Metalloporphyrin Cr(TPP)Cl-catalyzed Claisen rearrangement of simple aliphatic allyl vinyl ethers and its unique stereoselectivity

Article abstract of DOI:10.1016/j.tetlet.2005.02.136

The catalytic Z-selective Claisen rearrangement of simple aliphatic allyl vinyl ethers can be achieved using a chromium(III) porphyrin complex, Cr(TPP)Cl, as a catalyst: Cr(TPP)Cl significantly enhances reversal of E-Z selectivity in the thermal Claisen r

Full text of DOI:10.1016/j.tetlet.2005.02.136

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 2893–2896
Metalloporphyrin Cr(TPP)Cl-catalyzed Claisen rearrangement
of simple aliphatic allyl vinyl ethers and its unique stereoselectivity
Toshikatsu Takanami, Mikiko Hayashi and Kohji Suda*
Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan
Received 24 January 2005; revised 17 February 2005; accepted 18 February 2005
Abstract—The catalytic Z-selective Claisen rearrangement of simple aliphatic allyl vinyl ethers can be achieved using a chro-
mium(III) porphyrin complex, Cr(TPP)Cl, as a catalyst: Cr(TPP)Cl significantly enhances reversal of E–Z selectivity in the thermal
Claisen rearrangement of allyl vinyl ethers, especially, 4,5- and 4,6-disubstituted derivatives, at low catalyst loading.
Ó 2005 Elsevier Ltd. All rights reserved.
The Claisen rearrangement of allyl vinyl ethers is among
the most powerful synthetic tools for the construction of
carbon–carbon bonds.1,2 The reaction leads to forma-
tion of c,d–unsaturated carbonyl compounds, and virtu-
ally all cases proceed with high selectivity for the
products with E configuration.1a,3,4 However, there is
scarcely any precedent for the rearrangement with the
opposite Z-selectivity.4–6 The only reported example of
phyrin-based catalysts at 83 °C in dichloroethane.8 The
representative results are summarized in Table 1. Heat-
ing 1a under similar conditions without catalysts for
48 h gave a 97:3 mixture of 3-n-butyl-4-heptenal 2a with
Table 1. Evaluation of metalloporphyrin catalysts in the rearrange-
ment of vinyl ether of trans-3-octen-2-ol 1a
a
Lewis acid-mediated Z-selective rearrangement
X
Ph
requires the use of superstoichiometric quantities of a
bulky organoaluminum reagent, methylaluminum
bis(4-bromo-2,6-di-tert-butylphenoxide) (MABR).4
N
Ph
N
M
N
Ph
N
n-Bu
n-Bu
Ph
5 mol% M(TPP)X
ClCH2CH2Cl, 83°C
Recently, we have demonstrated that high-valent metal-
loporphyrin complexes work as an efficient and easy-to-
handle Lewis acid catalyst for the highly regio- and
stereoselective rearrangement of epoxides to carbonyl
compounds.6,7 Reported herein is a chromium(III)
tetra-phenylporphyrin chloride Cr(TPP)Cl-catalyzed
Claisen rearrangement of simple aliphatic allyl vinyl
ethers 1 at low catalyst loading (5 mol %), wherein the
Z-isomers of c,d-unsaturated aldehyde 2 are predomi-
nantly produced from 4,5- and 4,6-disubstituted allyl
vinyl ethers. These are, to the best of our knowledge,
the first example of catalytic Z-selective Claisen
rearrangement.
CHO
O
1a
2a
Ratio (E/Z)b
Entry
Catalyst
Time (h)
Yield (%)a
1Cr(TPP)OTf
4
37
12
:79 21
62
28
2
3
4
5
6
7
8
Cr(TPP)Cl
MABRc,d
None
28:72
27:73
97:3
0.5
48
48
69
Mn(TPP)Cl
Fe(TPP)Cl
Cr(salen)Cle
Mn(salen)Clf
30
30
97:3
99:1
64
36
30
30
83:17
94:6
57
a Isolated yield.
b Determined by 300 MHz 1H NMR.
c MABR: bis(4-bromo-2,6-di-t-butylphenoxide).
We commenced our studies with the rearrangement of
vinyl ether of trans-3-octen-2-ol 1a using different por-
d The reaction was carried out with 200 mol % MABR in CH2C12 at
ꢀ78 °C.
e Cr(salen)Cl: (S,S)-(+)-N,N0-bis(3,5-di-t-butylsalicylidene)-l,2-cyclo-
hexanediamino chromium(III) chloride.
Keywords: Allyl vinyl ether; Chromium(III) porphyrin complex; Clai-
sen rearrangement; Lewis acid catalyst; (Z)-c,d-unsaturated aldehyde.
f Mn(salen)Cl: (S,S)-(+)-N,N0-bis(3,5-di-t-butylsalicylidene)-1,2-cyclo-
hexanediamino manganase(III) chloride.
*
Corresponding author. Tel./fax: +814249 58780; e-mail: suda@
my-pharm.ac.jp
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.02.136

2894
T. Takanami et al. / Tetrahedron Letters 46 (2005) 2893–2896
high E selectivity in 48% combined yield (entry 4). On
the other hand, the reaction with 5 mol % Cr(TPP)OTf
reversed the selectivity and produced a 21:79 ratio of
2a favoring the Z–isomer (E/Z = 97:3) in 37% combined
yield (entry 1). Intriguingly, changing the catalyst to
selective rearrangement of 4,5-disubstituted allyl vinyl
ethers, 1e–g, was hardly achieved even using the bulky
organoaluminum reagent MABR, the use of a 5 mol %
Cr(TPP)Cl was, to our surprise, quite effective for the
Z-selective rearrangement of these substrates;11 (3) for
the rearrangement of 4-mono–substituted substrates, 1i
and 1j, the Cr(TPP)Cl catalyst showed only marginal
Z-selectivity, whereas MABR could effectively mediate
the Z-selective rearrangement of these substrates.
Cr(TPP)Cl, which is
a weaker Lewis acid than
Cr(TPP)OTf, further improved the reactivity with a
minimal loss of the stereoselectivity, the aldehyde 2a
being produced in 62% yield with the E/Z ratio of
28:72 (entry 2).9 It is also worth noting that these Z-
selectivities furnished with these porphyrin catalysts
were comparable to that obtained from the correspond-
ing reaction performed with 2 equiv of MABR at
ꢀ78 °C in dichloromethane (E/Z = 27:73) (entry 3). At-
tempts with other catalysts, such as Mn(TPP)Cl,
Fe(TPP)Cl, and metallosalen catalysts, Cr(salen)Cl and
Mn(salen)Cl,10 were unsuccessful under the conditions
examined, affording the undesired (E)-2a as the major
product in modest yields (entries 5–8).
Although details of the present catalytic process are not
clear as yet, the preferential formation of the Z-isomers
would be interpreted as follows: the Cr(TPP)Cl-cata-
lyzed rearrangement apparently starts with creating
coordination of the metal to the oxygen of the sub-
strates, and generates a less likely transition state con-
formation B with the C-4 substituent R1 axial, which
would be favored over a conformation A with the C-4
substituent R1 equatorial, in view of the 1,2-steric repul-
sion between the bulky porphyrin macrocycle and the C-
4 substituent R1 in A, furnishing the desired Z-alkenes
as major products (Scheme 1). In the case of 4-mono–
substituted substrates, however, the conformation B ini-
tially generated would change to the conformation A
due to their relatively long and loose Cr–O coordina-
tion, leading to the preferential formation of the unde-
sired E-alkenes. For the rearrangements of 4,5- and
4,6-disubstituted substrates, on the other hand, the sub-
stituents at the C-5 and C-6 positions would enhance
ring-reversal barriers, preventing the conformational
change from B to A, the desired Z-alkenes thus being
obtained successfully.
We then examined the scope of the Cr(TPP)Cl catalyst
system with several distinct types of allyl vinyl ethers
including 4-monosubstituted and 4,5- and 4,6-disubsti-
tuted allyl vinyl ethers (Table 2).8 As a whole, the pres-
ent catalytic method showed promising functional group
compatibility: the substrates bearing phenyl, olefinic,
and silylacetylenic moieties as well as those having sim-
ple alkyl chains were tolerated well, the corresponding
Claisen products being produced in good to high yields.
Several stereochemical features of the catalytic method
are as follows: (1) the Cr(TPP)Cl catalyst system pro-
vided appreciable Z-selectivities in the rearrangement
of 4,6-disubstituted substrates, 1a–d, which were almost
comparable to those obtained from the corresponding
stoichiometric reactions with MABR; (2) although Z-
To elucidate the transition state in the Cr(TPP)Cl cata-
lytic process, we examined the stereo–chemical features
Table 2. Cr(TPP)Cl-catalyzed Claisen rearrangement of allyl vinyl ethersa,b
R3
R3
R2
6
R2
R1
5 mol % Cr(TPP)Cl
1
5
ClCH2CH2Cl, 83°C
R1
4
O
2
O
3
1
2
Substrates
R1
R2
R3
Time (h)
Yield (%)c
Ratio (E/Z)d,e
1a
1b
1c
Me
nBu
Me
H
H
H
nBu
Me
Ph
12 (0.5)
7 (0.25)
7 (0.5)
62 (28)
59 (72)
94 (45)
28:72 (27:73)
30:70 (16:84)f
15:85 (15:85)
1d
H
Me
0.5 (0.5)
70 (58)
14:86 (6:94)
TMS
1e
1f
nBu
Me
Me
Me
H
H
H
9 (0.25)
3 (0.5)
3 (0.5)
64 (58)
85 (40)
41 (18)
25:75 (61:39)f
21:79 (64:36)
22:78 (69:31)
iBu
1g
H2C@CH(CH2)3
1h
Me
H
0.5 (0.5)
87 (66)
18:82 (20:80)
67:33 (9:91)f
TMS
nBu
iBu
1i
1j
H
H
H
H
7 (0.25)
6 (0.25)
48 (41)
57 (64)
f
69:31(7:93)
a Conditions: 5 mol % Cr(TPP)Cl, ClCH2CH2Cl, 83 °C.
b The data in parentheses refer to those in the MABR-mediated rearrangements; conditions: 2 equiv MABR, ꢀ78 °C, CH2Cl2.
c Isolated yield.
d Determined by 300 MHz 1H NMR, except for 2d and 2h E/Z ratios for 2d and 2h were determined by isolation.
e The yields and E/Z ratios obtained in the conventional non-catalytic thermal rearrangement (ClCH2CH2Cl, 83 °C) of 1a–j were as follows: 2a (22%,
97:3); 2b (44%, 98:2); 2c (42%, 97:3); 2d (65%, 48:52); 2e (40%, 94:6); 2f (50%, 86:14); 2g (55%, 84:16); 2h (82%, 57:43); 2i (40%, 96:4); 2j (50%, 93:7).
f Data quoted from Ref. 4b.

T. Takanami et al. / Tetrahedron Letters 46 (2005) 2893–2896
2895
R1
Acknowledgements
R2
R3
R1
R2
R3
O
O
Cr Cl
This work was financially supported by a Grant-in-Aid
for Scientific Research (C) (KAKENHI 16590020) from
the Japan Society for the Promotion of Science and a
Special Grant (GAKUCHO-GRANT) from Meiji Phar-
maceutical University.
R3
(E)-2
A
R2
R1
R1
O
R1
R3
R3
1
O
Cr Cl
O
R2
R2
(Z)-2
B
Supplementary data
Experimental procedure and characterization data for
products 2a–k and Cr(TPP)Cl catalyst are available.
Supplementary data associated with this article can be
found, in the online version at doi:10.1016/j.tetlet.
2005.02.136.
Scheme 1. Plausible reaction pathway for the Cr(TPP)Cl-catalyzed
Claisen rearrangement of allyl vinyl ethers: 4-monosubstituted allyl
vinyl ether, R2 = R3 = H; 4,5-disubstituted allyl vinyl ether, R3 = H;
4,6-disubstituted allyl vinyl ether, R2 = H.
in the rearrangement of optically active 4,6-disubstituted
substrate (R)-1k12 Scheme 2. The rearrangement of (R)-
1k (91% ee) with Cr(TPP)Cl under the same conditions
took place smoothly to provide a mixture of the corre-
sponding aldehydes, (R)-(Z)-2k, (S)-(Z)-2k, (R)-(E)-2k,
and (S)-(E)-2k, in 61% combined yield.13 The ratio of
these isomers was determined to be 4:72:23:1by capil-
lary GLC analysis after conversion of the aldehydes to
the corresponding acetals of (2R,4R)-2,4-pentandiol.
Thus, the chirality of the starting (R)-1k was almost per-
fectly transferred to the major product (S)-(Z)-2k (90%
ee, i.e., 99% chiral transmission),14 and this result
strongly supports the proposed catalytic process via a
less likely transition state B in Scheme 2.15
References and notes
1. For recent reviews, see: (a) Castro, A. M. M. Chem. Rev.
2004, 104, 2339–3002; (b) Nubbemeyer, U. Synthesis 2003,
961–1008; (c) Hiersemann, M.; Abraham, L. Eur. J. Org.
Chem. 2002, 1461–1471; (d) Chai, Y.; Hong, S.-p.;
Lindsay, H. A.; McFarland, C.; McIntosh, M. C. Tetra-
hedron 2002, 58, 2905–2928; (e) Ito, H.; Taguchi, T. Chem.
Soc. Rev. 1999, 28, 43–50.
2. For some examples of recent leading works on Claisen
rearrangement and related reactions, see: (a) Burger, E. C.;
Tunge, J. A. Org. Lett. 2004, 6, 2603–2605; (b) Akiyama,
K.; Mikami, K. Tetrahedron Lett. 2004, 45, 7217–7220; (c)
Abraham, L.; Korner, M.; Hiersemann, M. Terahedron
Lett. 2004, 45, 3647–3650; (d) Nordmann, G.; Buchwald,
S. L. J. Am. Chem. Soc. 2003, 125, 4978–4979; (e) Nelson,
S. G.; Bungard, C. J.; Wang, K. J. Am. Chem. Soc. 2003,
125, 13000–13002; (f) May, J. A.; Stolz, B. M. J. Am.
Chem. Soc. 2002, 124, 12426–12427; (g) Lambert, T. H.;
MacMillan, D. W. C. J. Am. Chem. Soc. 2002, 124, 13645–
13647; (h) Tamaya, E.; Saito, A.; Ooi, T.; Maruoka, K.
Tetrahedron 2002, 58, 8307–8312; (i) Miller, S. P.; Mor-
ken, J. P. Org. Lett. 2002, 4, 2743–2745; (j) Mulder, J. A.;
Hsung, R. P.; Frederick, M. O.; Tracey, M. P.; Zificsak, C.
A. Org. Lett. 2002, 4, 1383–1386; (k) Yoon, T. P.;
MacMillan, D. W. C. J. Am. Chem. Soc. 2001, 123,
2911–2912; (l) Abraham, L.; Czerwonka, R.; Hiersemann,
M. Angew. Chem., Int. Ed. 2001, 40, 4700–4703; (m) Wipf,
P.; Ribe, S. Org. Lett. 2001, 3, 1503–1505; (n) Hiersemann,
M.; Abraham, L. Org. Lett. 2001, 3, 49–52; (o) Higashino,
T.; Sakaguchi, S.; Ishii, Y. Org. Lett. 2000, 2, 4193–4195;
(p) Trost, B. M.; Schroeder, G. M. J. Am. Chem. Soc.
2000, 122, 3785–3786.
In summary, a novel and efficient catalyst system utiliz-
ing chromium porphyrin, Cr(TPP)Cl, for the Claisen
rearrangement of simple aliphatic allyl vinyl ethers has
been developed. The most notable advantage of the cat-
alyst system is its unique stereoselectivity: Cr(TPP)Cl
significantly enhances reversal of E–Z selectivity in the
Claisen rearrangement of allyl vinyl ethers, especially,
4,5- and 4,6-disubstituted derivatives, and dose so in a
catalytic fashion (5 mol %). This catalyst system also
offers an efficient entry to the highly stereoselective rear-
rangement of an enantioenriched 4,6-disubstituted allyl
vinyl ether to the corresponding optically active Z-ole-
finic aldehyde: the efficiency of the chiral transfer is
almost fully comparable to that obtained from the
corresponding stoichiometric reaction with MABR.3
Ongoing efforts are focused on both improving the ste-
reoselectivity of the present catalysis by tuning the por-
phyrin peripheral substituents and increasing its scope.
3. (a) Wipf, P. In Comprehensive Organic Synthesis;
Paquette, L. A., Ed.; Pergamon: Oxford, 1991; Vol. 5,
S
R
5 mol % Cr(TPP)Cl
+
Cl(CH2)2Cl, 83°C
O
iBu R O
O
iBu
(R)-(E)-2k (89% ee)
61 %, E / Z=24:76
iBu
(R)-1k (91% ee)
(S)-(Z)-2k (90% ee)
Scheme 2. Cr(TPP)Cl-catalyzed Claisen rearrangement of enantioenriched allyl vinyl ether (R)-lk. The absolute configurations of the Claisen
products were determined according to the literature procedure, see: Ref. 4b.

2896
T. Takanami et al. / Tetrahedron Letters 46 (2005) 2893–2896
Chapter 7.2, pp 827–873; (b) Burgstahler, A. W. J. Am.
Chem. Soc. 1960, 82, 4681–4685; (c) Brannock, K. C.
J. Am. Chem. Soc. 1959, 87, 3379–3383.
2004, 6, 3211–3214; (c) Chan, W.-K.; Liu, P.; Yu, W.-Y.;
Wong, M.-K.; Che, C.-M. Org. Lett. 2004, 6, 1597–1599;
(d) Li, G.-Y.; Che, C.-M. Org. Lett. 2004, 6, 1621–1623;
(e) Chen, Y.; Zhang, X. P. J. Org. Chem. 2004, 69, 2431–
2435.
4. Yamamoto et al. reported that 2 equiv of MABR can
promote the Z-selective rearrangement of two types of
substrates, 4-mono- and 4,6-disubstituted allyl vinyl
ethers, affording the corresponding Z-olefinic aldehydes
with the E/Z ratios of 3:97–40:60, see: (a) Maruoka, K.;
Nonoshita, K.; Banno, H.; Yamamoto, H. J. Am. Chem.
Soc. 1988, 110, 7922–7924; (b) Nonoshita, K.; Banno, H.;
Maruoka, K.; Yamamoto, H. J. Am. Chem. Soc. 1990,
112, 316–322.
9. All the substrates were prepared from Hg(OAc)2-mediated
ether exchange reaction of ethyl vinyl ether with allylic
alcohols: Takai, K.; Mori, I.; Oshima, K.; Nozaki, H. Bull.
Chem. Soc. Jpn. 1984, 57, 446–451.
10. As expected, lowering the reaction temperature increased
the Z-selectivity: an E/Z ratio of 83:17 was obtained under
similar conditions at 50 °C, though the yield was decreased
to 36%.
11. Jacobsen et al. reported that chromium and manganese
salen complexes are useful Lewis acid catalysts for
stereoselective ring-opening reactions of epoxides: Marti-
nez, L. E.; Leighton, J. L.; Carsten, D. H.; Jacobsen, E. N.
J. Am. Chem. Soc. 1995, 117, 5897–5898.
12. In the case of silylacetylenic derivative 1h, both MABR
and Cr(TPP)Cl showed fairly good Z-selectivity.
13. Gao, Y.; Hanson, R. M.; Klunder, J. M.; Ko, S. Y.;
Masamune, H.; Sharpless, K. B. J. Am. Chem. Soc. 1987,
109, 5765–5780.
14. The absolute configurations of the products were deter-
mined according to the literature procedure, see: Ref. 4b.
15. A minimal loss of the optical purity was also obtained in
the rearrangement of (R)-1k to (R)-(E)-2k (89% ee, i.e.,
98% chiral transmission). Unlike MABR-mediated rear-
rangement (see Ref. 4), therefore, virtually no ionic
mechanism would participate in the present catalytic
process.
5. Pradilla et al. reported sulfinyl auxiliary-controlled Z-
´
selective Claisen rearrangement: Fernandez de la Pradilla,
R.; Montero, C.; Tortosa, M. Org. Lett. 2002, 4, 2373–
2376.
6. Krafft et al. have developed a chelation-controlled Z-
selective Claisen rearrangement of metal ester enolate
derivatives: Krafft, M. E.; Dasse, O. A.; Jarrett, S.; Fievre,
A. J. Org. Chem. 1995, 60, 5093–5101.
7. (a) Takanami, T.; Hirabe, R.; Ueno, M.; Hino, F.; Suda,
K. Chem. Lett. 1996, 1031–1032; (b) Suda, K.; Baba, K.;
Nakajima, S.; Takanami, T. Tetrahedron Lett. 1999, 40,
7243–7246; (c) Suda, K.; Baba, K.; Nakajima, S.; Taka-
nami, T. Chem. Commun. 2002, 2570–2571; (d) Suda, K.;
Kikkawa, T.; Nakajima, S.; Takanami, T. J. Am. Chem.
Soc. 2004, 126, 9554–9555.
8. Several synthetically useful metalloporphyrin-catalyzed
reactions have recently been reported: (a) Chen, J.; Che,
C.-M. Angew. Chem., Int. Ed. 2004, 43, 4950–4954; (b)
Ferrand, Y.; Maux, P. L.; Simonneaux, G. Org. Lett.