25
1
2
3
4
5
6
7
8
9
tube at 60 °C in a water bath for 60 min. The benzene solution was taken up into three mL of
pentane and then extracted with three portions of water. The benzene/pentane phase was dried over
Na2SO4 and the solvents were removed using a rotary evaporator. The residue was filtered through
a small amount of silica gel in a pipet using pentane to rinse. Removal of the solvent using a rotary
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
evaporator gave 10.2 mg (87% yield) of 34b22 as a clear oil. H NMR of 34b (600 MHz, C6D6) δ
7.27 (d, J = 8.7 Hz, 2 H), 6.99 (d of d, J = 15.5, 11.0 Hz, 1 H), 6.77 (d, J = 8.7 Hz, 2 H), 6.46 (d, J =
15.5 Hz, 1 H), 6.05 (d, J = 11.0 Hz, 1 H), 3.29 (s, 1 H), 1.70 (br s, 3 H), 1.68 (br s, 3 H). 13C NMR
of 34b (150 MHz, CDCl3) δ 158.8, 135.3, 131.0, 129.1, 127.2, 125.5, 123.8, 114.0, 55.3, 26.2, 18.5.
Reaction of 4 with AgOTf in CH3OH. A solution 21.1 mg of methylenecyclopropane 4
(that contained 6% of 33 (R = CCCH3)) and 30.4 mg of AgOTf in 1.63 g of CH3OH was sealed in a
glass tube and heated in a water bath at 70 °C for 200 min. The CH3OH was then removed using a
rotary evaporator and the residue was taken up into water containing a drop of ammonium
hydroxide and 3 mL of pentane. The pentane extract was washed with 2 portions of water and then
dried over a mixture of Na2SO4 and MgSO4. The NMR spectrum of the crude material showed
methyl ether 37 (R = CCCH3), rearranged product 33 (R = CCCH3), and starting material 4 in a
37:56:7 ratio. After filtration the pentane volume was reduced to about 1 mL and the mixture was
then chromatographed on 2.5 g of silica gel. The column was eluted with increasing amounts of
ether in pentane. The unreacted starting material 4 and the rearranged product 33 (R = CCCH3)
eluted with pentane. The methyl ether ether 37 (R = CCCH3) (7.9 mg; 37% yield based on
unrecovered 4) eluted with 3-4% ether in pentane as a clear oil. 1H NMR of 37 (R = CCCH3) (600
MHz, CDCl3) δ 7.32 (d, J = 8.2 Hz, 2 H), 7.10 (d, J = 8.2 Hz, 2 H), 5.10 (m, 1 H), 4.63 (m, 1 H),
3.35 (br s, 2 H), 3.11 (s, 3 H), 2.05 (s, 3 H), 1.32 (s, 6 H). 13C NMR of 37 (R = CCCH3) (150
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 26 of 31
26
1
2
3
MHz, CDCl3) δ 152.1, 138.9, 131.4, 129.6, 121.5, 113.8, 85.3, 79.7, 77.3, 50.3, 37.1, 25.7, 4.4.
4
5
HRMS (EI) (M+) calculated for C16H20O 228.1514, found 228.1513.
6
7
8
9
Reaction of 13 with AgOTf in CH3OH. A solution 22.2 mg of methylenecyclopropane 13
(that contained 4% of 33 (R = H)) and 33.9 mg of AgOTf in 2.00 g of CH3OH was sealed in a glass
tube and heated in a water bath at 70 °C for 150 min. The CH3OH was then removed using a rotary
evaporator and the residue was taken up into water containing a drop of ammonium hydroxide and
3 mL of pentane. The pentane extract 1was washed with 2 portions of water and then dried over a
mixture of Na2SO4 and MgSO4. The NMR spectrum of the crude material showed methyl ether 37
(R = H), rearranged product 33 (R = H), and starting material 13 in a 40:26:34 ratio. After filtration
the pentane volume was reduced to about 1 mL and the mixture was then chromatographed on 2.6 g
of silica gel. The column was eluted with increasing amounts of ether in pentane. The unreacted
starting material 13 and the rearranged product 33 (R = H) eluted with pentane. The methyl ether
ether 37 (R = H) (6.1 mg; 36% yield based on unrecovered 13) eluted with 2-3% ether in pentane as
a clear oil. 1H NMR of 37 (R = H) (600 MHz, CDCl3) δ 7.30 (t, J = 7.6 Hz, 2 H), 7.23-7.17 (m, 3
H), 5.11 (m, 1 H), 4.64 (m, 1 H), 3.38 (br s, 2 H), 3.13 (s, 3 H), 1.34 (s, 6 H). 13C NMR of 37 (R =
H) (150 MHz, CDCl3) δ 152.4, 140.3, 129.7, 128.3, 125.9, 113.6, 77.4, 50.3, 37.2, 25.7. HRMS
(CI) (M+H)+ calculated for C13H19O 191.1436, found 191.1456.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Thermal Rearrangements of Methylenecyclopropanes. Kinetics Procedures. Rates of
1
rearrangements in Tables 1-3 were measured using our previously described H NMR method.6, 23
In order to avoid NMR spectral line broadening due to development of paramagnetic impurities,
rearrangement rates of cobalt complex 5 were measured using freshly chromatographed samples of
5 at concentrations of about 3 mg/mL of C6D6 in sealed NMR tubes under nitrogen.
ACS Paragon Plus Environment

Page 27 of 31
The Journal of Organic Chemistry
27
1
2
3
4
5
6
7
8
9
Rearrangement rates of cobalt complex 6 were measured using the following modified
procedure. About 3 mg of the freshly chromatographed cobalt complex 6 was dissolved in 1.5 mL
of C6D6. Portions of the solution were sealed in four tubes and the tubes were immersed in a
constant temperature bath at the appropriate temperature. The tubes were periodically withdrawn
from the bath and quenched at 15 °C at appropriate times. The C6D6 was removed from each
sample using a rotary evaporator and the residue was taken up into a small amount of pentane. The
pentane solution was passed through a small amount of silica gel in a pipet to remove paramagnetic
impurities. After pentane removal, the residue was re-dissolved in C6D6 and the sample was
analyzed by 600 MHz NMR. The areas due to the CH3 group of unreacted 6 at δ 1.18 and the
rearrangement product at δ 1.86 were monitored in the standard fashion.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Computational Studies. Ab initio molecular orbital calculations were performed at the
B3LYP/LANL2DZ level using the Gaussian 09 series of programs.11a
Structures were
characterized as energy minima via frequency calculations that showed no negative frequencies.
Associated Content
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI:
xxx.
Complete reference 11a.
Computational details
1H and 13C NMR spectra of new compounds
Data used for determination of rate constants in Tables 1-3.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 28 of 31
28
1
2
3
Author Information
4
5
6
7
8
9
Corresponding Author
creary.1@nd.edu
ORCID
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Xavier Creary: 0000-0002-1274-5769
Notes
The authors declare no competing financial interest.
References
(1) (a) Sternberg, H. W.; Greenfield, H.; Friedel, R. A.; Wotiz, J. H.; Markby, R.; Wender, I. J. Am.
Chem. Soc. 1954, 76, 1457. (b) Greenfield, H.; Sternberg, H. W.; Friedel, R. A.; Wotiz, J. H.;
Markby, R.; Wender, I. J. Am. Chem. Soc. 1956, 78, 120. (c) Ellgen, P. C. Inorg. Chem. 1972, 11,
691.
(2) Sly, W. G. J. Am. Chem. Soc. 1959, 81, 18.
(3) (a) Khand, I. U.; Knox, G. R.; Pauson, P. L.; Watts, W. E.; Foreman, M. I. J. Chem. Soc.,
Perkin Trans. 1, 1973, 977. (b) Pauson, P. L.; Khand, I. U. Ann. N. Y. Acad. Sci. 1977, 295, 2. (c)
Pauson, P. L. Tetrahedron 1985, 41, 5855. (d) Harrington, P. J. Transition Metals in Total Synthesis;
Wiley: New York, 1990; pp 259-301. (e) Schore, N. E. Org. React. 1991, 40, 1. (f) Schore, N. E. In
Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, 1991; Vol. 5, pp
1037-1064.
(4) (a) Connor, R. E.; Nicholas, K. M. J. Organometal. Chem. 1977, 125, C45. (b) Lockwood, R.
ACS Paragon Plus Environment

Page 29 of 31
The Journal of Organic Chemistry
29
1
2
3
4
5
6
7
F.; Nicholas, K. M. Tetrahedron Lett. 1977, 48, 4163. (c) Nicholas, K. M.; Mulvaney, M.; Bayer,
M. J. Am. Chem. Soc., 1980, 102, 2508. (d) Nicholas, K. M. Acc. Chem. Res. 1987, 20, 207. (e)
Teobald, B. J. Tetrahedron, 2002, 58, 4133.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(5) (a) Comyns, A. E.; Lucas, H. J. J. Am. Chem. Soc. 1957, 79, 4341. (b) Helmkamp, G. K.; Carter,
F. L.; Lucas, H. J. J. Am. Chem. Soc. 1957, 79, 1306. (c) Muhs, M. A.; Weiss, F. T. J. Am. Chem.
Soc. 1962, 84, 4697. (d) Lewandos, G. S.; Gregston, D. K.; Nelson, F. R. J. Organomet. Chem.
1976, 118, 363.
(6) For a review and leading references, see Creary, X. Acc. Chem. Res. 2006, 39, 761.
(7) (a) Kon, G. A. R.; Nanji, H. R. J. Chem. Soc. 1932, 2557. (b) Ettlinger, M. G. J. Am. Chem. Soc.
1952, 74, 5805. (c) Ullman, C. F. J. Am. Chem. Soc. 1960, 82, 505. (d) Chesick, J. P. J. Am. Chem.
Soc. 1963, 85, 2720. (e) Gilbert, J. C.; Butler, J. R. J. Am. Chem. Soc. 1970, 92, 2168.
(8) (a) Gajewski, J. J. J. Am. Chem. Soc. 1968, 90, 7178. (b) Gajewski, J. J. J. Am. Chem. Soc. 1971,
93, 4450. (c) Doering, W. v. E.; Birladeanu, L. Tetrahedron 1973, 29, 499. (d) Gajewski, J. J.; Chou,
S. K. J. Am. Chem. Soc. 1977, 99, 5696. (e) Gajewski, J.; Benner, C. W.; Stahly, B. N.; Hall, R. F.;
Sato, R. I. Tetrahedron 1982, 38, 853.
(9) Dowd, P. Acc. Chem. Res. 1972, 5, 242.
(10) For typical procedures, see (a) Creary, X. J. Org. Chem. 1978, 43, 1777. (b) Creary, X. J. Am.
Chem. Soc. 1980, 102, 1611.
ACS Paragon Plus Environment