M.B. Faraoni et al. / Journal of Organometallic Chemistry 693 (2008) 1877–1885
1879
propargyl alcohols, i.e., compounds 3, 5, 7, 9, and 11, the
adducts compared with that of their tributyl- and trimeth-
ylstannyl analogues [6b,9]. The stability of the trineophylst-
annyallyl alcohols enable their separation and purification
by column chromatography using silica gel 60 (in most
cases) as adsorbent, this resulting in a dramatic improve-
ment of the yields of pure isolated compounds.
1H NMR spectra show signals corresponding to a proton
2
attached to C(3) (HB) with J(Sn,H) coupling constants
values between 76 and 72 Hz indicating that this proton
and the organotin moiety are geminal. It should be noted
that due to the multiplicity of the signals and the overlap
between stannyl satellites and other signals, in many cases
3
it was not possible the measurement of J(Sn,H) coupling
3. Experimental
constants (see Tables 2 and 3).
The 13C NMR chemical shifts (Tables 2 and 3) were
assigned through the analysis of the multiplicity of the sig-
nals by means of DEPT experiments and taking into
account the magnitude of nJ(13C,119Sn) coupling constants.
3.1. General methods
NMR spectra were recorded on a Bruker ARX 300
instrument, using CDCl3 as solvent; chemical shifts (d)
Thus, the values of J(13C,119Sn)geminal coupling constants
are reported in ppm with respect to TMS, H and 13C,
2
1
for adducts 12, 14, 16, 18, and 20 (see C(1), Table 2), within
the range 31.7–22.7 Hz indicate that the configuration of
these compounds is (E) [7]. The (E) configuration of these
compounds is confirmed by the fact that the values of their
3J(13C,119Sn) coupling constants lie between 61.2 and
54.8 Hz, indicating that the R substituent at C(3) is trans
with respect to the the organotin moiety attached to
and with respect to Me4Sn in the case of 119Sn NMR spec-
tra. Mass spectra were obtained using a Finnigan MAT
Incos 50 Galaxy System (DIP-MS) at Cologne University
(Germany). Elemental analyses (C,H) were performed at
Cologne University (Germany). High resolution mass spec-
tra (HRMS) were recorded on a Finnigan Mat. 900 (HR-
EI-MS). All the solvents and reagents used were analytical
reagent grade. Trineophyltin hydride (1) was prepared as
described [10]. 1-Phenyl-2-heptyn-1-ol was obtained by
reduction of 1-phenyl-2-heptyn-1-one [11]. One experiment
is described in detail in order to illustrate the methods used.
2
C(2). Also, the J(13C,119Sn)geminal coupling constants with
values ranging from 40.0 to 23.7 Hz for adducts 2, 4, 6, 8,
and 10 (see C(1) in Table 2,) confirm that the vinyl groups
are terminal. Similarly, 3J(13C,119Sn)trans coupling constant
values of compounds 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21
range from 67.8 to 60.2 Hz (see C(1) in Table 3) demon-
strating the (E) stereochemistry of these adducts [7].
As shown in Table 1, the syn hydrostannation of substi-
tuted propargyl alcohols with trineophyltin hydride leads
in all cases but one (Table 1, entry 6), to mixtures of regioi-
somers in which the b-isomer is always formed in higher
proportion. These results could be explained [8] taking into
account that, due to steric effects the reactions might take
place through an intermediate complex A (Scheme 2) in
which the palladium residue adopts the distal position to
minimize the interaction between the metal and the R1
and/or R2, as shown in Scheme 2. In this way, the distal
stannane is obtained even when an additional R substituent
is attached to the C-c position.
On the other hand, in the case of the hydrostannation of
2-heptyn-1-ol (Table 1, entry 6) with trineophyltin hydride
(1) i.e., a compound in which the C-a is not substituted, the
proximal stannylated derivative is obtained as the major
regioisomer via the intermediate complex B (Scheme 2).
This result together with the results reported previously
[6a], clearly indicates that the proximal adduct will be the
major isomer whenever the C-a is not substituted and
whether or not the C-c is substituted.
3.2. Addition of trineophyltin hydride (1) to substituted
propargyl alcohols catalyzed by
bis(triphenylphosphine)palladium(II) chloride
All the reactions were carried out following the same
procedure. One experiment is described in detail in order
to illustrate the methods used.
To
a
solution of 2-phenyl-3-butyn-2-ol (0.11 g,
0.77 mmol) and bis(triphenylphosphine) palladium(II)
chloride (0.010 g, 0.015 mmol) in dry THF (3 mL) under
argon was added trineophyltin hydride (0.40 g, 0.77 mmol),
and the mixture was stirred at room temperature for 2 h.
Then, the solvent was distilled off under reduced pressure.
The 119Sn NMR spectrum of the crude product showed a
mixture of two compounds: a-2-trineophyltin-1-methyl-1-
phenyl-2-propen-1-ol (8; 28%) and (E)-b-3-trineophyltin-
1-methyl-1-phenyl-2-propen-1-ol (9; 72%). Column chro-
matography (silica gel 60) of the mixture afforded 8
(0.10 g, 0.16 mmol, 24%) and 9 (0.26 g, 0.39 mmol, 60%)
in the fractions eluted with 98:2 and 96:4 hexane–diethyl
ether, respectively.
3.3. Stille coupling reactions
The chemical reactivity of the new stannylated allyl
alcohols is similar to that of other vinyltriorganostannanes.
Thus, the Stille reactions of vinylstannanes 9 and 11 with p-
bromoanisole lead to the corresponding coupling products
in 62 (22) and 65% (23) yield.
The major advantages of the hydrostannation of prop-
argyl alcohols with trineophyltin hydride are not only the
higher yields but the greater stability of the resulting
All the reactions were carried out following the same
procedure. One experiment is described in detail in order
to illustrate the methods used.
To a mixture of 1-bromo-4-methoxybenzene (0.12 g,
0.74 mmol), PdCl2(PPh3)2 (0.011 g, 2%), and some crystals
of 2,6-di-tert-butyl-4-methylphenol under argon was added
a solution of 9 (0.25 g, 0.37 mmol) in dry THF (2 mL) at
Faraoni, María B.
