Rhodium catalyzed anti-Markovnikov addition of triphenylphosphine to 1,3-dienes a novel method to separate pure (Z)-1,3-alkadienes from isomeric mixtures

Article abstract of DOI:10.1246/cl.2002.272

Rhodium-catalyzed addition of triphenylphosphine and trifluoromethanesulfonic acid to (E)-1,3-dienes gives (E)-3-alkenylphosphonium salts in the anti-Markovnikov mode. The addition reactions to (E)-1,3-dienes proceed more rapidly than those to (Z)-1,3-die

Full text of DOI:10.1246/cl.2002.272

272
Chemistry Letters 2002
Rhodium Catalyzed Anti-Markovnikov Addition of Triphenylphosphine to 1,3-Dienes
A Novel Method to Separate Pure (Z)-1,3-Alkadienes from Isomeric Mixtures
Mieko Arisawa, Ryohei Momozuka, and Masahiko Yamaguchiꢀ
Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Sendai 980-8578
(Received November 14, 2001; CL-011149)
Table 1. Rhodium-catalyzed addition of PPh3 and CF3SO3H to
(E)-1,3-dienea
Rhodium-catalyzed addition of triphenylphosphine and
trifluoromethanesulfonic acid to (E)-1,3-dienes gives (E)-3-
alkenylphosphonium salts in the anti-Markovnikov mode. The
addition reactions to (E)-1,3-dienes proceed more rapidly than
those to (Z)-1,3-dienes, which can be utilized to separate pure (Z)-
1,3-dienes from isomeric mixtures.
We have previously reported that the regioselective addition
of triphenylphosphine (1) and methanesulfonic acid to alkynes
can be catalyzed by transition metal complexes. The Markovni-
kov adducts are obtained when a palladium complex is employed,
and anti-Markovnikov adducts with rhodium complexes.1 The
palladium complex also catalyzes the addition to allenes giving
allylphosphonium salts in the Markovnikov mode,2 the regio-
selectivity of which can be explained by the formation of ꢀ-allyl
complexes. Described here is the addition of 1 and trifluoro-
menthanesulfonic acid 2 to 1,3-dienes 3. A notable aspect of this
reaction is that a rhodium complex gives anti-Markovnikov 1,2-
adducts 4 with the phosphine attacking at the 1-carbon atom. In
addition, 1 and 2 add to (E)-3 more rapidly than (Z)-3, which can
be utilized to separate pure (Z)-3 from isomeric mixtures.
When (E)-6-phenyl-1,3-hexadiene (E)-3a was treated with
equimolar amounts of 1 and 2 in the presence of RhH(PPh3)4
(2.5 mol%) in THF at 0 ꢁC for 3 h, (E)-(6-phenyl-3-hexenyl)-
triphenylphosphonium PF6 salt (E)-4a was obtained in 89% yield
after anion exchange with LiPF6 and recrystallization. The
addition of phosphine and hydrogen occurs at the 1-carbon and
the 2-carbon atom of (EÞ-3a, respectively, and no other isomer is
detected by 1H-NMR examination of the crude reaction mixture.
The stereochemistry of (E)-4a was determined by the NOE
spectroscopy. The rhodium catalyst is essential for the addition,
and no reaction occurs in its absence. Reactions of several (E)-3
are shown in Table 1, which generally give the 1,2-adducts in the
anti-Markovnikov mode. The effect of substituents on the
aromatic ring is small as indicated by the reactions of 1-aryl-
1,3-butadienes (Run 4–6). The addition to isoprene 3g proceeds at
À20 ꢁC more selectively than at 0 ꢁC, and a 1,2-adduct 4g and a
1,4-adduct, 3-methyl-2-butenylphosphonium salt, are obtained in
a ratio of 7 : 1. Pure 4g is isolated from the mixture by
recrystallization in 67% yield.
Table 2. Rhodium-catalyzed addition of PPh3 and CF3SO3H to
(Z)-1,3-diene
Next, reactions of (Z)-1,3-dienes are examined. Treatment of
(Z)-3e with 1 and 2 at room temperature for 6 h gave 1,2-adduct
(Z)-4e in 45%, which was accompanied by a 1,4-adduct (E)-5e
(15%) (Table 2, Run 3). The stereochemistry of (Z)-4e was
determined by the 1H-NMR coupling constant (J ¼ 10:8 Hz), and
the double bond configuration is retained as is in the reactions of
(E)-3. The (E)-configuration of (E)-5e was determined by NOE
experiment. The yield of (Z)-4 decreases and that of (E)-5
increases, when aliphatic (Z)-3 is employed (Run 1 and 2).
Notably, (E)-3 reacts considerably faster than (Z)-3; for
example, while the reaction of (E)-3a takes place at 0 ꢁC, that of
(Z)-3a only at room temperature. The different rate can be utilized
to separate (Z)-3 from stereoisomeric mixture of 3. When 3a
(E=Z ¼ 50=50) was treated with 0.6 molar amounts of 1 and 2 at
1
0 ꢁC for 6 h, phosphonium salt (E)-4a (53% by H-NMR) was
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
273
obtained, which was accompanied by the recovered (Z)-3a
(Table 3, Run 1). The pure (Z)-3a can be separate by extraction in
41%yield based on 3a.3 As judgedfrom the yields of theproducts,
essentially no double bond isomerization appears to take place
during the reaction. Several other (Z)-1,3-dienes (Z)-3 are also
efficiently isolated from isomeric mixtures of 3 (Table 3).
Although (Z)-1,3-dienes are versatile synthetic intermediates
for natural products and functionalized polymers, their prepara-
tion is generally not straightforward. (Z)-Selective Wittig
reaction was reported by Schlosser using a sophisticated
allylphosphonium salt.4 Partial cis-hydrogenation of enyne5 or
metal-catalyzed cross-coupling of (Z)-alkenyl halides or (Z)-
alkenylmetals6 employed stepwise transfomations and/or geo-
metrically pure starting materials. The present method may
therefore be convenient, since it can isolate pure (Z)-1,3-dienes
from isomeric mixtures.
Dedicated to Prof. Teruaki Mukaiyama on the occasion of his
75th birthday.
References and Notes
1
2
3
M. Arisawa and M. Yamaguchi, J. Am. Chem. Soc., 122, 2387
(2000).
M. Arisawa and M. Yamaguchi, Adv. Synth. Cat., 343, 27
(2001).
Under an argon atmosphere, a mixture of RhH(PPh3)4
(290 mg, 2.5 mol%), 1 (6 mmol, 1.57 g), 3a (10 mmol,
1.58 g, E=Z ¼ 50=50), and 2 (0.53 mL, 6 mmol) in THF
(20 mL) was stirred at 0 ꢁC for 6 h. A small amount of
activated charcoal was added, and the mixture was stirred for
30 min to adsorp the metal complex. The insoluble materials
were removed by filtration, and the solution was concentrated
1
under reduced pressure (53% yield of (E)-4a by H-NMR).
The residue was washed with ether, and the ether solution was
washed with saturated NaHCO3 and brine. After being dried
over MgSO4 the solution was concentrated, and flash
chromatography (hexane) over silica gel gave (Z)-3a
(650 mg, 41%). The residue obtained by the ether washing
was dissolved in ethanol (10 mL), and LiPF6 (10 mmol,
1.52 g) was added. After being stirred at room temperature for
1 h, the precipitated solid was collected by filtration. To the
solid was added CHCl3, and insoluble CF3SO3Li was
removed by filtration. The solution was concentrated, and
the residue was recrystallized from ethanol giving (E)-4a
(586 mg, 21%) as colorless solid. Mp. 124.0–125.0 ꢁC. 31P-
NMR (162 MHz, CDCl3) ꢁ À143:7 (septet, J ¼ 435:8 Hz),
22.2.
Table 3. Separation of (Z)-1,3-diene from isomeric mixture
4
5
Q. Wang, M. EiKhoury, and M. Schlosser, Chem. Eur. J., 6,
420 (2000).
S. Siegel, in ‘‘Comprehensive Organic Synthesis,’’ ed. by
B. M. Trost and I. Fleming, Pergamon Press, New York
(1991), Vol. 8. p 417; M. H. J. P. Aerssens, R. Van der
Heiden, M. Heus, and L. Brandsma, Synth. Commun., 20,
3421 (1990).
In general, transition metal catalyzed addition reactions to
1,3-dienes give 1,4-adducts via ꢀ-allyl metal intermediates.7 The
anti-Markovnikov 1,2-addition in the present reaction is therefore
unusual. It is also noted that palladium-catalyzed additionof 1and
2 to unsaturated compounds studied so far gives the Markovnikov
adducts, and rhodium the anti-Markovnikov adducts.1;2 The
origin and the generalities of these selectivities are now under
investigation.
6
7
D. W. Knight, in ‘‘Comprehensive Organic Synthesis,’’ ed.
by B. M. Trost and I. Fleming, Pergamon Press, New York
(1991), Vol. 3. p 481; N. Miyaura and A. Suzuki, Chem. Rev.,
95, 2457 (1995).
J. Tsuji, ‘‘Palladium Reagents and Catalysts. Innovations in
Organic Synthesis,’’ John Wiley and Sons, Inc., New York
(1995). For examples, W.-J. Xiao, G. Vasapollo, and H.
Alper, J. Org. Chem., 65, 4138 (2000); H. Miyake and K.
Yamamura, Chem. Lett., 1992, 507; M. Satoh, Y. Nomoto, N.
Miyaura, and A. Suzuki, Tetrahedron Lett., 30, 3789 (1989).
M. A. expresses her thanks to JSPS for a Grant-in-Aid for
Encouragement of Young Scientists (No 13771323), and the
Hayashi Memorial Foundation for Female Natural Scientists.