Pd-catalyzed addition-carbocyclization of α,ω-diynes with H-P(O)R2 compounds

Article abstract of DOI:10.1016/j.tetlet.2009.08.094

Chelating phosphines are much higher performing than mono-dentate phosphines in palladium-catalyzed reaction of α,ω-diynes with HP(O)R¹R² (R¹,R² = Ph, alkoxy) to afford (E)-3-(phosphorylmethylene)-2-methylcyclop

Full text of DOI:10.1016/j.tetlet.2009.08.094

Tetrahedron Letters 50 (2009) 6196–6199
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Pd-catalyzed addition–carbocyclization of
with H–P(O)R2 compounds
a,x-diynes
*
Jun Kanada, Koh-ichiro Yamashita, Satish Kumar Nune, Masato Tanaka
Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Chelating phosphines are much higher performing than mono-dentate phosphines in palladium-cata-
lyzed reaction of
-diynes with HP(O)R1R2 (R1,R2 = Ph, alkoxy) to afford (E)-3-(phosphorylmethyl-
ene)-2-methylcyclopentenes.
Received 27 July 2009
Revised 26 August 2009
Accepted 27 August 2009
Available online 31 August 2009
a,x
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Palladium
Hydrophosphorylation
Cyclization
Homogeneous catalysis
The transition-metal-complex-catalyzed cyclizations of unsatu-
rated organic compounds have received increasing attention as
powerful tools for ring construction.1 The addition–carbocycliza-
R
R
H-[Pd]-P(O)R1R2
R
[Pd]-P(O)R1R2
P(O)R1R2
tion reactions of a,x
-diynes with inter-element bonds (E–E0 bonds:
Scheme 1.
E = heteroatom, E0 = H, metal, heteroatom or functional group)2 are
particularly useful, because the resulting cyclic compounds allow
numerous synthetic applications, depending on the element intro-
duced. Since 1996, we have been working on the addition reactions
of H–P(O) bonds with various unsaturated compounds.3 A great
feature of these reactions lies in the high regioselectivity, which
can be readily controlled by the selection of the central metal of
the catalyst, nature of the ligands, and addition of acidic additives.
Recently we have reported that dppe is a powerful branch-direct-
ing ligand in the addition reaction to alkynes, irrespective of the
substituent in the starting H–P(O) compound.4 The regioselectivity
for the branched products is likely to have come from participation
of (1-alken-2-yl)palladium species (Scheme 1).
Pd(OAc)2-
chelating
phosphine
1x
E
E
E
P(O)R1R2
+
P(O)R1R2
+
0xY: Not dected
HP(O)R1R2
3xY: Major product
2Y
in most cases
P(O)R1R2
+
1 a: E = CH2
b: E = N(p-Ts)
c: E = none
E
P(O)R1R2
6xY
E
+
+
E
d: E = CH2CH2
P(O)R1R2
P(O)R1R2
5xY
4xY
2 A: R1 = Ph, R2 = Ph
B: R1 + R2 = O(CMe2)2O
C: R1 = OMe, R2 = OMe
D: R1 = OEt, R2 = OEt
E: R1 = OEt, R2 = Ph
Preliminary experiments with the (1-alken-2-yl)palladium spe-
cies in mind have led us to find addition–cyclization reaction of
P(O)R1R2
P(O)R1R2
P(O)R1R2
E
+
a
,
x
-diynes with H–P(O) bonds (Scheme 2), which will be reported
in this letter. Pioneering work by Parsons and later that by Jang
have disclosed radical addition–cyclization reactions of -dienes
with H–P(O) bonds.5 However, addition–cyclization reaction of
-diynes has never been documented.
In a representative experiment (Table 1, the first entry), a mix-
8xY
E
7xY
a,x
Scheme 2.
a,x
70 °C for 14 h in the presence of Pd(OAc)2 (5 mol %) and 1,2-
bis(diphenylphosphino)benzene (abbreviated as dppben, 1.5 equiv
relative to Pd; phosphorus/Pd = 3). 1H NMR analysis, after evapora-
tion of the resulting mixture and addition of p-dimethoxybenzene
(internal standard) and CDCl3, revealed that (E)-3-(diphenylphos-
phinylmethylene)-2-methylcyclopentene (3aA) was formed in
ture of 1,6-heptadiyne 1a (2.10 mmol) and diphenylphosphine
oxide 2A (2.00 mmol) in chlorobenzene (5 mL) was heated at
* Corresponding author. Tel.: +81 45 924 5244; fax: +81 45 924 5279.
E-mail address: m.tanaka@res.titech.ac.jp (M. Tanaka).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.08.094

J. Kanada et al. / Tetrahedron Letters 50 (2009) 6196–6199
6197
Table 1
Reaction of
a,
x
-diynes 1x with H–P(O) compounds 2Ya
1x
2Y
L
Solvent, temp (°C), timeb (h)
Productc, yieldd (%)
P(O)Ph2
1a
2A
2B
2C
2D
2E
2A
2D
2E
2A
2A
dppben
C, 70, 14
T, 100, 12
E, 130, 3
E, 130, 3
E, 130, 3
D, 100, 3
E, 130, 3
E, 130, 3
T, 100, 2
T, 100, 2
3aA 74 (68)
P(O)(OCMe2)2
1a
1a
1a
1a
1b
1b
1b
1c
dppben
dppben
dppe
3aB 66 (64)
P(O)(OMe)2
3aC 76 (69)
P(O)(OEt)2
3aD 51 (47)
P(O)Ph(OEt)
dppben
dppe
3aE 62 (59)
P(O)Ph2
8bA 33 (27)
N
N
P(O)Ph2
3bA 24
P(O)(OEt)2
dppben
dppben
dppe
8bD 57 (41)
N
P(O)Ph(OEt)
8bE 50 (39)
N
P(O)Ph2
3cA 0
P(O)Ph2
4cA 2
P(O)Ph2
1d
dppe
3dA 26
a
Reaction conditions: 1x (2.1 mmol), 2Y (2.0 mmol), Pd(OAc)2 (5.0 mol %), L (7.5 mol %; P/Pd = 3).
T = toluene, C = chlorobenzene, E = ethylbenzene, D = dioxane.
N = N(p-Ts).
b
c
d
Determined by 1H NMR spectroscopy. The figures in parentheses are isolated yields.
74% yield, together with 2,6-bis(diphenylphosphinyl)-1,6-heptadi-
analysis, X-ray diffraction study (3aB, 8bA), and/or comparison with
an authentic sample synthesized by a separate procedure.
ene (7aA; 10%) and traces of other byproducts shown in Scheme 2.
Evaporation of the mixture followed by column chromatography
(silica gel, hexane/acetone = 1/1) led to isolation of 3aA as colorless
powder in 68% yield.
Another reaction using dppe as the ligand and toluene as the
solvent also made the cyclization mainly, but was somewhat less
selective to afford 3aA (43%), 2-(diphenylphosphinylmethyl)
-1-methylenecyclopentane (4aA; 6%), 1,2-bis(diphenylphosphi-
nylmethyl)cyclopentene (5aA; <1%), 2-diphenylphosphinyl-1
-hepten-6-yne (6aA; 6%), and 2,6-bis(diphenylphosphinyl)-1,6-
heptadiene (7aA; 12%). The products inclusive of the byproducts
were carefully identified by spectroscopic measurements, elemental
The foregoing two reactions clearly indicate that chelating
phosphines direct the reaction to cyclization. On the other hand,
the use of PPh3 (3 equiv relative to Pd) resulted in low-yielding
nonselective formation of 3aA, 4aA, 5aA, 6aA, and 7aA in 5%,
10%, <1%, 5%, and 5% yields, respectively (Scheme 3). Thus, the
use of
cyclization.6
After these trial experiments, we ran a series of reactions of
-diynes with various H–P(O) bonds. Table 1 discloses that the
a chelating phosphine is a prerequisite for efficient
a,x
procedure using either dppe or dppben ligand works fairly well
with hydrogen phosphonates 2B–D and hydrogen phosphinate 2E.

6198
J. Kanada et al. / Tetrahedron Letters 50 (2009) 6196–6199
2A
carbon–Pd bond like the I-30–I-5 conversion, rather than that into
1a +
3aA + 4aA + 5aA + 6aA + 7aA
chlorobenzene
100 °C, 1 h
a Pd–P(O) bond.9
Another issue to be addressed is the favorable role of chelating
phosphine. The key intermediate at the dichotomous branching
point is I-3. As one of us has reported, the final product forming
reductive elimination appears to be rate-determining in the addi-
tion reaction of 2A with alkynes8b and also in the addition reaction
of 2B with alkenes.8c The dichotomous reactivity of I-3 is presum-
ably dependent on the ease of its reductive elimination. Given the
reductive elimination proceeding via three coordinate species, de-
spite some controversies,10,11 the P–C reductive elimination from
I-3 ligated by monodentate phosphine(s) is presumed to be more
facile than that ligated by a chelating phosphine,10a,b leading to
the formation of 6. In chelating phosphine-Pd-catalyzed reactions,
on the other hand, the lack or difficulty of generation of three coor-
dinate species eventually allows the coordination of the other tri-
ple bond to generate I-30, which is ready for the ring closure.
As for the events after the formation of 0, there are three op-
tions. One is further reaction with the H–P(O) compound affording
5. Palladium-catalyzed 1,4-addition of an H–P(O) bond with conju-
gated dienes has been reported by one of us.12 The formation of 5
3aA 4aA 5aA 6aA 7aA
70
5
3
5
5
11
5
Pd(OAc)2 + 1.5dppe
Pd(OAc)2 + 3PPh3
< 1
10 < 1
Scheme 3.
N,N-Dipropargyl-p-tosylamide (1b) also reacted similarly, but
the major products were pyrroles 8bA, 8bD, and 8bE. Type 5 and
6 products appeared to be formed in small quantities as judged
by NMR spectroscopy. However, type 3 compound was formed
only in the reaction with 2A, which furnished 3bA in 24% (indicat-
ing that the total cyclization yield inclusive of 8bA was 57%).
Byproduct 3bA was found to readily isomerize to 8bA.7
On the other hand, shorter- or longer-chained
a,x-diynes did
not cyclize smoothly. The reaction of 1,5-hexadiyne 1c with 2A
(80 °C, 2 h, toluene) afforded only 6cA (64%) and 7cA (30%); no cy-
clized product 3cA was formed. The same reaction run at 100 °C for
2 h did not give 3cA either, although a minute quantity (2%) of par-
tially hydrogenated product 4cA was formed. Likewise, 1,7-octa-
diyne 1d gave 6dA (40%) and 7dA (33%) along with a trace of
3dA (80 °C, 2 h, toluene). However, another reaction run at
100 °C formed 3dA in 26% yield together with 6dA (23%) and
7dA (32%), indicating that 1d was somewhat less reluctant than
1c to undergo the cyclization.
presumably takes place via
g
3-allylic species (vide infra).
Another option is the isomerization to 3. Hydropalladation of 0
with I-2 is envisioned to generate g3-allylic species I-6, I-60, and I-
7 (Scheme 5). Species I-60 results in the isomerization to 3 via b-hy-
dride elimination, but if I-7 is generated, formation of 5 via P–C
reductive elimination takes place. The stereochemistry of 3 is pre-
sumably predetermined at g3-allylic intermediate I-60. Since the
The formation of the cyclized products and other byproducts is
rationalized as depicted in Scheme 4.
syn-g
3-allylic complex is normally more stable than the anti-iso-
mer, associated with the steric demand of the substituent,13 one
can predict that I-60, which is more stable than I-6, proceeds to
b-hydride elimination, affording 3, as was indeed observed.
The route involving intermediates I-2 and I-3, leading to 6 (and
further to 7), is conceivable in view of precedent publications.3a,4
Oxidative addition of H–P(O) compounds with Pd(0) and insertion
of alkyne into the H–Pd bond have been reported by one of us.8 The
process similar to that from I-3 to 6 has been established with sim-
ple terminal alkynes and alkenes.8b,8c Intermediate 0 is also rea-
sonable since such compounds are obtained as final products in
related addition–cyclization reactions.1,2
One of the remaining issues to be addressed is the mechanism
of the ring-forming process (I-4 vs I-5). We propose that the route
through I-5 appears more reasonable. If we presume I-4 being
responsible for the cyclization, the cyclization of 1c through a
five-membered intermediate should have been easier than that
of 1d through a seven-membered intermediate, in view of the
strain of the cyclic intermediates. In addition, literature survey
has shown a plethora of reactions involving insertion into a
P
LnPPd
LnPPd
P
HPdPLn
P
I-2
0
E
E
I-6'
E
I-6
HPdPLn
I-2
- HPdPLn
PdPLn
P
P
3
P
P
- PdLn
E
E
I-7
5
E
Scheme 5.
P
PdLn
I-1
P
H
P
P
2
N
0
E
E
(p-Ts)
6
E
E
P
3
8
P
P
HPdPLn
I-2
E
E
PdLn
PdPLn
E
P
5
I-5
P
P
7
I-4
P
E
4
E
PdPLn
PdPLn
E
E
1
I-3
I-3'
Scheme 4. P = P(O)R1R2.

J. Kanada et al. / Tetrahedron Letters 50 (2009) 6196–6199
6199
P(OMe)2
O
References and notes
H-P(O)(OMe)2
+
N
N
others
+
+
1. Review: (a) Tamao, K.; Kobayashi, K.; Ito, Y. Synlett 1992, 539; (b) Ojima, I.;
Tzamarioudaki, M.; Li, Z.; Donovan, R. J. Chem. Rev. 1996, 96, 635; (c)
Montgomery, J. Acc. Chem. Res. 2000, 33, 467; (d) Aubert, C.; Buisine, O.;
Malacria, M. Chem. Rev. 2002, 102, 813; (e) Zeni, G.; Larock, R. C. Chem. Rev.
2004, 104, 2285; (f) Zeni, G.; Larock, R. C. Chem. Rev. 2006, 106, 4644.
2. For selected examples: (a) Singidi, R. R.; RajanBabu, T. V. Org. Lett. 2008, 10,
3351. and references cited therein; (b) Kim, H.; Goble, S. D.; Lee, C. J. Am Chem.
Soc. 2007, 129, 1030; (c) Hirabayashi, T.; Okimoto, Y.; Saito, A.; Morita, M.;
Sakaguchi, S.; Ishii, Y. Tetrahedron 2006, 62, 2231; (d) Liu, C. Ph.D. thesis, Duke
University, 2006.; (e) Goble, S. D. Ph.D. thesis, Princeton University, 2006.; (f)
Trost, B. M.; Rudd, M. T. Org. Lett. 2003, 5, 1467; (g) Suginome, M.; Matsuda, T.;
Ito, Y. Organometallics 1998, 17, 5233; (h) Onozawa, S.-y.; Hatanaka, Y.; Tanaka,
M. Chem. Commun. 1997, 1229; (i) Onozawa, S.-y.; Hatanaka, Y.; Choi, N.;
Tanaka, M. Organometallics 1997, 16, 5389.
N
9bC 17% (isolated)
(MeO)2(O)P
4bC 32% (NMR)
[N = N(p-Ts)]
D
D
D-P(O)(OMe)2
+
N
H-P(O)(OMe)2
+
N
D
D
2C-d1
2C
Ha
1b-d2
1b-d2
Hb
D content
D content
1.60D
N
P(O)(OMe)2
Ha + Hb
a + Hb
He
1.10D
0.42D
1.19D
H
Hc
Hc
0.76D
1.90D
Hc
Hd
Hd + He
Hd + He
4bC
3. (a) Tanaka, M. Top. Curr. Chem. 2004, 232, 25. and references cited therein; (b)
Han, L.-B.; Zhao, C.-Q.; Tanaka, M. WO 2002/064604.; (c) Han, L.-B.; Zhang, C.;
Tanaka, M. WO 2003/097654.
Scheme 6.
4. (a) Nune, S. K.; Tanaka, M. Chem. Commun. 2007, 2858; (b) Dobashi, N.; Fuse, K.;
Hoshino, T.; Kanada, J.; Kashiwabara, T.; Kobata, C.; Nune, S. K.; Tanaka, M.
Tetrahedron Lett. 2007, 48, 4669.
A third option is the formation of 4, which must have come
from partial hydrogenation of 0. The following observation appears
relevant to the provenance of the hydrogen required for the partial
hydrogenation. While we were searching for other byproducts un-
der different conditions, we came across the formation of
alkynylphosphonate 9bC (Scheme 6) and 4bC in 17% NMR and
32% isolated yields, respectively, along with traces of other uniden-
tified products [Pd(PPh3)4 3 mol %, THF, 68 °C, 48 h]. Given that the
real yield of the alkynylphosphonate (by NMR) is much higher than
the isolated yield, for example, ꢀ30%, it is reasonable to assume
that the hydrogen has come, at least partly, from the alkynylphos-
phonate formation process. Deuterium-labeling experiments to
look into the possibility under identical conditions (Scheme 6) ap-
pear to support the assumption. Thus, the reaction of 1b-d2 with
2C and also the reaction of 1b-d2 with 2C-d1 furnished partially
deuterated 4bC. The D content at relevant positions in 4bC (by
1H NMR spectroscopy) agrees fairly well with the calculated value,
if we allow possible H–D scrambling with a potential H source (sol-
vent, moisture) present in the reaction system.14 The failure of
detection of alkynylphosphorus compounds in the catalytic reac-
tions using chelating phosphines is presumably because the forma-
tion of such compounds, if any, should be very small in light of 4
being a minor product in these reactions. Isolation or detection
of such compounds in these reactions is not an easy task due to
the complexity of the mixture of minor products having the same
phosphorus functionality.
5. (a) Jessop, C. M.; Parsons, A. F.; Routledge, A.; Irvine, D. J. Eur. J. Org. Chem. 2006,
1547. and references cited therein; (b) Cho, D. H.; Jang, D. O. Synlett 2005, 59.
6. Another similar reaction of 1a with dimethyl phosphonate 2C in chlorobenzene
using PPh3 also resulted in nonselective formation of 3aC, 4aC, 5aC, 6aC, and
7aC in 1%, 8%, 9%, 3%, and 3% yields, respectively.
7. A freshly prepared CDCl3 solution of 3bA displayed neat 1H NMR spectrum, but
the spectrum was changing over a period of 2 h at room temperature to
eventually display the spectrum of 8bA.
8. (a) Han, L.-B.; Tanaka, M. J. Am. Chem. Soc. 1996, 118, 1571; (b) Han, L.-B.; Choi,
N.; Tanaka, M. Organometallics 1996, 15, 3259; (c) Han, L.-B.; Mirzaei, F.; Zhao,
C.-Q.; Tanaka, M. J. Am. Chem. Soc. 2000, 122, 5407.
9. We proposed such elemental process, but were unable to provide convincing
evidence. See: Han, L.-B.; Hua, R.; Tanaka, M. Angew. Chem., Int. Ed. 1998, 37, 94;
However, insertion into a Pd–P bond appears possible. See: Wicht, D. K.;
Kourkine, I. V.; Kovacik, I.; Glueck, D. S.; Concolino, T. E.; Yap, G. P. A.; Incarvito,
C. D.; Rheingold, A. L. Organometallics 1999, 18, 5381.
10. For mechanistic work on P–C reductive elimination, see: (a) Levine, A. M.;
Stockland, R. A., Jr.; Clark, R.; Guzei, I. Organometallics 2002, 21, 3278; (b)
Stockland, R. A., Jr.; Levine, A. M.; Giovine, M. T.; Guzei, I. A.; Cannistra, J. C.
Organometallics 2004, 23, 647; (c) Kohler, M. C.; Stockland, R. A., Jr.; Rath, N. P.
Organometallics 2006, 25, 5746; (d) Kalek, M.; Stawinski, J. Organometallics
2008, 27, 5876; (e) Kohler, M. C.; Grimes, T. V.; Wang, X.; Cundari, T. R.;
Stockland, R. A., Jr. Organometallics 2009, 28, 1193.
11. For selected examples on other heteroatom-C or C–C reductive elimination in
palladium complexes, see: (a) Gillie, A.; Stille, J. K. J. Am. Chem. Soc. 1980, 102,
4933; (b) Ozawa, F.; Ito, T.; Nakamura, Y.; Yamamoto, A. Bull. Chem. Soc. Jpn.
1981, 54, 1868; (c) Driver, M. S.; Hartwig, J. F. J. Am. Chem. Soc. 1997, 119, 8232;
(d) Marcone, J. E.; Moloy, K. G. J. Am. Chem. Soc. 1998, 120, 8527; (e) Yin, J.;
Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 6043; (f) Macgregor, S. A.; Neave, G.
W.; Smith, C. Faraday Discuss. 2003, 124, 111; (g) Mann, G.; Shelby, Q.; Roy, A.
H.; Hartwig, J. F. Organometallics 2003, 22, 2775; (h) Espinet, P.; Echavarren, A.
M. Angew. Chem., Int. Ed. 2004, 43, 4704; (i) Ananikov, V. P.; Musaev, D. G.;
Morokuma, K. Eur. J. Inorg. Chem. 2007, 5390.
In summary, we have developed hydrophosphorylative carbo-
cyclization of 1,6-heptadiyne derivatives. Cyclic compounds hav-
ing phosphorus substituents have been studied actively, aiming
at diverse applications.15 The new procedure disclosed in this letter
may find utility in the relevant area of applications.
12. Mirzaei, F.; Han, L.-B.; Tanaka, M. Tetrahedron Lett. 2001, 42, 297.
13. For a review of
g
3-allyl–metal complexes, see: Clarke, H. L. J. Organomet. Chem.
1974, 80, 155.
14. A reaction of 1a with 2B (130 °C, 3 h, in ethylbenzene, Pd(OAc)2-dppe) afforded
3aB and 4aB in 60% and 9% NMR yields while the same reaction effected using
10-fold excess of 2B resulted in a higher yield of 4aB (21%) at the expense of
3aB (6%). This may imply that H–P(O) alone could also be a hydrogen source
although we could not find possible coproducts like (O)P–P(O) species.
Stockland and coworkers reported the formation of a Pd[P(O)(OPh)2]2 species
in the reaction of MePd[P(O)(OPh)2] with HP(O)(OPh)2, liberating methane: See
Ref. 10b.
Acknowledgments
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We thank Dr. Makoto Tanabe for his assistance in X-ray crystal-
lography. This work was supported by a Grant-in-Aid for Scientific
Research on Priority Areas (No. 18065008, ‘Chemistry of Concerto
Catalysis’) from the Ministry of Education, Culture, Sports, Science
and Technology, Japan.
Supplementary data
Experimental details, spectral data of new compounds and crys-
tallographic data for 3aB and 8bA in CIF format are available. Sup-
plementary data associated with this article can be found, in the
online version, at doi:10.1016/j.tetlet.2009.08.094.