For the interpretation of these results, we considered the
following mechanism for the present reaction. Theoretically
arylselenenic acids 3 can react with alkenes to afford b-
hydroxyalkyl aryl selenides,6 but these acids 3 are thermally
unstable and readily undergo disproportionation into 4 and 5.
This disproportionation appears to suffer much inhibition in the
supercage of zeolite NaY. Thus 2 and 3 recombine to 6 or 7 with
the participation of RAOH (H2O or MeOH, respectively).
Control experiments for the formation of 6a were carried out.
(The petroleum ether used in control experiments was pre-dried
over 4A zeolite.) (i) Dried NaY loaded with 1a was heated at
70 ~ 75 °C for 8 h under N2 (99.999%) and gave no 6a;
1-dodecene and diphenyl diselenide were obtained as main
products. (ii) Heating dried NaY loaded with 1a at 70 ~ 75 °C
under dried air also afforded no 6a. The main products were the
same as for (i) and the color of the powder NaY turned to
slightly pink from white. (iii) Heating dried NaY loaded with 1a
at 70 ~ 75 °C under wet N2 afforded 6a. ( iv) Grinding dried
NaY, loaded with one of selenoxides 1a–1d, with several drops
of dry methanol, followed by standing overnight under N2 and
then heating at 70 ~ 75 °C under N2 afforded 7a–7d, re-
spectively (Table 1). These experiments support that 6a was not
formed by the direct addition of ArSeOH 3 to the alkene 2, but
by the participation of water.
Since the supercages are highly polar and possess strong
electric fields,7 the above interpretation can be understood by a
mechanism involving carbonium ion 8 (Scheme 2).9 In the
supercage of NaY, selenoxides undergo fragmentation into
alkenes and ArSeOH. Arylselenenic acids (ArSeOH 3) are
stable because sterically they cannot contact each other in the
supercages. The stabilized ArSeOH ionises into ArSe+ and
2OH when it is heated. It is conceivable that the hydroxide
anions move to relatively positive electric field and the ArSe+
move to relatively negative field. This results in separation
between the hydroxide anions and the ArSe+. On the other hand,
hydroxide anions may coordinate with Na+ into NaOH (or ion
pair) because Na+ is a hard acid and 2OH is a hard base,
whereas the ArSe+ tends to coordinate with oxygen atoms of the
zeolite framework because ArSe+ is a relatively soft cation. The
coordination immobilizes 2OH because the sodium cations are
located on relatively fixed sites in the supercage of NaY, and
almost immovable when water is absent.2 Thus 2OH is
obstructed from attacking the carbonium ion 8 produced by the
attack of ArSe+ to an alkene upon heating. Namely, only neutral
nucleophilic reagents such as water and methanol could move
relatively freely in supercages under those conditions, so b-
hydroxyselenides could not be obtained in the absence of water.
In fact, to the best of our knowledge, organic reactions between
anions and cations in the supercages of zeolites are seldom
found in literature. This fact may be another support to the
proposed mechanism.
from the lack of space in the supercage for formation of the
more bulky 9, the steric hindrance of substituent R, the role of
NaY in stabilizing charges and the absence of solvent.
The methanol participating reactions (Entries 8–11 in Table
1) had low yields because the molecule size of methanol is
larger than that of water and methanol has more difficulties in
going into the supercages. Further investigation indicated that
ethanol and n-butanol could participate in the thermal reactions
of 1a within NaY and gave considerably decreasing yields (9%
and a trace respectively) of corresponding b-alkoxyselenides
with the increase of the size of the alkanols. However
2-propanol could not be adsorbed into the supercages of the
NaY to form b-2-propoxyselenide. All these results revealed
that the valid diameter of entrance considerably diminished
after the adsorption of 1a to NaY.
In conclusion, in addition to the establishment of a new
procedure for preparing b-hydroxyselenides 6 and b-methox-
yselenides 7 from alkyl aryl selenoxides 1 by utilizing zeolite
NaY as a microreactor, the possible generalities, that zeolite
NaY is able to stabilise reactive intermediates and to separate
the small inorganic anions from organic cations in organic
reactions in the supercages, were disclosed.
The authors thank the National Natural Science Foundation
of China (No. 20072018) for financial support.
Notes and references
† The structures of four new compounds are determined by the spectra and
element analytical data. 6b: white plates, Mp.28–29 °C IR(KBr): 3377
cm21 (OH). 1H NMR (200 MHz, CDCl3): d 7.41 (d, 2H, 3J = 7.9 Hz), 7.06
(d, 2H, 3J = 7.9 Hz), 3.60 (m, 1H), 3.05 (q, 1H, 2 JAB = 13.1 Hz, 3JAC
=
2
3
4.3), 2.85 (q, 1H, JAB = 13.1 Hz, JBC = 8.7 Hz), 2.41 (s, 1H), 2.30 (s,
3H), 1.50–1.10 (m, 18H), 0.86 (t, 3H, 3J = 6.4 Hz). Anal. Calcd. for
C19H32OSe (355): C, 64.22; H, 9.01. Found: C, 64.13; H, 9.00. 6e: yellow
oil. IR(KBr): 3420 cm21 (OH). 1H NMR (200 MHz, CDCl3): d 7.40 (d, 2H,
3J = 7.9 Hz), 7.05 (d, 2H, 3J = 7.9 Hz), 3.60 (m, 1H), 3.18 ~ 2.73 (m, 2H),
2.30 (s, 3H), 1.51 ~ 1.18 (m, 10H), 0.87 (t, 3H, 3J = 6.8 Hz). Anal. Calcd.
for C15H24OSe (299): C, 60.20; H, 8.03. Found: C, 60.24; H, 8.07%. 7a:
yellow oil. 1H NMR (200 MHz, CDCl3): d 7.50 ~ 7.21(m, 5H), 3.57 ~ 3.44
(m, 1H), 3.31 (s,3H),3.15 ~ 2.85 (m, 2H), 1.65 ~ 1.13 (m, 18H), 0.86 (t, 3H,
3J = 6.8 Hz). Anal. Calcd. for C19H32OSe (355): C,64.23; H,9.01. Found:
C,64.17; H,9.06%. 7b: yellow oil. 7.41 (d, 2H, 3J = 7.9 Hz), 7.05 (d, 2H),
3.40 ~ 3.53 (m, 1H), 3.13 ~ 2.87 (m, 2H), 2.30 (s, 3H), 1.65 ~ 1.13 (m, 18H),
0.86 (t, 3H, 3J = 6.8 Hz). Anal. Calcd. for C20H34OSe (365): C, 65.04; H,
9.21. Found: C, 65.02; H, 9.18%.
We believe that carbonium ion 8 instead of seleniranium 9
suggested by J. Remion10 was involved in the final step because
the reactions gave only one of the two possible regioisomers
exclusively. Similar high regioselectivity was also observed in
the presence of MgSO4.6 The priority of 8 over 9 may result
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6 K. B. Sharpless and T. Hori, J. Org. Chem., 1978, 43, 1689.
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82, 1953.
8 M. R. Detty, J. Org. Chem., 1980, 45, 274.
9 K. Pitchumani, A. Joy, N. Prevost and V. Ramamurthy, Chem.
Commun., 1997, 127.
10 J. Remion and A. Krief, Tetrahedron Lett., 1976, 3743.
11 D. L. J. Clive, J. Chem. Soc., Chem. Commun., 1974, 100.
12 M. R. Detty, Tetrahedron Lett., 1978, 5087.
13 A. Toshimitsu, T. Aoai, S. Uemura and M. Okano, J. Org. Chem., 1980,
45, 1953.
Scheme 2 A possible mechanism of the formation of 6 and 7 from 2 and 3
by the participation of RAOH in the supercage of NaY.
CHEM. COMMUN., 2003, 498–499
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