Platinum-catalyzed intramolecular vinylchalcogenation of alkynes with β-phenylchalcogeno conjugated amides

Article abstract of DOI:10.1021/ja804121j

Platinum-catalyzed intramolecular vinylthiolation and -selenation of internal alkynes with vinylchalcogenides 1 having a carbamoyl group on cis-β-position of vinyl moiety was developed. The conjugated six-membered lactam framework 2 was constructed in high yields. Density functional theory calculations for alkyne insertion processes suggest seven-membered platinacycle 3 is a kinetically favored intermediate of this catalytic system. Copyright

Full text of DOI:10.1021/ja804121j

Published on Web 07/17/2008
Platinum-Catalyzed Intramolecular Vinylchalcogenation of Alkynes with
ꢀ-Phenylchalcogeno Conjugated Amides
Masashi Toyofuku,† Shin-ichi Fujiwara,*,‡ Tsutomu Shin-ike,‡ Hitoshi Kuniyasu,† and
Nobuaki Kambe*,†
Department of Applied Chemistry, Graduate School of Engineering, Osaka UniVersity, Suita, Osaka 565-0871,
Japan, and Department of Chemistry, Osaka Dental UniVersity, Hirakata, Osaka 573-1121, Japan
Received June 1, 2008; E-mail: fujiwara@cc.osaka-dent.ac.jp; kambe@chem.eng.osaka-u.ac.jp
Simultaneous addition of carbon and heteroatom units (repre-
sented as “C” and “E”, respectively) to alkynes with the cleavage
of “C-E” bond by transition metal complexes has attracted great
interest in recent organic and organometallic chemistry.1–5 This
reaction proceeds with cis-selective stereochemistry to give mul-
tifunctionalized alkenyl heteroatom compounds. Introduction of
allyl,1 alkynyl,2 acyl,3 and cyano4 groups as carbon units has been
well studied. However the corresponding introduction of vinyl group
(addition of the “vinyl-E” molecule across the triple bond) leading
to 1,3-dienes remains as a challenging theme.6–9 When the new
“vinyl-E” unit exhibits the reactivity similar to that of starting vinyl
heteroatom compounds, further reaction or oligomerization could
be a serious problem.5c To the best of our knowledge, successful
examples reported so far have been limited to the ring-expansion
reaction via addition of three- or four-membered heterocyclic
compounds such as silacyclopropenes,5a methylidenesiliranes,5b
allene episulfides,5c and silacyclobutenes5d to alkynes. In these
systems, ring strain of starting compounds may promote the initial
cleavage of the “vinyl-E” bond by the metal catalyst.
Recently, we found that an anion stabilizing group on the
ꢀ-position of acyclic vinyl sulfides and selenides enhanced oxidative
addition to Pt(0) complex.10 This finding led us to develop a new
type of catalytic reaction using vinyl sulfides and selenides.11 Here
we disclose Pt(0) catalyzes intramolecular cis-vinylthiolation and
-selenation of alkynes leading to effective construction of six-
membered lactam framework 2 or 3 having a high degree of
unsaturation (eq 1).
rise to alkyne-coordinated complex 6 and/or carbonyl-coordinated
complex 7. Subsequent insertion of alkyne into the Pt-Y bond
occurs on 6 affording the platinacycle 8. Reductive elimination leads
to the cyclized products 2 and regenerates the Pt(0) species.
When toluene (0.5 mL) containing a vinyl sulfide 1a (0.2 mmol)
and Pt(PPh3)4 (5 mol%) was heated at reflux for 2.5 h, intramo-
lecular vinylthiolation product 2a was obtained in 90% yield with
excellent stereoselectivity (Table 1, run 1).13 In contrast with an
intermolecular reaction (eq 2), the stereochemistry of the substrates
was essential in this cyclization. While intramolecular vinylselena-
tion of 1b took place efficiently to form lactam 2b (run 2), the
reaction of the trans-isomer of 1b gave no detectable product under
similar reaction conditions. In the oxidative addition adduct of trans-
isomer, intramolecular alkyne coordination affording the intermedi-
ate like 6 might be conformationally impossible. Bulkier alkyl
substituents on nitrogen, for example, 1-phenylethyl, did not retard
the reaction (run 3). The reaction of vinyl sulfide 1d and selenide
1e having a TMS group at the terminus gave the corresponding
lactam 2d and 2e in high yields (runs 4 and 5). This catalytic system
was not able to apply to terminal alkynes (R′ ) H, eq 1) probably
due to further reaction or oligomerization.14 However, 2e easily
underwent desilylation with K2CO3 in MeOH to afford 3e in 90%
total yield from 1e (run 6). Longer alkyl substituents on nitrogen
of 1f, for example, 2-phenylethyl, affected the reaction rate and
stereoselectivity (run 7). Interestingly, a crude E/Z mixture of 2f
was treated with K2CO3 in MeOH to form desilylated lactam 3f
with high E-selectively in high yield (run 8).15 Similarly, 1g having
unprotected indole ring gave desilylated E-lactam 3g in 86% yield
(run 9). Vinyl sulfide 1h having aryl group at the terminus also
At first, the reaction of vinyl selenides 4 (cis and trans) having
a carbamoyl group on ꢀ-position of vinyl moiety with 1-octyne
was examined to check the possibility of vinylchalcogenation of
alkynes, since this electron withdrawing group may accelerate
oxidative addition of the vinyl-SePh bond to Pt(0).10b,12 When
toluene (0.4 mL) containing cis-4 or trans-4 (0.3 mmol), 1-octyne
(3 equiv), and Pt(PPh3)4 (5 mol%) was heated at reflux for 12 h,
1,3-dienes 5 were obtained in moderate yields (eq 2). The
stereochemistry of 4 did not affect the yield of 5. Then, we
undertook intramolecular vinylchalcogenation and the working
hypothesis is shown in Scheme 1. The first step in this process is
oxidative addition of vinyl-YPh (Y ) S, Se) bond to Pt(0) giving
Scheme 1. A Possible Pathway Leading to Six-Membered Lactams
† Osaka University.
‡ Osaka Dental University.
9
10504 J. AM. CHEM. SOC. 2008, 130, 10504–10505
10.1021/ja804121j CCC: $40.75
2008 American Chemical Society

C O M M U N I C A T I O N S
Table 1. Pt(0)-Catalyzed Intramolecular Vinylchalcogenation of
H.; Hiyama, T. J. Am. Chem. Soc. 1999, 121, 10221. (c) Tong, X.; Zhang,
Z.; Zhang, X. J. Am. Chem. Soc. 2003, 125, 6370. (d) Mart´ın-Matute, B.;
Bun˜uel, E.; Me´ndez, M.; Nieto-Oberhuber, C.; Ca´rdenas, D. J.; Echavarren,
A. M. J. Organomet. Chem. 2003, 687, 410. (e) Tong, X.; Li, D.; Zhang,
Z.; Zhang, X. J. Am. Chem. Soc. 2004, 126, 7601. (f) Hua, R.; Takeda, H.;
Onozawa, S.; Abe, Y; Tanaka, M. Org. Lett. 2007, 9, 263. (g) Yamashita,
K.; Takeda, H.; Kashiwabara, T.; Hua, R.; Shimada, S.; Tanaka, M.
Tetrahedron Lett. 2007, 48, 6655.
Alkynes to Form Six-Membered Lactams (eq 1)a
run
1
Y
R
R′
Product, %b
E/Zc
d
d
d
1
2
3
4
5
1a
S
CH2Ph
Et
Et
Et
TMS
TMS
TMS
TMS
TMS
2a, 90
2b, 92 (99)
2c, 88
2d, 92
2e, 95
>99/1
>99/1
>99/1
96/4
1b Se CH2Ph
1c
1d
1e Se CH2Ph
1e Se CH2Ph
1f
1f
1g Se (CH2)2(3-Indolenyl) TMS
1h CH2Ph
S
S
CH(Me)Ph
CH2Ph
(2) (a) Shirakawa, E.; Yoshida, H.; Kurahashi, T.; Nakao, Y; Hiyama, T. J. Am.
Chem. Soc. 1998, 120, 2975. (b) See ref 1b. (c) Suginome, M.; Shirakura,
M.; Yamamoto, A. J. Am. Chem. Soc. 2006, 128, 14438.
96/4
e
d
3e, 90
6
>99/1
71/29
95/5
(3) (a) Kashiwabara, T.; Kataoka, K.; Hua, R.; Shimada, S.; Tanaka, M. Org.
Lett. 2005, 7, 2241. (b) Hua, R.; Onozawa, S.; Tanaka, M. Chem.sEur. J.
2005, 11, 3621. (c) Hua, R.; Shimada, S.; Tanaka, M. J. Am. Chem. Soc.
1998, 120, 12365. (d) Hua, R.; Takeda, H.; Onozawa, S.; Abe, Y.; Tanaka,
M. J. Am. Chem. Soc. 2001, 123, 2899. (e) See ref 1b. (f) Hua, R.; Onozawa,
S.; Tanaka, M. Organometallics 2000, 19, 3269. (g) Toyofuku, M.;
Fujiwara, S.; Shin-ike, T.; Kuniyasu, H.; Kambe, N. J. Am. Chem. Soc.
2005, 127, 9706.
(4) (a) Chatani, N.; Takeyasu, T.; Horiuchi, N.; Hanafusa, T. J. Org. Chem.
1988, 53, 3539. (b) Suginome, M.; Kinugasa, H.; Ito, Y. Tetrahedron Lett.
1994, 35, 8635. (c) Suginome, M.; Yamamoto, A.; Murakami, M. J. Am.
Chem. Soc. 2003, 125, 6358. (d) Suginome, M.; Yamamoto, A.; Murakami,
M. Angew. Chem., Int. Ed. 2005, 44, 2380. (e) Suginome, M.; Yamamoto,
A.; Sasaki, T.; Murakami, M. Organometallics 2006, 25, 2911. (f) Kamiya,
I.; Kawakami, J.; Yano, S.; Nomoto, A.; Ogawa, A. Organometallics 2006,
25, 3562.
f
Se (CH2)2Ph
Se (CH2)2Ph
2f, (94)
3f, 78 (85)
3g, 86
7
8
e,f
>99/1d
e,f
9
10
S
p-ClC6H4 2h, (82)
96/4
a Conditions: 1 (0.2 or 0.3 mmol), Pt(PPh3)4 (5 mol %), toluene (0.5
or 0.8 mL), reflux, 2.0-3.5 h. b Isolated yields. Numbers in parentheses
are NMR yields. c Determined by 1H NMR. d Z-isomer was not detected
in crude 1H NMR analysis. e Sequential treatment of crude 2 with
K2CO3 (5 equiv) in MeOH (2-3 mL) at room temp for 12-14 h.
f Reaction run for 12 h.
Scheme 2. Computational Models for Alkyne Insertion Processes
(5) (a) Sayferth, D.; Shannon, M. L.; Vick, S. C.; Lim, T. F. O. Organometallics
1985, 4, 57. (b) Saso, H.; Ando, W. Chem. Lett. 1988, 1567. (c) Choi, N.;
Kabe, Y.; Ando, W. Tetrahedron Lett. 1991, 32, 4573. (d) Liu, J.; Sun,
X.; Miyazaki, M.; Liu, L.; Wang, C.; Xi, Z. J. Org. Chem. 2007, 72, 3137.
(6) Decarbonylative addition of “RC()O)-E” bonds (R ) alkenyl) to alkynes
leading to 1,3-dienes: (a) Kokubo, K.; Matsumasa, K.; Miura, M.; Nomura,
M. J. Org. Chem. 1996, 61, 6941. (b) Sugoh, K.; Kuniyasu, H.; Sugae, T.;
Ohtaka, A.; Takai, Y.; Tanaka, A.; Machino, C; Kambe, N; Kurosawa, H.
J. Am. Chem. Soc. 2001, 123, 5108. (c) Hirai, T.; Kuniyasu, H.; Kato, T.;
Kurata, Y.; Kambe, N. Org. Lett. 2003, 5, 3871. (d) Nakao, Y.; Satoh, J.;
Shirakawa, E.; Hiyama, T. Angew. Chem., Int. Ed. 2006, 45, 2271.
(7) Lewis acid catalyzed trans-vinylsilylation of alkynes with acyclic vinyl-
siranes (a) Asao, N.; Shimada, T.; Yamamoto, Y. J. Am. Chem. Soc. 1999,
121, 3797. (b) Asao, N.; Shimada, T.; Shimada, T.; Yamamoto, Y. J. Am.
Chem. Soc. 2001, 123, 10899. (c) Asao, N.; Nabatame, K.; Yamamoto, Y.
Chem. Lett. 2001, 982.
(8) Dimerization-vinylstannylation of alkynes: (a) Shirakawa, E.; Yoshida, H.;
Nakao, Y.; Hiyama, T. J. Am. Chem. Soc 1999, 121, 4290. (b) Yoshida,
H.; Shirakawa, E.; Nakao, Y.; Honda, Y.; Hiyama, T. Bull. Chem. Soc.
Jpn. 2001, 74, 637.
(9) Au- and Pd-cocatalyzed vinylstannylation of ynones was recently reported: Shi,
Y.; Peterson, S. M.; Haberaecker, W. W., III; Blum, S. A. J. Am. Chem.
Soc. 2008, 130, 2168.
(10) (a) Kuniyasu, H.; Ohtaka, A.; Nakazono, T.; Kinomoto, M.; Kurosawa, H.
J. Am. Chem. Soc. 2000, 122, 2375. (b) Kuniyasu, H.; Kato, T.; Inoue, M.;
Terao, J.; Kambe, N. J. Organomet. Chem. 2006, 691, 1873. For other
examples for the cleavage of vinyl-chalcogen bonds by transition metals,
see: (c) Boyar, E.; Deeming, A. J.; Henrick, K.; McPartlin, M.; Scott, A.
J. Chem. Soc., Dalton Trans. 1986, 1431. (d) Planas, J. G.; Marumo, T.;
Ichikawa, Y.; Hirano, M.; Komiya, S. J. Chem. Soc., Dalton Trans. 2000,
2613. (e) Goj, L. A.; Lail, M.; Pittard, K. A.; Riley, K. C.; Gunnoe, T. B.;
Petersen, J. L. Chem. Commun. 2006, 982.
(11) Cross-coupling reaction of vinyl chalcogenides with organometallic reagents
is well-known. For recent exmples, see: (a) Silveira, C. C.; Braga, A. L.;
Vieira, A. S.; Zeni, G. J. Org. Chem. 2003, 68, 662. (b) Itami, K.; Higashi,
S.; Mineno, M.; Yoshida, J. Org. Lett. 2005, 7, 1219.
underwent intramolecular vinylthiolation to afford the desired lactam
2h (run 10).16
Next, density functional theory (DFT) calculations were per-
formed to get information on the mechanism. In Scheme 2, A is
the model compound for alkyne-coordinated complex 6. TS1 and
TS2 are transition state models for the reaction proceeding from A
and calculated energies of optimized TS1 and TS2 relative to A
are shown in parentheses.17 TS1 is 5.8 kcal/mol more stable than
TS2 and this result indicates that selenoplatination leading to
platinacycle-like 8 is kinetically the more favored pathway than
carboplatination.18 In the case of Pd, the transition state for
selenopalladation (+9.1 kcal) is less stable than TS1 (+8.2 kcal).
In fact, Pd(PPh3)4 worked as catalyst in this system but the
efficiency was lower than Pt(PPh3)4.19
In summary, Pt(PPh3)4 catalyzes intramolecular vinylthiolation
and -selenation of internal alkynes with vinyl chalcogenides having
a carbamoyl group on the cis-ꢀ-position of the vinyl moiety giving
rise to the highly conjugated δ-lactam frameworks.20 DFT calcula-
tions for alkyne insertion processes suggest the formation of seven-
membered platinacycle is kinetically favored. Introduction of
electron withdrawing groups to ꢀ-position on vinyl moiety may be
a key to develop a new type of catalytic reaction using vinyl
heteroatom compounds.
(12) In a stoichiometric reaction of cis-4 with Pt(PPh3)4 in C6D6, formation of
the oxidative adduct was confirmed by 31P NMR analysis. See Supporting
Information for the details.
(13) Radical mechanism can be denied since radical scavengers such as TEMPO
and galvinoxyl did not retard the reaction of 1a.
(14) The reaction of vinyl selenide 1i (Y ) Se, R ) CH2Ph, R′ ) H, eq 1)
gave a complex mixture and neither Z-3e nor E-3e was detected.
(15) Similar thermodynamic resolution of E/Z mixture was also observed in
2e. See Supporting Information for the details.
Acknowledgment. This work was supported by a Grant-in-Aid
for Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology, Japan. M.T. expresses his special
thanks for JSPS Research Fellowship for Young Scientist for
financial support and The Global COE Program of Osaka University.
(16) 2h was easily hydrolyzed during purification by PTLC or HPLC. Formation
of 2h was confirmed by crude 1H NMR, 13C NMR, and HRMS analysis.
In addition, the hydrolyzed product was isolated and characterized. See
Supporting Information for the details.
(17) For the details about calculations, see Supporting Information.
(18) For insertion of alkynes into Pt-SAr bond: Kuniyasu, H.; Yamashita, F.;
Terao, J.; Kambe, N. Angew. Chem., Int. Ed. 2007, 46, 5929.
Supporting Information Available: Experimental and calculation
details and characterization data of all new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
(19) Although Pd(PPh3)4 worked as catalyst for cyclization of 1a, the reaction
was slower and 2a was obtained in 37% NMR yield after 2.5 h.
(20) Attempts to lactone synthesis using a vinyl selenide 9 (Z)-PhSe-CH)CH-
C(O)OCH2t CMe failed. This result as well as substituent effect on nitrogen
described in the text may indicate that accessibility of alkyne unit to Pt is
important for the present vinylchalcogenation to take place.
References
(1) (a) Kaneda, K.; Kawamoto, F.; Fujiwara, Y.; Imanaka, T.; Teranishi, S.
Tetrahedron Lett. 1974, 1067. (b) Shirakawa, E.; Yamasaki, K.; Yoshida,
JA804121J
9
J. AM. CHEM. SOC. VOL. 130, NO. 32, 2008 10505