5364 J . Org. Chem., Vol. 66, No. 16, 2001
Kanth and Brown
All the olefins were also commercial products. Diborane was
generated using the reported procedure.10
contents were further stirred at 10 °C for another 1 h, by which
time the 11B NMR examination of the reaction mixture showed
the clean formation of dioxane-BHCl2 (+8.2, doublet, >98%)
and the disappearance of the peak due to dioxane-BCl3
(+11.7, singlet).
Among the other Lewis bases selected, monoglyme and
â-chloroethyl ether gave pure (>97%) dichloroborane adducts.
However, they required excess diborane gas to shift the
equilibrium in favor of the dichloroborane adduct. The results
are listed in Table 1.
P r ep a r a t ion of t h e Bor on Tr ich lor id e Ad d u ct s. The
procedure followed for all of the Lewis bases is same and
procedure used for dioxane is representative. Two procedures
were followed for the preparation of these boron trichloride
adducts.
(a ) By th e Rea ction of BCl3 Ga s w ith Dioxa n e. An oven-
dried marked centrifuge tube having a septum inlet was cooled
to -75 °C under nitrogen, and boron trichloride gas (11.72 g,
100 mmol) was condensed into this. An oven-dried 100 mL
round-bottom flask provided with stirring bar, septum inlet,
gas inlet, and a condenser whose end was connected to a
mercury bubbler was cooled to 10 °C under nitrogen. The flask
was charged with dioxane (8.81 g, 100 mmol) and boron
trichloride gas, earlier condensed into a marked centrifuge
tube was slowly passed in. (Caution! Exothermic reaction and
rapid passing can result in the formation of charred com-
pounds). The reaction of boron trichloride with the selected
Lewis bases is instantaneous, and the boron trichloride adduct
is formed as soon as the addition is complete. The reaction of
boron trichloride with dioxane results in the quantitative
formation of the dioxane-BCl3 adduct, melting point 35-38
°C with decomposition. The purity was confirmed using 11B
NMR examination. 11B NMR (in dichloromethane): +11.3 ppm
(singlet).
(b) By th e Rea ction of BCl3 in Dich lor om eth a n e w ith
Dioxa n e. An oven-dried marked centrifuge tube provided with
a septum inlet was cooled to -75 °C under nitrogen. Boron
trichloride gas (11.72 g, 100 mmol) was condensed into the
tube and dry dichloromethane (20 mL) was added. To this
solution dioxane (8.81 g, 100 mmol) was added slowly during
30 min, and the contents were slowly brought to 0 °C.
Pumping-off the volatile dichloromethane at that temperature
provided a white solid of dioxane-BCl3.
The dioxane-BCl3 thus obtained is stable for several hours
at 0 °C. The stability details for other boron trichloride adducts
are listed in Table 1. However, it was observed that it is
desirable to prepare the BCl3 adducts and to use them
immediately for further reactions.
P r ep a r a tion of Mon och lor obor a n e Ad d u cts. The pro-
cedure followed for dioxane, monoglyme, ethyl acetate, and
â-chloroethyl ether is similar, and the procedure used for
dioxane is representative.
An oven-dried 100 mL round-bottom flask provided with
stirring bar, septum inlet, gas inlet, a condenser whose end
was connected to a mercury bubbler was cooled to 10 °C under
dry nitrogen. The flask was charged with dioxane-BCl3 (21.33
g, 100 mmol) in dioxane (19.38 g, 220 mmol). The diborane
gas (110 mmol) was bubbled slowly into the dioxane-BCl3 and
dioxane through a sintered tip gas bubbler during 3 h (a rate
at which most of the diborane gas is absorbed). The contents
were further stirred at 10 °C for another 1 h, by which time
the 11B NMR examination of the reaction mixture showed
clean formation of dioxane-BH2Cl (+7.9, triplet, 97%) and
disappearance of the peak due to dioxane-BCl3 (+11.8,
singlet).
Among the other Lewis bases selected, only monoglyme gave
reasonably pure (80%) monochloroborane adduct (containing
20% dichloroborane adduct). The results are listed in Table 1.
P r ep a r a tion of Dich lor obor a n e Ad d u cts. The procedure
followed for dioxane, monoglyme, ethyl acetate, and â-chloro-
ethyl ether is similar, and the procedure used for dioxane is
representative.
P r ep a r a tion of Dioxa n e-BH2Cl, by th e Rea ction of
Sod iu m Bor oh yd r id e w ith Dioxa n e-BCl3. An oven-dried
100 mL round-bottom flask provided with stirring bar and
septum inlet was cooled to 10 °C under dry nitrogen. The flask
was charged with sodium borohydride (7.92 g, 220 mmol). To
this was added dioxane-BCl3 (42.67 g, 200 mmol) in dioxane
(19.38 g, 220 mmol), and the contents were stirred for 10 min.
Triglyme (1.5 mL, 9 mmol, 3% volume) was added to the
reaction mixture, and the contents were further stirred at room
temperature for 36 h. The contents were allowed to settle (can
be centrifuged for quantitative precipitation of the sodium
chloride formed) and the clear supernatant solution decanted
under nitrogen. The 11B NMR examination showed clean
formation of dioxane-BH2Cl (+7.8, triplet, 97%).
P r ep a r a tion of Dioxa n e-BHCl2, by th e Rea ction of
Sod iu m Bor oh yd r id e w ith Dioxa n e-BCl3. An oven-dried
100 mL round-bottom flask provided with stirring bar and
septum inlet was cooled to 10 °C under dry nitrogen. The flask
was charged with dioxane-BCl3 (64.00 g, 300 mmol) in dioxane
(9.69 g, 110 mmol). To this was added sodium borohydride
(3.96 g, 110 mmol), and the contents were stirred for 10 min.
Triglyme (1.5 mL, 9 mmol, 3% volume) was added to the
reaction mixture, and the contents were further stirred at room
temperature for 36 h. The contents were allowed to settle (can
be centrifuged for quantitative precipitation of the sodium
chloride formed) and the clear supernatant solution decanted
under nitrogen. The 11B NMR examination showed the clean
formation of dioxane-BHCl2 (+8.2, doublet, >98%).
Hyd r obor a tion of Rep r esen ta tive Olefin s Usin g Di-
oxa n e-BH2Cl. Hydroboration of representative olefins, such
as 1-octene, 1-decene, styrene, R-methylstyrene, 2-methyl-1-
pentene, cis-4-methyl-2-pentene, 2-methyl-2-butene, â-pinene,
cyclohexene, R-pinene, 3-carene, 1-phenyl-2-methyl-1-propene,
2,3-dimethyl-2-butene, and 1,2-dimethylcyclopentene, with
dioxane-BH2Cl was carried out in dioxane and dichloro-
methane solvents. The procedure followed for all the olefins
in both the solvents are same. The procedure followed for
1-decene in dichloromethane is representative.
An oven-dried 50 mL round-bottom flask provided with a
septum inlet and stirring bar was cooled to 0 °C under
nitrogen. The flask was charged with dioxane-BH2Cl in
dichloromethane (8.7 mL, 5 mmol). To this was added 1-decene
(1.4 g, 10 mmol). The final solution is 0.5 M in BH2Cl and 1.0
M in 1-decene. The contents were further stirred at room
temperature. The course of reaction was followed by 11B NMR
and hydride analysis of residual active hydride. Both of these
studies showed the completion of the reaction after 15 min.
11B NMR after 15 min: +75 (broad singlet), +52 (singlet, after
methanolysis) and hydride analysis showed no active hydride
after 15 min.
The reaction mixture was treated with slow addition of
water followed by the addition of sodium hydroxide (7.0 mL,
3 M, 21 mmol). Methanol (3.0 mL) was added followed by the
slow addition of hydrogen peroxide (6 mmol), and the contents
were further stirred at room temperature (3 h) and 40 °C (1
h) to ensure complete oxidation. The organic compound was
extracted into diethyl ether. Drying and evaporation of the
solvent provided essentially pure 1-decanol in 98% (by GC):
isolated 1.48 g, 95% yield. The GC analysis did not show the
presence of 2-decanol. These results are summarized in Table
3.
An oven-dried 100 mL round-bottom flask provided with
stirring bar, septum inlet, gas inlet, and a condenser, whose
end was connected to a mercury bubbler, was cooled to 10 °C
under dry nitrogen. The flask was charged with dioxane-BCl3
(42.67 g, 200 mmol) in dioxane (9.67 g, 110 mmol). The
diborane gas (55 mmol) was bubbled slowly into dioxane-BCl3
and dioxane through a sintered tip gas bubbler during 2 h (a
rate at which most of the diborane gas is absorbed). The
Hyd r obor a tion of Rep r esen ta tive Olefin s Usin g Di-
oxa n e-BHCl2. Hydroboration studies of representative ole-
fins such as 1-octene, 1-decene, 2-methyl-1-butene, â-pinene,
methylenecyclopentane, cis-4-methyl-2-pentene, cyclohexene,
(10) Kanth, J . V. B.; Brown, H. C. Inorg. Chem. 2000, 39, 1795.