Buta-2,3-dienylstannanes, effective reagents for regioselective buta-1,3-dienylation of aldehydes and acetals

Article abstract of DOI:10.1039/a809081e

Two buta-2,3-dienylstannanes, 1-tri-n-butylstannylbuta-2,3-diene and 1-triphenylstannylbuta-2,3-diene, have been prepared and shown to react with aldehydes and acetals under Lewis acid catalyzed conditions producing (buta-1,3-dien-2-yl)methanol derivative

Full text of DOI:10.1039/a809081e

Buta-2,3-dienylstannanes, effective reagents for regioselective
buta-1,3-dienylation of aldehydes and acetals
Meiming Luo, Yoshiharu Iwabuchi and Susumi Hatakeyama*
Faculty of Pharmaceutical Sciences, Nagasaki University, Nagasaki 852-8521, Japan.
E-mail: susumi@net.nagasaki-u.ac.jp
Received (in Cambridge, UK) 20th November 1998, Accepted 11th December 1998
Two buta-2,3-dienylstannanes, 1-tri-n-butylstannylbuta-
2,3-diene and 1-triphenylstannylbuta-2,3-diene, have been
prepared and shown to react with aldehydes and acetals
under Lewis acid catalyzed conditions producing (buta-
1,3-dien-2-yl)methanol derivatives in high yields.
solvent for this reaction, the yield of 3 decreased to 42%,
possibly because of its further protodestannylation giving buta-
1,3-diene. It is important to note that purification of 3 by silica
gel column chromatography caused isomerization to 2-tri-n-
butylstannylbuta-1,3-diene 8. The ratio of 3 and 8 was at best
1:1 under these unsatisfactory conditions and varied depending
upon the amount of silica gel used. This isomerization,
however, could be completely suppressed by use of silica gel
pretreated with Et3N. Compound 3 thus purified was thermally
stable and no isomerization occurred during distillation.
We also investigated the reaction of Ph3SnCl or Bu3SnCl
with the Grignard reagent 96 prepared from chloroprene
(2-chlorobuta-1,3-diene) (Scheme 2). We found that, in the case
of Ph3SnCl, the reaction occurred preferentially at the C4
position to give a 88:12 mixture of 1-triphenylstannylbuta-
2,3-diene 4 and 2-triphenylstannylbuta-1,3-diene 10 in quanti-
tative yield. Recrystallization of this mixture from n-hexane
afforded pure 4 in 73% yield.¶ Interestingly, as previously
reported,7 Bu3SnCl reacted with the Grignard reagent 9 with
complete C2 selectivity to give 2-tri-n-butylstannylbuta-
1,3-diene 8 quantitatively.
Recently, buta-2,3-dienylsilanes 1 (M = SiR3)1,2 and buta-
2,3-dienylboronates 1 [M = B(OR)2],3 have appeared as useful
reagents for the synthesis of (buta-1,3-dien-2-yl)methanol
derivatives 2 from aldehydes and acetals. In addition, we have
demonstrated that these dienols 2 are valuable precursors for the
syntheses of a variety of natural products.1,4 As part of our
interest in developing a catalytic asymmetric reaction of a buta-
2,3-dienylmetal 1 with an aldehyde using a chiral Lewis acid,†
we directed our attention to buta-2,3-dienylstannanes 1 (M =
SnR3) which are unprecedented as synthetic reagents. Here, we
report the first practical syntheses of 1-tri-n-butylstannylbuta-
2,3-diene 3 and 1-triphenylstannylbuta-2,3-diene 4 and their
Lewis acid catalyzed reactions with aldehydes and acetals.
OR' R1
R3
R2
M
SnR3
R
2
4
ClMg
R3Sn
SnR3
•
•
i
R1
•
+
R3
R2
3 R = Bu
4 R = Ph
5 R = Me
2
1
9
R = Bu: 3 (0%)
R = Ph: 4 (88%)
8 (98%)
10 (12%)
Reich and co-workers reported5 that treatment of 1,4-bis-
(trimethylstannyl)but-2-yne with HCl in CDCl3 caused proto-
monodestannylation to give 1-trimethylstannylbuta-2,3-diene
5. However, to the best of our knowledge, the results of this
NMR experiment have not been further examined in detail. This
situation allowed us to examine in detail protomonodestannyl-
ations of 1,4-bis(trialkylstannyl)but-2-ynes as one possible
route to buta-2,3-dienylstannanes (Scheme 1). After many
discouraging results, we eventually found good reaction
conditions wherein large quantities of 1-tri-n-butylstannylbuta-
2,3-diene 3 are obtained with > 95% purity from 1,4-bis(tri-n-
butylstannyl)but-2-yne 7. Thus, treatment of 7, prepared by the
reaction of 1,4-dichlorobut-2-yne 6 with tri-n-butylstannylli-
thium,‡ with concentrated HCl in a 16:1 mixture of Et2O and
THF at 0 °C gave 3 cleanly in 90% yield.§ This HCl-promoted
protomonodestannylation also turned out to proceed in a
reasonable yield (77%) in Et2O although the reaction was rather
sluggish even at room temperature. When THF was used as
Scheme 2 Reagents and conditions: i, Bu3SnCl or Ph3SnCl, THF,
278 °C.
Having developed practical methods for the preparation of
buta-2,3-dienylstannanes 3 and 4, we then investigated their
Lewis acid catalyzed reactions with various aldehydes and
acetals (Scheme 3). Table 1 summarizes Lewis acid catalyzed
additions of 3 and 4 to aldehydes. It is evident that this reaction
has broad applicability for the preparation of 12 (R2 = H) and
BF3·Et2O is the catalyst of choice, except for the two examples
listed in entries 8 and 10. It is also apparent that 3 is much more
reactive than 4 in this reaction. Compound 3 was found to
gradually isomerize to 8 under these conditions, whereas
compound 4 did not undergo such Lewis acid catalyzed
isomerization.
As can be seen from Table 2, both 3 and 4 again reacted with
acetals in good yields. The mixed titanium reagent [3TiCl4·
Ti(OPri)4] was found to give better results than BF3·Et2O,
especially in the cases of aliphatic acetals (entries 1, 2, 10 and
11). Conversely, the reaction of cinnamaldehyde dimethyl
acetal with 3 took place almost quantitatively under BF3·Et2O
i
60%
Cl
Cl
Bu3Sn
SnBu3
OR2
6
7
SnR3
R1
Lewis acid
R1CH=X
Bu3Sn
•
+
SnBu3
ii
•
3 R = Bu
4 R = Ph
11
12
90%
3
8
(R2 = H or Me)
X = O or (OMe)2
Scheme 1 Reagents and conditions: i, Bu3SnLi, THF, 278 °C; ii, conc.
HCl, Et2O–THF, 0 °C.
Scheme 3
Chem. Commun., 1999, 267–268
267

Table 1 Lewis acid catalyzed addition of 3 and 4 to aldehyde 11 (X = O) giving 12 (R2 = H)a
Entry
3 or 4
R1
Lewis acid
Solvent
t/h
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
3
3
3
3
3
3
3
3
3
4
4
3
4
3
4
Ph(CH2)2
Ph(CH2)2
Ph(CH2)2
Ph(CH2)2
Ph(CH2)2
PhCH2
PhCH2
(E)-PhCHNCH
Ph
Ph
Ph
n-C7H15
n-C7H15
c-C6H11
c-C6H11
BF3·Et2O
BF3·Et2O
TiCl4
CH2Cl2
toluene
CH2Cl2
toluene
CH2Cl2
toluene
CH2Cl2
toluene
toluene
CH2Cl2
CH2Cl2
toluene
CH2Cl2
toluene
CH2Cl2
2
9
10
8
4
12
0.3
10
9
10
10
12
23
12
16
57
92
17c
44c
51d
83
64
0e
96
0e
40 (65)f
87
85
90
86
3TiCl4·Ti(OPri)4
MgI2
BF3·Et2O
TiCl4
BF3·Et2O
BF3·Et2O
BF3·Et2O
3TiCl4·Ti(OPri)4
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
a
All reactions were carried out at 278 °C in the indicated solvent (0.13 mol dm23) using buta-2,3-dienylstannane (2 equiv.), aldehyde (1 equiv.), and
Lewis acid (1 equiv.) unless stated otherwise. b Isolated yield. c The aldehyde was partly cyclyzed to indan-1-ol which underwent further reaction to produce
several by-products. d The reaction was carried out at room temperature. e Most of the aldehyde was recovered. f Yield in parenthesis based on the consumed
aldehyde.
Table 2 Lewis acid catalyzed addition of 3 and 4 to acetal 11 (X = (OMe)2) giving 12 (R2 = Me)a
Entry
3 or 4
R1
Lewis acid
Solvent
t/h
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
3
3
3
3
3
3
3
4
4
3
3
4
3
4
Ph(CH2)2
Ph(CH2)2
PhCH2
(E)-PhCHNCH
(E)-PhCHNCH
Ph
Ph
Ph
Ph
n-C7H15
n-C7H15
n-C7H15
c-C6H11
c-C6H11
BF3·Et2O
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
CH2Cl2
toluene
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
12
5
5
10
10
10
4
10
6
9
4
7
4
0c
95
81
99
48
89
89
86
70
0c
3TiCl4·Ti(OPri)4
3TiCl4·Ti(OPri)4
BF3·Et2O
3TiCl4·Ti(OPri)4
BF3·Et2O
3TiCl4·Ti(OPri)4
BF3·Et2O
3TiCl4·Ti(OPri)4
BF3·Et2O
3TiCl4·Ti(OPri)4
3TiCl4·Ti(OPri)4
3TiCl4·Ti(OPri)4
3TiCl4·Ti(OPri)4
86
91
96
89
8
a
Reactions were carried out at 278 °C in the indicated solvent (0.13 mol dm23) using buta-2,3-dienylstannane (3: 2 equiv. 4: 1.2 equiv.), acetal (1
equiv.) and Lewis acid (1 equiv.). b Isolated yield. c Most of the aldehyde was recovered.
catalyzed conditions and 3TiCl4·Ti(OPri)4 produced poor result
in this particular case (entries 4 and 5).
concentrated in vacuo. Purification by column chromatography [SiO2 (30 g)
pretreated with Et3N (30 g); n-hexane] afforded 3 (3.86 g, 90%), bp 150 °C
(0.2 mmHg) (Kugelröhr).
In conclusion, we have successfully synthesized two buta-
2,3-dientylstannanes, 1-tri-n-butylstannylbuta-2,3-diene 3 and
1-triphenylstannylbuta-2,3-diene 4, in > 95% isomeric purity
for the first time. These buta-2,3-dienylstannanes react with
various aldehydes and acetals regioselectively in a 1,3-re-
arrangement fashion to give (buta-1,3-dien-2-yl)methanol de-
rivatives in excellent yields. In comparison with the related
silicon1 and boron reagents,3 buta-2,3-dienylstannanes have the
advantage of broad applicability in buta-1,3-dienylations of
both aldehydes and acetals. The development of a catalytic
asymmetric reaction of buta-2,3-dienylstannanes with alde-
hydes is the focus of current investigations.
¶ Experimental procedure for 4: A flame-dried flask was charged with THF
(30 ml) and Grignard reagent 9 (1.6 mol dm–3 in THF, 12.5 ml, 20 mmol)
under argon and then a solution of Ph3SnCl (7.71 g, 20 mmol) in THF (15
ml) was added dropwise at 278 °C. After being stirred at 278 °C for 30
min, the reaction mixture was quenched with 5% NaOH (10 ml) and
extracted with Et2O. The extract was dried over MgSO4, concentrated in
vacuo, and chromatographed [SiO2 (30 g) pretreated with Et3N (30 g); n-
hexane] to give an 88:12 mixture of 4 and 10 as a colorless viscous oil (8.05
g) which solidified during overnight storage in a refrigerator. Recrystalliza-
tion of this crystalline solid from n-hexane afforded 4 (5.86 g, 73%) as
colorless crystals (mp 54–55 °C).
1 For a review on buta-2,3-dienylsilanes, see: S. Hatakeyama, J. Synth.
Org. Chem. Jpn., 1997, 55, 793.
2 T. Nishiyama, T. Esumi, Y. Iwabuchi, H. Irie and S. Hatakeyama,
Tetrahedron Lett., 1998, 39, 43.
3 B. Zheng and M. Srebnik, J. Org. Chem., 1995, 60, 486; R.
Soundararajan, G. Li and H. C. Brown, J. Org. Chem., 1996, 61, 100; B.
Zheng and M. Srebnik, Synth. Commun., 1996, 26, 393.
4 S. Hatakeyama, M. Yoshida, T. Esumi, Y. Iwabuchi, H. Irie, T.
Kawamoto, H. Yamada and M. Nishizawa, Tetrahedron Lett., 1997, 38,
7887.
5 H. J. Reich, I. L. Reich, K. E. Yelm, J. E. Holladay and D. Gschneidner,
J. Am. Chem. Soc., 1993, 115, 6625.
6 S. Nunomoto and Y. Yamashita, J. Org. Chem., 1979, 44, 4788.
7 E. Wada, S. Kanemasa, I. Fujiwara and O. Tsuge, Bull. Chem. Soc. Jpn.,
1985, 58, 1942; G. S. Bates, M. D. Fryzuk and C. Stone, Can. J. Chem.,
1987, 65, 2612.
This work was supported by the Japan Society for the
Promotion of Science (postdoctoral fellowship for M. L.). We
gratefully acknowledge the Tosoh Corporation (Nanyo Re-
search Laboratory, Japan) for providing chloroprene.
Notes and references
† A catalytic asymmetric version of this process using either buta-
2,3-dienylsilanes or buta-2,3-dienylboronates has not been successfully
achieved yet.
‡ Prepared according to Reich’s method for 1,4-bis(trimethylstannyl)but-
2-yne (ref. 5).
§ Experimental procedure for 3: To a stirred solution of 7 (7.93 g, 12.5
mmol) in Et2O (80 ml) with cooling in an ice bath was added a mixture of
concentrated HCl (1.3 ml) and THF (5 ml). After stirring at 0 °C for 8 h, the
reaction mixture was basified with 5% NaOH (10 ml) and extracted with
Et2O. The extract was washed with water, dried over MgSO4, and
Communication 8/09081E
268
Chem. Commun., 1999, 267–268