3224
J . Org. Chem. 1996, 61, 3224-3225
Communications
Ta ble 1. Hyd r obor a tion of Olefin s w ith Ca tech olbor a n e
Hyd r obor a tion of Olefin s w ith
in th e P r esen ce of N,N-Dim eth yla ceta m id ea (Eq 1)
Ca tech olbor a n e a t Room Tem p er a tu r e in
th e P r esen ce of N,N-Dim eth yla ceta m id e
Christine E. Garrett and Gregory C. Fu*
Department of Chemistry, Massachusetts Institute of
Technology, Cambridge, Massachusetts 02139
Received February 27, 1996
In comparison with boron hydrides such as BH3-THF
or 9-BBN,1 catecholborane (CB) is much less reactive
toward olefins, typically requiring elevated temperatures
(70-100 °C) for addition.2,3 During the past decade, a
number of catalysts for the hydroboration of olefins with
catecholborane have been reported. Virtually all of the
work has focused on transition metal- and lanthanide
metal-based systems,4-6 due in part to their potential for
effecting enantioselective catalysis.5,7 In this paper, we
report that hydroboration of mono-, di-, tri-, and tetra-
substituted olefins proceeds efficiently at room temper-
ature upon treatment with catecholborane in the pres-
ence of 10-20 mol % N,N-dimethylacetamide (eq 1).
a
Amount of N,N-dimethylacetamide used: entries 1-4, 10 mol
b
%; entries 5-6, 20 mol %. Less than 3% of any other isomer is
observed, except for entry 1 (94:6, primary:secondary) and entry
2 (85:15, primary:secondary). c Average of two runs. The modest
d
yield may be due in part to the volatility of the product alcohol.
(Table 1, entry 1, 94:6;12 entry 2, 85:15), with regioselec-
tivity similar to that observed with BH3-THF (94:6 and
80:20, respectively1). Reactions of 1,1-disubstituted (Table
1, entry 3), 1,2-disubstituted (Table 1, entry 4), trisub-
stituted (Table 1, entry 5), and tetrasubstituted (entry
6) olefins also proceed cleanly under the standard condi-
tions. The stereochemistry of the product illustrated in
entry 6 (Table 1) establishes that the boron hydride adds
in a cis fashion to the olefin.
Reaction of an olefin with catecholborane (2 equiv) and
N,N-dimethylacetamide (10-20 mol %) in CH2Cl2 for 3
h at room temperature, followed by an oxidative workup,
provides the desired alcohol in good yield (Table 1).8-11
The hydroborations of alkyl- and aryl-substituted termi-
nal olefins afford the primary alcohols preferentially
In two instances, we have isolated B-alkylboronic
esters from the unoxidized reaction mixtures (eqs 2 and
3).13 11B NMR spectroscopy reveals that a significant
(1) For leading references, see: (a) Pelter, A.; Smith, K.; Brown, H.
C. Borane Reagents; Academic: New York, 1988. (b) Brown, H. C.
Hydroboration; W. A. Benjamin: New York, 1962.
(2) Brown, H. C.; Gupta, S. K. J . Am. Chem. Soc. 1975, 97, 5249-
5255.
(3) For overviews of the chemistry of catecholborane, including
synthetic applications of B-alkylboronic esters, see: (a) Lane, C. F.;
Kabalka, G. W. Tetrahedron 1976, 32, 981-990. (b) Kabalka, G. W.
Org. Prep. Proc. Int. 1977, 9, 131-147. (c) Brown, H. C.; Chan-
drasekharan, J . J . Org. Chem. 1983, 48, 5080-5082. (d) VanNieu-
wenhze, M. S. In Encyclopedia of Reagents for Organic Synthesis;
Paquette, L. A., Ed.; Wiley: New York, 1995.
(4) Ma¨nnig, D.; No¨th, H. Angew. Chem., Int. Ed. Engl. 1985, 24,
878-879.
(5) For reviews, see: (a) Fu, G. C.; Evans, D. A.; Muci, A. R. In
Advances in Catalytic Processes; Doyle, M. P., Ed.; J AI: Greenwich,
CT, 1995; Vol. 1, pp 95-121. (b) Burgess, K.; Ohlmeyer, M. J . Chem.
Rev. 1991, 91, 1179-1191.
(8) Representative experimental procedure (Table 1, entry 1):
1-Dodecene (228 µL, 1.03 mmol), N,N-dimethylacetamide (9.4 µL, 0.10
mmol), and CH2Cl2 (0.68 mL) were added sequentially to a reaction
vessel. The resulting solution was cooled to 0 °C, and catecholborane
(220 µL, 2.06 mmol) was added dropwise (bubbling observed). Following
completion of the addition of catecholborane, the reaction mixture was
allowed to warm to room temperature and stirred for 3 h. It was then
cooled to 0 °C, and 1:1 THF:EtOH (2 mL), 2 N NaOH (2 mL), and 30%
H2O2 (2 mL) were added. The reaction mixture was allowed to warm
to room temperature and stirred for 2 h. It was then extracted (Et2O/1
N NaOH), the organic layer was dried, and the solvent was removed
in vacuo. Flash chromatography afforded 0.184 g (96%) of 1- and
2-dodecanol in a 94:6 ratio (GC).
(6) A notable exception to this generalization is the observation by
Arase that the presence of 10 mol % lithium borohydride facilitates
the hydroboration of olefins with catecholborane: Arase, A.; Nunokawa,
Y.; Masuda, Y.; Hoshi, M. J . Chem. Soc., Chem. Commun. 1991, 205-
206. The structure of the preoxidation product of the olefin hydro-
boration reaction (e.g., B-alkylboronic ester or trialkylborane) was not
determined (no mechanistic studies of this system have been de-
scribed). The regioselectivities reported by Arase for the hydroboration
of 1-hexene and of styrene (94:6 and 85:15 (primary:secondary),
respectively) are similar to those reported for BH3-THF (94:6 and 80:
20 (primary:secondary), respectively (ref 1)). We have found that
treatment of 0.1 equiv of LiBH4 with catecholborane (THF, room
temperature, 5 min) results in the complete consumption of LiBH4 and
in the clean formation of BH3-THF and Li(B(C6H4O2)2) in a 2:1 ratio
(cf. Ma¨nnig, D.; No¨th, H. J . Chem. Soc., Dalton Trans. 1985, 1689-
1692). Subsequent addition of 1-dodecene leads to the generation of
tri(n-dodecyl)borane.
(9) All reactions were conducted under an inert atmosphere with
purified reagents (see the supporting information). However, in
preliminary experiments we have found that the hydroboration of
1-dodecene proceeds equally smoothly when the reaction is run open
to the air with unpurified reagents.
(10) Control experiments for each reaction establish that <10%
conversion is observed in the absence of N,N-dimethylacetamide under
otherwise identical conditions.
(11) Although we have not yet conducted a comprehensive screening
of common Lewis-basic functional groups, we have determined that
the hydroboration of olefins with catecholborane is facilitated by
secondary amides and tertiary amines, but not by simple ethers. We
suspect in general that extremely weak and extremely strong Lewis
bases will not accelerate the hydroboration of olefins with catecholbo-
rane. In the context of a report that secondary amides direct iridium-
catalyzed hydroboration reactions with catecholborane (Evans, D. A.;
Fu, G. C. J . Am. Chem. Soc. 1991, 113, 4042-4043), it is important to
note that we have found that the hydroboration of 4-(N-(phenylmethyl)-
carboxamido)cyclohexene is not directed by the amide in the absence
of [Ir(cod)(PCy3)(py)]PF6.
(7) For early work, see: (a) Burgess, K.; Ohlmeyer, M. J . J . Org.
Chem. 1988, 53, 5178-5179. (b) Hayashi, T.; Matsumoto, Y.; Ito, Y. J .
Am. Chem. Soc. 1989, 111, 3426-3428.
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