Triethylborane-induced radical addition of halogenated compounds to alkenes and alkynes in water

Article abstract of DOI:10.1055/s-1998-1985

Treatment of a mixture of α-iodo-γ-butyrolactone and phenylacetylene in water with a catalytic amount of triethylborane provided the corresponding adduct in good yield via intermolecular radical addition reaction. The triethylborane-mediated radical react

Full text of DOI:10.1055/s-1998-1985

December 1998
SYNLETT
1351
Triethylborane-Induced Radical Addition of Halogenated Compounds to Alkenes and
Alkynes in Water
T. Nakamura, H. Yorimitsu, H. Shinokubo, K. Oshima*
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
Fax: +81-75-761-8846; E-mail: oshima@fm1.kuic.kyoto-u.ac.jp
Received 1 September 1998
Abstract: Treatment of a mixture of α-iodo-γ-butyrolactone and
phenylacetylene in water with a catalytic amount of triethylborane
provided the corresponding adduct in good yield via intermolecular
radical addition reaction. The triethylborane-mediated radical reaction
in aqueous media could be performed under acidic or basic conditions.
Recently, much attention has been paid to free radical reactions for the
1
synthesis of organic molecules. Various organic solvents have been
widely used for the radical reactions. On the other hand, there has been
2
little investigation of the reaction in aqueous solvent. We have reported
that triethylborane-mediated intramolecular radical cyclization reactions
of allyl iodoacetate providing γ-butyrolactone are much more efficient
3
in water than in organic solvents such as benzene or hexane. Here we
report further exploitation of Et B-induced radical reaction in water for
3
the intermolecular addition of halogenated compounds to carbon-carbon
multiple bonds as well as the intramolecular cyclization reaction.
Triethylborane (1.0 M methanol solution (1 M = 1 mol dm–3), 0.1 mL,
0.1 mmol) was added to a mixture of α-iodolactone 1a (212 mg,
1.0 mmol) and phenylacetylene (0.31 g, 3.0 mmol) in water (9 mL) at
25°C under argon atmosphere. The resulting mixture was stirred for 20
h and the product was extracted with ethyl acetate (3 x 20 ml). The
combined organic layers were dried over anhydrous Na SO4 and
2
concentrated in vacuo. Purification of the residual oil by silica gel
4
column chromatography gave an adduct 2 (E/Z = 67/33, 0.29 g) in 94%
yield (Scheme 1). The reaction of trimethylsilylacetylene (5.0 mmol)
with perfluoroalkyl iodide, C6F13I (1.0 mmol) in the presence of a
catalytic amount of Et B (0.2 mmol) in water (9 mL) also gave the
3
corresponding adduct 3 (E/Z = 61/39) in 58% yield along with 2:1
adduct 4 (21%, single isomer, the stereochemistry could not be
determined.) (Scheme 2).
Scheme 1
Scheme 2
We chose three halogenated compounds (1a, 1b, and 1c) and examined
5
the addition reactions of these compounds to a variety of alkenes. The
representative results are shown in Table 1. Several comments are worth
noting. (1) These halogenated compounds easily reacted with terminal
alkenes as well as terminal alkynes to give the corresponding atom
triethylborane gave the corresponding adduct 11 or 14 in 37% or 46%
yield, respectively (Entry 7 and 10). (3) The use of dienes such as diallyl
ether and 2,2-diallyl-1,3-propanediol provided cyclized products 6, 9,
and 13 upon treatment with the halogenated compounds in water in the
presence of a catalytic amount of triethylborane (Entry 2, 5, and 9). (4)
The reactions in water were much more effective compared to the
6
transfer products in good yields. (2) Internal alkenes were less reactive
compared to terminal alkenes in the addition reaction of the halogenated
compounds and provided the adducts in only moderate yields. For
instance, treatment of (E)-4-octene with 1b or 1c in the presence of

1
352
LETTERS
SYNLETT
reactions without solvent. For instance, treatment of a mixture of
a (1.0 mmol) and allyl alcohol (5.0 mmol) with Et B (1.0 M methanol
Fleming, I.; Heathcock, C. H. Eds; Pergamon Press: Oxford,
1991. Vol. 4, Chap. 4.1 p 715; (d) Ryu, I.; Sonoda, N.; Curran, D.
P. Chem. Rev. 1996, 96, 177-194.
1
3
solution, 0.1 mL, 0.1 mmol) without any solvent provided 5 in only 32%
8
yield along with recovered 1a (61%) after 3 days at 25°C. The reaction
(
2) Minisci, F. Synthesis 1973, 1-24; Yamazaki, O.; Togo, H.;
of 1a with 2,2-diallyl-1,3-propanediol without solvent was also less
effective than the reaction in water and gave the desired product 6 in
only 5% along with a complex mixture containing 15 (46%). (5) The
reaction proceeded equally well in aqueous methanol. Thus, treatment
of a mixture of 1a (1.0 mmol) and phenylacetylene (3.0 mmol) in
Nogami, G.; Yokoyama, M. Bull. Chem. Soc. Jpn. 1997, 70, 2519–
2
523.
(
3) Yorimitsu, H.; Nakamura, T.; Shinokubo, H. Oshima, K. J. Org.
Chem. in press.
(
4) 2 (E/Z = 67/33): IR (nujol) 1762, 1449, 1154, 1018, 694 cm–1; 1H
aqueous MeOH (MeOH (9 mL) and H O (3 mL)) with Et B (0.1 mmol)
2
3
NMR (CDCl ) δ 7.30–7.50 (m, 5H), 6.38 (d, 0.67H), 6.02 (d,
afforded 2 in 95% yield.
3
0
.33H), 4.45 (ddd, 0.33H), 4.33 (ddd, 1H), 4.09 (ddd, 0.67H), 3.70
(
ddd, 0.33H), 3.26 (ddd, 0.67H), 2.77 (m, 0.33H), 2.28 (m,
0
6
1
3
.67H), 2.17 (m, 1H); 13C NMR (CDCl ) δ 29.0, 29.5, 42.5, 48.1,
3
6.3, 66.8, 101.1, 110.8, 128.4, 128.5, 128.6 (2C), 128.9, 129.0,
33.1, 136.4, 140.9, 142.2, 176.1, 176.5. Found: C, 45.59; H,
.62%. Calcd for C12H11IO : C, 45.88; H, 3.53%.
2
(5) The reaction of 2-iodopropane with trimethylsilylacetylene gave
an adduct in only 14% yield (E/Z = 94/6) upon treatment with
It is interesting that this Et B-induced radical reaction proceeded in
Et B in water.
3
3
various acidic and basic aqueous solution. The reaction between
(
6) Curran, D. P.; Chang, C. -T. Tetrahedron. Lett. 1987, 28, 2477-
bromotrichloromethane 1b and diallyl ether in 1 M HCl or 1 M NaOH
2
480.
9
afforded the adduct 9 in 71% or 59% yield, respectively. Moreover, the
(
7) 5 (44:56 diastereomer mixture): IR (neat) 3324, 2912, 1753 cm–1
;
reaction took place even in concentrated HCl to give 9 in 38% yield.
The results indicated that triethylborane was fairly stable in these
aqueous solution and acted as a radical initiator in the presence of a
trace amount of oxygen.
1
H NMR (CDCl ) δ 4.74–4.65 (m, 0.44H), 4.46–4.34 (m, 1H),
3
4.31–4.19 (m, 1.56H), 3.92–3.75 (m, 2H), 2.94–2.71 (m, 1.44H),
2
2
3
4
.60–2.42 (m, 1.56H), 2.31–2.21 (m, 0.56H), 2.17–1.81 (m,
.44H); 13C NMR (CDCl ) δ 179.4, 178.2, 68.5, 67.8, 66.7, 66.5,
3
9.6, 39.1, 37.5, 36.8, 36.0 (2C), 29.4, 28.7. Found: C, 30.83; H,
Acknowledgment
.08%. Calcd for C H IO : C, 31.13; H, 4.11%.
7
11
3
This work was supported by Grant-in Aid for Scientific Research on
Priority Areas (No. 283, “Innovative Synthetic Reactions”) from the
Ministry of Education, Sports, and Culture, Government of Japan.
(
8) The reaction proceeded in benzene and gave 5 in 74% yield after
stirring for 30 h. In aqueous methanol (MeOH (5 mL) and H O (5
2
mL)), 5 was obtained in 85% yield after stirring for 7 h.
(
9) Representative experimental procedure: Triethylborane (1.0 M
References and Notes
methanol solution, 0.1 mL, 0.1 mmol) was added to
a
(
1) (a) Curran, D. P.; Porter, N. A.; Giese, B. Stereochemistry of
Radical Reactions; VCH Verlagsgesellschaft mbH.; Weinheim,
heterogeneous solution of 1b (198 mg, 1.0 mmol) and diallyl ether
(0.49 g, 5.0 mmol) in 1 M HCl (10 mL) at 25°C with vigorous
stirring. Extractive work up (ethyl acetate and brine) followed by
purification by silica gel column chromatography gave 9 (0.22 g)
in 71% yield.
1996; (b) Giese, B.; Kopping, B.; Göbel, T.; Dickhaut, J.; Thoma,
G.; Kulicke, K. J.; Trach, F. Org. React. 1996, 48, 301-856; (c)
Curran, D. P. in Comprehensive Organic Synthesis; Trost, B. M.;