Asymmetric C-H insertion of Rh(II) stabilized carbenoids into acetals: A C-H activation protocol as a Claisen condensation equivalent

Article abstract of DOI:10.1016/j.jorganchem.2005.08.026

The dirhodium tetraprolinate, Rh₂(S-DOSP)₄ is an efficient catalyst in an enantioselective C-H activation protocol. Rh ₂(S-DOSP)₄ catalyzed decomposition of aryldiazoacetates or vinyldiazoacetates results in the

Full text of DOI:10.1016/j.jorganchem.2005.08.026

Journal of Organometallic Chemistry 690 (2005) 6111–6124
www.elsevier.com/locate/jorganchem
Asymmetric C–H insertion of Rh(II) stabilized carbenoids into
acetals: A C–H activation protocol as a Claisen condensation equivalent
*
Huw M.L. Davies , Jaemoon Yang, Joachim Nikolai
Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, NY 14260-3000, United States
Received 20 June 2005; accepted 4 August 2005
Available online 11 October 2005
Abstract
The dirhodium tetraprolinate, Rh2(S-DOSP)4 is an efficient catalyst in an enantioselective C–H activation protocol. Rh2(S-DOSP)4
catalyzed decomposition of aryldiazoacetates or vinyldiazoacetates results in the formation of transient rhodium carbenoid intermedi-
ates. These intermediates are capable of selectively inserting into the C–H bond of acetals. The resulting products are protected b-keto
esters, and so the C–H activation protocol can be considered as strategically equivalent to the Claisen condensation.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Rhodium carbenoid; C–H Insertion; C–H activation; Claisen condensation equivalent
1. Introduction
ence of the donor group (typically vinyl or aryl), carbenoids
2 are much more stabilized than conventional carbenoids,
which contain only electron acceptor groups (typically es-
ter, keto, phosphonate, sulfonate, cyano or nitro) [8,20].
Furthermore, if the reactions of these carbenoids are cata-
lyzed by air-, moisture- and heat-stable dirhodium tetrapro-
linates like Rh2(S-DOSP)4 (3a) or Rh2(S-TBSP)4 (3b) or the
bridged variants Rh2(S-biDOSP)2 (4a) or Rh2(S-biTISP)2
(4b) (Fig. 1) high asymmetric induction can be obtained
routinely [21–23] (Scheme 1).
It has been demonstrated that with donor/acceptor-
substituted rhodium carbenoids 2 in conjunction with cat-
alysts 3a,b or 4a,b very efficient chemo- and stereoselective
intermolecular C–H functionalization reactions are feasible
[7,24]. These reactions can often be seen as complementary
carbenoid versions of many of the classic synthetic reac-
tions of organic chemistry. For example, b-hydroxy esters,
normally prepared by an aldol reaction are stereoselectively
accessible by C–H functionalization a to oxygen. (Eq. (1),
Scheme 2) [25–27]. Similarly, b-amino esters, products of
a Mannich condensation, are obtained by C–H activation
a to nitrogen (Eq. (2), Scheme 2) [28–30]. This approach
has been used successfully by the Davies and Winkler
groups to gain direct access to threo-methylphenidate, the
Developing reliable methods for catalytic C–H activa-
tion has been a long-term goal in organometallic chemistry.
The majority of the published studies on C–H activation
have focused on the use of highly reactive metal complexes,
which are able to activate the C–H bond via oxidative addi-
tion [1–5]. An alternative method for C–H activation is by
means of metal carbenoid induced C–H functionalization
[6–12]. Efficient and enantioselective carbon hydrogen
bond-insertions of carbenoids were long limited to intramo-
lecular reactions, since intermolecular C–H insertions of
carbenes or carbenoids were considered to be unselective,
producing mixtures of products [8,13,14]. In addition to
their lack of selectivity, the intermolecular insertion reac-
tions suffer from competing secondary reactions such as for-
mation of formal carbene dimers [15]. In recent years,
however, it has become apparent that the reactivity profile
of carbenoids is very dependent on the carbenoid structure
[7,16,17] and catalyst system [18,19]. Because of the pres-
*
Corresponding author. Tel. +1 716 645 6800x2186; fax: +1 716 645
6547.
E-mail address: hdavies@acsu.buffalo.edu (H.M.L. Davies).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.08.026

6112
H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
active diastereomer of Ritalinꢁ [28–30]. Allylic C–H activa-
O Rh
tion can lead to c,d-unsaturated esters, classically prepared
via a Claisen rearrangement (Eq. (3), Scheme 2), or O-sily-
lated 1,5-dicarbonyl compounds, the typical products of a
Michael addition (Eq. (4), Scheme 2) [31,32].
N
O Rh
4
SO2Ar
3
Besides their very high diastereo- and enantioselectivity,
C–H functionalizations with donor/acceptor substituted
carbenes 2 show a remarkable chemoselectivity for the site
of functionalization. In the same manner as silyl ethers fa-
vor C–H functionalization a to oxygen (Eq. (1), Scheme 2),
an acetoxy group deactivates this site and C–H functional-
ization is favored at the allylic site in 5 or the benzylic posi-
tion, activated by a p-methoxyphenyl substituent, in 6
(Scheme 3) [27].
Effects governing the chemoselectivity in C–H function-
alizations are subtle: Although it has been established for
hydrocarbons that C–H activation at primary sites is least
favored [33] and it is known that carbenoids 2 preferen-
tially insert into methylene C–H bonds a to a heteroatom
(vide supra), in linear 1,2-dialkoxyalkanes such as 7, func-
tionalization of the methyl group was observed (Scheme 4).
This b oxygen effect is rationalized by inductive deactiva-
tion of the methylene sites by the b-oxygen atom [34].
Steric effects at the site of insertion can open alternative
reaction pathways to C–H functionalization as is seen in
the reaction of cumene (8, Scheme 5). Cyclopropanation
of the phenyl ring competes with C–H activation at the ter-
tiary site, which is somewhat sterically protected [35].
In this article we report the results of our studies into the
C–H activation of tertiary sites in acetals to form, chemo-
and stereoselectively, ketal-protected b-keto esters (Eq. (5),
Scheme 6). This transformation could be considered as a
surrogate to the Claisen condensation (Eq. (6), Scheme
6), although it has a major advantage because stereocontrol
is unlikely in the standard Claisen condensation due to the
epimerizable center in unprotected b-keto esters.
a: Ar = p-C12H25C6H4 Rh2(S-DOSP)4
b: Ar = p-t-BuC6H4 Rh2(S-TBSP)4
SO2Ar
H
H
H
H
H
N
O
N
O
Rh
Rh
SO2Ar
O
O
O
O
SO2Ar
N
O
O
N
H
H
H
SO2Ar
4
a: Ar = p-C12H25C6H4 Rh2(S-biDOSP)2
b: Ar = 2,4,6-i-PrC6H2 Rh2(S-biTISP)2
Fig. 1.
EWG
EDG
EWG
LnRh(II)
LnRh
N2
EDG
1
2
R1
R2 CH
R3
R1
R2
R3
EWG
H
EDG
C
EWG = CO2R, COR, PO(OR)2, SO2R, CN, NO2
EDG = vinyl or aryl
Scheme 1.
N2
N2
R
R
Ar
CO2Me
Ar
CO2Me
R2
R2
Rh2(S-DOSP)4
then TFA
Rh2(S-DOSP)4
50 oC
R1
(Eq 1)
R1
Ar
(Eq 2)
OTBS
CO2Me
N
N
H
Ar
TBSO
Boc
CO2Me
up to 92% de
up to 94% ee
up to 94% de
up to 92% ee
N2
N2
Ar
CO2Me
Ar
CO2Me
TIPSO
R1
OTIPS
R
R
R1
Rh2(S-DOSP)4
23 oC
Rh2(S-DOSP)4
(Eq 4)
(Eq 3)
CO2Me
CO2Me
23 oC
R2
R2
H
H
Ar
Ar
up to 88% de
up to 95% ee
up to 90% de
up to 95% ee
Scheme 2.

H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
6113
N2
(p-Br)Ph
CO2Me
Me
Rh2(S-DOSP)4
50 oC
AcO
CO2Me
Ph(p-Br)
yield: 68%
AcO
5
de: 33%
ee: 76%
N2
(p-Br)Ph
(p-Br)Ph
CO2Me
AcO
OMe
CO2Me
Rh2(S-DOSP)4
AcO
50 oC
OMe
6
yield: 90%
de: 35%
ee: 50%
Scheme 3.
N2
O
R1
(p-Br)Ph
CO2Me
O
Rh2(S-DOSP)4
Rh2(S-DOSP)4
23 oC
O
R1
O
OCH3
+
CO2Me
H3CO
N2
R2
R2
CO2Me
7
(Eq 5)
Ph(p-Br)
CO2Me
O
O
+
H3CO
R1
R2
OMe
O
yield: 72%
ee: 76%
base
CO2Me
R1
R2
Scheme 4.
CO2Me
(Eq 6)
(Claisen condensation)
Scheme 6.
N2
2. Results and discussion
(p-Br)Ph
CO2Me
Rh2(S-DOSP)4
50 oC
To explore the possibility of C–H activation of a tertiary
center adjacent to heteroatoms, which might activate this
site electronically, the reaction of dioxolane 9 was
examined (Scheme 7). 2,2-Dimethylbutane (2,2-DMB)
was chosen as the solvent because this hydrocarbon solvent
is relatively inert towards intermolecular C–H insertion
[33]. Interestingly, beside C–H insertion into the sterically
hindered acetal C–H bond of 9, C–H activation at the
dioxolane ring was also observed. The C–H insertion prod-
ucts 10a,b were formed in up to 80% combined yield
(Scheme 7). The yields did not change whether the reaction
was conducted at 50 or ꢀ15 ꢂC. However, the use of two
equivalents of the phenyldiazoacetate relative to the
8
CO2Me
Ph(p-Br)
H
H
MeO2C
(p-Br)Ph
H
H
CO2Me
(p-Br)Ph
ratio: 60 : 40
Scheme 5.

6114
H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
N2
N2
(2 equiv)
(2 equiv)
O
(p-Br)Ph
CO2Me
Ph
CO2Me
O
O
Rh2(S-DOSP)4 (1 mol%)
2,2-DMB
O
Rh2(S-DOSP)4 (1 mol%)
2,2-DMB
9
9
CO2Me
Ph
O
O
O
CO2Me
O
CO2Me
O
O
O
CO2Me
O
Ph
10a
Ph(p-Br)
Ph(p-Br)
10b
11a
11b
ratioa
10a + 10b 10a/10b
de [%] 10ba
temp. [oC]
yield [%]
ratioa
11a + 11b 11a/11b
de [%] 11ba
temp. [oC]
yield [%]
50
25
76
78
80
41
71:29
74:26
80:20
82:18
30
35
50
54
25
75
79
89:11
94:6
33
53
-15b
-15
-30b
aratio determined from crude proton NMR
bconducted with R-DOSP. The absolute
configuration of the product is opposite to
that drawn for 11a.
aratio determined from crude proton NMR
bconducted with R-DOSP. The absolute
configuration of the product is opposite to
that drawn for 10a.
Scheme 8.
Scheme 7.
served (Scheme 8). These results suggest that the formation
of b-insertion products 10b and 11b is a less favorable pro-
cess due to electronic reasons and becomes less productive
at lower temperatures and with more electron deficient
carbenoids.
Esters 10 and 11 were inseparable by column chroma-
tography. However, the corresponding alcohols 12a,b and
13a,b could be separated on silica gel and fully character-
ized. For alcohols 12a and 13a, derived from the corre-
sponding C–H insertion products formed at 25 ꢂC, the
enantioselectivity was determined to be 61 and 70% ee,
respectively (Scheme 9).
From studies on the C–H insertion of the donor/accep-
tor substituted carbenoids at benzylic sites, it is known that
electron donating substituents in the para position greatly
enhance the reactivity of benzylic C–H bonds [35]. We con-
sequently examined the reactivity of acetals 14a–c in the
reaction with methyl p-bromophenyldiazoacetate catalyzed
by Rh2(S-DOSP)4 at ꢀ15 ꢂC (Scheme 10). At this temper-
ature, 2,2-DMB did not dissolve the employed acetals
sufficiently but previous studies had shown that a,a,a-
trifluorotoluene (PhCF3) is an adequate replacement for
hydrocarbon solvents in Rh2(S-DOSP)4 catalyzed carbene
reactions [37]. Under these conditions the desired ketals
15a–c were formed with moderately high asymmetric
induction (68–75% ee). No C–H insertion into the dioxo-
lane ring of the acetal was observed. A more significant
example of the carbenoid selectivity is the reaction of the
substrate was necessary in all cases to ensure good yields.
For example, using two equivalents of substrate relative
to phenyldiazoacetate resulted in only 42% combined yield
of 10a,b for the reaction of 9 catalyzed by Rh2(S-DOSP)4
at 25 ꢂC. The formation of 10a could be deduced unequiv-
1
ocally from the H NMR spectrum showing a distinct sin-
glet at 4.19 ppm, which can be assigned to the proton
attached to the newly formed tertiary carbon atom [36].
In contrast, for the minor b-insertion product, the signal
for the acetal proton was still found at 5.90 ppm for the
major diastereomer and at 5.96 ppm for the minor isomer.
The reaction temperature clearly influences the formation
of b-insertion product 10b: lowering the temperature to
ꢀ30 ꢂC resulted in a 82:18 ratio of 10a vs. 10b. At this tem-
perature the de of 10b also increased to 54% (Scheme 7).
Compared to the carbenoid derived from methyl phenyl-
diazoacetate, the carbenoid derived from methyl p-bromo-
phenyldiazoacetate is more electron deficient and favors
more strongly sites that would stabilize positive charge
build-up on the carbon of the C–H bond [33]. Therefore,
it was not surprising to find greater selectivity in favor of
insertion into the acetal C–H bond when using the latter
diazo compound as the formation of 11b is a less favored
process due to the aforementioned deactivation of the
methylene site by the b-oxygen effect (Scheme 8) [34]. At
ꢀ15 ꢂC almost exclusive formation of ketal 11a was ob-

H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
6115
The reaction of the protected anisaldehyde 14d led to the
formation of a third type of product in addition to the de-
sired ketal. The dioxane 16 was observed beside ketal 15d
(Scheme 11). Compound 16 could be identified unambigu-
ously from its gs-HMBC and gs-HSQC NMR spectra as
well as from comparison to published NMR data [38].
The formation of 16 can be rationalized by the intermedi-
ate formation of an oxonium ylide formed from the carbe-
noid with one oxygen atom of the dioxolane ring followed
by a [1,2] Stevens-type rearrangement [39,40]. The forma-
tion of 16 with 47% ee is noteworthy and suggests that dur-
ing the ylide formation/rearrangement, the chiral catalyst is
not dissociated completely from the ylide and therefore is
still able to influence the stereochemical outcome of the
rearrangement. The formation of 16 in 47% ee adds a fur-
ther example to the enantioselective reactions potentially
possible by Rh2(S-DOSP)4 (vide infra) [41–45].
OH
O
O
O
O
R
CO2Me
R
12a,b
LiAlH4
10a,11a
-78 oC, THF
CO2Me
O
O
O
O
OH
R
R
13a,b
10b,11b
12a
yield [%]
12a
ee [%]
13a
yield [%]
R
An excellent substrate for selective C–H insertion into
an acetal was found to be dioxolane 17 derived from cinna-
maldehyde. It possesses a phenyl ring that is able to
efficiently enhance the C–H insertion event through conju-
gation (vide supra). At the same time, this bulky group is
attached via a sterically less demanding vinyl group to
the acetal carbon atom. Initial optimization studies clearly
favor Rh2(S-DOSP)4 in PhCF3 at 25 ꢂC (Scheme 12). Un-
der these conditions the C–H insertion product 18a was
formed in 53% yield and 84% ee. Even higher yields could
be obtained using 2,2-DMB as solvent but the results were
variable due to inhomogeneity of the reaction mixtures. In
contrast, using Rh2(S-DOSP)4 in CH2Cl2 at 25 ꢂC afforded
the C–H insertion product only in 22% yield and 69% ee.
Even with the bridged Rh2(S-biTISP)2 catalyst this result
could not be improved although it is known that this cata-
lyst is an excellent alternative to Rh2(S-DOSP)4 in cases
where CH2Cl2 must be used as the solvent [22,29]. In all
cases only the desired ketal 18a was observed and no
b-insertion product on the dioxolane ring was detected.
Reactions with various aryldiazoacetates consistently
afforded ketals 18b–f in moderate yields (51–65%). Com-
pared to the ketals derived from dioxolane 9, the observed
enantioinduction was significantly higher for all diazoace-
tates tested (73–91%) (Scheme 13). We believe that this is
due to a sterically less crowded transition state for the
C–H insertion which allows for a more efficient catalyst
control of the stereochemical outcome of the reaction.
Here, as observed in the benzaldehyde series (vide
supra), para-methoxy substitution opened a reaction chan-
nel leading to the [1,2] rearrangement product 20.
However, in this case, rearrangement product 20 was the
major product and was formed as a racemic mixture
(Scheme 14). Decreasing enantioselectivity at higher
reaction temperatures has been reported in various cases
for C–H functionalizations with donor–acceptor substi-
tuted carbenoids [27,33,46]. On the other hand, reaction
yields tend to be higher at elevated temperatures
[27,33,46]. For substrate 19, it was found that at lower
temperatures (0 and ꢀ15 ꢂC) the combined yield of 18g
Ph
57
61
9
12b
yield [%]
12b
ee [%]
13b
yield [%]
R
(p-Br)Ph
76
70
2
Scheme 9.
N2
(2 equiv)
CO2Me
(p-Br)Ph
O
Rh2(S-DOSP)4 (1 mol%)
- 15 oC, PhCF3
O
R
14a-c
O
O
CO2Me
R
Br
15a-c
ee [%]
R
yield [%]
15
Br
70
61
59
68
a
b
c
70a
75
CH3
CH2CH3
aconducted with R-DOSP. The absolute
configuration of the product is opposite to
taht drawn for 15.
Scheme 10.
ethyl derivative 14c, which resulted in only insertion into
the ketal C–H bond and no insertion into the benzylic
methylene C–H bonds [35].

6116
H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
N2
(2 equiv)
CO2Me
O
O
(p-Br)Ph
O
O
O
O
CO2Me
CO2Me
Rh2(R-DOSP)4 (1 mol%)
- 15 oC, PhCF3
MeO
MeO
Br
MeO
Br
16
14d
15d
33% yield
47% ee
25% yield
74% ee
Scheme 11.
N2
N2
(2 equiv)
O
(2 equiv)
O
O
CO2Me
Ph
CO2Me
R
CO2Me
O
O
Rh2(S-DOSP)4 (1 mol%)
25 oC, PhCF3
catalyst (1 mol%)
O
17
18a
yield [%]
17
temp. [oC]
catalyst
solvent
ee [%]
O
O
R
CO2Me
Rh2(S-DOSP)4
25
50
2,2 DMB
2,2-DMB
CH2Cl2
PhCF3
up to 60a
up to 57a
22
83
78
Rh2(S-DOSP)4
Rh2(S-DOSP)4
Rh2(S-DOSP)4
18b-f
25
25
69
84
yield [%]
ee [%]
86
R
18
53
Rh2(S-DOSP)4
Rh2(S-biTISP)4
103
25
PhCF3
CH2Cl2
38
20
48
66
65
57
62
b
c
d
e
(p-Br)-Ph
88
91
73
(p-CH3)-Ph
(p-MeO)-Ph
2-naphthyl
(p-Cl)-Ph
a yields show considerable variation
due to inhomogenous reaction mixture
59
51
Scheme 12.
f
85a
aconducted with R-DOSP. The abolute
configuration of the product is opposite to
that drawn for 18.
and 20 dropped considerably (20–30%) due to significant
dimerization of the carbenoid. This result and the finding
that dioxolane 16 was formed in 47% ee at ꢀ15 ꢂC (Scheme
11) suggest that there is a subtle interplay between sub-
strate structure and reaction conditions which need to be
carefully adjusted in order to obtain good yield and stere-
oselectivity in these [1,2] rearrangement reactions.
Even though acetals such as 17 would be expected to be
electronically highly activated for C–H activation, their
overall reactivity behavior suggested that they were not
especially favorable substrates. In order to test this, a com-
petition study was conducted between 17 and 21 revealing
that the formation of TBS-protected aldol 22 [27] from 21
was considerably favored over formation of acetal 18a.
This result suggests that steric factors are playing a role
in decreasing the reactivity of the acetals towards C–H acti-
vation. Compound 18a was not even observed by ESI-MS
of the reaction mixture (Scheme 15).
Scheme 13.
could be prepared in 68% yield and 86% ee (Scheme 16).
Normally, alkynes are prone to cyclopropenation, but the
steric demands of the donor/acceptor substituted carbe-
noids limit cyclopropenation to mono-substituted alkynes
[47].
Finally we turned our attention to rhodium(II) carbe-
noids derived from the decomposition of phenylvinyldi-
azoacetate (25) with Rh2(S-DOSP)4 in the presence of
acetal 9 (Scheme 17). Although yields for C–H insertion
to form 26 with this carbenoid precursor were lower (42–
48%) than the aryldiazoacetates, the enantioselectivity was
much higher (80–89% ee). Unlike in the phenyldiazoacetate
series no b-insertion product was observed. Again, we
explain this selectivity on the basis of the reduced steric
demand at the site of C–H activation; this time achieved
by reducing the steric demand of the carbenoid center. It
should be noted that despite serious attempts, no C–H
insertion products were isolated from the reactions of 25
In order to test the steric issues further, the alkyne deriv-
ative 23 was prepared. The linear nature of the alkyne
would make the acetal C–H bond less sterically encum-
bered than the other acetal substrates, and thus 23 would
be predicted to be a superior substrate in this chemistry.
This was indeed the case as the C–H insertion product 24

H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
6117
N2
(2 equiv)
O
O
O
O
O
O
(p-Br)Ph
CO2Me
CO2Me
CO2Me
Rh2(R-DOSP)4 (1 mol%)
25 oC, PhCF3
MeO
Br
Br
MeO
MeO
19
18g
22% yield
81% ee
20
49% yield
0% ee
Scheme 14.
O
N2
O
OTBS
CO2Me
(2 equiv)
25
O
Rh2(S-DOSP)4
2,2-DMB
17
21
O
N2
(0.25 equiv)
25 oC, PhCF3
9
Ph
CO2Me
Rh2(S-DOSP)4 (1 mol%)
O
O
CO2Me
Ph
CO2Me
OTBS
18a
26
temp. [oC]
22
catalyst [mol%]
ee [%]
yield [%]
Scheme 15.
25
25
50
2
4
4
48
46
42
80
89
81
N2
(2 equiv)
O
O
(p-Br)Ph
CO2Me
Scheme 17.
Rh ( -DOSP) (1 mol%)
2 S
4
with other acetal substrates such as 17 or 19. As seen previ-
ously for the reaction of acetal 9 with phenyldiazoacetates,
the use of a twofold excess of the acetal resulted in a consid-
erable drop in yield for the Rh2(S-DOSP)4 catalyzed reac-
tion of 9 with 25 (only 22% isolated yield).
25 oC, PhCF3
23
The absolute configuration of the stereocenter created in
the C–H insertion reaction was deduced from diol 28. Diol
28 was prepared from 12a by hydrolysis of the ketal [48]
followed by syn reduction [49] of the resulting ketone 27
(Scheme 18). In an independent study, the absolute stereo-
chemistry of diol 28 has been assigned as (1R,2S) with
O
O
CO2Me
25
½aꢁD ¼ 45 [50]. Comparing the respective specific optical
rotations of diol 28 from that study and 28 prepared in this
work, the asymmetric carbon in 10a could be assigned as
(S). The stereochemistry of the other C–H activation prod-
ucts is tentatively assigned assuming a similar trajectory of
approach of the substrate leading to the same sense of
asymmetric induction.
Br
24
68% yield
86% ee
Scheme 16.

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H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
The stereochemical result emphasizes once again the
high predictability of the C–H insertion process catalyzed
by Rh2(S-DOSP)4. Based on the model developed in our
group [16,17,21,51] (Scheme 19), approach of the
substrate from the front to the carbene coordinated to
the chiral Rh(II) catalyst, an (S) configuration of the
formed asymmetric carbon atom would be expected. In
the predictive model shown in Scheme 19 the D2
symmetric Rh2(S-DOSP)4 is assumed to have an
a,b,a,b conformation [23] to which the carbene is bound
in the manner shown allowing for only one defined
approach of the substrate.
O
OH
H
OH
H
O
O
I2, acetone
27
66% yield
12a
NaH/LiBH4, TiCl4, -78 oC
syn
This study demonstrates the subtle interplay between
steric and electronic effects that controls the regioselectivity
of the C–H activation chemistry. The acetal site is electron-
ically highly activated but is close to the limit in terms of
steric crowding. The best substrate is alkyne 23, which is
the least sterically demanding. Due to the steric crowding,
a competing reaction at the C-3 position of the acetal can
occur to a small extent even though electronically this is
considerably less favored, especially as it contains a b-
oxygen group.
OH OH
H
(1S,2R)-28
[α]25D = - 25o
Scheme 18.
SO2Ar
N
H
H
O
N
O
Rh
Rh
SO2Ar
O
O
O
O
SO2Ar
O
O
N
N
H
H
SO2Ar
3a
Rh2(S-DOSP)4
(
)-3a
β
,
α
β,
α
,
approach from front
S
M
L
H
S
M
δ+
L
H
M eO2C
Ph
Rh
M eO2C
Ph
δ−
Rh
L = Ph
M,S = -O-(CH2)2-O-
O
Ph
Ph
O
MeO2C
H
(S)-10a
Scheme 19.

H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
6119
O
O
Rh
CO2Me
+
O
O
_
Ar
Rh
CO2Me
Ar
29
X
X
C-H insertion
X = H, Alkyl, Br, MeO
[1,2] rearrangement
X = MeO
O
O
O
O
CO2Me
CO2Me
Ar
Ar
X
X
30
31
Scheme 20.
One of the most intriguing aspects of the current study is
the observation of the Stevens rearrangement product
when the acetal had a methoxy substituent on the aromatic
ring. One of the remarkable features of the intermolecular
C–H insertion chemistry of the donor/acceptor substituted
rhodium carbenoids is that the chemistry is compatible
with various mildly nucleophilic sites. The highly electro-
philic carbenoids would be expected to be reactive towards
nucleophiles and the fact that C–H activation still occurs
would suggest that the reaction of these stabilized carbe-
noids with weak nucleophiles to form an ylide like 29 might
be reversible. In this case the presence of the methoxyphe-
nyl substituent would not influence the ability of the acetal
to react with the carbenoid to form an ylide, but once ylide
29 is formed the methoxyphenyl group would be expected
to enhance the [1,2] rearrangement to dioxane 31 (Scheme
20) [52]. It is thus tempting to speculate that all the acetals
are forming ylides but this is an unproductive step and
probably reversible except in the case of the methoxyphe-
nyl derivative.
In summary, we have shown that chemo- and stereose-
lective C–H activation of tertiary C–H bonds with donor/
acceptor carbenoids is in fact a feasible and predictable
process if the C–H bond is (a) electronically sufficiently
activated as in dioxolanes which have either an aryl or vi-
nyl aryl substituent attached to the site of C–H insertion
and/or (b) the site of C–H activation is not too crowded.
Steric hindrance can be avoided either by using sterically
less crowded substrates or carbenoids derived from
phenylvinyldiazoacetates.
trifluorotoluene (PhCF3) had purity > 99% and was de-
gassed prior to use. NMR spectra were recorded at
1
293 K at 400 or 500 MHz for H and 75 or 125 MHz for
1
13C. All 13C NMR spectra were recorded H decoupled.
1
TMS (d = 0.0) served as internal standard for H NMR
spectra and CDCl3 (d = 77.0) for 13C. Assignments of
13C chemical shifts were based on DEPT 135 experiments.
IR spectra were recording on a FT-IR instrument using an
ATR unit (diamond crystal) for oils and as KBr pellets for
solids. Melting points are uncorrected (heating rate 2 ꢂC/
min). Analytical TLC was performed on 0.25 mm E. Merck
silica gel (60F-254) plates. Phosphomolybdic acid (PMA)
in ethanol was used as visualizing reagent to detect com-
pounds with no or only weak UV absorbtion at 254 nm.
Flash column chromatography was performed on silica
gel 60A (230–400 mesh). Enantiomeric excess (ee) was
determined by HPLC with UV detection using isopropa-
nol/hexanes as eluent.
Starting materials. All diazo compounds were prepared
analogously to published procedures [53] and gave satisfac-
tory spectroscopic data. Acetals 14a,b, 17 and 19 were pre-
pared following NoyoriÕs protocol [54]. Acetal 23 was
prepared as published [55]. Detailed spectroscopic data
for 14c are reported here, since they have not yet been
reported.
3.1. 2-(4-Ethylphenyl)-1,3-dioxolane (14c)
Preparation from 4-ethylbenzaldehyde and 1,2-bis(tri-
methylsiloxy)ethane according to the literature [54]; color-
less oil, b.p. 100 ꢂC/5 mbar. IR (film): m = 2964 (m), 2877
1
3. Experimental
(m), 1080 (s), 966 (m), 941 (m), 825 (s) cmꢀ1. H NMR
(CDCl3): d = 1.22 (t, J = 7.3 Hz, 3H), 2.65 (q, J = 7.3 Hz,
2H), 4.00–4.04 (m, 2H), 4.10–4.14 (m, 2H), 5.78 (s, 1H),
7.20 (d, J = 8.1 Hz, 2H), 7.38 (d, J = 8.1 Hz, 2H). 13C
NMR (CDCl3): d = 15.5 (CH3), 28.6, 65.2 (both CH2),
103.7, 126.4, 127.8 (all CH), 135.1, 145.4 (both C). HRMS
(EI): Calc. C11H14O2 178.0994; found 177.0912 [M+-1].
All reactions sensitive to air and moisture were carried
out in rigorously dried glassware under an Ar atmosphere.
2,2-Dimethylbutane (2,2-DMB) was distilled from Na un-
der argon. CH2Cl2 was dried by passage through a solvent
purification system packed with Al2O3. Purchased a,a,a-

6120
H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
3.2. (S)-Methyl 2-phenyl-2-(2-phenyl-1,3-dioxolan-2-
yl)acetate (10a) and methyl 2-phenyl-2-(2-phenyl-1,3-
dioxolan-4-yl)acetate (10b)
(Regis RR-Whelk 4 · 250 mm, 3% isopropanol in hexane,
1 ml/min, 254 nm): 61% (major: 16.3 min; minor:
19.1 min); 13a: Yield: 34 mg (9%), colorless oil; Rf = 0.37
(PMA, petroleum ether/diethyl ether 1:4). Only the major
diastereomer of 13a could be isolated. 12a: IR (film):
m = 3442 (br), 3063 (w), 3028 (w), 2951 (w), 2891 (w),
1495 (w), 1169 (m), 1026 (s), 955 (m), 764 (m), 698 (s)
To a stirred solution of 9 (0.17 g, 1.1 mmol) and Rh2(S-
DOSP)4 (42 mg, 0.022 mmol) in 2,2-DMB (5 ml) at 25 ꢂC
was added methyl 2-diazophenylacetate (0.39 g, 2.2 mmol)
in 2,2-DMB (10 ml) via a syringe pump over 2 h. The reac-
tion mixture was stirred at 25 ꢂC for 1 h and then concen-
trated in vacuo. The crude product was purified via column
chromatography (petroleum ether/diethyl ether 5:1) to af-
ford an inseparable mixture of 10a and 10b (0.25 g, 78%)
1
cmꢀ1. H NMR (CDCl3): d = 2.78 (br t, 1H), 3.38 (dd,
J = 7.3, 5.4 Hz, 1H), 3.65–3.69 (m, 1H), 3.74–3.83 (m,
2H), 3.94–4.03 (m, 2H), 4.18–4.24 (m, 2H), 7.00–7.03 (m,
2H), 7.13–7.19 (m, 8H). 13C NMR (CDCl3): d = 56.6
(CH), 63.3, 63.9, 64.7 (all CH2), 111.7 (C), 126.2, 126.8,
127.6, 127.7, 127.9, 129.6 (all CH), 137.4, 140.4 (both C).
HRMS (ESI): Calc. for C17H18O3Na 293.1148; found
293.1145. 13a: IR (film): m = 3410 (br), 3032 (w), 2883
1
as colorless oil; Rf = 0.52. From the H NMR spectrum
of the crude reaction mixture the ratio of 10a:10b was
determined as 74:26; de for 10b 35%. 10a: 1H NMR
(CDCl3): d = 3.58 (s, 3H), 3.72–3.79 (m, 2H), 3.84–3.93
(m, 2H), 4.19 (s, 1H), 7.23–7.25 (m, 6H), 7.30–7.32 (m,
2H), 7.37–7.38 (m, 2H). Compare also the literature [36].
13C NMR (CDCl3): d = 51.8 (CH3), 60.5 (CH), 64.9, 65.3
(both, CH2), 109.4 (C), 126.3, 127.5, 127.6, 127.7, 128.1,
130.3 (all CH), 133.5, 140.8, 170.4 (all C). Compound
10b was characterized as the corresponding alcohol 13a.
(w), 1217 (m), 1066 (m), 1026 (m), 758 (m), 696 (s) cmꢀ1
.
1H NMR (CDCl3): d = 1.73 (br t, 1H), 3.06 (ddd,
J = 6.6, 6.6, 6.6 Hz, 1H), 3.67 (dd, J = 8.0, 8.0 Hz, 1H),
3.93–4.04 (m, 2H), 4.24 (dd, J = 8.4, 6.2 Hz, 1H), 4.60
(ddd, J = 8.0, 6.2, 5.5 Hz, 1H), 5.71 (s, 1H), 7.28–7.41
(m, 10H). 13C NMR (CDCl3): d = 50.6 (CH), 64.5, 68.7
(both CH2), 76.6 103.8, 126.3, 127.4, 128.3, 128.7, 129.1,
129.2 (all CH), 138.03, 138.3 (both C).
3.3. (S)-Methyl 2-(4-bromophenyl)-2-(2-phenyl-1,3-
dioxolan-2-yl)acetate (11a) and methyl 2-(4-bromophenyl)-
2-(2-phenyl-1,3-dioxolan-2-yl)acetate (11b)
3.5. (R)-2-(4-Bromophenyl)-2-(2-phenyl-1,3-dioxolan-2-
yl)ethanol (12b) and 2-(4-bromophenyl)-2-(2-phenyl-1,3-
dioxolan-4-yl)ethanol (13b)
From 9 (0.05 g, 0.36 mmol) and Rh2(R-DOSP)4 (13 mg,
0.007 mmol) in 2,2-DMB (5 ml) and methyl 2-diazo-(4-
bromophenyl)acetate (0.18 g, 0.73 mmol) in 2,2-DMB
(10 ml). Yield: 0.10 g (75%), colorless oil; Rf = 0.43 (petro-
leum ether/diethyl ether 5:1). From the 1H NMR spectrum
of the crude reaction mixture the ratio of 11a:11b was
determined as 89:11; de for 11b 33%. 11a: 1H NMR
(CDCl3): d = 3.58 (s, 3H), 3.72–3.80 (m, 2H), 3.85–3.93
(m, 2H), 4.15 (s, 1H), 7.25–7.27 (m, 5H), 7.30–7.32 (m,
2H), 7.35–7.37 (m, 2H). 13C NMR (CDCl3): d = 51.9
(CH3), 59.9 (CH), 64.9, 65.3 (both CH2), 109.1, 121.9 (both
C), 126.2, 127.8, 128.2, 130.9, 132.1 (all CH), 132.5, 140.5,
170.0 (all C). Compound 11b was characterized as the cor-
responding alcohol 13b.
From 11a,b (0.8 g, 2.1 mmol) dissolved in THF (15 ml)
and LiAlH4 (2.12 ml, 1 M in THF) in THF (5 ml) at
ꢀ78 ꢂC. 12b: Yield: 0.57 g (76%), colorless oil; Rf = 0.54
(PMA, petroleum ether/diethyl ether 1:4). ee (Regis RR-
Whelk 4 · 250 mm, 5% isopropanol in hexanes, 1 ml/min,
254 nm): 70% (major: 14.8 min; minor: 21.3 min); 13b:
Yield: 11 mg (2%), colorless oil; Rf = 0.37 (PMA, petro-
leum ether/diethyl ether 1:4). Only the major diastereomer
of 13b could be isolated. 12b: IR (film): m = 3441 (br), 3061
(w), 2951 (w), 2889 (w), 1489 (m), 1038 (s), 1011 (s), 733 (s),
1
702 (s) cmꢀ1. H NMR (CDCl3): d = 2.77 (br t, 1H), 3.34
(dd, J = 7.3, 5.5 Hz, 1H), 3.67 (m, 1), 3.76 (m, 2H), 3.97
(m, 2H), 4.15 (dd, J = 10.8, 7.3 Hz, 1H), 5.26 (s, 1H),
6.90 (d, J = 8.4 Hz, 2H), 7.18 (m, 5H), 7.27 (d,
J = 8.4 Hz, 2H). 13C NMR (CDCl3): d = 56.0 (CH), 63.0,
64.0, 64.7 (all CH2), 111.3, 120.9 (both C), 126.1, 127.8,
128.1, 130.8, 131.3 (all CH), 136.6, 140.2 (both C). HRMS
(ESI): Calc. for C17H17BrO3Na 371.0253; found 371.0255 –
Calc. for C17H1781BrO3Na 373.0233; found 373.0241. 13b:
IR (film): m = 3431 (br), 3032 (w), 2924 (w), 2885 (w), 1489
(m), 1402 (w), 1217 (w), 1070 (s), 1011 (s), 758 (m), 733 (s),
3.4. (R)-2-Phenyl-2-(2-phenyl-1,3-dioxolan-2-yl)ethanol
(12a) and 2-phenyl-2-(2-phenyl-1,3-dioxolan-4-yl)ethanol
(13a)
To a solution of LiAlH4 (1.42 ml, 1 M in THF) in THF
(5 ml) at ꢀ78 ꢂC was added dropwise 10a,b dissolved in
THF (10 ml). The reaction mixture was stirred for 15 min
at this temperature and then for 2.5 h at 0 ꢂC. The reaction
mixture was quenched at 0 ꢂC by successive additions of
water (55 ll), 4 N NaOH (55 ll) and water (160 ll) [56].
The white precipitate was removed by filtration and
washed with diethyl ether (50 ml). Removal of the solvent
afforded a colorless oil that was further purified by column
chromatography. 12a: Yield: 0.22 g (57%), colorless oil;
Rf = 0.47 (PMA, petroleum ether/diethyl ether 1:4). ee
1
698 (s) cmꢀ1. H NMR (CDCl3): d = 1.66 (br t, 1H), 3.01
(ddd, J = 6.6, 6.6, 6.6 Hz, 1H), 3.72 (dd, J = 8.0, 8.0 Hz,
1H), 3.90–4.00 (m, 2H), 4.25 (dd, J = 8.4 Hz, 6.2 Hz,
1H), 4.57 (ddd, J = 7.7, 7.7, 5.5 Hz, 1H), 7.21 (d,
J = 8.4 Hz, 2H), 7.33–7.40 (m, 5H), 7.47 (d, J = 8.4 Hz,
2H). 13C NMR (CDCl3): d = 50.1 (CH), 64.4, 68.7 (both
CH2), 76.3, 103.8 (both CH), 121.3 (C), 126.3, 128.3,
129.1, 130.9, 131.9 (all CH), 137.2, 138.1 (both C).

H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
6121
3.6. (S)-Methyl 2-(2-(4-bromophenyl))-2-(2-(4-bromo-
phenyl)-1,3-dioxolan-2-yl)acetate (15a)
(s), 831 (m) cmꢀ1 1H NMR (CDCl3): d = 1.21 (t,
.
J = 7.7 Hz, 3H), 2.61 (q, J = 7.7 Hz, 2H), 3.57 (s, 3H),
3.69–3.91 (m, 4H), 4.14 (s, 1H) 7.07 (d, J = 8.4 Hz, 2H),
7.19 (d, J = 8.4 Hz, 2H), 7.26 (d, J = 8.5 Hz, 2H), 7.35
(d, J = 8.5 Hz, 2H). 13C NMR (CDCl3): d = 15.3 (CH3),
29.4 (CH2), 51.8 (CH3), 59.9 (CH), 64.8, 65.3 (both CH2),
109.1, 121.8 (both C), 126.1, 127.2, 130.8, 132.0 (all CH),
132.6, 137.7, 144.2, 170.1 (all C). HRMS (ESI): Calc. for
C20H21BrO4Na 427.0515; found 427.0512 – Calc. for
C20H2181BrO4Na 429.0495; found 429.0503.
To a stirred solution of 14a (0.11 g, 0.49 mmol) and
Rh2(S-DOSP)4 (19 mg, 0.01 mmol) in PhCF3 (5 ml) at
ꢀ15 ꢂC was added methyl 2-diazo(4-bromophenyl)acetate
(0.25 g, 0.98 mmol) in PhCF3 (5 ml) via a syringe pump
over 2 h. The reaction mixture was allowed to warm to
25 ꢂC over night and then concentrated in vacuo. The
sticky, green oil was purified via column chromatography
(petroleum ether/diethyl ether 5:1) to afford 15a (0.16 g,
70%) as colorless oil; Rf = 0.30 (PMA). ee (Chiralcel
OD-H 4 · 250 mm, 1% isopropanol in hexanes, 1 ml/min,
230 nm): 68% (major: 12.3 min; minor: 14.0 min). IR (film):
m = 2950 (w), 2890 (w), 1744 (s), 1488 (m), 1154 (m), 1012
3.9. (S)-Methyl 2-(4-bromophenyl)-2-(2-(-methoxyphenyl)
-1,3-dioxolan-2-yl)acetate (15d) and methyl 2-(4-bromo-
phenyl)-3-(4-methoxyphenyl)-1,4-dioxane-2-carboxylate
(16)
1
(s), 822 (m) cmꢀ1. H NMR (CDCl3): d = 3.59 (s, 3H),
3.70–3.77 (m, 2H), 3.86–3.94 (m, 2H), 4.09 (s, 1H), 7.14–
7.18 (m, 2H), 7.23–7.25 (m, 2H), 7.36–7.39 (m, 4H). 13C
NMR (CDCl3): d = 52.0 (CH3), 59.6 (CH), 65.0, 65.4 (both
CH2), 108.8, 122.1, 122.5 (all C), 128.2, 130.9, 131.0, 131.9
(all CH), 132.1, 139.6, 169.8 (all C). Anal. Calc. for
C18H16Br2O4 (456.12): C, 47.40; H, 3.54. Found: C,
47.34; H, 3.32.
From 14d (0.09 g, 0.49 mmol) and Rh2(R-DOSP)4
(18 mg, 0.01 mmol) in PhCF3 (5 ml) and methyl 2-diazo-
(4-bromophenyl)acetate (0.25 g, 0.98 mmol) in PhCF3
(5 ml). 15d: Yield: 50 mg (25%), colorless oil; Rf = 0.54
(PMA, petroleum ether/ethyl acetate 5:1). ee (Chiralcel
OD-H 4 · 250 mm, 1% isopropanol in hexanes, 1 ml/min,
230 nm): 74% (major: 18.6 min; minor: 21.4 min); 16:
Yield: 66 mg (33%), colorless oil; Rf = 0.28 (PMA, petro-
leum ether/ethyl acetate 5:1). ee (Chiralcel OD-H
4 · 250 mm, 1% isopropanol in hexanes, 1 ml/min,
230 nm): 47% (major: 21.3 min; minor: 25.9 min). 15d: IR
(film): m = 2950 (m), 2892 (m), 2838 (m), 1739 (s), 1608
(m), 1508 (m), 1249 (s), 1153 (s), 906 (s), 829 (m), 729 (s)
3.7. (S)-Methyl 2-(4-bromophenyl)-2-(2-p-tolyl-1,3-di-
oxolan-2-yl)acetate (15b)
From 14b (80 mg, 0.49 mmol) and Rh2(R-DOSP)4
(18 mg, 0.01 mmol) in PhCF3 (5 ml) and methyl 2-diazo-
(4-bromophenyl)acetate (0.25 g, 0.98 mmol) in PhCF3
(5 ml). Yield: 0.12 g (61%), colorless oil; Rf = 0.27 (PMA,
petroleum ether/diethyl ether 5:1). ee (Chiralcel OD-H
4 · 250 mm, 1% isopropanol in hexanes, 1 ml/min,
230 nm): 70% (major: 9.5 min; minor: 15.3 min). IR (film):
m = 2950 (w), 2892.8 (w), 1743 (s), 1149 (s), 1010 (s), 817
1
cmꢀ1. H NMR (CDCl3): d = 3.59 (s, 3H), 3.71–3.80 (m,
2H), 3.78 (s, 3H), 3.83–3.92 (m, 2H), 4.13 (s, 1H), 6.77
(d, J = 8.8 Hz, 2H), 7.21 (d, J = 8.8 Hz, 2H), 7.26 (d,
J = 8.5 Hz, 2H), 7.36 (d, J = 8.5 Hz, 2H). 13C NMR
(CDCl3): d = 51.9, 55.1 (both CH3), 59.9 (CH), 64.8, 65.2
(CH2), 109.0 (C), 113.0 (CH), 121.8 (C), 127.5, 130.8,
132.0 (all CH), 132.5, 132.6, 159.4, 170.1 (all C). HRMS
(ESI): Calc. for C19H19O5BrNa 429.0308; found 429.0315
– Calc. for C19H19O581BrNa 431.0288; found 431.0303.
16: IR (film): m = 2953 (w), 2877 (w), 2836 (w), 1735 (s),
1610 (m), 1511 (s), 1247 (s), 1178 (m), 1008 (m), 731 (s)
1
(m), 763 (m), 736 (m) cmꢀ1. H NMR (CDCl3): d = 2.31
(s, 3H), 3.58 (s, 3H), 3.71–3.78 (m, 2H), 3.83–3.91 (m,
2H), 4.14 (s, 1H), 7.06 (d, J = 8.3 Hz, 2H), 7.18 (d,
J = 8.3 Hz, 2H), 7.27 (d, J = 8.5 Hz, 2H), 7.36 (d,
J = 8.5 Hz, 2H). 13C NMR (CDCl3): d = 21.0, 52.5 (both
CH3), 59.8 (CH), 64.8, 65.2 (both CH2), 109.1, 121.8 (both
C), 126.1, 128.4, 130.8, 132.0 (all CH), 132.6, 137.5, 137.8,
170.0 (all C). HRMS (ESI): Calc. for C19H19BrO4Na
413.0359; found 413.0369 – Calc. for C19H1981BrO4Na
415.0338; found 415.0351.
1
cmꢀ1. H NMR (CDCl3): d = 3.37 (dd, J = 12.3, 3.3 Hz,
1H), 3.72 (s, 3H), 3.79 (ddd, J = 12.3, 12.3, 3.3 Hz, 1H)
3.80 (s, 3H), 4.02 (dd, J = 12.3, 3.3 Hz, 1H), 4.26 (ddd,
J = 12.3, 12.3, 3.3 Hz), 6.71 (d, J = 8.9 Hz, 2H), 7.31 (s,
4H), 7.35 (d, J = 8.9 Hz, 2H). 13C NMR (CDCl3):
d = 53.1, 55.0 (CH3) 57.5, 64.1 (CH2), 76.2 (CH), 81.4
(C), 113.1 (CH), 121.9, 126.7 (both C), 126.9, 131.3,
132.4 (CH), 137.2, 158.9, 171,8 (all C). HRMS (ESI): Calc.
for C19H19BrO5 406.0410; found 406.0403 – Calc. for
C19H1981BrO5 408.0390; found 408.0392.
3.8. (S)-Methyl 2-(4-bromophenyl)-2-(2-(4-ethylphenyl)-
1,3-dioxolan-2-yl)acetate (15c)
From 14c (0.10 g, 0.56 mmol) and Rh2(S-DOSP)4
(21 mg, 0.011 mmol) in PhCF3 (5 ml) and methyl 2-diazo-
(4-bromophenyl)acetate (0.28 g, 1.12 mmol) in PhCF3
(5 ml). Yield: 0.13 g (59%), colorless oil; Rf = 0.42 (PMA,
petroleum ether/diethyl ether 5:1). ee (Chiralcel OD-H
4 · 250 mm, 1% isopropanol in hexanes, 1 ml/min,
230 nm): 75% (major: 18.6 min; minor: 7.8 min). IR (film):
m = 2964 (w), 2893 (w), 1743 (s), 1489 (m), 1149 (s), 1012
3.10. (S)-Methyl 2-phenyl-2-(2-styryl-1,3-dioxolan-2-
yl)acetate (18a)
To a stirred solution of 17 (0.12 g, 0.68 mmol) and
Rh2(S-DOSP)4 (26 mg, 0.014 mmol) in PhCF3 (5 ml) at
25 ꢂC was added methyl 2-diazo phenylacetate (0.24 g,

6122
H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
1.36 mmol) in PhCF3 (7 ml) via a syringe pump over 2 h.
The reaction mixture was stirred at 25 ꢂC for 1 h and then
concentrated in vacuo. The crude product was purified via
column chromatography (petroleum ether/diethyl ether
5:1) to afford 18a (0.12 g, 53%) as colorless oil; Rf = 0.44.
ee (Chiralcel OD-H 4 · 250 mm, 2% isopropanol in hex-
anes, 1 ml/min, 254 nm): 84% (major: 18.2 min; minor:
20.8 min). IR (film): m = 3028 (w), 2951 (w), 2891 (w),
1738 (s), 1448 (w), 1155 (m), 972 (w), 744 (s), 731 (s), 694
CH), 136.0, 137.3, 170.8 (all C). HRMS (ESI): Calc. for
C21H22O4Na 361.1410; found 361.1406.
3.13. (S)-Methyl 2-(4-methoxyphenyl)-2-(2-styryl-1,3-
dioxolane-2-yl)acetate (18d)
From 17 (0.10 g, 0.56 mmol) and Rh2(S-DOSP)4
(21 mg, 0.011 mmol) in PhCF3 (5 ml) and methyl 2-diazo-
(4-methoxyphenyl)acetate (0.23 g, 1.12 mmol) in PhCF3
(10 ml). Yield: 0.12 g (62%), colorless oil; Rf = 0.32 (petro-
leum ether/diethyl ether 5:1). ee (Chiralcel AS-H
4 · 250 mm, 0.8% isopropanol in hexanes, 0.5 ml/min,
254 nm): 91% (major: 27.5 min; minor: 32.9 min). IR (film):
m = 3025 (m), 2952 (m), 2893 (m), 1741 (s), 1611 (s), 1513
(s), 1250 (s), 1179 (s), 1037 (s), 834 (s), 759 (m), 744 (m),
1
(s) cmꢀ1. H NMR (CDCl3): d = 3.67 (s, 3H), 3.84–3.94
(m, 4H), 4.09 (s, 1H), 6.25 (d, J = 15.7 Hz, 1H), 6.59 (d,
J = 15.7 Hz, 1H), 7.21–7.36 (m, 8H), 7.47–7.49 (m, 2H).
13C NMR (CDCl3): d = 51.9 (CH3), 59.6 (CH), 64.8, 65.4
(both CH2), 108.4 (C), 126.8, 127.0, 127.6, 127.9, 128.0,
128.4, 130.0, 131.4 (all CH), 133.6, 136.1, 171.7 (all C).
HRMS (ESI): Calc. for C20H20O4Na 347.1254; found
347.1245.
1
694 (m) cmꢀ1. H NMR (CDCl3): d = 3.68, 3.78 (both s,
3H), 3.85–3.96 (m, 4H), 4.04 (s, 1H), 6.25 (d,
J = 16.3 Hz, 1 h), 6.59 (d, J = 16.3 Hz, 1H), 6.83 (d,
J = 8.8 Hz, 2H), 7.22–7.36 (m, 5H), 7.39 (d, J = 8.8 Hz,
2H). 13C NMR (CDCl3): d = 51.9, 55.0 (both CH3), 58.7
(CH), 64.8, 65.3 (CH2), 108.4 (C), 113.4 (CH), 125.7 (C),
126.8, 127.0, 127.9, 128.5, 131.1, 131.3 (all CH), 136.0,
159.1, 170.9 (all C). HRMS (ESI): Calc. for C21H22O5Na
377.1359; found 377.1371.
3.11. (S)-Methyl 2-(4-bromophenyl)-2-(2-styryl-1,3-
dioxolan-2-yl)acetate (18b)
From 17 (0.10 g, 0.56 mmol) and Rh2(S-DOSP)4
(21 mg, 0.011 mmol) in PhCF3 (5 ml) and methyl 2-diazo-
(4-bromophenyl)acetate (0.28 g, 1.10 mmol) in PhCF3
(6 ml). Yield: 0.15 g (65%), colorless oil; Rf = 0.28 (petro-
leum ether/diethyl ether 5:1). ee (Chiralcel OD-H
4 · 250 mm, 2% isopropanol in hexanes, 1 ml/min,
254 nm): 86% (major: 28.6 min; minor: 19.3 min). IR (film):
m = 2951 (w), 2891 (w), 1740 (s), 1489 (m), 1161 (s), 1012
3.14. (S)-Methyl 2-(naphthalen-3-yl)-2-(2-styryl-1,3-
dioxolan-2-yl)acetate (18e)
From 17 (0.13 g, 0.74 mmol) and Rh2(S-DOSP)4
(28 mg, 0.015 mmol) in PhCF3 (5 ml) and methyl 2-diazo-
(2-naphthyl)acetate (0.33 g, 1.48 mmol) in PhCF3 (7 ml).
Yield: 0.16 g (59%), white solid m.p. = 118 ꢂC; Rf = 0.43
(petroleum ether/diethyl ether 5:1). ee (Chiralcel OD-H
4 · 250 mm, 2% isopropanol in hexanes, 1 ml/min,
254 nm): 73% (major: 24.9 min; minor: 35.5 min). IR
(KBr): m = 2950 (m), 1741 (s), 1599 (w), 1535 (w), 1160
1
(s), 737 (s), 692 (s) cmꢀ1. H NMR (CDCl3): d = 3.68 (s,
3H), 3.82–3.96 (m, 4H), 4.04 (s, 1H), 6.20 (d,
J = 15.8 Hz, 1H), 6.59 (d, J = 15.8, 1H), 7.25–7.44 (m,
9H). 13C NMR (CDCl3): d = 52.0 (CH3), 58.9 (CH),
64.8, 65.4 (both CH2), 108.2, 122.0 (both C), 126.7,
126.8, 128.1, 128.5, 131.1, 131.7, 131.8 (all CH), 132.7,
135.8, 170.3 (C). HRMS (ESI): Calc. for C20H19BrO4Na
425.0359; found 425.0370 – Calc. for C20H1981BrO4Na
427.0338; found 427.0340.
1
(m), 1044 (m), 834 (m), 752 (m) cmꢀ1. H NMR (CDCl3):
d = 3.67 (s, 3H), 3.82–3.95 (m, 4H), 4.27 (s, 1H), 6.29 (d,
J = 15.6 Hz, 1H), 6.64 (d, J = 15.6 Hz, 1H), 7.21–7.34
(m, 5H), 7.42–7.47 (m, 2H), 7.64 (d, J = 8.7 Hz, 1H),
7.77–7.84 (m, 3H), 7.94 (s, 1H). 13C NMR (CDCl3):
d = 52.03 (CH3), 59.7 (CH), 64.8, 65.4 (both CH2), 108.5
(C), 125.9, 126.8, 127.1, 127.4, 127.9, 128.0, 128.1, 128.5,
129.3 (all CH), 131.1 (C), 131.5 (CH), 132.8, 133.0, 136.0,
170.7 (all C). HRMS (ESI): Calc. for C24H22O4Na
397.1410; found 397.1407. Anal. Calc. for C24H22O4
(374.43): C, 76.99; H, 5.92. Found: C, 76.60; H, 5.95.
3.12. (S)-Methyl 2-(2-styryl-1,3-dioxolan-2-yl)-2-p-
tolylacetate (18c)
From 17 (0.10 g, 0.56 mmol) and Rh2(S-DOSP)4
(21 mg, 0.011 mmol) in PhCF3 (5 ml) and methyl 2-diazo-
(p-tolyl)acetate (0.21 g, 1.12 mmol) in PhCF3 (6 ml) added
over 4 h via syringe pump. Yield: 0.11 g (57%), colorless
oil; Rf = 0.32 (petroleum ether/diethyl ether 5:1). ee (Chi-
ralcel OD-H 4 · 250 mm, 2% isopropanol in hexanes,
1 ml/min, 254 nm): 88% (major: 20.0 min; minor:
23.8 min). IR (film): m = 3026 (w), 2950 (w), 2884 (w),
1740 (s), 1269 (m), 1157 (m), 1040 (m), 970 (m), 754 (s),
3.15. (S)-Methyl 2-(4-chlorophenyl)-2-(2-styryl-1,3-
dioxolan-2-yl)acetate (18f)
739 (s), 692 (s) cmꢀ1
.
1H NMR (CDCl3): d = 2.32 (s,
From 17 (0.20 g, 1.12 mmol) and Rh2(R-DOSP)4
(42 mg, 0.022 mmol) in PhCF3 (5 ml) and methyl 2-diazo-
(4-chlorophenyl)acetate (0.48 g, 2.28 mmol) in PhCF3
(10 ml). Yield: 0.21 g (51%), colorless oil; Rf = 0.5 (petro-
leum ether/diethyl ether 5:1). ee (Chiralcel OD-H
4 · 250 mm, 2% isopropanol in hexanes, 1 ml/min,
3H), 3.67 (s, 3H), 3.88–3.93 (m, 4H), 4.05 (s, 1H), 6.26
(d, J = 16.1 Hz, 1H), 6.60 (d, J = 16.1 Hz, 1H), 7.10 (m,
2H), 7.24–7.37 (m, 7H). 13C NMR (CDCl3): d = 21.0,
51.9 (both CH3), 59.2 (CH), 64.8, 65.3 (CH2), 108.5 (C),
126.8, 127.0, 127.9, 128.5, 128.7, 129.8, 130.6, 131.3 (all

H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
6123
254 nm): 85% (major: 18.7 min; minor: 29.3 min). IR (film):
added methyl 2-diazo-(4-bromophenyl)acetate (0.29 g,
1.14 mmol) in PhCF3 (5 ml) via a syringe pump over 2 h.
The reaction mixture was stirred at 25 ꢂC for 1 h and then
concentrated in vacuo. The crude product was purified via
column chromatography (petroleum ether/diethyl ether
5:1) to afford 24 (0.16 g, 68%) as colorless oil; Rf = 0.50.
ee (Chiralcel OD-H 4 · 250 mm, 2% isopropanol in hex-
anes, 1 ml/min, 254 nm): 86% (major: 20.1 min; minor:
25.6 min). IR (film): m = 2950 (w), 2896 (w), 2225 (w),
m = 2950 (w), 2892 (w), 1739 (s), 1492 (m), 1161 (s), 1091
1
(m), 806 (m), 744 (m), 694 (m) cmꢀ1. H NMR (CDCl3):
d = 3.68 (s, 3H), 3.83–3.95 (m, 4H), 4.06 (s, 1H), 6.21 (d,
J = 16.2 Hz, 1H), 6.59 (d, J = 16.2 Hz, 1H), 7.25–7.35
(m, 7H), 7.42–7.44 (d, J = 8.5 Hz, 2H). 13C NMR (CDCl3):
d = 52.1 (CH3), 58.8 (CH), 64.9, 65.4 (both CH2), 108.3
(C), 126.7 126.8, 128.0, 128.1, 128.5, 131.5, 131.7 (all
CH), 132.1, 133.7, 135.8, 170.4 (all C). HRMS (ESI): Calc.
for C20H20ClO4 359.1045; found 359.1042.
1739 (s), 1488 (m), 1157 (s), 756 (s), 732 (s), 690 (s) cmꢀ1
.
1H NMR (CDCl3): d = 3.74 (s, 3H), 3.93–3.99 (m, 2H),
4.12–4.17 (m, 2H), 4.21 (s, 1H), 7.26–7.39 (m, 5H), 7.48
(pseudo-s, 4H). 13C NMR (CDCl3): d = 52.3 (CH3), 59.1
(CH), 65.3, 65.4 (both CH2), 85.0, 86.0, 102.6, 121.6,
122.5 (all C), 128.2, 128.9, 131.2, 131.8, 131.9, 132.1 (all
CH), 132.1, 169.9 (both C). HRMS (ESI): Calc. for
C20H17BrO4Na 423.0202; found 423.0199 – Calc. for
C20H1781BrO4Na 425.0182; found 425.0187.
3.16. (S)-Methyl 2-(2-(4-methoxystyryl)-1,3-dioxolan-2-
yl)-2-(4-bromophenyl)acetate (18g) and methyl 3-(4-
methoxystyryl)-2-(4-bromophenyl)-1,4-dioxane-2-
carboxylate (20)
From 19 (0.1 g, 0.48 mmol) and Rh2(R-DOSP)4 (17 mg,
0.009 mmol) PhCF3 (5 ml) and methyl 2-diazo-(4-brom-
ophenyl)acetate (0.24 g, 0.96 mmol) PhCF3 (5 ml). 18g:
Yield: 46 mg (22%), colorless oil; Rf = 0.50 (PMA, petro-
leum ether/diethyl ether 1:1). ee (Chiralcel OD-H
4 · 250 mm, 3% isopropanol in hexanes, 1 ml/min,
230 nm): 81% (major: 16.8 min; minor: 22.3 min); 20:
Yield: 0.13 g (49%), colorless oil; Rf = 0.21 (PMA, petro-
leum ether/diethyl ether 1:1). ee (Chiralcel OD-H
4 · 250 mm, 5% isopropanol in hexanes, 1 ml/min,
254 nm): 0% (14.1 min, 14.9 min). 18g: IR (film): m = 2954
(w), 2877 (w), 2838 (w), 1735 (s), 1604 (m), 1511 (m),
1245 (s), 1103 (m), 1006 (m), 821 (m), 775 (m), 732 (m)
3.18. (S,E)-Methyl 4-phenyl-2-(2-phenyl-1,3-dioxolan-2-
yl)but-3-enoate (26)
To a stirred solution of 9 (0.1 g, 0.69 mmol) and Rh2(S-
DOSP)4 (104 mg, 0.055 mmol) in 2,2-DMB (10 ml) at
25 ꢂC was added (E)-methyl 2-diazo-4-phenylbut-3-enoate
(0.28 g, 1.38 mmol) in 2,2-DMB (10 ml) via a syringe pump
over 2 h. The reaction mixture was stirred at 25 ꢂC for 1 h
and then concentrated in vacuo. The crude product was
purified via column chromatography (petroleum ether/
diethyl ether 5:1) to afford 26 (0.10 g, 46%) as colorless
oil; Rf = 0.25. ee (Chiralcel AS-H 4 · 250 mm, 0.5% isopro-
panol in hexanes, 0.8 ml/min, 254 nm): 89% (major:
15.5 min; minor: 19.4 min). IR (film): m = 2951 (w), 2918
(w), 2850 (w), 1732 (s), 1431 (w), 1236 (m), 1028 (m), 991
1
cmꢀ1. H NMR (CDCl3): d = 3.70 (s, 3H), 3.83 (s, 3H),
3.85–3.96 (m, 4H), 4.06 (s, 1H), 6.08 (d, J = 16.2 Hz,
1H), 6.56 (d, J = 16.2 Hz, 1H), 6.87 (d, J = 8.8 Hz, 2H),
7.30 (d), 7.39 (d, J = 8.3 Hz 2H), 7.39 (d, 8.8 Hz, 2H),
7.44 (d, J = 8.3 Hz, 2H). 13C NMR (CDCl3): d = 52.1,
55.3 (both CH3), 59.1 (CH), 64.8, 65.4 (both CH2), 108.4
(C), 114.0, 124.5 (both CH), 127.8 (C), 128.1, 131.1,
131.2, 131.9 (all CH), 132.8, 159.6, 170.4 (all C). 20: IR
(film): m = 2954 (w), 2931 (w), 2873 (w), 2838 (w), 1735
(s), 1604 (m), 1511 (s), 1245 (s), 1103 (s), 1010 (s), 821
1
(m), 754 (s), 696 (s) cmꢀ1. H NMR (CDCl3): d = 3.52 (s,
3H), 3.67 (d, J = 8.2 Hz, 1H), 3.71–3.73 (m, 2H), 3.96–
3.99 (m, 2H), 6.21–6.29 (m, 2H), 7.11–7.25 (m, 8H), 7.37
(m, 2H). 13C NMR (CDCl3): d = 51.9 (CH3), 59.4 (CH),
64.9, 65.2 (both CH2), 109.4 (C), 122.5 (CH),
126.2,.126.4, 127.6, 127.8, 128.3, 128.4, 134.8 (all CH),
136.6, 140.4, 170.5 (all C). HRMS (ESI): Calc. for
C20H20O4Na 347.1254; found 347.1246. Anal. Calc. for
C20H20O4 (324.37): C, 74.06; H, 6.21. Found: C, 73.96;
H, 6.31.
1
(m), 775 (m), 732 (m) cmꢀ1. H NMR (CDCl3): d = 3.50
(dd, J = 11.5, 2.2 Hz, 1H), 3.78 (s, 3H), 3.81 (s, 3H), 3.96
(dd, J = 11.5, 2.2 Hz, 1H), 4.05–4.19 (m, 2H), 5.24 (d,
J = 7.7 Hz, 1H), 6.08 (dd J = 16.0, 7.7 Hz), 6.61 (d,
J = 16.0 Hz, 1H), 6.79 (d, 8.8 Hz, 2H), 7.15 (d, J =
8.8 Hz, 2H), 7.36 (d, J = 8.8 Hz, 2H), 7.43 (d, J = 8.8 Hz,
2H). 13C NMR (CDCl3): d = 53.0, 55.2 (both CH3), 58.6,
63.8 (both CH2), 76.3 (CH), 81.5 (C), 113.8, 120.4 (both
CH), 122.3 (C), 126.9, 127.7 (both CH), 129.0, 131.2 (both
C), 131.5, 136.4 (both CH). HRMS (ESI): Calc. for
3.19. (R)-3-Hydroxy-1,2-diphenylpropan-1-one (27)
From 12a 0.14 g (0.52 mmol) and iodine (13 mg,
0.05 mmol) in acetone (20 ml) analogously to published
procedure [48]. Yield: 78 mg (66%), slightly yellow oil;
Rf = 0.3 (petroleum ether/diethyl ether 1:4). Identity of
26 confirmed by comparison with published data [49].
C21H21BrO5 432.0567; found 432.0555
C21H2181BrO5 434.0546; found 434.0539.
– Calc. for
3.17. (S)-Methyl 2-(4-bromophenyl)-2-(2-(2-
phenylethynyl)-1,3-dioxolan-2-yl)acetate (24)
3.20. (1S,2R)-1,2-Diphenylpropane-1,3-diol (28)
To a stirred solution of 23 (0.1 g, 0.57 mmol) and Rh2(S-
DOSP)4 (21 mg, 0.011 mmol) in PhCF3 (5 ml) at 25 ꢂC was
From 27 (30 mg, 0.13 mmol), NaH (4 mg, 0.17 mmol)
TiCl4 (0.17 ml, 1 M in CH2Cl2) and LiBH4 (4 mg,

6124
H.M.L. Davies et al. / Journal of Organometallic Chemistry 690 (2005) 6111–6124
[18] A. Caballero, M.M. Diaz-Requejo, T.R. Belderrain, M.C. Nicasio,
S. Trofimenko, P.J. Perez, J. Am. Chem. Soc. 125 (2003) 1446.
[19] M.M. Diaz-Requejo, T.R. Belderrain, M.C. Nicasio, S. Trofimenko,
P.J. Perez, J. Am. Chem. Soc. 124 (2002) 896.
[20] H.M.L. Davies, E.G. Antoulinakis, Org. Reactions 57 (2001) 1.
[21] H.M.L. Davies, Eur. J. Org. Chem. (1999) 2459.
[22] H.M.L. Davies, S.A. Panaro, Tetrahedron Lett. 40 (1999) 5287.
[23] H.M.L. Davies, P.R. Bruzinski, D.H. Lake, N. Kong, M.J. Fall, J.
Am. Chem. Soc. 118 (1996) 6897.
0.18 mmol) in THF (5 ml) as published [49]. Identity of 28
confirmed by comparison with published data [49].
3.21. Competition study: formation of (S)-methyl 2-phenyl-
2-(2-styryl-1,3-dioxolan-2-yl)acetate (18a) vs. (2R,3S)-
methyl 3-(tert-butyldimethylsiloxy)-2,5-diphenylpent-4-
enoate (22)
[24] H.M.L. Davies, O. Loe, Synthesis 16 (2004) 2595.
[25] H.M.L. Davies, E.G. Antoulinakis, T. Hansen, Org. Lett. 1 (1999)
383.
[26] H.M.L. Davies, E.G. Antoulinakis, Org. Lett. 2 (2000) 4153.
[27] H.M.L. Davies, R.E.J. Beckwith, E.G. Antoulinakis, Q. Jin, J. Org.
Chem. 68 (2003) 6126.
[28] H.M.L. Davies, T. Hansen, D.W. Hopper, S.A. Panaro, J. Am.
Chem. Soc. 121 (1999) 6509.
[29] H.M.L. Davies, C. Venkataramani, T. Hansen, D.W. Hopper, J.
Am. Chem. Soc. 125 (2003) 6462.
[30] J.M. Axten, R. Ivy, L. Krim, J.D. Winkler, J. Am. Chem. Soc. 121
(1999) 6511.
[31] H.M.L. Davies, P. Ren, Q. Jin, Org. Lett. 3 (2001) 3587.
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[33] H.M.L. Davies, T. Hansen, M.R. Churchill, J. Am. Chem. Soc. 122
(2000) 3063.
The setup of the reaction follows the general procedure
established in our laboratory to asses reactivity differences
of substrates in C–H insertion reactions [27].
To a stirred solution of 17 (0.35 g, 2.0 mmol), 21 (0.49 g,
2.0 mmol) and Rh2(S-DOSP)4 (8 mg, 0.004 mmol) in
PhCF3 (10 ml) at 25 ꢂC was added methyl 2-diazo-phenyl-
acetate (88 mg, 0.5 mmol) in PhCF3 (2.5 ml) via a syringe
pump over 2 h. The reaction mixture was stirred at 25 ꢂC
for 1 h, concentrated in vacuo and excess substrate was re-
1
moved via Kugelrohr distillation. H NMR and ESI-MS
analysis of the residual green oil revealed that 22 [27] was
the only product formed in the reaction.
[34] H.M.L. Davies, J. Yang, Adv. Synth. Catal. 345 (2003) 1133.
[35] H.M.L. Davies, Q. Jin, P. Ren, A.Y. Kovalevsky, J. Org. Chem. 67
(2002) 4165.
Acknowledgements
Financial support of this work by the National Science
Foundation (CHE-0350536) is gratefully acknowledged.
J.N. thanks the Deutsche Forschungsgemeinschaft (DFG)
for a postdoctoral fellowship.
[36] E. Akgun, M. Tunali, U. Pindur, Monatsh. Chem. 118 (1987)
¨
363.
[37] H.M.L. Davies, Q. Jin, Proc. Nat. Acad. Sci. 101 (2004) 5472.
[38] A.I. Rakhmankulov, R.M. Sultanova, S.S. Zlotskii, V.A. Dokichev,
Dokl. Chem. 357 (1997) 287.
[39] C.D. Gutsche, M. Hillman, J. Am. Chem. Soc. 76 (1954) 2236.
[40] A. Padwa, S.F. Hornbuckle, Chem. Rev. 1991 (1991) 263.
[41] D.M. Hodgson, P.A. Stupple, F.Y.T.M. Pierard, A.H. Labande, C.
Johnstone, Chem. Eur. J. 7 (2001) 4465.
[42] D.M. Hodgson, A.H. Labande, R. Glen, A.J. Redgrave, Tetrahedron
Asym. 14 (2003) 921.
[43] D.M. Hodgson, A.H. Labande, F.Y.T.M. Pierard, Synlett (2003) 59.
[44] D.M. Hodgson, A.H. Labande, F.Y.T.M. Pierard, M.A. Exposito
Castro, J. Org. Chem. 68 (2003) 6153.
[45] M. Yan, N. Jacobsen, W. Hu, L.S. Gronenberg, M.P. Doyle, J.T.
Coyler, D. Bykowski, Angew. Chem. Int. Ed. 43 (2004) 6713.
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[47] H.M.L. Davies, G.H. Lee, Org. Lett. 6 (2004) 1233.
[48] J. Sun, Y. Dong, L. Cao, X. Wang, S. Wang, Y. Hu, J. Org. Chem.
69 (2004) 8932.
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