1072
L. Tian, G.-Y. Xu, Y. Ye and L.-Z. Liu
Vol. 40
b
c
to H and H is almost 90°, hence coupling is not observed
b
c
between H and H .
To further ascertain the configuration of 4, a single-crys-
tal X-ray diffraction study was performed on 4a. The crys-
tal was grown from toluene and petroleum ether (1:2), and
is shown in Figure 1. Crystallographic analysis shows that
the nitrile oxide carbon is bonded to the unsaturated car-
bon connected to the –SO group, while the oxygen of
3
nitrile oxide is bonded to the other unsaturated carbon of
the sultone. This shows that the cycloaddition reaction
between substituted benzonitrile oxide and prop-1-ene-1,3
sultone 1 takes place with high regioselectivity. The prod-
ucts are consistent with the regiochemistry reported for
cycloaddition of benzonitrile oxides to α,β-unsaturated
lactones [9]. This cis-stereospecificity and regiospecificity
is best explained by a concerted process [9].
Selected bond distance (Å) and angles (°): C(6)–C(7) =1.454(4), C(7)-
C(8) =1.512(4), C(8)-C(9) =1.523(5), C(9)-C(10) = 1.501(5), C(7)-
N(1) =1.280(4), N(1)-O(1) =1.401(3), O(1)-C(9) =1.459(4), C(8)-
S(1) =1.804(3), S(1)-O(2) =1.577(3), O(2)-C(10) =1.458(5); C(6)-C(7)-
C(8) =126.2(3), C(7)-C(8)-C(9) =102.1(3), C(8)-C(9)-C(10) =109.2(3),
C(6)-C(7)-N(1) =121.2(3), N(1)-O(1)-C(9) =110.1(2), C(9)-C(8)-
S(1) =103.8(2), C(7)-C(8)-S(1)=112.5(2)
EXPERIMENTAL
Melting points were determined with a Thomas-Hoover melt-
ing-point apparatus. IR spectra were recorded on a Bruker
Figure 1. X-ray structure of compound 4a.
1
EQUINOX55 spectrometer. H NMR spectra were determined
Scheme 2
13
with a Bruker AC-P200 in CDCl . C NMR were determined
3
with a Bruker AC-P200 in (CD ) CO solution. Elemental
3 2
Analyses were performed on Yanaco Chn Cor Der MF-3 appara-
tus. X-ray reflection from compound 4a was measured on the
Bruker Smart 1000 single-crystal diffractometer.
Various substituted benzonitrile oxides 3 have been widely
employed as 1,3-dipoles. There are several methods for their
preparation, dehydrohalogenation of the corresponding hydrox-
imic acid halide with base is the more usual method [10,6].
Cycloaddtion reactions were carried out at room temperature
with an excess of dipole 3(a-l) generated “in situ” with triethy-
lamine from chloro-benzaldoxime [6].
Confirmation of the Cycloaddition Direction.
The reaction of 1 with nitrile oxides afforded only one
regioisomeric adduct (structure 4, not structure 4’ in
Scheme 3). The structural assignment of the cycloadducts
4 was corroborated using proton nmr data. The H NMR
spectra of 4 showed that the chemical shift of H , which
Preparation of Prop-1-ene-1,3-sultone.
1
Among numerous synthetic methods [1,11-12], two routes
attracted our attention. Of those, we repeated and improved on
two methods (A and B).
b
appeared as double doublet, resonates farther down field
a
b
than that of H . This shows that the carbon bonded to H is
connected to the oxygen atom of the nitrile oxide (struc-
ture 4 in Scheme 3). Owing to paramagnetic shift caused
by the adjacent oxygen atom, the resonance corresponding
Method A [1].
To a boiling solution of allyl chloride (20 g, 261 mmol) in 95%
EtOH (100 mL) and H O (50 mL) was added dropwise a solution
2
of Na SO (15.75 g, 125 mmol, in 60 mL of H O). The mixture
2
3
2
b
a
to H appears at a lower field than that of H . All of the
was then allowed to continue refluxing for 4 h. The solvent was
removed on a rotary evaporator, and the residue was dried in
vacuo. The crude products were purified by recrystallization with
95% EtOH, resulting in 13.5 g of sodium prop-2-ene sulfonate
(yield 75%); mp 239-241 °C. To a solution of sodium prop-2-ene
cycloadducts show large J values (8.69-9.35 Hz) consis-
ab
tent with their cis-orientation [7,8]. No exception to the
rigid cis-stereospecificity of the addition was observed.
The dihedral angle between the C-H bonds corresponding
sulfonate (5.5 g, 38.19 mmol) in water (22 mL) was added Br
2
(2.06 mL) dropwise. The solution was then stirred for 2 h at r.t. A
very little amount of Na SO was added to decompose the excess
Scheme 3
2
3
Br . The solvent was then removed in vacuo to furnish the white
2
solid dibromosulfonate quantitatively. Without purification, the
dibromosulfonate was treated with conc. HCl (22 mL) by stirring
at r.t. for one day to give the 2,3-dibromopropane-1-sulfonic
acid. Without further purification, the sulfonic acid was subjected
to heating at 150-160 °C under reduced pressure followed by