Palladium-catalyzed borylstannylative carbocyclization of diynes and an enyne compound

Article abstract of DOI:10.1021/om970704q

Highly regio- and stereoselective borylstannylative carbocyclization of diynes 2a-f with the borylstannane 1 are efficiently catalyzed at room temperature by a series of palladium complexes such as Cl₂Pd(PPh₃)₂, Cl₂Pd[P(o-tolyl)₃]₂, Pd(PPh₃)₄, and Pd-(dba)₂, giving 1-(borylmethylidene)-2-(stannylmethylidene)cycloalkane derivatives 3a-f in high yields. A 1,6-enyne (2g) also reacts similarly to afford a high yield of the corresponding cyclized product 3g.

Full text of DOI:10.1021/om970704q

Organometallics 1997, 16, 5389-5391
5389
P a lla d iu m -Ca ta lyzed Bor ylsta n n yla tive Ca r bocycliza tion
of Diyn es a n d a n En yn e Com p ou n d
Shun-ya Onozawa, Yasuo Hatanaka, Nami Choi, and Masato Tanaka*
National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 305, J apan
Received August 11, 1997X
Sch em e 1
Summary: Highly regio- and stereoselective borylstan-
nylative carbocyclization of diynes 2a -f with the bor-
ylstannane 1 are efficiently catalyzed at room tempera-
ture by a series of palladium complexes such as
Cl2Pd(PPh3)2, Cl2Pd[P(o-tolyl)3]2, Pd(PPh3)4, and Pd-
(dba)2, giving 1-(borylmethylidene)-2-(stannylmeth-
ylidene)cycloalkane derivatives 3a -f in high yields. A
1,6-enyne (2g) also reacts similarly to afford a high yield
of the corresponding cyclized product 3g.
ylstannyl)-2-bora-1,3-diazacyclopentane (1; 0.582 mmol)
and 1,6-heptadiyne (2a ; 0.873 mmol) at 0 °C. The
mixture was warmed to room temperature and stirred
for 1 h. Analysis of the resulting reaction mixture by
GC, GC-MS, and NMR indicated that the starting
materials were completely consumed and that 1-[(Z)-
(1,3-dimethyl-2-bora-1,3-diazacyclopent-2-yl)methylidene]-
2-[(Z)-(trimethylstannyl)methylidene]cyclopentane (3a )
The transition-metal-complex-catalyzed cyclizations
of unsaturated organic compounds have received in-
creasing attention as powerful tools for ring construc-
tion.1 The addition-carbocyclization reactions of di-
ynes,2,3 enynes,2,3a,4 or bis(dienes)5 with reagents having
inter-heteroatom bonds (E-E′ bonds: E, E′ ) metals
or heteroatoms) are particularly useful, because the
resulting metal- or heteroatom-containing cyclic com-
pounds allow numerous synthetic applications. How-
ever, such reactions are still very rare. Recently, we2,6
and Ito’s group7 have reported palladium-catalyzed
addition reactions of inter-heteroatom bonds such as
B-Sn and B-Si bonds with alkynes. The high regio-
and stereoselectivity of these reactions prompted us to
study the reactivities of R,ω-diynes toward borylstan-
nane 18 (Scheme 1). We report herein that this reaction
proceeds smoothly in the presence of a palladium
catalyst under very mild conditions (room temperature,
1-5 h), affording good yields of 1-(borylmethylidene)-
2-(stannylmethylidene)cycloalkanes with extremely high
regio- and stereoselectivity.9
1
was formed as the sole product in 98% H NMR yield
(Table 1, entry 1). Isolation of this product was very
easy; evaporation of the solvent, addition of pentane (10
mL) to the residue, filtration, and bulb-to-bulb distilla-
tion of the concentrated filtrate afforded analytically
pure 3a in 79% yield.10 Despite serious congestion,
product 3a (and other products also) adopts the Z,Z-
configuration, as evidenced by the NOE experiments
(see ref 11 and Chart 1). The configuration was further
confirmed by X-ray crystallography in the case of 3d
(vide infra). With regard to the catalyst, besides
Cl2Pd(PPh3)2, a series of palladium complexes such as
Cl2Pd[P(o-tolyl)3]2, Pd(PPh3)4, and Pd(dba)2 exhibited
equally excellent catalytic activity; when they were
applied to the reaction of 1 with 2a under the same
conditions, these palladium catalysts gave 3a in nearly
A representative procedure was as follows. To a
benzene solution (3 mL) of Cl2Pd(PPh3)2 (1 mol %) and
decane (50 µL, an internal standard for GC analysis)
in a Schlenk tube were added 1,3-dimethyl-2-(trimeth-
1
quantitative yields (determined by H NMR).
The analogous borylsilylative carbocyclization reac-
tion of diynes with a borylsilane usually gave a mixture
of a desired cyclization product and another undesired
product arising from simple addition of the borylsilane
to one of the two acetylenic bonds of diynes.2 Depending
on the structure of the diynes, the undesired product
could be the main product of the reaction. On the other
hand, such a byproduct was not formed in the present
X Abstract published in Advance ACS Abstracts, November 1, 1997.
(1) (a) Ojima, I.; Tzamarioudaki, M.; Li, Z.; Donovan, R. J . Chem.
Rev. 1996, 96, 635. (b) Trost, B. M. Acc. Chem. Res. 1990, 23, 34. (c)
Schore, N. E. Chem. Rev. 1988, 88, 1081. (d) Vollhardt, K. P. C. Angew.
Chem., Int. Ed. Engl. 1984, 23, 539.
(2) Onozawa, S.-y.; Hatanaka, Y.; Tanaka, M. Chem. Commun. 1997,
1229.
(3) (a) Chatani, N.; Morimoto, T.; Muto, T.; Murai, S. J . Organomet.
Chem. 1994, 473, 335. (b) Tamao, K.; Kobayashi, K.; Ito, Y. J . Am.
Chem. Soc. 1989, 111, 6478. (c) Chatani, N.; Takeyasu, T.; Horiuchi,
N.; Hanafusa, T. J . Org. Chem. 1988, 53, 3539.
(4) Ojima, I.; Donovan, R. J .; Shay, W. R. J . Am. Chem. Soc. 1992,
114, 6580.
(5) Obora, Y.; Tsuji, Y.; Kakeshi, T.; Kobayashi, M.; Shinkai, Y.;
Ebihara, M.; Kawamura, T. J . Chem. Soc., Perkin Trans. 1 1995,
599.
(6) Onozawa, S.-y.; Hatanaka, Y.; Sakakura, T.; Shimada, S.;
Tanaka, M. Organometallics 1996, 15, 5450.
(7) Suginome, M.; Nakamura, H.; Ito, Y. Chem. Commun. 1996,
2777.
(10) 3a : bp 110-115 °C/5.5 × 10-3 Torr; IR (neat) 766, 1253, 1291,
1350, 1404, 1439, 1500, 1632, 2792, 2848 cm-1; 1H NMR (C6D6) δ 0.17
(s, J H-Sn ) 55.0 Hz, 9H, SnCH3), 1.53-1.64 (m, 2H, CH2), 2.36-2.44
(m, 4H, CH2), 2.52 (s, 6H, NCH3), 3.04 (s, 4H, NCH2), 5.35 (s, 1H,
dCHB), 5.73 (s, J H-Sn ) 63.6 Hz, 1H, dCHSn); 13C NMR (C6D6) δ -8.5
(J C-Sn ) 350 Hz, SnCH3), 21.9, 35.0 (NCH3), 36.7, 37.6, 52.0 (NCH2),
116.9 (broad, dCHB), 123.5 (J C-Sn ) 485 Hz, dCHSn), 158.3 (Cd),
160.3 (Cd); 119Sn NMR (C6D6) δ -51.4; 11B NMR δ 29.7 (broad); GC-
MS (70 eV, EI) m/z (relative intensity) 354 (M+ for 3a having 11B and
120Sn isotopes, 0.05; molecular peaks corresponding to other isotopes
were also observed), 189 (100), 188 (28), 187 (15), 174 (84), 173 (38).
Anal. Calcd for C14H27BN2Sn: C, 47.65; H, 7.71; N, 7.94. Found: C,
48.00; H, 7.86; N, 8.04.
(8) Borylstannane 1 can be easily prepared according to the litera-
ture procedure. See: Niedenzu, K.; Rothgery, E. F. Synth. Inorg. Met.-
Org. Chem. 1972, 2, 1.
(9) A part of this work was presented at the 43rd Symposium on
Organometallic Chemistry, Osaka, J apan, Oct 31-Nov 1, 1996; Kinki
Chemical Society: Osaka, J apan, 1996; Abstract PB231.
(11) The stereochemistry of the diene moiety was confirmed by NOE
experiments, in which irradiation at allylic protons in the ring resulted
in enhancement of vinylic proton (or allylic protons in the side chain
for 3f) signals, as shown in Chart 1.
S0276-7333(97)00704-8 CCC: $14.00 © 1997 American Chemical Society

5390 Organometallics, Vol. 16, No. 25, 1997
Communications
Ta ble 1. Bor ylsta n n yla tive Ca r bocycliza tion of
Diyn esa
rivative 3d . Since recrystallization of crude 3d from
pentane-toluene afforded colorless parallelepipeds (82%,
entry 4), the structure was unequivocally confirmed by
X-ray crystallography.13 As the ORTEP14 drawing
(Figure 1) shows, the structure of the diene moiety of
3d is considerably distorted from planarity, the dihedral
angle between the two π planes being 39°. This distor-
tion is apparently due to the steric repulsion between
the boryl and stannyl groups bound to the diene moiety.
Dipropargyl ether (2e) also underwent borylstannylative
carbocyclization to give the 3,4-dimethylidenetetrahy-
drofuran derivative 3e in 83% yield (entry 5).
The versatility of the present method in the prepara-
tion of various types of dialkylidenecycloalkanes is
further substantiated by the cyclization of the unsym-
metrical diyne 2f with 1 (entry 6). In this case, the boryl
group was selectively introduced to the terminal acety-
lenic bond. The corresponding cyclized product 3f was
isolated in 86% yield without formation of other regio-
and stereoisomers. 1H and 13C NMR spectra and NOE
analysis11 completely agreed with the structure of 3f.
An enyne such as the hept-6-en-1-yne derivative 2g
also undergoes the borylstannylative carbocyclization
with 1 in a completely regioselective fashion. Despite
a
All reactions were carried out in benzene using 1 (1.0 equiv),
2 (1.5 equiv), and Cl2Pd(PPh3)2 (1 mol %) at room temperature.
b
Sn ) SnMe3, B ) BNMeCH2CH2NMe. c Isolated yields based on
borylstannane 1. Yields in parentheses were determined by GC
(entries 1, 2, and 5) or 1H NMR (entry 3). Isolated by recrystal-
d
lization from toluene/pentane.
Ch a r t 1a
the presence of both olefinic and acetylenic bonds in 2g,
the boryl group was introduced exclusively to the
acetylenic bond to give isomerically pure 3g in 82%
yield. Its structure was confirmed by NOE analysis11
as well as 13C NMR spectroscopy, which displayed
signals assignable to methylene and olefinic carbons
bound to tin (18.4 ppm, J Sn-C ) 350 Hz) and boron
(115.3 ppm, broad), respectively.15
The mechanism of the present reaction has not been
investigated in detail; however, on the basis of the regio-
and stereoselectivities observed, it appears reasonable
to assume the catalytic cycle depicted in Scheme 2. The
oxidative addition of the B-Sn bond to a palladium(0)
species, generating the cis-boryl(stannyl)palladium(II)
species 4, was verified by us previously.6 Coordination
of a diyne (or an enyne) to 4 followed by cis insertion of
an acetylenic moiety into the Pd-B bond affords 6. The
a
R ) COOEt.
reaction, indicating that the borylstannylative carbocy-
clization with 1 appears to be more general and selec-
tive. Accordingly, the reaction could be readily appli-
cable to various diynes, as summarized in Table 1. The
reaction of 1,7-octadiyne (2b) with 1 under the same
conditions proceeded smoothly to give the corresponding
1,2-dimethylidenecyclohexane derivative 3b in 74%
yield (entry 2). Surprisingly, even a strained four-mem-
bered ring could be readily formed; a similar procedure
starting with 1,5-hexadiyne (2c) and 1 furnished the 1,2-
dimethylidenecyclobutane derivative 3c in 64% yield
(entry 3).12
Nitrogen- and oxygen-containing 1,6-diynes also ef-
ficiently participated in the palladium-catalyzed boryl-
stannylative carbocyclization, providing a facile route
to 1,2-dimethylidene heterocyclic compounds. For in-
stance, the reaction of N,N-dipropargyltosylamine (2d )
with 1 afforded the 3,4-dimethylidenepyrrolidine de-
(13) X-ray data for 3d : C20H32BN2O2SSn, Mr ) 508.10, colorless
crystal, crystal size 0.55 × 0.40 × 0.20 mm3, triclinic, a ) 9.832(2) Å,
b ) 11.362(3) Å, c ) 11.534(6) Å, R ) 90.68(3)°, â ) 103.04(2)°, γ )
102.19(2)°, V ) 1224.6(7) Å3, space group P1h, Z ) 2, µ(Mo KR) ) 11.454
cm-1, Fcalcd ) 1.38 g/cm3. The 5627 independent reflections (|Fo| >
3σ|Fo|, θ < 27°) were measured on a Mac Science MXC18 diffractometer
using Mo KR radiation and a ω-2θ scan. The structure was solved by
direct methods, and all non-hydrogen atoms were refined anisotropi-
cally by full-matrix least squares to R ) 0.0582, Rw ) 0.0820, and GOF
) 0.856.
(12) Distillation of 3c at 105-110 °C (bath temperature)/3.2 × 10-3
Torr caused deterioration of the product, leading to a significant
decrease of the isolated yield as compared with the 1H NMR yield
(97%).
(14) J ohnson, C. K. ORTEP, a FORTRAN Thermal-Ellipsoid Plot
Program for Crystal Structure Illustrations; Report ORNL-3794; Oak
Ridge National Laboratory: Oak Ridge, TN, 1970.

Communications
Organometallics, Vol. 16, No. 25, 1997 5391
Sch em e 2
F igu r e 1. ORTEP drawing of 3d . Selected bond distances
(Å): C(1)-C(2), 1.332(8); C(2)-C(3), 1.472(7); C(3)-C(4),
1.348(8). Selected torsion angles (deg): Sn-C(1)-C(2)-
C(3), 7.2(5); C(1)-C(2)-C(3)-C(4), 39.1(7); C(2)-C(3)-
C(4)-B, 4.3(6).
In conclusion, the palladium-catalyzed borylstanny-
lative carbocyclization of diyne and enyne compounds
provides a versatile method for synthesizing a variety
of cyclic compounds with high selectivities. Stereo- and
regiochemical control in transition-metal-complex-cata-
lyzed carbocyclizations is apparently one of the most im-
portant subjects in organic synthesis. The chemistry
presented here would give unique and elegant solutions
to these problems. Further studies are under way to
clarify the mechanistic aspects of the reactions of vari-
ous inter-heteroatom bonds with unsaturated organic
compounds and to develop new synthetic methodologies.
preferential insertion into the Pd-B bond rather than
the Pd-Sn bond is strongly supported by the regiose-
lective introduction of the boryl group into the more
reactive terminal acetylene in the reaction of unsym-
metrical diyne 2f and enyne 2g. Subsequent cis inser-
tion of the other acetylenic (or the olefinic) moiety into
the resulting Pd-alkenyl bond and reductive elimina-
tion of 7 give the cyclized product and regenerate the
palladium(0) species (path a). An alternative mecha-
nistic pathway (path b) involving the palladacycle
intermediate 8 cannot be excluded at the moment.
Ack n ow led gm en t. We are grateful to the J apan
Science and Technology Corporation (J ST) for partial
financial support through the CREST (Core Research
for Evolutional Science and Technology) program and
for a postdoctoral fellowship to N.C.
(15) 3g: bp 135 °C/3.7 × 10-3 Torr; IR (neat) 766, 1065, 1098, 1181,
1212, 1243, 1290, 1404, 1437, 1499, 1645, 1734, 2788, 2892, 2980 cm-1
;
1H NMR (C6D6) δ 0.11 (s, J H-Sn ) 52.4 Hz, 9H, SnCH3), 0.92 (t, J )
7.1 Hz, 3H, CH3CH2O), 0.93 (t, J ) 7.1 Hz, 3H, CH3CH2O), 1.02 (dd,
J ) 10.8, 12.9 Hz, J H-Sn ) 56.4 Hz, 1H, CH2Sn), 1.29 (dd, J ) 3.2,
12.9 Hz, J H-Sn ) 56.4 Hz, 1H, CH2Sn), 1.93 (dd, J ) 9.3, 12.4 Hz, 1H,
CH2), 2.58 (s, 6H, NCH3), 2.90-3.13 (m, 6H, NCH2, CH, CH2), 3.25 (d,
J ) 16.2 Hz, 1H, CH2), 3.40 (d, J ) 2.4, 16.2 Hz, 1H, CH2), 3.92-4.00
(m, 4H, CH3CH2O), 5.48 (s, 1H, dCHB); 13C NMR (C6D6) δ -9.6 (J C-Sn
) 318 Hz, SnCH3), 14.0 (CH3CH2O), 18.4 (J C-Sn ) 350 Hz, CH2Sn),
34.4 (NCH3), 41.2 (J C-Sn ) 20 Hz, CH), 43.8 (J C-Sn ) 14 Hz, CH2),
44.3 (CH2), 51.8 (NCH2), 59.2 (C(CO)2), 61.2 (CH3CH2O), 115.3 (broad,
dCHB), 160.4 (J C-Sn ) 56 Hz, Cd), 171.6 (CdO); 119Sn NMR (C6D6) δ
-3.4; 11B NMR δ 31.0 (broad). Anal. Calcd for C20H37BN2O4Sn: C,
48.14; H, 7.47; N, 5.61. Found C, 48.24; H, 7.67; N, 5.50.
Su p p or tin g In for m a tion Ava ila ble: Text giving detailed
experimental procedures and characterization data for 1-(bo-
rylmethylidene)-2-(stannylmethylidene)cycloalkanes 3a -f and
1-(Z)-(borylmethylidene)-2-(stannylmethyl)cycloalkane 3g and
text and tables giving full details of the crystal structure
analysis for 3d (12 pages). Ordering information is given on
any current masthead page.
OM970704Q