Direct preparation and structure determination of tertiary and secondary amine boranes from primary or secondary amine boranes

Article abstract of DOI:10.1016/j.jorganchem.2005.01.059

New secondary and tertiary amine borane derivatives were prepared in a one-pot reaction starting from primary amine boranes. The reaction involves treatment of an amine borane with 2 equivalents of s-BuLi at -78 °C. In general, mixtures of mono and di metallated products were obtained. Alkyl iodides and benzyl chloride reacted with the lithiated amine, but aldehydes and ketones were reduced. Conversion was high as determined by NMR, but moderate to low yields were obtained after chromatography, possibly due to decomposition on silica. Crystal structures were obtained for the compounds 3a, 3b and 3c.

Full text of DOI:10.1016/j.jorganchem.2005.01.059

Journal of Organometallic Chemistry 690 (2005) 2180–2185
www.elsevier.com/locate/jorganchem
Direct preparation and structure determination of tertiary
and secondary amine boranes from primary or secondary
amine boranes
a
Amal Shibli , Hijazi Abu Ali , Israel Goldberg , Morris Srebnik
a
b
a,
*
a
Department of Natural Products and Medicinal Chemistry, School of Pharmacy, Hebrew University in Jerusalem, Jerusalem 91120, Israel
b
School of Chemistry, Sackler Faculty of Exact Science, Tel-Aviv University, Ramat-Aviv, Israel
Received 19 October 2004; accepted 28 January 2005
Available online 14 April 2005
Abstract
New secondary and tertiary amine borane derivatives were prepared in a one-pot reaction starting from primary amine boranes.
The reaction involves treatment of an amine borane with 2 equivalents of s-BuLi at ꢀ78 ꢀC. In general, mixtures of mono and di
metallated products were obtained. Alkyl iodides and benzyl chloride reacted with the lithiated amine, but aldehydes and ketones
were reduced. Conversion was high as determined by NMR, but moderate to low yields were obtained after chromatography, pos-
sibly due to decomposition on silica. Crystal structures were obtained for the compounds 3a, 3b and 3c.
ꢁ 2005 Elsevier B.V. All rights reserved.
Keywords: Sec-amine borane; tert-amine borane; N-deprotonation; X-ray structures
1. Introduction
amine borane complexes introduced a new route in
preparation of new amine borane derivatives which in
turn were converted to the free amines in ethanolic
acidic conditions. In a recent review on the previously
published work in this field [20], no methods were re-
ported for the preparation of tertiary amine boranes di-
rectly from primary amine boranes by reaction with
simple alkyl or benzyl halides. In this work, we report
a new direct method for the synthesis of secondary
and tertiary amine boranes starting from primary amine
boranes, using N-deprotonation. In some cases crystals
were obtained for some compounds and their structures
were determined by X-ray diffraction.
Deprotonation of tertiary [1] and secondary [2] amine
boranes is a well known method used to prepare valu-
able intermediates in organic synthesis [3]. Various
applications of such compounds were published in the
literature such as their use in aqueous reduction of alde-
hydes and ketones [4], reductive amination [5], olefin
hydroboration [6] and amide reduction [7]. They are also
widely used in palladium catalyzed systems [8–10], as
well as chiral transfer reagents [11], as activators for a-
deprotonation of tertiary amines [2e,12], and as protec-
tive groups against nitrogen lone pair oxidation [13].
Boron complexation facilitates N-deprotonation due to
the covalent attachment to the nitrogen atom of the
amine [14–16]. Because of the contrasting regiochem-
istry in metallation of these compounds, the use of
2. Results and discussion
2.1. Syntheses
*
Treatment of a primary or secondary amine borane 1
with 2 equivalents of s-BuLi in THF at ꢀ78 ꢀC then
Corresponding author. Tel.: +972 2 675 7301; fax: +972 2 675 8201.
E-mail address: msrebni@md.huji.ac.il (M. Srebnik).
0022-328X/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.01.059

A. Shibli et al. / Journal of Organometallic Chemistry 690 (2005) 2180–2185
2181
R
R
R1
R2
R1
R2
R1
R
1) s-BuLi
NH
N
+
N
2) RX
BH3
BH3
2
BH3
1
3
Scheme 1. Substitution of amine borane complexes 1 via metallation.
warmed to room temperature, followed by cooling to
ꢀ78 ꢀC and addition of an alkyl iodide or benzyl halide
gave two products, the mono alkylated 2 and the double
alkylated 3 adducts (Scheme 1). The need to use excess
of s-BuLi was necessary because using fewer than two
equivalents resulted in a complex reaction, with recovery
of unreacted starting material. We suspect that it may be
due to the known instability of organolithium reagents
in THF [17]. It is also possible that some limited destruc-
tion of the borane complexes occurred by nucleophilic
attack of s-BuLi resulting in partial consumption of
the base. It is also suspected that this may be partially
due to the high affinity of these complexes for water.
n-BuLi was ineffective [12,16], and led to a very complex
reaction mixture and low yields. Using ether as solvent
gave similar results.
With MeI, only the dialkylated product was obtained
(Table 1, entries a, e, h). For more hindered electrophiles
(n-PrI) both 2 and 3 were obtained, while 3 is the major
product (entry b). However, with n-BuI, the mono in-
serted adduct 2 was the major product (entry c). We sus-
pect that the reaction is controlled mainly by steric
considerations. When a hindered amine borane (iPr–
NH2 Æ BH3) was reacted with n-PrI and n-BuI, the mono
alkylated species 2, became the major product (entries f,
g). When a very bulky amine complex was used (t-Bu-
NH2 Æ BH3), the only product obtained was the mono
alkylated species, 2 (entries i, j). Benzyl chloride gave
the mono inserted adduct in low yield with recovery of
the starting complexed amine and the electrophile (entry
Fig. 1. Molecular structure of 3a in the crystal.
Fig. 2. Molecular structure of 3b in the crystal.
Fig. 3. Molecular structure of 3c in the crystal.
Table 1
Tertiary and secondary amine boranes, prepared from primary amine
boranes 1
Entry R1
R2
RX
Isolated
yields
(%)
Yield by NMR (%)
d). Secondary amine borane were less reactive. Indeed
(iPr2–NH Æ BH3) reacted only with MeI (entry k). Thus
when the amine complex or the electrophile are bulky,
the mono adduct 2 is the major product. The products
were obtained either as solids or oils. The majority of
the products were purified by flash chromatography,
which decreased the quantitative yield substantially.
Some of these purified products were crystallized from
THF. On the other hand, several products could not
be eluted from silica (entries 2b, 2c and 2d) so the spec-
tral data for them was reported for the crude mixtures
(see Tables 1 and 3).
2
3
a
b
c
d
e
f
PhCH2
H
H
H
H
H
H
H
H
H
H
CH3I
n-PrI
0
45 >99
25 75 >99
35 >99
35
25 >95
PhCH2
PhCH2
PhCH2
iPr
n-BuI
PhCH2Cl
CH3I
n-PrI
–
0
0
–
iPr
iPr
31 15 >99
28 18 >99
g
h
i
n-BuI
CH3I
n-PrI
t-Bu
t-Bu
t-Bu
iPr
0
25
30
15
40
0
60
60
80
80
j
n-BuI
0
k
iPr CH3I
0

2182
A. Shibli et al. / Journal of Organometallic Chemistry 690 (2005) 2180–2185
Table 2
Crystal data and structure refinement for compounds 3a, 3b and 3c
Compound 3a
Compound 3b
Compound 3c
Empirical formula
Formula mass (g molꢀ1
Habit
C9H16BN
149.04
Prisms
C13H24BN
205.14
Plates
C15H28BN
233.19
)
Needles
Colorless
110(2)
Color
Temperature (K)
Radiation
Colorless
110(2)
Colorless
110(2)
Mo Ka
0.35 · 0.30 · 0.20
Orthorombic
Pna21
Mo Ka
–
Mo Ka
–
Crystal size (mm)
Crystal system
Space group
Monoclinic
C2/c
Monoclinic
P21/c
˚
a (A)
20.07900 (10)
5.9570 (2)
7.8770 (5)
90.00
24.3900(7)
5.8380(2)
19.0350(7)
90.00
13.8450 (3)
5.99800 (10)
18.8290 (6)
90.00
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
90.00
90.00
104.7500(11)
90.00
104.1590 (9)
90.00
3
˚
V (A )
942.17 (7)
4
1.0507
2621.05(15)
8
1.0397
1516.10 (6)
4
1.0216
Z
Dcalcd (g cmꢀ3
F(0 0 0)
l (mmꢀ1
2h range (ꢀ)
Number of unique reflections
)
328
0.059
912
0.058
520
0.057
)
1.41–27.88
1197
1.73–27.83
2933
1.41–28.28
3611
Number of restraints
hkl limits
1
0
0
0–26, 0–7, 0–10
103
1107
0–31, 0–6, ꢀ24 to 24
139
2068
0–18, 0–7, ꢀ14 to 23
157
2468
Number of parameters
Number of reflections with [I > 2r(I)]
Final R indicesa [I > 2r(I)]
0.0396
0.1050
0.0553
0.1248
0.0574
0.1307
a
R1
b
wR2
ꢀ3
˚
jDqj (e A
)
60.216
1.040
60.224
1.028
60.257
1.020
GOF
P
P
a
R1 = iFoj ꢀ jFci/ jFoj.
n
P
2
o
1=2
P
2
b
wR2 ¼
½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁ
.
Table 3
Molecular structures of the three compounds 3a, 3b
and 3c were determined at ca. 110 K with relatively high
precision. They represent three independent and inter-
nally consistent determinations. The covalent parame-
ters exhibit standard values characteristic to boron in
tetrahedral sp3 hybridization. The conformation around
the boron atom is nearly ideally tetrahedral, with N–B–
H bond angles of 109ꢀ (Table 2).
˚
Selected bond length (A) and angels (ꢀ) for compounds 3a, 3b and 3c
Compound 3a
Compound 3b
Compound 3c
B–N
1.620(2)
1.490(2)
1.514(2)
1.623(2)
1.5097 (18)
1.627(19)
1.5109 (19)
N–C1
N–C3
N–C7
N–C9
–
–
–
–
1.5197(19)
–
–
1.5204(19)
B–N–C
N–B–H
C–N–C
C–N–B
108.70(13)
109.5
111.54(11)
109.5
111.08(11)
109.5
108.66(14)
108.70(13)
107.98(11)
111.54(11)
112.03(11)
111.08(11)
3. Conclusions
A series of secondary and tertiary amine boranes
were prepared in good to excellent yields in a short time
reaction and high purity, using a one-pot operation,
starting with an alkyl amine borane or benzyl amine
borane and treated with the appropriate electrophile.
The molecular structures of 3a, 3b and 3c were deter-
mined by single-crystal X-ray diffraction. Studies are
presently directed at examining the scope of this ap-
proach with more complicated electrophiles, and deter-
mining their biological activity.
2.2. Crystal structure analyses
Crystals suitable for X-ray structure determination
were obtained for compound 3a, 3b and 3c. Their molec-
ular structures were determined by single-crystal X-ray
diffraction. The results of the diffraction analysis, crystal
data, and details of the structure determination are
shown in Figs. 1–3, and the data are summarized in
Table 2.

A. Shibli et al. / Journal of Organometallic Chemistry 690 (2005) 2180–2185
2183
4. Experimental
1.53 (m, 2H), 2.42 (t, 2H, J = 15), 3.60 (s, 2H), 7.28
(m, 5H).
4.1. Syntheses
4.1.4. N,N,N-dipropylbenzylamine borane (3b)
4.1.1. General comments
White solid, m.p. = 85 ꢀC, 25% (53 mg) yield. 1H
NMR (CDCl3): d 0.88 (t, 3H, J = 14.7), 1.20–2.10
(v.br BH3), 1.86 (m, 2H), 2.57 (t, 2H, JH–H = 16.8),
3.96 (s, 2H), 7.35 (m, 5H). 13C NMR (CDCl3) {H}: d
11.79, 17.17, 60.87, 63.45, 128.46, 129.04, 131.83,
132.49. 11B NMR (CDCl3): d ꢀ13.56 (q, JB–H = 87.84).
Anal. Calc. for C13H24NB: C, 76.09; H, 11.70; N, 6.83.
Found: C, 76.11; H, 11.69; N, 6.80%.
All reactions were carried out under a dry nitrogen
atmosphere in oven-dried glassware. Solvents were dried
over sodium/benzophenone and freshly distilled before
use. All other chemicals were obtained from Sigma–
Aldrich and used as received without any further
purification. All amine boranes complexes were pre-
pared from borane methylsulfide and the corresponding
amine using the literature method [18].
Melting points were determined on a Fisher scientific
1
4.1.5. N,N-butylbenzylamine borane (2c)
melting point apparatus. H, 13C and 11B NMR spectra
White solid in mixture with the N,N,N-dibutylbenzyl-
amine borane, could not be isolated so the data were re-
corded from the mixture. 1H NMR (CDCl3): d 0.80–1.80
(v.br, BH3), 0.87 (t, 3H, JH–H = 14.4), 1.28 (m, 2H), 1.44
(m, 2H), 2.39 (t, 2H, JH–H = 14.7), 3.54 (s, 2H) 7.29 (m,
5H). 13C NMR (CDCl3) {H}: d 14.02, 20.55, 29.04,
53.11, 58.48, 126.62, 128.02, 128.84, 131.71. 11B NMR
(CDCl3): d ꢀ17.88 (q, JB–H = 94.2).
were recorded on a Varian Unity spectrometer (300, 75,
96 MHz), respectively. Chemical shifts were recorded rel-
ative to an internal standard Me4Si for 1H and 13C NMR
and Et2O Æ BF3 as an external standard for 11B NMR.
Data were reported in the following order: chemical shifts
are given in d (ppm); multiplicities are indicated as s (sin-
glet), d (doublet), t (triplet), q (quartet), m (multiplet), dd
(doublet of doublet); coupling constants, J, are reported
in hertz. Liquid chromatography was performed using
column chromatography of the indicated solvent system
on Merck silica gel 60 (0.040–0.063 mm).
4.1.6. N,N,N-dibutylbenzylamine borane (3c)
1
White solid, m.p. = 67–68 ꢀC, 35% (83 mg) yield. H
NMR (CDCl3): d 0.80–2.10 (v.br BH3), 0.95 (t, 3H,
JH–H = 14.4), 1.28 (m, 2H), 1.79 (m, 2H), 2.61 (t, 2H,
JH–H = 16.8), 3.95 (s, 2H), 7.34 (m, 5H). 13C NMR
(CDCl3) {H}: d 13.80, 20.60, 25.59, 58.85, 63.27,
128.12, 128.74, 131.67, 132.26. 11B NMR (CDCl3): d
ꢀ13.69 (q, JB–H = 90.10). Anal. Calc. for C15H28NB:
C, 77.25; H, 12.02; N, 6.01. Found: C, 77.26; H, 12.04;
N, 7.98%.
4.1.2. General procedure
A solution of s-BuLi in cyclohexane (1.3 M, 2 mmol)
was added drop wise to a solution of benzylamine bor-
ane (0.121 g, 1 mmol) in THF (10 ml) at ꢀ78 ꢀC. The
solution was stirred for 30 min at ꢀ78 ꢀC, then it was al-
lowed to warm up to room temperature for 30 min, be-
fore recooling down to ꢀ78 ꢀC and addition of CH3I
(0.125 ml, 2 mmol) in one portion. After 5 min the cool-
ing bath was removed, and the reaction mixture was stir-
red for 1 h at room temperature. A saturated NaHCO3
solution (10 ml) was added where the aqueous layer was
extracted with ether (3 · 10 ml); the combined organic
layers were after dried over sodium sulfate. After evap-
oration of the solvents the residue was purified by flash
chromatography on silica gel (10% EtOAc in petroleum
ether) to give (3a) N,N,N-dimethylbenzylamine borane as
4.1.7. Dibenzylamine borane (2d)
It was obtained in a mixture with the starting mate-
rial and the benzyl chloride although it was stirred after
addition of the electrophile over-night at room temper-
ature, it was stocked in the column and cannot be puri-
fied, the data could be reported from the crude mixture
1H NMR (CDCl3): d 3.57 (s, 4H), 7.35 (m, 10H). 13C
NMR (CDCl3): d 58.67, 128.18, 128.9, 129.56, 130.22.
1
white solid m.p. = 101 ꢀC (68 mg) 45% yield, H NMR
4.1.8. N,N,N-dimethylisopropylamine borane (3e)
Colorless oil, 25% (27 mg) yield. 1H NMR (CDCl3): d
0.88 (t, 3H, JH–H = 14.7), 1.10–2.18 (v.br BH3), 1.26 (d,
6H, JH–H = 7.8), 2.51 (s, 6H,), 3.06 (m, 1H). 13C NMR
(CDCl3) {H}: d 17.64, 48.41, 61.68. 11B NMR (CDCl3):
d ꢀ12.29 (q, JB–H = 96.96).
(CDCl3): d 1.23–2.60 (v.br BH3), 2.50 (s, 6H), 3.98 (s,
2H), 7.25 (m, 5H). 13C NMR (CDCl3) {H}: d 49.62,
67.51, 128.45, 129.10, 131.20, 131.19. 11B NMR
(CDCl3): d ꢀ9.46 (q, JB–H = 96.86). Anal. Calc. for
C9H16NB: C, 72.48; H, 10.73; N, 9.39. Found: C,
72.50; H, 10.75; N, 9.42%.
4.1.9. N,N-propylisopropylamine borane (2f)
4.1.3. N,N-propylbenzylamine borane (2b)
Colorless oil, 31% (35 mg) yield. 1H NMR (CDCl3): d
0.89 (t, 3H, JH–H = 14.7), 1.19 (dd, 6H, J1H–H ¼ 6.6,
J2H–H ¼ 14.4), 1.60 (m, 2H), 1.80 (m, 1H), 2.62 (m, 1H),
3.19 (m, 1H), BH3 cannot be detected. 13C NMR
White solid in mixture with the N,N,N-dipropylben-
zylamine borane, it could not be isolated so the only
data could be recorded from the mixture was. 1H
NMR (CDCl3): d 0.80–2.20 (v.br, BH3), 0.84 (t, 3H),

2184
A. Shibli et al. / Journal of Organometallic Chemistry 690 (2005) 2180–2185
(CDCl3) {H}: d 11.12, 17.87, 18.37, 20.36, 52.86, 54.07.
11B NMR (CDCl3): d ꢀ18.32 (q, JB–H = 95.04).
4.1.16. N,N,N-methyldiisopropylamine borane (3k)
Colorless oil, 15% (20 mg) yield. 1H NMR (CDCl3): d
1.22 (d, 6H, JH–H = 6.6), 1.33 (d, 6H, JH–H = 6.6), 2.30
(s, 3H), 3.29 (m, 1H), BH3 cannot be detected. 13C
NMR (CDCl3) {H}: d 16.99, 18.20, 39.93, 57.84. 11B
NMR (CDCl3): d ꢀ17.29 (q, JB–H = 95.13).
4.1.10. N,N,N-dipropylisopropylamine borane (3f)
1
Yellow oil, 15% (25 mg) yield. H NMR (CDCl3): d
0.87 (t, 6H, JH–H = 14.7), 1.23 (d, 6H, JH–H = 6.6),
1.77 (m, 4H), 2.57 (m, 4H), 3.16 (m, 1H), BH3 cannot
be detected. 13C NMR (CDCl3) {H}: d 11.76, 16.27,
17.03, 58.28, 58.42. 11B NMR (CDCl3): d ꢀ14.03 (q,
JB–H = 95.13).
4.2. Crystal structure analyses
Colorless single crystals of compounds 3a, 3b and 3c,
suitable for X-ray diffraction analysis were obtained
from a saturated THF solution at 25 ꢀC. The crystal
data and structure refinement parameters are summa-
rized in Table 2. All diffraction measurements were car-
ried out on a Nonius KappaCCD diffractometer at ca.
110 K, using graphite monochromated Mo Ka
4.1.11. N,N-butylisopropylamine borane (2g)
1
Yellow oil, 28% (40 mg) yield. H NMR (CDCl3): d
0.91 (t, 3H, JH–H = 14.4), 1.20 (dd, 6H, J1H–H ¼ 6.6,
J2H–H ¼ 14.7), 1.31 (m, 2H), 1.55 (m, 1H), 1.72 (m, 1H),
2.66 (m, 2H), 3.20 (m, 1H), BH3 cannot be detected.
13C NMR (CDCl3) {H}: d 13.91, 18.18, 18.77, 20.35,
29.51, 51.34, 54.37. 11B NMR (CDCl3): d ꢀ18.31 (q,
JB–H = 93.21).
˚
(k = 0.71073 A) radiation and 1ꢀ u-scans. The intensity
data was integrated and scaled by DENZO-SMN and
Scalepack programs. The structures were solved by di-
rect methods (SIR-97) [15], and refined by full-matrix
least-squares on F2 (SHELXL-97) [19].
4.1.12. N,N,N-dibutylisopropylamine borane (3g)
Colorless oil, 18% (35 mg) yield. 1H NMR (CDCl3): d
0.93 (t, 6H, JH–H = 14.7), 1.23 (d, 6H, JH–H = 6.9), 1.26
(m, 4H), 1.65 (m, 4H), 2.69 (m, 4H), 3.16 (m, 1H), BH3
cannot be detected. 13C NMR (CDCl3) {H}: d 13.80,
17.03, 20.74, 24.96, 56.46, 58.25. 11B NMR (CDCl3): d
ꢀ14.06 (q, JB–H = 89.66).
Acknowledgements
The authors thank the Hebrew University Internal
Funds for support of this work.
4.1.13. N,N,N-dimethylt-butylamine borane (3h)
White solid, m.p. = 110 ꢀC, 40% (46 mg) yield. 1H
NMR (CDCl3): d 1.34 (s, 9H), 2.54 (s, 6H), BH3 cannot
be detected. 13C NMR (CDCl3) {H}: d 24.88, 47.39,
62.31. 11B NMR (CDCl3): d ꢀ13.24 (q, JB–H = 98.68).
Anal. Calc. for C6H18NB: C, 62.61; H, 15.65; N, 12.17.
Found: C, 62.70; H, 15.55; N, 12.11%.
Appendix A. Supplementary material
Crystallographic data for the crystal structures re-
ported in this paper have been deposited with the Cam-
bridge Crystallographic Data Center as supplementary
publication numbers CCDC-252714 (2a), CCDC-
252716 (3a) and CCDC-252715 (4a). Copies of the data
may be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: +44 1223 336033; e-mail:deposit@ccdc.cam.ac.uk).
4.1.14. N,N-propylt-butylamine borane (2i)
1
White solid, m.p. = 50–52 ꢀC, 25% (35 mg) yield. H
NMR (CDCl3): d 0.91 (t, 3H, JH–H = 15), 1.27 (s, 9H),
1.57 (m, 1H), 1.93 (m, 1H), 2.52 (m, 1H), 2.76 (m, 1H),
BH3 cannot be detected. 13C NMR (CDCl3) {H}: d
11.23, 21.90, 26.39, 52.40, 57.96. 11B NMR (CDCl3): d
ꢀ20.44 (q, JB–H = 95.04). Anal. Calc. for C7H20NB: C,
65.12; H, 15.50; N, 10.85. Found: C, 65.19; H, 15.41;
N, 10.80%.
References
[1] (a) D.J. Peterson, H.R. Hays, J. Org. Chem. 30 (1965) 1939;
(b) D.J. Peterson, J. Am. Chem. Soc. 93 (1971) 4027;
(c) A.R. Lepley, W.A. Khan, J. Org. Chem. 31 (1966) 2061;
(d) A.R. Lepley, W.A. Khan, J. Chem. Soc. Chem. Commun.
(1967) 1198.
4.1.15. N,N-butylt-butylamine borane (2j)
White solid, m.p. = 42 ꢀC, 30% (44 mg) yield. 1H
NMR (CDCl3): d 0.92 (t, 3H, JH–H = 14.4), 1.27 (s,
9H), 1.51 (m, 2H), 1.88 (m, 2H), 2.53 (m, 1H), 2.82 (m,
1H), BH3 cannot be detected. 13C NMR (CDCl3) {H}:
d 13.65, 20.15, 26.42, 30.89, 50.59, 58.04. 11B NMR
(CDCl3): d ꢀ20.26 (q, JB–H = 92.16). Anal. Calc. for
C8H22NB: C, 67.13; H, 15.38; N, 9.79. Found: C,
67.08; H, 15.42; N, 9.82%.
[2] (a) R.O. Hutchins, K. Learn, F. El-Telbany, Y.P. Stercho, J. Org.
Chem. 49 (1984) 2438;
(b) E. Vedejs, J.T. Kendall, J. Am. Chem. Soc. 119 (1997) 6941;
(c) A. Pross, L. Radom, Tetrahedron 36 (1980) 673;
(d) D.R. Armstrong, P.G. Perkins, G.T.J. Walker, Mol. Struct.
(THEOCHEM) 122 (1985) 189;
(e) M.R. Ebden, N.S. Simpkins, D.N. Fox, Tetrahedron Lett. 36
(1996) 8697.

A. Shibli et al. / Journal of Organometallic Chemistry 690 (2005) 2180–2185
2185
[3] (a) P. Beak, W.J. Zajdel, D.B. Reitz, Chem. Rev. 25 (1984) 471;
(b) R.O. Hutchins, K. Learn, B. Nazer, A. Pelter, Org. Prep.
Proced. Int. 16 (1984) 335;
(b) V. Ferey, P. Veddrenne, L. Toupet, T. Le Gall, C. Mioskow-
ski, Angew. Chem. Int. Ed. Engl. 35 (1996) 430.
[12] M.R. Ebden, N.S. Simpkins, D.N.A. Fox, Tetrahedron Lett. 36
(1995) 8697.
(c) C.F. Lane, Aldrichimica Acta 6 (1973) 51;
(d) M. Follet, Chem. Ind. (1986) 123;
[13] T.W. Greene, P.G.M. Wuts, Protective Groups in Organic
Chemistry, 3rd ed., John Wiley & Sons, New York, 1999, p. 593.
[14] (a) S.V. Kessar, R. Vohra, N.P. Kaur, K.N. Singh, P.J. Singh, J.
Chem. Soc. Chem. Commun. (1994) 1327;
(e) B. Carboni, L. Monnier, Ttrahedron 55 (1999) 1197.
[4] G.C. Andrews, T.C. Crawford, Tetrahedron Lett. 21 (1980) 693.
[5] (a) M.D. Bomann, I.C. Guch, M. Dimare, J. Org. Chem. 60
(1995) 5995;
(b) S.V. Kessar, P.J. Singh, R. Vohra, N.P. Kaur, K.N. Singh, J.
Chem. Soc. Chem. Commun. (1991) 568.
(b) A. Pelter, R.M. Rosser, J. Chem. Soc. Perkin Trans 1 (1984)
718.
[15] (a) See also E. Vedejs, S.C. Fields, S. Lin, M.R. Schrimpf, J. Org.
Chem. 60 (1995) 3028;
[6] (a) H.C. Brown, J.V.B. Kanth, P.V. Dalvi, M. Zaidlewicz, J. Org.
Chem. 65 (2000) 4655;
(b) E. Vedejs, S.C. Fields, S. Lin, M.R. Schrimpf, J. Am. Chem.
Soc. 115 (1993) 11612.
(b) J.A. Soderquist, J.R. Medina, R. Huertas, Tetrahedron Lett.
39 (1998) 6119;
[16] S.V. Kessar, P. Singh, Chem. Rev. 97 (1997) 721.
[17] (a) H. Gilman, B. Gaj, J. Org. Chem. 22 (1957) 1165;
(b) A. Rembaum, S.P. Siao, N. Indictor, J. Polym. Sci. 56 (1962)
S17;
(c) J.A. Soderquist, J.R. Medina, Tetrahedron Lett. 39 (1998)
6123.
[7] (a) H.C. Brown, J.V.B. Kanth, P.V. Dalvi, M. Zaidlewicz, J. Org.
Chem. 64 (1999) 6263;
(c) S.C. Honeycutt, J. Organomet. Chem. 29 (1971) 1;
(d) R.B. Bates, L.M. Kroposki, D.E. Potter, J. Ogr. Chem. 37
(1972) 560;
(b) H.C. Brown, J.V.B. Kanth, P.V. Dalvi, M. Zaidlewicz, J. Org.
Chem. 63 (1998) 5154.
[8] H. David, L. Dupuis, M.G. Guillerez, F. Guibe, Tetrahedron
Lett. 41 (2000) 3335.
(e) A. Maercker, Angew. Chem. Int. Ed. Engl. 26 (1987) 972.
[18] M.R. Ebden, N.S. Simpkins, D.N.A. Fox, Tetrahedron 54 (1998)
12923.
[9] B.H. Lipshutz, D.J. Buzard, R.W. Vivian, Tetrahedron Lett. 40
(1999) 6861.
[19] G.M. Scheldrick, SHELXL-97, Program for the Refinement of the
Crystal Structures from Difrraction Data, University of Goettin-
gen, Germany, 1997.
[10] P. Gomez-Martinez, M. Dessolin, F. Guibe, F. Albericio, J.
Chem. Soc. Perkin Trans 120 (1999) 2871.
[11] (a) V. Ferey, P. Veddrenne, L. Toupet, T. Le Gall, C. Mioskow-
ski, J. Org. Chem. 61 (1996) 7244;
[20] C.J. Collins, M. Lanz, C.T. Goralski, B. Singaram, J. Org. Chem.
64 (1999) 2574.