Synthesis of phosphine-ligated zinc acetylide dimers: Enhanced reactivity in carbonyl additions

Article abstract of DOI:10.1021/om200581f

Phosphine-ligated dinuclear zinc acetylides effectively promote the alkynylation of carbonyl derivatives. Good to excellent yields (46-91%) of the corresponding propargylic alcohols were obtained from a wide range of substrates. Crystallographic evidence

Full text of DOI:10.1021/om200581f

ARTICLE
pubs.acs.org/Organometallics
Synthesis of Phosphine-Ligated Zinc Acetylide Dimers: Enhanced
Reactivity in Carbonyl Additions
Erin E. Wilson,† Allen G. Oliver,† Russell P. Hughes,‡ and Brandon L. Ashfeld*,†
†Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
‡Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, United States
S Supporting Information
b
ABSTRACT: Phosphine-ligated dinuclear zinc acetylides effec-
tively promote the alkynylation of carbonyl derivatives. Good to
excellent yields (46ꢀ91%) of the corresponding propargylic
alcohols were obtained from a wide range of substrates. Crystal-
lographic evidence for a phosphineꢀzincꢀacetylide dimer was
obtained with bonding energies obtained by DFT calculations.
Phosphine ligation in the carbonꢀcarbon bond-forming event
is further corroborated by the synthesis of an enantioenriched
propargylic alcohol through the addition of chiral phosphines.
’ INTRODUCTION
(4-MeO-C6H4)3P enabled alkynylation to provide alcohol 3a
in 78% yield. The ability to accelerate the addition of alkynyl-
zinc reagents to carbonyl derivatives through the ligation of
phosphine expands the synthetic potential of this already
versatile, readily accessible, and structurally diverse class of
ligands.
The importance of propargylic alcohols as synthetic inter-
mediates is exemplified by recent reports of their use in the
construction of biologically active natural products and pharma-
ceutical targets.1 The most widely used method for the synthesis
of this versatile functional group is the addition of zinc acetylides
to carbonyl derivatives.2 Zinc acetylides are often prepared
through the addition of zinc(II) salts, such as Zn(OTf)2 and
ZnCl2, to a terminal alkyne in the presence of an amine base.
However, it is well documented that the use of Zn(OTf)2 can
provide inconsistent zinc acetylide generation in which acetylide
reactivity is highly dependent on the particle size and dryness of
the Zn(OTf)2.3g,4 Yadav’s alkynylation with iodoacetylenes and
zinc dust offers an alternative to Zn(II) acetylide generation.2g
Unfortunately, this method requires elevated temperatures that
may prove incompatible with more functionally complex sub-
strates. In an effort to devise a mild method for the synthesis of
propargylic alcohols that avoids the use of Zn(II) salts and
elevated temperatures, we hypothesized that phosphine ligation
to alkylzinc acetylides would lead to enhanced ligand-assisted
reactivity toward carbonyl derivatives. Herein, we report the
synthesis of phosphine-ligated dinuclear zinc acetylides and their
enhanced reactivity in carbonyl addition chemistry.
During our studies with titanocene-based catalysts for the
allylation of carbonyl derivatives and the sequential alkylation of
dielectrophilic aldehydes, we found that improved yields and
substantially shorter reaction times were obtained when sub-
stoichiometric phosphine was present.5 A similar effect was
observed in the synthesis of propargylic alcohols from zinc
acetylides generated via iodineꢀzinc exchange.6 In the absence
of phosphine, treatment of aldehyde 1a and iodoalkyne 2a
with Et2Zn failed to provide propargylic alcohol 3a after 2 h at
room temperature (eq 1). However, the addition of 40 mol % of
’ RESULTS AND DISCUSSION
Excited by this initial result, we examined how the electronic
and structural properties of the phosphine additive affected zinc
acetylide reactivity. Although the electron-rich triarylphosphine
(4-MeO-C6H4)3P provided alcohol 3b in 69% yield, PPh3
increased the yield to 81% (Table 1, entries 1 and 2). The
improved yield with PPh3 is likely a result of an increase in the
rate of metalation and carbonyl addition based on the yield of
recovered aldehyde. Trialkylphosphines PCy3 and PtBu3 led to a
modest decrease in acetylide reactivity, whereas bisphosphines
dppp and dppe provided alcohol 3b in 38% and 31% yields,
respectively (entries 3ꢀ6). Notably, poor mass recovery was also
observed with these bisphosphine ligands. Upon further exam-
ination, we discovered that as little as 5 mol % of PPh3 was
Received: July 1, 2011
Published: September 08, 2011
r
2011 American Chemical Society
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Table 1. Effect of Phosphine Additivesa
Table 2. Effect of Phosphine Additivea
entry
R
X
additiveb
Et3N
time (h)
yield (%)c
amt of X
yield of
3 (%)b
1d
2d
3d
4d
5e
6e
OTf
OTf
Cl
H (4)
H (4)
H (4)
H (4)
H (4)
I (2a)
5
5
15
45
30
35
16
89
entry
phosphine
(mol %)
R
Et3N, PPh3
Et3N
1
2
3
4
5
6
7
8
9
(4-MeO-C6H4)3P
PPh3
40
40
40
40
40
40
5
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
Ph (2a)
69 (81)c (3b)
81 (89)
59 (74)
51 (64)
38 (63)
31 (62)
89
5
Cl
Et3N, PPh3
PPh3
5
PCy3
PtBu3
Et
24
2
Et
PPh3
dppp
a For detailed experimental procedures, see the Supporting Informa-
tion. b 1.5 equiv of Et3N and/or 5 mol % of PPh3. c Isolated yields.
d Solvent PhMe. e Solvent CH2Cl2.
dppe
PPh3
PPh3
5
p-MeO-C6H4 (2b)d
p-F3C-C6H4 (2c)d
n-Bu (2d)d
51 (3c)
72 (3d)
51 (3e)
PPh3
5
bond distance is shorter (2.010(3) Å) than the Zn1ꢀC30 bond
(2.340(3) Å). The Zn1ꢀC4 contact is outside of normal bonding
distances. Examination of the RꢀZn1ꢀC30 bond angles (R = P1,
C1, C3) reveals a distorted environment that deviates signifi-
cantly from an ideal tetrahedral geometry (109.5°). However, the
same angles to the acetylene centroid show a more regular geometry
(P1ꢀZn1ꢀcent = 96.0°, C1ꢀZn1ꢀcent =104.7°, C30-Zn1ꢀ
cent = 107.3°). Additional evidence that the zinc bisacetylide
complex 5 is a potential intermediate was obtained by redissol-
ving 5 in CH2Cl2 with aldehyde 1b present to provide alcohol 3b
in 65% yield.
In an effort to rationalize the disparate reactivity in CH2Cl2
versus THF, recrystallization of the zinc acetylide complex from a
THF solution afforded the dialkynyl zinc species 6 (Figure 2).
The structure consists of a four-coordinate Zn ligated by two
THF moieties and σ-bound to two phenylacetylides. The
geometry is a highly distorted “see-saw” with a C1ꢀZnꢀC10
angle of 143.05(13)° and O1ꢀZnꢀO10 angle of 94.41(13)° to
yield a C1ꢀZnꢀO1 angle (101.66(8)°) that deviates from an
ideal tetrahedral arrangement. The C1ꢀC2 bond distance
(1.208(3) Å) suggests that the formal triple bond is still present
within the phenylacetylide ligand. This structure confirms that
coordination by phosphine is precluded in THF to generate a less
reactive dialkynylzinc complex.
With evidence to support phosphine ligation in the carbonꢀ
carbon bond-forming step, we chose to investigate the effect
added phosphine was playing in the metalꢀhalogen exchange
reaction to yield the bisacetylide dimer 5. 1H NMR analysis of the
reaction resulting from the addition of diethylzinc to iodoacety-
lene 2a in the presence of triphenylphosphine revealed two
prominent signals at 3.21 and 1.83 ppm corresponding to the
formation of ethyl iodide (Figure 3a). Interestingly, in the
absence of triphenylphosphine substantially less ethyl iodide is
generated in relation to the ZnꢀEt signals at 1.11 and 0.27
ppm (Figure 3b). Whether the phosphine is driving the equilib-
rium toward formation of ethyl iodide or providing a kinetic rate
acceleration is unclear. What is evident from our experimental
observations is that the addition of phosphine promotes the
metalꢀhalogen exchange event and subsequent carbonyl addi-
tion to yield the desired propargyl alcohol.
10 PPh3
5
a Reaction conditions: 1b (0.4 mmol), 2 (0.48 mmol), Et2Zn (0.4
mmol), and phosphine at 0.25 M for 2 h at room temperature. b Isolated
yields. c Yield based on recovered starting material in parentheses. d The
reaction time was 7 h.
necessary to achieve an 89% yield of alcohol 3b (entry 7).
However, if the reaction was run in a coordinating solvent such
as THF, only 3% of alcohol 3b was obtained. This would indicate
that phosphineꢀzinc ligation is crucial to the enhanced reactivity
of the organozinc reagent. Iodoalkyne substitution was examined
by the treatment of benzaldehyde (1b) with iodoalkynes 2bꢀd
under our optimized conditions. The electron-rich and electron-
poor aryl-substituted iodoalkynes 2b,c provided alcohols 3c,d in
51% and 72% yields, respectively (entries 8 and 9). Simple
aliphatic substitution had little impact on the efficiency of the
alkynylation, as evidenced by formation of n-butyl-substituted
propargylic alcohol 3e (entry 10).7
To determine whether phosphines have a similar effect on the
carbonyl reactivity of zinc acetylides generated from zinc(II)
salts, amines, and terminal alkynes, we examined the addition of
PPh3 to benzaldehyde (1b), phenylacetylene (4), Zn(OTf)2, and
Et3N. In the absence of any additive, a mere 15% yield of alcohol
3bwas obtained after5 h (Table 2, entry1). However, the addition
of 5 mol % PPh3 increased the yield of 3b to 45% (entry 2).
Interestingly, the addition of PPh3 did not substantially improve
the yield of 3b when ZnCl2 was used in place of Zn(OTf)2 (entries 3
and 4). The poor yield of 3b with acetylene 4 and Et2Zn, even in the
presence of PPh3, highlights the need for an iodoalkyne (entry 5).
The best results we observed involved metalation of the iodoalkyne
with Et2Zn in the presence of 5 mol % PPh3 (entry 6).
To gain insight into the effect of phosphine on the zinc
acetylide, a crystal structure was obtained from the mixture of
iodoalkyne 2a, Et2Zn, and PPh3 in CH2Cl2 (Figure 1). The com-
pound crystallizes as a dimer, consisting of two zinc centers, each
coordinated to a triphenylphosphine ligand, an ethyl group, and a
phenylacetylide in a distorted-tetrahedral fashion.8 One mole-
cule of the dimer resides in the triclinic unit cell and crystallizes
about the inversion center. The phenylacetylide ligands adopt a
k2 coordination geometry in which the terminal carbon is σ-
bonded to one Zn of the dimer and datively bound to the second
Zn atom of the dimer in an apparent “side-on”fashion.9 TheZn1ꢀC3
The synthesis of this phosphine-ligated dinuclear zinc bisace-
tylide complex introduces a new class of organozinc reagents for
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Figure 1. ORTEP of the phosphine-ligated dinuclear zinc bisacetylide complex 5. Selected bond lengths (Å) and angles (deg): Zn(1)ꢀC(1) =
1.976(3), Zn(1)ꢀC(3) = 2.010(3), Zn(1)ꢀC(3)0 = 2.340(3), Zn(1)ꢀP(1) = 2.5407(8), Zn(1)ꢀZn(1)0 = 2.9911(7), C(3)ꢀC(4) = 1.203(4);
C(1)ꢀZn(1)ꢀC(3) = 136.25(11), C(1)ꢀZn(1)ꢀC(3)0 = 117.65(10), C(3)ꢀZn(1)ꢀC(3)0 = 93.46(10), C(1)ꢀZn(1)ꢀP(1) = 109.45(8),
C(3)ꢀZn(1)ꢀP(1) = 96.10(8), C(3)0ꢀZn(1)ꢀP(1) = 95.67(7), C(1)ꢀZn(1)ꢀZn(1)0 = 148.04(8), C(3)ꢀZn(1)ꢀZn(1)0 = 51.34(7), C(3)0ꢀZn-
(1)ꢀZn(1)0 = 42.12(7), P(1)ꢀZn(1)ꢀZn(1)0 = 98.55(2), C(2)ꢀC(1)ꢀZn(1) = 114.47(19), C(4)ꢀC(3)ꢀZn(1) = 171.3(2), C(4)ꢀC(3)ꢀZn(1)0 =
95.43(19), Zn(1)ꢀC(3)ꢀZn(1)0 = 86.54(10).
Figure 2. ORTEP of the THF-ligated dialkynyl zinc species 6. Selected bond lengths (Å) and angles (deg): Zn(1)ꢀC(1) = 1.947(2), Zn(1)ꢀO(1) =
2.0961(17), C(1)ꢀC(2) = 1.208(3); C(1)ꢀZn(1)ꢀC(1)0 = 143.05(13), C(1)ꢀZn(1)ꢀO(1) = 101.66(8), O(1)0ꢀZn(1)ꢀO(1) = 94.41(13),
C(2)ꢀC(1)ꢀZn(1) = 176.2(2).
potential use in synthetic applications. To the best of our knowl-
edge, this finding constitutes the first phosphineꢀzincꢀacetylide
complex to exhibit enhanced reactivity toward carbonyl substrates
in comparison to its ligandless counterpart. This structure is
consistent with our finding that monophosphines provide the
corresponding propargylic alcohols in superior yields over bi-
sphosphine additives.
To better understand the nature of the σ-ZnꢀP bond and the
σ- and π-Znꢀalkyne bonding interactions in dimer 5 and how
they may influence the transition state in the carbonꢀcarbon
bond-forming event, computational analysis using DFT methods
implemented in the Jaguar and ADF program packages was
employed.10 The optimized DFT structure of 5 reproduced the
crystallographic structure; a structural superposition is shown in
the Supporting Information along with full details of all compu-
tational methods. Computations were also performed on the
simplified analogues 6a,b and the phosphine-free dimer 6c.
The KohnꢀSham HOMO of 6c illustrates contributions from
both the CtC π-system and the σ*-antibonding component of
the ZnꢀCH3 bond to the zinc acetylide dimer (Figure 4A). An
NBO11 analysis of 6c demonstrates weak donation from CtC π
into the ZnꢀCH3 σ* acceptor orbital (Figure 4B); the stabilizing
delocalization energy associated with each of these two interac-
tions is ca. 13 kcal/mol. NBO shows no evidence of significant
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Figure 3. 1H NMR spectra taken 20 min after the addition of neat Et2Zn to (a) a solution of PPh3 (1 equiv) and 2a (1 equiv) in CD2Cl2 and (b) 2a
(1 equiv) in CD2Cl2.
Figure 4. (A) Kohn-Sham HOMO of 6c. (B) NBO showing donation from the CtC π-bond on one Zn into the other ZnꢀMe σ*-acceptor orbital of
6c. (C) ETS-NOCV deformation density illustrating electron “flow” from red to blue regions on combining two MeZnCtCMe fragments to give 6c. Zn
atoms are pink.
back-bonding from Zn to alkyne π*. Using the ETS-NOCV12
method coupled with bond decomposition analysis (BDA),13 the
intramolecular interactions in dimers 5 and 6aꢀc were investi-
gated. Using each half of the dimer as a fragment in the analysis,
the NOCV deformation densities were obtained. The principal
NOCV contribution in 6c is shown in Figure 4C, showing the
“flow” of electron density from red to blue regions of space on
forming the dimer, with transfer of electron density from the
CtC π to Zn. This NOCV contribution is weak and contributes
only 27 kcal/mol to the binding energy.
summarized in Table 3. The dominance of the electrostatic term
(ΔVestat) over the orbital interaction term (ΔEoi) in each case is
consistent with the overall interaction being mostly ionic.14
Addition of phosphorus ligands to the dimer does not signifi-
cantly affect the overall binding within the dimer; small decreases
in the electrostatic and orbital contributions are offset by corre-
sponding increases in dispersion forces. Finally, application of
the QTAIM15 method to 6aꢀc locates bond critical points
between the alkyne π-system and the neighboring Zn atoms
and, for compounds 6a,b, between the Zn and P atoms; very low
electron densities and the signs of the density Laplacian15a,16 at
these bond critical points are also indicative of mostly polar
Total bonding energies between halves of the dimer and their
component contributions13c were obtained by BDA and are
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Table 3. Bond Decomposition Analyses for AlkynylꢀZinc
natural product synthesis.3,21 Thus, we chose to examine the
effect of chiral phosphines in the addition of iodoalkyne 2a to
aldehyde 1b to determine if phosphine is present in the CꢀC
bond-forming event (eq 3). Gratifyingly, the addition of 20 mol %
of (R)-MonoPhos (7) in place of PPh3 provided alcohol 3b in
25% ee. The ability to yield alcohol (ꢀ)-3b with a measure of
enantioenrichment indicates that the chiral phosphine additive is
an active participant in the carbonꢀcarbon bond-forming event.
This observation bolsters our finding that the phosphine-ligated
dinuclear zinc acetylide structure 5 is key to understanding the
enhanced reactivity of these reagents toward carbonyl derivatives.
Dimersa
compd ΔEPauli ΔVestat
ΔEoi
ΔEdispersion total bonding energy
6a
6b
6c
5
+76.97 ꢀ65.43 ꢀ40.74
+72.93 ꢀ63.33 ꢀ37.37
+82.24 ꢀ68.31 ꢀ44.76
+77.43 ꢀ59.24 ꢀ40.29
ꢀ8.91
ꢀ11.93
ꢀ6.54
ꢀ38.11
ꢀ39.70
ꢀ37.37
ꢀ43.83
ꢀ21.73
a Energies in kcal/mol.
interactions with very little covalency. Although it is unclear at
present whether the reacting acetylenic zinc complex is a dimer or
monomer in the transition state, these weak interactions holding the
Zn dimer together are possible sites of carbonyl association.
Although rare, phosphine-ligated zinc(II) halide complexes
are known.17 However, their synthetic utility in organozinc
additions has yet to be examined.18 In contrast, phosphine oxides
and phosphoramides are excellent ligands for organozinc re-
agents through ligation with zinc at either oxygen or nitrogen.19
To rule out the possibility that the enhanced reactivity observed
is due to an in situ oxidation to the phosphine oxide, we com-
pared the acetylide addition of 2a to aldehyde 1f in the presence
of Ph3PdO and PPh3 separately. A 72% yield of alcohol 3f was
obtained when PPh3 was added, whereas Ph3PdO led to a mere
13% yield (eq 2). These results, in conjunction with crystal
structure 5, would indicate that phosphine, not phosphine oxide,
is responsible for the observed reactivity.
In conclusion, we have demonstrated that the presence of
substoichiometric phosphine additives can dramatically increase
the efficiency of alkynylzinc additions to carbonyl derivatives
under ambient conditions. The isolation of an unprecedented
phosphineꢀdinuclear zinc acetylide complex sheds light on the
nature of this enhanced reactivity and provides the impetus for
further development of alternative zinc ligand designs. This
reliable procedure complements existing alkynylation technol-
ogy and lays the foundation for future applications of phosphine-
mediated organozinc additions to carbonyl compounds. Addi-
tionally, our study illustrates the first example of a chiral phosphine-
accelerated enantioselective alkynylzinc addition to aldehydes.
The procedure described represents a unique opportunity to-
ward confronting challenges in asymmetric organozinc additions
by enabling an entirely new class of ligands to facilitate these
transformations. Additional work on the effect of phosphorus
ligands in organozinc chemistry and their application in asym-
metric synthesis through the use of chiral phosphine ligands are
currently being explored and will be reported in due course.
To examine the scope of the phosphine-accelerated alkynyla-
tion, a series of carbonyl derivatives 1 were treated with 2a and
Et2Zn in the presence of PPh3 (5 mol %) (Table 4). In general,
good to excellent yields of propargylic alcohols 3 were obtained
regardless of the carbonyl component. Both electron-rich and
electron-poor benzaldehyde derivatives proved to be viable
substrates, providing the corresponding benzylic alcohols in
72ꢀ91% yield (entries 1ꢀ5). The presence of aryl halides and
benzoates did not hinder the metalation of alkyne 2a or efficiency
of the carbonyl addition event (entries 2 and 3). Electron-poor
aromatic aldehydes 1j,k yielded similar results, and heteroaro-
matic aldehydes 1l,m underwent smooth alkynylation in good to
excellent yields (entries 4ꢀ7). α,β-Unsaturation proved incon-
sequential, as acrolein (1n) and crotonaldehyde (1o) underwent
regioselective 1,2-addition to provide alcohols 3n,o (entries 8
and 9). The aliphatic aldehyde 1p and hexanal (1q), paraformal-
dehyde (1r), and cyclohexanone (1s) underwent alkynylation to
their respective alcohols (entries 10ꢀ13). The results in Table 4
illustrate that the phosphine-accelerated alkynylzinc addition
procedure complements existing methods of zinc acetylide
generation en route toward propargylic alcohols.
’ EXPERIMENTAL SECTION
The known alkynyl iodides 2aꢀd were prepared according to litera-
ture procedures.22 1H NMR data for known compounds 3aꢀh,jꢀl,nꢀs
are consistent with the values reported in the literature.23 The absolute
stereochemistry for the known compound (S)-3b was consistent with
reported literature data.24
General Procedure for the Synthesis of Propargylic Alco-
hols. A vial equipped with a magnetic stir bar was charged with
triphenylphosphine (4.9 mg, 0.019 mmol), purged with nitrogen for
5 min, and then diluted with dry CH2Cl2 (0.75 mL). A solution of
diethylzinc (0.38 mL, 0.377 mmol, 1.0 M in hexanes) and then alkynyl
iodide 2a (0.086 g, 0.377 mmol) were added followed by the dropwise
addition of a solution of the carbonyl derivative 1 (0.367 mmol) in
CH2Cl2 (0.75 mL) (Caution! Care should be taken when using Et2Zn
due to its pyrophoricity.) The resulting mixture was stirred at room
temperature for 2 h or until complete consumption of 1 was observed by
TLC. The crude mixture was then diluted with 1 M HCl, extracted with
CH2Cl2 (3 ꢁ 3 mL), dried (MgSO4), and concentrated under reduced
pressure. The resulting crude mixture was purified by flash column
The results presented thus far indicate that phosphine plays a
pivotal role in the alkynylation event. With the advent of chiral β-
amino alcohols, 1,2-diamines, and 1,2-diols as chiral ligands20 for
the enantioselective addition of alkynylzinc reagents, the construction
of optically active propargylic alcohols has become a staple in
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Table 4. Scope of Carbonyl Substratesa
a Reaction conditions: 1(0.45mmol),2a (0.45mmol),Et2Zn(0.45mmol),andPPh3 (0.02 mmol) at 0.25 M in CH2Cl2 for 2 h at room temperature. b Isolated yields.
chromatography, with CH2Cl2 (100%) as eluent, to yield the propargylic
alcohol indicated.
1-(4-Chlorophenyl)-3-phenylprop-2-yn-1-ol (3a). Propargylic alcohol
3a was obtained in 81% yield (0.500 mmol scale, 98 mg) after 2 h as a pale
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yellowsolid. 1H NMR (500 MHz): δ 7.59ꢀ7.54 (m, 2 H), 7.51ꢀ7.45 (m,
2 H), 7.40 (t, J = 4.0 Hz, 1 H), 7.38ꢀ7.32 (m, 4 H), 5.68 (s, 1 H), 2.43 (br
s, 1 H). Mp: 47ꢀ49 °C.
7.38ꢀ7.31 (m, 3 H), 6.54 (d, J = 3.5 Hz, 1 H), 6.41 (dd, J = 2.0,
3.5 Hz, 1 H), 5.72 (d, J = 7.0 Hz, 1 H), 2.41 (d, J = 7.0 Hz, 1 H).
3-Phenyl-1-(1-tosyl-1H-indol-3-yl)prop-2-yn-1-ol (3m). Propargylic
alcohol 3m was obtained in 65% yield (0.267 mmol scale, 70 mg) after
1,3-Diphenylprop-2-yn-1-ol (3b). Propargylic alcohol 3b was ob-
tained in 89% yield (0.609 mmol scale, 120 mg) after 2 h as a yellow oil.
1H NMR (500 MHz): δ 7.64 (d, J = 7.5 Hz, 2 H), 7.51ꢀ7.48 (m, 2 H),
7.45ꢀ7.41 (m, 2 H), 7.39ꢀ7.32 (m, 4 H), 5.71 (s, 1 H), 2.39 (s, 1 H).
3-(4-Methoxyphenyl)-1-phenylprop-2-yn-1-ol (3c). Propargylic al-
cohol 3c was obtained in 51% yield (0.540 mmol scale, 66 mg) after 7 h
as a dark yellow oil. 1H NMR (500 MHz): δ 7.63 (d, J = 8.0 Hz, 2 H),
7.43ꢀ7.41 (m, 4 H), 7.37ꢀ7.35 (m, 1 H), 6.87ꢀ6.85 (m, 2 H), 5.69 (s,
1 H), 3.82 (s, 3 H), 2.29 (br s, 1 H).
1
2 h as a yellow oil. H NMR (500 MHz): δ 7.99 (d, J = 8.5 Hz, 1H),
7.80ꢀ7.84 (m, 3 H), 7.77 (d, J = 1.0 Hz, 1 H), 7.48ꢀ7.52 (m, 2 H),
7.36ꢀ7.33 (m, 4 H), 7.26ꢀ7.29 (m, 1 H), 7.24 (d, J = 8.5 Hz, 2 H), 5.89
(s, 1 H), 2.34 (s, 3 H). 13C NMR (125 MHz): δ 145.5, 135.8, 135.4,
132.1, 130.2, 129.1, 128.7, 127.2, 125.3, 124.4, 123.7, 122.6, 122.4, 120.8,
113.9, 87.7, 86.3, 58.8, 21.9. IR (thin film) 3524, 3053, 2922, 2228, 1446,
1371, 1120 cmꢀ1. Mass spectrum (ESI): m/z 424.1002 (C24H19NO3S
(M + Na) requires 424.0978).
1-Phenyl-3-(4-(trifluoromethyl)phenyl)prop-2-yn-1-ol (3d). Propargylic
alcohol 3d was obtained in 72% yield (0.534 mmol scale, 107 mg) after
5-Phenylpent-1-en-4-yn-3-ol (3n). Propargylic alcohol 3n was ob-
tained in 65% yield (0.535 mmol scale, 55 mg) after 2 h as a pale yellow
oil. 1H NMR (500 MHz): δ 7.49ꢀ7.44 (m, 2 H), 7.36ꢀ7.31 (m, 3 H),
6.11ꢀ6.05 (m, 1 H), 5.57 (dt, J = 1.0, 16.0 Hz, 1 H), 5.29 (dt, J = 1.0, 9.5
Hz), 5.12 (d, J = 5.5 Hz), 2.02 (br s, 1 H).
1
7 h as a white solid. H NMR (500 MHz): δ 7.61ꢀ7.63 (m, 2 H),
7.56ꢀ7.59 (m, 4 H), 7.42ꢀ7.45 (m, 2 H), 7.36ꢀ7.40 (m, 1 H), 5.72
(d, J = 6 Hz, 1 H), 2.27 (d, J = 6 Hz, 1 H). 13C NMR (125 MHz): δ 140.4,
132.2, 130.5 (q, J = 33 Hz), 128.9, 126.8, 126.9, 126.4 (d, J = 1.0 Hz),
125.4 (q, J = 3.75 Hz), 124.0 (q, J = 271 Hz), 91.3, 85.4, 65.2. IR (thin
film): 3358, 3061, 2985, 2304, 1614, 1324 cmꢀ1. Mass spectrum (ESI):
m/z 277.0876 (C16H12F3O (M + 1) requires 277.0835).
(E)-1-Phenylhex-4-en-1-yn-3-ol (3o). Propargylic alcohol 3o was
obtained in 72% yield (0.713 mmol scale, 88 mg) after 3 h as a yellow
solid. 1H NMR (500 MHz): δ 7.48ꢀ7.45 (m, 2 H), 7.33ꢀ7.31 (m, 3 H),
6.03ꢀ5.96 (m, 1 H), 5.76ꢀ5.71 (m, 1 H), 5.07 (s, 1 H), 1.92 (br s, 1 H),
1.79ꢀ1.77 (m, 3 H). Mp: 44ꢀ47 °C.
1-Phenylhept-2-yn-1-ol (3e). Propargylic alcohol 3e was obtained in
51% yield (0.48 mmol scale, 46 mg) after 7 h as a clear oil. 1H NMR (500
MHz): δ 7.57ꢀ7.54 (m, 2 H), 7.42ꢀ7.33 (m, 3 H), 5.46 (d, J = 10.0 Hz,
1 H), 2.29 (dt, J = 3, 11.5 Hz, 2 H), 2.14 (d, J = 9.0 Hz, 1 H), 1.60ꢀ1.37
(m, 4 H), 0.93 (t, J = 12.5 Hz, 3 H).
1-Cyclohexyl-3-phenylprop-2-yn-1-ol (3p). Propargylic alcohol 3p
was obtained in 89% yield (0.446 mmol scale, 85 mg) after 2 h as a pale
yellow oil. 1H NMR (500 MHz): δ 7.47ꢀ7.43 (m, 2 H), 7.34- 7.31 (m, 3
H), 4.39 (s, 1 H), 1.95ꢀ1.93 (m, 2 H), 1.83ꢀ1.80 (m, 2 H), 1.73ꢀ1.61
(comp, 2 H), 1.34ꢀ1.11 (comp, 5 H).
3-Phenyl-1-(o-tolyl)prop-2-yn-1-ol (3f). Propargylic alcohol 3f was
obtained in 72% yield (0.416 mmol scale, 66 mg) after 4 h as a white
solid. 1H NMR (500 MHz): δ 7.76ꢀ7.71 (m, 1 H), 7.49ꢀ7.43 (m, 2 H),
7.34ꢀ7.29 (m, 3 H), 7.28ꢀ7.19 (m, 3 H), 5.84 (s, 1 H), 2.50, (s, 3 H),
2.20 (br s, 1 H). Mp: 56ꢀ58 °C.
1-Phenyloct-1-yn-3-ol (3q). Propargylic alcohol 3q was obtained in
81% yield (0.499 mmol scale, 81 mg) after 3 h as a yellow oil. 1H NMR
(500 MHz): δ 7.46ꢀ7.39 (comp, 2 H), 7.33ꢀ7.29 (comp, 3 H), 4.56 (t,
J = 11.0 Hz, 1 H), 1.88 (br s, 1 H), 1.84ꢀ1.76 (m, 2 H), 1.58ꢀ1.48 (m, 2
H), 1.39ꢀ1.29 (m, 4 H), 0.91 (app t, J = 11.5 Hz, 3 H).
1-(4-Methoxyphenyl)-3-phenylprop-2-yn-1-ol (3g). Propargylic al-
cohol 3g was obtained in 91% yield (0.175 mmol scale, 38 mg) after 2 h
3-Phenylprop-2-yn-1-ol (3r). Propargylic alcohol 3r was obtained in
46% yield (0.800 mmol scale, 49 mg) after 4 h as a yellow oil. 1H NMR
(500 MHz): δ 7.48ꢀ7.42 (m, 2 H), 7.35ꢀ7.30 (m, 3 H), 4.51 (d, J = 7.5
Hz, 2 H), 1.86 (br s, 1 H).
1
as a pale yellow solid. H NMR (500 MHz): δ 7.58ꢀ7.54 (m, 2 H),
7.53ꢀ7.46 (m, 2 H), 7.37ꢀ7.31 (m, 3 H), 6.97ꢀ6.92 (m, 2 H), 5.66 (s,
1 H), 3.84 (s, 3 H), 2.22 (br s, 1 H). Mp: 58ꢀ62 °C.
1-(Phenylethynyl)cyclohexanol (3s). Propargylic alcohol 3s was
obtained in 68% yield (0.509 mmol scale, 69 mg) after 2 h as a clear
oil. 1H NMR (500 MHz): δ 7.45ꢀ7.43 (m, 2 H), 7.33ꢀ7.30 (m, 3 H),
2.04ꢀ2.01 (m, 2 H), 1.77ꢀ1.57 (m, 7 H), 1.32ꢀ1.26 (m, 1 H).
1-(2-Bromophenyl)-3-phenylprop-2-yn-1-ol (3h). Propargylic alcohol
3h was obtained in72% yield (0.270 mmolscale, 56 mg) after 2 h asa clear
oil. 1H NMR (500 MHz): δ 7.86 (dd, J = 2.5, 12.5 Hz, 1 H), 7.61 (dd, J =
2.0, 13 Hz, 1 H) 7.52ꢀ7.46 (m, 2 H), 7.40 (dt, J = 2.5, 12.5 Hz, 1 H),
7.36ꢀ7.31 (m, 3 H), 7.23 (dt, J = 2.5, 13 Hz, 1 H), 6.03 (d, J = 9.0 Hz,
1 H), 2.56 (d, J = 9.0 Hz, 1 H).
’ ASSOCIATED CONTENT
Methyl 4-(1-Hydroxy-3-phenylprop-2-yn-1-yl)benzoate (3i). Pro-
pargylic alcohol 3i was obtained in 74% yield (0.609 mmol scale, 120
mg) after 3 h as a pale yellow solid. 1H NMR (500 MHz): δ 8.08 (d, J =
8.5 Hz, 2 H), 7.70 (d, J = 8.5 Hz, 2 H), 7.47ꢀ7.49 (m, 2 H), 7.31ꢀ7.36
(m, 3 H), 5.76 (d, J = 5.0 Hz, 1 H), 3.93 (s, 3 H), 2.51 (d, J = 5.0 Hz, 1 H).
13C NMR (125 MHz): δ 167.0, 145.6, 131.9, 130.2, 130.1, 129.0, 128.6,
126.8, 122.3, 88.3, 87.3, 64.8, 52.4. IR (thin film): 3431, 3054, 2952,
2198, 1720, 1437, 1280, 1114, 1031 cmꢀ1. Mass spectrum (ESI): m/z
267.1043 (C17H15O3 (M + 1) requires 267.1016). Mp: 47 - 50 °C.
4-(1-Hydroxy-3-phenylprop-2-yn-1-yl)benzonitrile (3j). Propargylic
alcohol 3j was obtained in 81% yield (0.175 mmol scale, 33 mg) after 2 h
as a white solid. 1H NMR (500 MHz): δ 7.76ꢀ7.68 (m, 4 H), 7.49ꢀ7.43
(m, 2 H), 7.38ꢀ7.31 (m, 3 H), 7.49ꢀ7.44 (m, 2 H), 5.76 (s, 1 H), 2.60
(br s, 1 H). Mp: 84ꢀ86 °C.
S
Supporting Information. Text, figures, and tables giving
b
experimental and computational procedures and spectral data
for all new compounds and CIF files giving crystal data for 5 and 6.
This material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: bashfeld@nd.edu.
’ ACKNOWLEDGMENT
3-phenyl-1-(4-(trifluoromethyl)phenyl)prop-2-yn-1-ol (3k). Pro-
pargylic alcohol 3k was obtained in 86% yield (0.287 mmol scale, 68 mg)
after 2 h as a pale yellow oil. 1H NMR (500 MHz): δ 7.77ꢀ7.66 (m, 4
H), 7.50ꢀ7.47 (m, 2 H), 7.39ꢀ7.31 (m, 3 H), 5.77 (d, J = 6.5 Hz, 1 H),
2.43 (br s, 1 H).
We thank Professor Seth N. Brown for helpful discussions
and the University of Notre Dame for financial support of this
research.
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NMR (500 MHz): δ 7.51ꢀ7.48 (m, 2 H), 7.47ꢀ7.46 (m, 1 H),
5220
dx.doi.org/10.1021/om200581f |Organometallics 2011, 30, 5214–5221

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