Pathways to Functionalized Heterocycles: Propargyl Rearrangement using B(C6F5)3

Article abstract of DOI:10.1021/acs.organomet.5b00753

The reactions of propargyl amides, ureas, carbamates, and carbonates with B(C₆F₅)₃ proceed via an intramolecular 5-exo-dig cyclization across the alkyne unit to yield the corresponding vinyl borate species. The generated sp² carbocation is stabilized by the flanking heteroatoms, allowing for isolation of oxazoline intermediates. The fate of these intermediates is strongly dependent upon the propargyl-functionalized starting material, with the carbamates and carbonates undergoing a ring-opening mechanism (propargyl rearrangement) to give cyclic allylboron compounds, while prolonged heating of the urea derivatives shows evidence of oxazole formation. In a deviation away from the reactivity of carbamates stated previously, the benzyl carbamate substrate undergoes dealkylation at the benzylic position, liberating 5-methyloxazol-2-(3H)-one.

Full text of DOI:10.1021/acs.organomet.5b00753

Article
pubs.acs.org/Organometallics
Pathways to Functionalized Heterocycles: Propargyl Rearrangement
using B(C6F5)3
Lewis C. Wilkins,† Philipp Wieneke,‡ Paul D. Newman,† Benson M. Kariuki,† Frank Rominger,‡
A. Stephen K. Hashmi,‡,§ Max M. Hansmann,*,‡ and Rebecca L. Melen*,†
†School of Chemistry, Cardiff University, Main Building, Cardiff CF10 3AT, Cymru/Wales, U.K.
‡Organisch-Chemisches Institut, Ruprecht-Karls-Universitat Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
̈
§Chemistry Department, King Abdulaziz University (KAU), Jeddah 21589, Saudi Arabia
S
* Supporting Information
ABSTRACT: The reactions of propargyl amides, ureas,
carbamates, and carbonates with B(C6F5)3 proceed via an
intramolecular 5-exo-dig cyclization across the alkyne unit to
yield the corresponding vinyl borate species. The generated sp2
carbocation is stabilized by the flanking heteroatoms, allowing
for isolation of oxazoline intermediates. The fate of these
intermediates is strongly dependent upon the propargyl-
functionalized starting material, with the carbamates and
carbonates undergoing a ring-opening mechanism (propargyl
rearrangement) to give cyclic allylboron compounds, while
prolonged heating of the urea derivatives shows evidence of
oxazole formation. In a deviation away from the reactivity of carbamates stated previously, the benzyl carbamate substrate
undergoes dealkylation at the benzylic position, liberating 5-methyloxazol-2-(3H)-one.
interactions have been detected.14 Further to this, a range of
cyclization reactions have been shown to occur when terminal
INTRODUCTION
■
Functionalized heterocycles are key components of a diverse
and internal diyne substrates have been used, giving a broad
range of both natural products and synthetic pharmaceuticals.
product range including fused polycyclic dibenzopentalene
Oxazoles are particularly important for their role in a range of
units15 as well as five-membered boracyclic compounds
biologically active compounds, including anti-inflammatory,1
(Scheme 1).16 When diynes are used in conjunction with
antirheumatic,2 and antidiabetic3 treatments inter alia.4 In
addition to these applications, oxazoles and oxazolines have
Scheme 1. Previous Work on B(C6F5)3-Promoted
Rearrangement Reactions
been used as ligands in coordination chemistry5 and as
protecting groups.6
Given their prominent position in a range of pharmaceutical
products, investigations into alternative pathways utilizing
main-group elements are becoming more attractive, as the
formation of such heterocyclic structures through cyclization
reactions are most often effected via transition-metal catalysts
such as gold,7 palladium,8 and silver.9 Nevertheless, recent
developments have led to alternative approaches in which the
d-block metal is replaced by a main-group element.10 More
recently Saito et al. reported an elegant methodology involving
an iodine-mediated oxidative annulation reaction between an
alkyne and nitrile that proceeds via the formation of an
alkenyliodonium intermediate followed by reductive elimina-
tion to give the 2,4,5-trisubstituted oxazole.11
Research by Erker et al. has shown a strong propensity for
1,1-carboboration when tris(pentafluorophenyl)borane, B-
(C6F5)3, is reacted with terminal alkynes.12 While gold and
other π Lewis acidic transition metals can form strong
interactions with π bonds,13 an analogous boron π bond
Received: September 3, 2015
complex has yet to be isolated, although weak van der Waals
© XXXX American Chemical Society
A
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bulky phosphine reagents such as P(o-tolyl)3 as the Lewis basic
component of a frustrated Lewis pair (FLP) system, 1,1-
carboboration occurs with subsequent 1,2-addition of the
second alkyne unit, resulting in an eight-membered heterocyclic
product (Scheme 1).12b,17 In addition to this, contemporary
work has indicated that B(C6F5)3 is an extremely versatile
reagent for oxazole formation from amide precursors.18 The
reactivity of B(C6F5)3 has also been exploited for use as an
allylation reagent generated by propargyl ester rearrangement.19
However, the increasing interest in main-group-mediated
chemistry has led to a new focus on the application of p-block
elements over precious transition metals. Our previous research
on the activation of terminal alkynes using the strong Lewis
acid B(C6F5)3 showed that propargyl amides underwent an
intramolecular cyclization reaction to form oxazolines and
oxazoles,18 while propargyl esters rearranged to give allylboron
reagents or dioxolium compounds (Scheme 2).19,20 These
studies have led us to explore further the range of functional
groups which are amenable to these main-group activation
reactions to generate heterocyclic compounds.
latter case the additional alkyne functionality would enable
further reactions or tandem processes. Interestingly, when N,N-
dipropargyl amides 1 and B(C6F5)3 were reacted in a 1:1 ratio,
exclusive formation of the 5-exo-oxoboration cyclization
product 8 (Scheme 3) was observed, with the second alkyne
Scheme 3. Reactions of Dipropargyl Amide Derivatives with
B(C6F5)3
unit remaining untouched. This reactivity follows a pathway
analogous to that previously observed where the N-substituted
propargyl amides undergo a 1,2-addition process to give a vinyl
borate species.18
Scheme 2. Previously Observed Reactivity of Terminal
Propargyl Amides and Esters with B(C6F5)3
The initial species formed upon mixing N,N-dipropargyl
amides 1 and B(C6F5)3 was the Lewis acid/base adduct
between the Lewis basic amide oxygen atom and the vacant p
orbital on boron. The resultant compounds 7a,b were isolated
in 77% and 41% yields, respectively, and structurally
characterized (vide infra). Subsequent cyclization via π
activation of one of the terminal alkynes was achieved by
heating to 45 °C for 2 days to give compounds 8. The time
frame was reduced to 60 min at room temperature, giving very
good conversion (86%) for the electron-withdrawing p-nitro-
substituted aryl group (8c). This would suggest that the
electron-withdrawing effect of the nitro group reduces the
Lewis basicity of the amide oxygen, therefore increasing the
dissociation of the adduct. This in turn leads to greater
concentrations of unbound B(C6F5)3 in solution, which is able
to activate the π system of the alkyne toward cyclization. This
trend holds true for other experimental results seen in this
investigation and is in accordance with our recent studies in this
area.18
The formation of adducts 7 can be used to elucidate the
reaction pathway whereby the initial B−O Lewis adduct is
formed in equilibrium with the dissociated B(C6F5)3. The free
Lewis acid then activates the π system of the alkyne toward
cyclization, as evidenced by the presence of two peaks in the
11B NMR spectra, one at ca. δ −0.5 ppm for the dative B−O
adduct and a second at ca. δ −16.9 ppm associated with the
rapid ensuing cyclization. The expected 5-alkylidene-4,5-
dihydrooxazolium borate products (8) were characterized by
multinuclear NMR spectroscopy, all of which displayed sharp
singlets in the 11B spectra between δ −16.9 and −17.0 ppm,
indicating the formation of the aforementioned four-coordinate
vinyl borate species. This is supported by the 19F NMR spectra,
which showed three signals in a 2:2:1 ratio as a result of the
ortho (δ −132.7 to −132.8 ppm), meta (δ −164.7 to −165.3
ppm), and para (δ −160.3 to −160.9 ppm) fluorine atoms of
the pentafluorophenyl rings. In accordance with previous work
the π activation of the alkyne and cyclization gives the 1,2-
addition product in the E configuration exclusively.18
While previous work focused solely on propargyl esters or
amides (Scheme 2), the current work describes the applications
of B(C6F5)3 to these types of propargyl rearrangements and
gives a detailed view into the influence of the functionality
installed in the propargylic position (see Figure 1).
RESULTS AND DISCUSSION
■
Reactivity of Dipropargyl Amides. In investigations of
dipropargyl amide systems, it was questionable whether a diyne
cyclization reaction similar to those reported by the Erker
group would proceed (Scheme 1),15a or if the propargyl amide
cyclization would be the favored reaction pathway.21 In the
Single-crystal X-ray diffraction was used to explore the solid-
state structures of the majority of the compounds produced in
Figure 1. Propargyl-functionalized starting materials discussed herein.
B
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these reactions. The initial B−O adducts 7 between B(C6F5)3
and the carbonyl oxygen of the dipropargyl amide crystallized
readily from solution, and their solid-state molecular structures
are shown in Figure 2. The metrics for adducts 7a,b are very
Table 1. Experimental Bond Lengths for 8c,d and 9a,b
bond length/Å
bond
8c
8d
9a
9b
C1−C2
C2−C3
C3−N
C4−N
C4−X
C2−O
C4−O
C1−B
1.303(4)
1.503(4)
1.475(4)
1.300(3)
1.468(4)
1.468(3)
1.305(4)
1.623(4)
1.315(2)
1.510(2)
1.475(2)
1.298(2)
1.489(2)
1.459(2)
1.307(2)
1.628(2)
1.309(3)
1.512(3)
1.465(2)
1.313(3)
1.317(2)
1.461(2)
1.304(2)
1.619(3)
1.310(4)
1.508(5)
1.455(4)
1.312(5)
1.309(5)
1.460(4)
1.309(4)
1.618(5)
product of the intramolecular cyclization reaction of the
dipropargyl amides 1c,d with B(C6F5)3. Delocalization of the
positive charge about the N−C4−O moiety is indicated by a
shortening of both the C4−O bond (ca. 1.305 Å) and the C4−
N bond (ca. 1.299 Å) in comparison to those of a formal single
bond at 1.368 and 1.346 Å, respectively.22 Another point of
note is the rotation of the p-nitrophenyl group of 8c out of the
O−C4−N plane by ca. 41°. This observation may be reasoned
simply as the result of reduced steric strain between the
adjacent propargyl group and the C4 substituent in these
orientations. The structural parameters are presented in the
Supporting Information.
The reactivity observed here clearly shows that the propargyl
amide cyclization is outcompeting any potential diyne
cyclization or 1,1-carboboration mechanisms. Furthermore,
the second alkyne moiety remains untouched and enables the
potential for further functionalization such as hydroboration or
application in tandem processes.
Reactivity of Propargyl Ureas. In an effort to gain an
insight into the reactivity of the Lewis basic carbonyl of these 5-
exo-dig cyclization reactions, the amide carbon substituent was
replaced with a strongly donating secondary amine to give the
corresponding urea derivative (2) that was anticipated to give
the 5-alkylidene-4,5-dihydrooxazol-2-amino borate species (9).
Observation of the 11B NMR spectra of the reaction between
compounds 2a,b and B(C6F5)3 showed little to no conversion
to the corresponding 5-alkylidene-4,5-dihydrooxazol-2-amino
borate product (9; Scheme 4) after 2 days at ambient
temperature. However, broad resonances in the δ −1.6 to
−1.8 ppm region of the 11B NMR spectra did indicate adduct
formation.23 Upon heating at 50 °C for 7 days (9a) or 14 days
(9b), a sharp peak emerged at ca. δ −17.0 ppm representing
the expected four-coordinate vinyl borate species which were
both generated in yields of 31%. Prolonged heating of the
reaction mixture with 2b led to a further rearrangement, as
indicated by a new broad peak at δ −10 ppm (Figure 3), which
is attributed to the oxazole compound II (Figure 3).
Figure 2. Solid-state structures of 7a,b and 8c,d (from top to bottom).
Toluene solvent is omitted for clarity. Color code: B, yellow-green; C,
black; N, blue; F, pink; O, red. Thermal ellipsoids are shown at 50%
probablility.
similar to individual bond lengths within the expected range,
albeit with a very slight contraction of the C4−N bond (ca.
1.324 Å), reflecting stabilization of the cationic carbonyl oxygen
via resonance. In both cases the donation of the lone pair of the
sp2 orbital on oxygen leads to a bent geometry and a cis
configuration with respect to the substituent R group. The
molecular structures of 8c,d (Figure 2, Table 1) show the
The reduced reaction rates for these transformations can be
attributed to two main components, the first being the sparse
solubility of the urea substrates in a range of organic solvents
which leads to increased reaction times. The second relates to
the stronger donor ability of the urea in comparison to the
amide functionality as well as the stabilizing effect of the
delocalized positive charge about the N2CO fragment, giving
C
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Scheme 4. Proposed Mechanistic Pathway of the Reaction
between Propargyl Ureas and B(C6F5)3
Figure 4. Solid-state molecular structures of 9a (top) and 9b
(bottom). Color code: B, yellow-green; C, black; N, blue; F, pink; O,
red. Thermal ellipsoids are shown at 50% probability.
analysis of the metric parameters of the structures of 9a,b
(Table 1). Both data sets agree well with expected bond
lengths, with both the C4−N1 and C4−N2 bonds being between
the accepted values for single and double C−N bonds at
∼1.313 Å. This is clarified further on investigation of the
planarity of the N2CO fragment, with the N2−C4−N1−C3
fragment of 9a showing a torsional angle of −179.8(2)°.
Reactivity of Propargyl Carbamates. In contrast to the
reactivity of ureas, the carbamates underwent a more
complicated cyclization/ring-opening mechanism (propargyl
rearrangement) upon addition of B(C6F5)3 to 3a−c. Although
the cyclization to intermediates 10a,c proceeded under mild
conditions to give yields of 64% and 60% respectively, long
reaction times (24−120 h) were needed to afford the final
allylboron products 11a−c (Scheme 5). Complete reaction of
3a to give 11a with B(C6F5)3 was achieved in 16 h when the
temperature was raised to 50 °C. These carbamates behave in a
manner similar to that for the propargyl esters upon treatment
with B(C6F5)3.19 In order to probe further the mechanism for
the generation of the allylboron compounds 11, which contain
a carbamate-boron chelate, the reactions were performed at low
Figure 3. In situ 11B NMR spectra of the reaction between 2b and
B(C6F5)3.
stronger adduct formation. This stabilized adduct would lower
the concentration of dissociated free B(C6F5)3, leading to
reduced rates of π activation of the alkyne. Therefore, more
harsh reaction conditions are required to ensure conversion of
2 to the corresponding 2-amino-5-alkylidene-4,5-dihydroox-
azole borate species (9) and subsequent protonation/
tautomerization to the 2-amino-5-methyl-4,5-dihydrooxazole
product II (Scheme 4). Workup of the reaction mixtures from
2a,b after the appropriate time gave colorless crystals of 9a,b
(Figure 4).
Scheme 5. Reaction between 3 and B(C6F5)3 To Give 11
The 11B NMR spectra confirmed the assignments made from
the in situ studies that are supported by the 19F NMR spectra,
which reveal three resonances in a 2:2:1 ratio for the ortho (δ
−132.1 to −132.6 ppm), meta (δ −165.1 to −165.2 ppm), and
para (δ −161.1 to −161.3 ppm) aryl fluorine atoms closely akin
to those seen previously with the products from the analogous
reactions with dipropargyl amides.
Earlier assumptions that the cationic charge generated by the
cyclization step could be delocalized about the structure via
lone pair donation from the adjacent heteroatoms into the
vacant p orbital of the carbocation were further validated on
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temperature (retarding the ring-opening step) to enable
isolation of the 2-amino-1,3-dihydrooxolium intermediates
(10). Previously reported rearrangements of dihydrooxolium
compounds were rapid, with unstabilized propargyl esters
giving the resultant allylboron reagent in as little as 15 min with
the quaternary boron intermediate proving very challenging to
isolate.19 However, the inclusion of the amido nitrogen appears
to aid the stabilization of the delocalized cationic charge about
the NCO2 moiety in 10, leading to isolation of the
corresponding intermediates. Analysis of intermediates 10a,c
was carried out by multinuclear NMR spectroscopy using
cooled deuterated solvent to delay further reactions. The NMR
spectra exhibited typical characteristics of such vinyl boron
complexes, with a single sharp resonance being seen in the 11B
NMR spectra (δ −17.0 ppm) and three peaks in the 19F NMR
spectra in a 2:2:1 ratio for the ortho (δ −133.0 to −132.6
ppm), meta (δ −166.2 to164.9 ppm), and para (δ −161.9 to
−160.5 ppm) fluorine atoms of the perfluorophenyl rings.
When the reaction mixture was warmed to room temperature,
the ensuing rearrangement reaction proceeded, yielding the
allylboron species 11 (Scheme 5).
These allylboron compounds 11 could be identified by a
typically broad peak at ca. δ 0.0 ppm in the 11B NMR spectra
signifying the new B−O adduct. More prominent features of
these products are the vinylic proton resonances seen in the 1H
NMR spectra, which occur as doublets (11a,c) or a quartet
(11b) in the δ 4.3−5.0 ppm region. The conversion of 10 to 11
leads to a change in the 19F NMR spectra, with the three
originally identical C6F5 rings giving way to nine new peaks of
the now inequivalent perfluorophenyl rings of 11.
There is an emerging trend whereby an increase in the
number of stabilizing heteroatoms flanking the carbocation
decreases the ease of the 5-exo-oxoboration cyclization. There is
basis for the argument that increasing the Lewis basicity of the
carbonyl oxygen would cause the reaction to undergo a more
rapid cyclization once dissociation occurs.20 However, the rate-
determining step of the reaction is the cleavage of the B−O
dative bond; hence, if this bond is stabilized via resonance of
the N2CO moiety, then the rate of conversion is stunted.
Importantly, the additional amido group not only stabilizes
the intermediate 10 but also increases the stability of the boron
chelate in 11. Prolonged heating of 11a at 60 °C did not lead to
the 1,3-carboboration product through a 1,3-allylboron shift,
showing reactivity different from that of the propargyl esters.19
In addition to the in situ multinuclear NMR analysis of the
propargyl carbamate rearrangement, the intermediates 10 and
the allylboron compounds 11 (Figure 5) were structurally
characterized by single-crystal X-ray diffraction. The solid-state
structures of 11b,c verify the outlined trans-oxyboration
mechanism presented in Scheme 5. The structural parameters
are summarized in Tables 2 and 3.
Upon comparison of the structures of these intermediates
(10) with those formed with the propargyl ureas (9), it is noted
that the C−N bond distance in 9a is longer than that of 10a at
1.313(3) vs 1.290(3) Å, respectively. This is in good agreement
with the more strongly electron donating effect of the single
amino group in comparison with the stabilization over the two
amino functionalities in the urea derivatives.
Examination of the solid-state structures of the products
11b,c (Figure 5 and Table 3) confirmed the rearrangement of
the vinyl borate compounds 10b,c to give the corresponding
six-membered allylboron heterocycles. Inspection of the metric
parameters show the expected bond lengths for the predicted
Figure 5. Solid-state molecular structures of 10a,c and 11b,c (from
top to bottom), Color code: B, yellow-green; C, black; N, blue; F,
pink; O, red. Thermal ellipsoids are shown at 50% probability.
structure, with the C2−C3 bond exhibiting typical double-bond
character (1.309(3) Å) and shortening of the C4−N bond
(1.320(3) Å) in accordance with previous assertions regarding
the bond order (Table 3).
The former transformations used propargyl carbamates
which were derived from propargyl alcohols. The reverse
combination of a propargyl carbamate derived from a propargyl
amine was also investigated in the reaction with B(C6F5)3
(Scheme 6). On investigation of the reaction between
compound 4 and B(C6F5)3 an unexpected result was observed
whereby the anticipated stable zwitterionic species was not the
major product of the reaction. Multinuclear NMR spectro-
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B(C6F5)3 to be used in the formation of such oxazolone
derivatives are more often observed in gold or palladium
catalysis.24
Table 2. Experimental Bond Lengths for 10a,c
X-ray crystallographic studies of 12 revealed the structure for
the 5-methyl-2-(3H)-oxazolone-B(C6F5)3 adduct (Figure 6).
bond length/Å
bond
10a
10c
C1−C2
C2−C3
C3−O2
C4−O2
C4−N
C2−O1
C4−O1
C1−B
1.302(3)
1.509(3)
1.468(3)
1.309(3)
1.290(3)
1.440(3)
1.307(3)
1.616(4)
1.304(4)
1.505(4)
1.466(4)
1.297(3)
1.305(3)
1.464(3)
1.305(3)
1.627(4)
Figure 6. Solid-state molecular structure of 12, Color code: B, yellow-
green; C, black; N, blue; F, pink; O, red. Thermal ellipsoids are shown
at 50% probability.
Table 3. Experimental Bond Lengths for 11b,c
Delocalization of electron density about the carbamate
functionality leads to contraction of the heteroatom−carbon
bonds as noted above. The structural parameters are
summarized in the Supporting Information.
Reactivity of Propargyl Carbonates. To extend the
substrate scope, the reactivity of propargyl carbonates was
investigated. It was seen that the reaction of 5a with B(C6F5)3
proceeded in the same fashion as for the propargyl esters and
carbamates, displaying comparable stability of the intermediate,
leading to a long reaction time of 3 days to give the allylboron
product 13; however, a good yield of 81% was obtained
(Scheme 7). Analysis via X-ray crystallography further
bond length/Å
bond
11b
11c
C1−C2
C2−C3
C2−O2
C4−O1
C4−O2
C4−N
C1−B
1.498(6)
1.324(7)
1.438(5)
1.280(6)
1.332(6)
1.325(6)
1.633(7)
1.570(6)
1.492(3)
1.309(3)
1.436(2)
1.263(3)
1.315(3)
1.320(3)
1.647(4)
1.555(2)
Scheme 7. Reactions of Propargyl Carbonate 5a in Propargyl
Rearrangements with B(C6F5)3
O1−B
Scheme 6. Oxazolone Synthesis from the Reaction between
B(C6F5)3 and 4
expounded the delocalization about the heteroatom-flanked
carbon center, with all three C−O bonds displaying similar
lengths of 1.246(2), 1.298(2), and 1.292(2) Å (Figure 7).
In a departure from the observed reactivity of these systems
described above, the introduction of a tert-butyl group to the
scopic and X-ray crystallographic (see later) analysis clearly
shows the product to be 5-methyl-2-(3H)-oxazolone (12;
Scheme 6) and not the cyclized vinyl borate as observed with
similar substrates.
The 11B NMR spectrum of 12 shows a resonance at δ 0.7
1
ppm indicative of a carbonyl boron adduct, and the H NMR
spectrum unmistakably shows the formation of the methyl
group produced through isomerization (δ 2.18 ppm) along
with the vinyl proton at δ 6.56 ppm. It is presumed that trace
amounts of water trigger the dealkylation of the benzyl group
after cyclization followed by tautomerization to yield the
oxazolone derivative 12. Attempts to render this transformation
catalytic have met with limited success. However, reactions
using 10 mol % of B(C6F5)3 with 1 equiv of water under
ambient conditions show the emergence of a singlet at δ 4.63
ppm in the 1H NMR, indicating the formation of benzyl alcohol
from the dealkylation step. This exemplifies the potential of
Figure 7. Solid-state molecular structure of 13, Color code: B, yellow-
green; C, black; F, pink; O, red. Thermal ellipsoids are shown at 50%
probability.
F
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propargyl carbonate as in 5b resulted in the loss of the Boc
group in the presence of B(C6F5)3 (Scheme 8).
might be useful in aldehyde allylation reactions, and work on
this topic and other aspects of the reactivity of these
compounds and their applications in organic chemistry is
ongoing.
Scheme 8. Boc Deprotection of Propargyl Carbonates using
10 mol % B(C6F5)3
EXPERIMENTAL SECTION
■
General Experimental Considerations. With the exception of
the starting materials, all reactions and manipulations were carried out
under an atmosphere of dry, O2-free nitrogen using standard double-
manifold techniques with a rotary oil pump. An argon- or nitrogen-
filled glovebox (MBraun) was used to manipulate solids, including the
storage of starting materials, room-temperature reactions, product
recovery, and sample preparation for analysis. All solvents (toluene,
CH2Cl2, pentane, hexane) were dried by employing a Grubbs-type
column system (Innovative Technology) or an MB SPS-800 solvent
purification system and stored under a nitrogen atmosphere.
Deuterated solvents were distilled and/or dried over molecular sieves
before use. Chemicals were purchased from commercial suppliers and
used as received. 1H, 13C, 11B, and 19F NMR spectra were recorded on
Bruker Avance III-300, Bruker Avance DRX-300, Bruker Avance II
400, Bruker Avance 500, Bruker Avance III 600, and JEOL Eclipse 300
spectrometers. Chemical shifts are expressed as parts per million
Analysis of the 1H NMR spectra showed that isobutylene was
generated in addition to the corresponding propargyl alcohol
and CO2. This was conducted on a catalytic scale using 10 mol
1
(ppm, δ) downfield of tetramethylsilane (TMS), and H/13C signals
are referenced to CDCl3 (7.26/77.16 ppm) and CD2Cl2 (5.32/53.80
ppm) as internal standards. 19F, 31P, and 11B NMR spectra were
referenced to CFCl3 (19F), H3PO4 (31P), and BF3·Et2O/CDCl3 (11B).
The description of signals include s = singlet, d = doublet, t = triplet, q
= quartet, sep = septet, m = multiplet, and br = broad. All coupling
constants are absolute values and are expressed in hertz (Hz). Yields
are given as isolated yields. All spectra were analyzed assuming a first-
order approximation. IR spectra were measured on an FT-IR Bruker
Vector 22 machine or Shimadzu IRAffinity-1 photospectrometer. Mass
spectra were measured on JEOL JMS-700, Waters LCT Premier/XE,
Waters GCT Premier, and Bruker ApexQe hybrid 9.4 spectrometers.
Elemental analyses were conducted at London Metropolitan
University by Mr. Stephen Boyer or using the in-house services at
Heidelberg University.
1
% of B(C6F5)3, with the H NMR spectrum showing almost
complete deprotection after 17 h at room temperature, as
evidenced by the presence of a septet at δ 4.64 ppm for the
isobutylene.
A shift in the resonance position of the methyl groups of the
alcoholic moiety from δ 1.70 to 1.67 ppm is also noted. While
catalytic deprotection traditionally occurs through the addition
of a strong Brønsted acid such as trifluoroacetic acid and HCl/
acetic acid, if other acid-sensitive functionalities are present in a
given compound, then a milder approach may be necessary.25
While this conversion has also been effected by other main-
group compounds,26 this is a nice example where tris-
(pentafluorophenyl)borane has been used for the catalytic
removal of Boc protecting groups.
Reactivity of Propargyl Phosphates and Phosphi-
nates. Further substrates were also tested in an attempt to
introduce varying heteroatoms into the cyclized product. To
this end terminal and internal propargyl phosphates (6a,b) and
phosphinates (6c,d) were tested in the reaction with B(C6F5)3.
In the case of 6a strong adduct formation could be observed
and decomposition occurred at elevated temperatures (20 h, 80
°C in C6D6), while 6b decomposed directly upon addition of
B(C6F5)3. The reactions of propargyl phosphinates 6c,d gave
classical adducts which did not undergo further reaction even at
elevated temperatures (18 h at 80 °C). These experiments
clearly indicate that phosphates and phosphinates behave
differently from the previously studied propargyl ester,
carbamate, and carbonate systems. This might be attributed
to the longer P−O bond and the stronger bond energy of the
P−O→B dative bond.
Synthesis of 1. General Procedure. N,N-Dipropargylcarboxa-
mides were prepared according to literature methods.21 Et3N (2.0
equiv) and DMAP (0.02 equiv) were added to a solution of N,N-
dipropargylamine hydrochloride (1.0 equiv) in CH2Cl2 at room
temperature under a nitrogen atmosphere, and the resulting solution
was stirred for 15 min. The solution was then cooled to 0 °C, and the
corresponding acyl chloride (1.0 equiv) was added dropwise and
stirred for 30 min at this temperature. The reaction mixture was then
warmed to room temperature and was stirred for a further 3 h. The
reaction was then quenched with water, the aqueous layer was
extracted with CH2Cl2 (×2), and the combined organic phases were
washed with brine. The organic phase was then dried with Na2SO4 and
filtered. Removal of the solvent yielded the crude product, which was
purified by column chromatography.
1
Characterization Data for 1a. H NMR (400 MHz, CDCl3, 298
3
4
4
K): 7.22 (dd, JHH = 8.2 Hz, JHH = 1.9 Hz, 1H), 7.17 (d, JHH = 1.9
3
Hz, 1H), 6.89 (d, JHH = 8.2 Hz, 1H), 4.33 (br s, 4H), 3.91 (s, 3H),
3.91 (s, 3H), 2.33 (br s, 2H). 13C NMR (101 MHz, CDCl3, 298 K):
170.8 (s), 151.0 (s), 148.8 (s), 126.7 (s), 120.8 (s), 111.0 (s), 110.6
(s), 78.6 (br s), 72.8 (br s), 56.1 (s).
1
Characterization Data for 1b. H NMR (400 MHz, CDCl3, 298
CONCLUSIONS
K): 5.82 (m, 1H), 4.33 (s, 2H), 4.21 (s, 2H), 2.28 (s, 1H), 2.21 (s,
1H), 1.93 (d, 4JHH = 1.1, 3H), 1.86 (d, 4JHH = 1.1 Hz, 3H). 13C NMR
(101 MHz, CDCl3, 298 K): 167.6 (s), 149.6 (s), 116.8 (s), 78.6 (s),
78.1 (s), 73.0 (s), 72.1 (s), 36.8 (br s), 33.3 (br s), 26.6 (br s), 20.5 (br
s).
■
The addition of the strong Lewis acid B(C6F5)3 to propargyl
amides and ureas provides a potentially catalytic synthetic route
to oxazoline derivatives. In contrast to recent studies by the
Erker group, this work shows that 5-exo-oxoboration of these
nonaromatic nitrogen derived diyne systems occurs preferen-
tially over any carboboration steps.12b It was seen that π
activation of the carbamates and carbonates yields allylboron
products via a C6F5 migration rearrangement. These species
1
Characterization Data for 1c. H NMR (400 MHz, CDCl3, 298
K): 8.31 (d, 3JHH = 8.8 Hz, 2H), 7.74 (d, 3JHH = 8.6 Hz, 2H), 4.50 (br
s, 2H), 4.10 (br s, 2H), 2.40 (br s, 1H), 2.32 (br s, 1H). 13C NMR
(101 MHz, CDCl3, 298 K): 168.7 (s), 150.0 (s), 140.7 (s), 128.4 (s),
124.1 (s), 77.4 (s), 74.2 (s), 73.2 (s), 38.3 (s), 34.0 (s).
G
DOI: 10.1021/acs.organomet.5b00753
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
Characterization Data for 1d. H NMR (400 MHz, CDCl3, 298
K): 4.31 (d, 4JHH = 2.1 Hz, 2H), 4.23 (d, 4JHH = 2.1 Hz, 2H), 2.50 (m,
1H), 2.30 (br s), 2.20 (br s), 1.84−1.72 (m, 4H), 1.86 (m, 1H), 1.48
(m, 2H), 1.34−1.16 (m, 3H). 13C NMR (100.6 MHz, CDCl3, 298 K):
175.6 (s), 78.8 (s), 78.3 (s), 72.9 (s), 72.2 (s), 41.0 (s), 36.1 (s), 33.9
(s), 29.4 (s), 25.8 (s). HRMS (EI+): m/z calculated for [M]+
C13H17NO+ 203.1306, found 203.1310. IR (cm−1): νmax 3281, 3223,
2926, 2922, 2855, 1728, 1643, 1452, 1435, 1418, 1343, 1310, 1290,
1273, 1265, 1244, 1204, 1175, 1136, 953, 922, 893, 856, 640.
Synthesis of 2. General Procedure. Propargyl ureas were prepared
according to similar literature methods.27 To the amine (1.00 equiv)
dissolved in water (ca. 50 mL) at 4 °C was added carbonyldiimidazole
(CDI) (2.00 equiv), and the resulting mixture was stirred for 1 h at
this temperature. The solution was then warmed to room temperature,
and after complete formation of the carbonylimidazolide, propargyl
amine (1.00 equiv) was added and the mixture stirred at room
temperature for ca. 2 h until the reaction was complete. The product
was isolated by filtration, washed with cold water, and dried in vacuo
to give a white solid.
10H, Ph-H), 4.68 (s, 2H, CH2), 2.37 (s, 1H, CH). 13C NMR (126
MHz, CDCl3, 298 K): 154.1 (s), 142.4 (s), 129.1 (s), 127.1 (s), 126.5
(s), 78.2 (s), 74.9 (s), 53.5 (s). IR (cm−1): νmax 3087, 3062, 3027,
2950, 2922, 2870, 1944, 1861, 1803, 1730, 1605, 1495, 1461, 1379,
1304, 1210, 1180, 1083, 1059, 1031, 896, 735. HRMS (AP+): m/z
calculated for [M + H]+ [C16H14NO]+ 252.1025, found 252.1017.
Synthesis of 4. The propargyl carbamate was synthesized by the
following method. Propargylamine (0.51 mL, 8 mmol) was added to a
solution of chloroformate (1.2 mL, 8 mmol) and NaHCO3 (0.67 g, 8
mmol) in 10 mL of EtOH/H2O (1/1) at 0 °C. The solution was
warmed to room temperature and stirred overnight. The solution was
diluted with EtOH/H2O and the aqueous phase extracted with diethyl
ether (3 × 20 mL). The combined organic phases were then washed
with saturated NH4Cl solution (3 × 20 mL), dried over sodium
sulfate, and filtered, and the solvent was removed in vacuo. The crude
product was purified by recrystallization from petroleum ether 40−60
with a few drops of Et2O to solubilize the solid left at −40 °C. Yield:
1
1.48 g, 7.82 mmol, 98%. H NMR (500 MHz, CDCl3, 298 K): 7.36
(m, 5H, Ph-H), 5.13 (s, 2H, CH2-O), 4.98 (br s, 1H, NH), 4.00 (s,
4
2H, N-CH2), 2.24 (t, JHH = 2.5 Hz, 1H, CH). 13C NMR (126
Characterization Data for 2a. Yield: 1.4 g, 10.3 mmol, 51%. Mp:
178−184 °C. 1H NMR (500 MHz, DMSO-d6, 298 K): 6.32 (t, 3JHH
=
MHz, CDCl3, 298 K): 156.0 (s), 136.2 (s), 128.6 (s), 128.3 (m), 127.1
(s), 79.8 (s), 71.7 (s), 67.2 (s), 30.9 (s). IR (cm−1): υmax= 3421, 3308,
3087, 3064, 3030, 2982, 2922, 2875, 2739, 2123, 1950, 1864, 1811,
1732, 1606, 1511, 1457, 1381, 1353, 1325, 1227, 1176, 1141, 1085,
1047, 987, 939, 908, 870, 775. HRMS (EI+): m/z calculated for [M]+
[C11H11NO2]+ 189.0785, found 189.0790.
3
4
5.8 Hz, 2H, NH), 3.78 (dd, JHH = 5.8 Hz, JHH = 2.5 Hz, 4H, CH2),
3.04 (t, JHH = 2.5 Hz, 2H, CH). 13C NMR (126 MHz, DMSO-d6,
4
298 K): 156.9 (s), 82.3 (s), 72.5 (s), 28.8 (s). HRMS (EI+): m/z
calculated for [M]+ [C7H9N2O]+ 137.0715, found 137.0711.
Characterization Data for 2b. Yield: 1.7 g, 9.0 mmol, 91%, Mp:
117−120 °C. 1H NMR (500 MHz, DMSO-d6, 298 K): 7.29−7.17 (m,
Synthesis of 5a. n-Butyllithium (2.00 mL, 2.5 M in hexane, 5.00
mmol) was added to a solution of 1-pentyn-3-ol (0.43 mL, 5.00 mmol)
in THF (10−20 mL) at −78 °C and the resulting solution stirred for 1
h. Diethyl pyrocarbonate (0.73 mL, 5.00 mmol) in 20 mL of THF was
then added to the cooled solution and the mixture warmed to room
temperature and subsequently stirred for 12−24 h. The reaction
mixture was quenched with saturated NH4Cl solution (20 mL) and
the aqueous phase extracted with diethyl ether (3 × 20 mL). The
combined organic phases were then washed with saturated NH4Cl
solution (3 × 20 mL), dried over NaSO4, and filtered, and the solvent
was removed in vacuo. The product was purified by column
chromatography using SiO2 (PE/EE, 95/5 to 80/20) to give the
pure product. Yield: 0.57 g, 3.65 mmol, 73%. Rf = 0.44 (PE/EE 95/5).
3
3
5H, Ph-H), 6.39 (t, JHH = 5.4 Hz, 1H, NH), 6.20 (t, JHH = 5.4 Hz,
1H, NH), 4.22 (d, 3JHH = 5.9 Hz, 2H, CH2), 3.82 (m, 2H, CH2), 2.81
(s, 1H, CH). 13C NMR (126 MHz, DMSO-d6, 298 K): 157.4 (s),
140.3 (s), 127.9 (s), 126.9 (s), 126.4 (s), 82.0 (s), 71.9 (s), 42.9 (s),
28.8 (s). HRMS (EI+): m/z calculated for [M]+ [C11H12N2O]+
188.0950, found 188.0941.
Synthesis of 3. General Procedure. Propargyl carbamates were
synthesized by the following method. Carbamoyl chloride (1.00 equiv)
and DMAP (0.05 equiv) were added to a solution of propargyl alcohol
(1.00 equiv) in pyridine (5 mL), and the resulting mixture was heated
overnight at 80 °C. The reaction mixture was quenched with saturated
NH4Cl solution (10 mL), and the aqueous phase was extracted with
diethyl ether (3 × 20 mL). The combined organic phases were then
washed further with saturated NH4Cl solution (3 × 20 mL), dried over
sodium sulfate, and filtered, and the solvent was removed in vacuo.
Characterization Data for 3a. Purification by column chromatog-
raphy gave a colorless oil (SiO2, PE/EA 95/5). Yield: 0.35 g, 1.64
3
4
1H NMR (500 MHz, CDCl3, 298 K): 5.09 (dt, JHH = 6.5 Hz, JHH
=
1.3 Hz, 1H, CH), 4.22 (q, 3JHH = 7.2 Hz, 2H, CH2), 2.50 (d, 4JHH = 1.3
Hz, 1H, CH), 1.88−1.81 (m, 2H, CH2), 1.32 (t, 3JHH = 7.2 Hz, 3H,
CH3), 1.04 (t, 3JHH = 7.4 Hz, 3H, CH3). 13C NMR (125 MHz, CDCl3,
298 K): 154.7 (s), 80.8 (s), 74.7 (d), 69.0 (d), 64.7 (t), 28.2 (t), 14.6
(q), 9.5 (q). IR (cm−1): νmax 3293, 2979, 2940, 2882, 2358, 2125,
1756, 1515, 1465, 1396, 1373, 1342, 1302, 1275, 1177, 1094, 1062,
1046, 1007, 948, 932, 893, 857, 791, 670. MS-EI: 128.0 (39), 127.0
(8), 91.0 (12), 84.1 (7), 83.1 (51), 69.0 (30), 67.1 (82), 66.0 (100),
63.0 (20). HRMS (EI+): m/z calculated for [M − C2H4]+ [C6H8O3]+
128.0473, found 128.0487.
1
mmol, 67%. Rf = 0.44 (PE/EA 80/20). H NMR (300 MHz, CDCl3,
298 K): 4.70 (d, JHH = 2.5 Hz, 2H), 4.92 (br s, 2H), 2.42 (t, JHH
4
4
=
2.5 Hz, 1H), 1.22 (d, JHH = 6.8 Hz, 12H). 13C NMR (75 MHz,
CDCl3, 298 K): 154.8 (s), 79.1 (s), 74.1 (s), 52.2 (s), 46.2 (br s), 21.1
(br s). IR (ATR) (cm−1): νmax 3247, 2971, 1702, 1443, 1370, 1310,
1294, 1219, 1160, 1136, 1069, 960, 771, 719, 624, 606. MS-EI: 183.1
(13), 169.1 (11), 168.1 (100), 161.9 (6), 151.0 (6), 126.1 (39),
102.1(5), 82.1 (11), 70.0 (11). HRMS (EI+): m/z calculated for [M +
H]+ [C10H17NO2]+ 183.1259, found 183.1239.
3
Synthesis of 5b. Propargyl carbonate 5b was synthesized
according to a similar literature method.28 Propargyl alcohol (1.7
mL, 30 mmol) was dissolved in dichloromethane in combination with
Characterization Data for 3b. Purification by column chromatog-
Hunig’s base (13.1 mL, 75 mmol) alongside DMAP (10 mol %). After
̈
raphy gave a colorless oil (SiO2, PE/EA 95/5). Yield: 0.61 g, 3.10
the mixture was cooled to 0 °C, Boc anhydride (8.51 g, 39 mmol) was
added portionwise, ensuring the reaction mixture was not allowed to
reflux, and then stirred until completion. The resultant solution was
quenched with saturated NH4Cl solution (20 mL) and the aqueous
phase extracted with dichloromethane (3 × 20 mL). The combined
organic phases were then washed with 1 M HCl, saturated NaHCO3
solution, and brine (all 2 × 20 mL), dried over MgSO4, and filtered,
and the solvent was removed in vacuo to give a colorless oil. The
product was sufficiently pure for subsequent reactions. Yield: 3.4 g,
21.8 mmol, 73%. 1H NMR (500 MHz, CDCl3, 298 K): 2.53 (s, 1H, 
CH), 1.68 (s, 6H, CH3), 1.48 (s, 9H, CH3). 13C NMR (125 MHz,
CDCl3, 298 K): 151.5 (s), 84.6 (s), 82.4 (s), 73.0 (s), 72.5 (s), 29.0
(s), 28.0 (s).
1
mmol, 62%. Rf = 0.33 (PE/EE 95/5). H NMR (300 MHz, CDCl3,
3
4
298 K): 5.42 (dq, JHH = 6.7 Hz, JHH = 2.1 Hz, 1H), 4.28−3.55 (m,
2H), 2.40 (d, 4JHH = 2.1 Hz, 1H), 1.50 (d, 3JHH = 6.7 Hz, 3H), 1.21−
1.18 (m, 12H). 13C NMR (75 MHz, CDCl3, 298 K): 154.6 (s), 83.3
(s), 72.3 (s), 60.2 (s), 46.0 (br s), 21.8 (s), 21.1 (br s). IR (cm−1): νmax
3312, 3248, 2972, 2937, 2876, 2121, 1694, 1437, 1370, 1344, 1319,
1284, 1210, 1191, 1158, 1133, 1091, 1045, 918, 768, 661. MS ESI:
197.1 (31), 183.1 (12), 182.1 (100), 161.9 (5), 150.9 (5), 138.1 (5),
130.0 (35), 128.1 (11), 102.0 (11), 96 (18), 88.0 (17), 86.1 (23), 86.0
(19). HRMS (EI+): m/z calculated for [M + H]+ [C11H19NO2]+
197.1416, found 197.1422.
Characterization Data for 3c. Purification by recrystallization from
petroleum ether 40−60 with a few drops of Et2O to solubilize the solid
at −40 °C gave a pale yellow solid. Yield: 1.07 g, 4.26 mmol, 71%. Mp:
Synthesis of 6. General Procedure. To a solution of alcohol (3.00
mmol, 1.00 equiv) in CH2Cl2 were added NEt3 (3.00 mmol, 1.00
equiv) and DMAP (2 mol %), and the solution was cooled to 0 °C.
1
128−133 °C. H NMR (400 MHz, CDCl3, 298 K): 7.28−7.13 (m,
H
DOI: 10.1021/acs.organomet.5b00753
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
For 6a,b diphenylphosphoryl chloride (3.00 mmol, 1.00 equiv) or for
6c,d diphenylphosphinoyl chloride (3.00 mmol, 1.00 equiv) was
dissolved in CH2Cl2 (20 mL) and was added at this temperature. The
solution was stirred for 1 h and slowly warmed to room temperature
and stirred overnight. Water (20 mL) was added, the phases were
separated, and the aqueous phase was extracted with Et2O (3 × 20
mL). The combined organic phases were washed with brine, dried
over Na2SO4, and filtered, and the solvent was removed under reduced
pressure. The products were sufficiently pure for subsequent reactions.
Characterization Data for 6a. Yield: 0.92 g, 3.00 mmol, quant. Rf
(EI+): m/z calculated for [M]+ [C18H19O2P]+ 298.1123, found
298.1130.
Synthesis of 7a. 3,4-Dimethoxy-N,N-di(prop-2-yn-1-yl)-
benzamide (1a; 52 mg, 0.2 mmol) was dissolved in toluene (2 mL)
and added to B(C6F5)3 (102 mg, 0.2 mmol) to give a yellow solution.
After 1 h small crystals formed, which were redissolved by briefly
warming the solution slightly and adding a few drops of CH2Cl2. Upon
cooling large colorless blocks of the adduct formed which were suitable
for X-ray diffraction. The crystals were washed with petroleum ether
40−60 (3 × 3 mL) to give the adduct 7a. Yield: 119 mg, 0.15 mmol,
1
1
77%. H NMR (400 MHz, CDCl3, 298 K): 7.2−7.1 (m, ca. 2H, tol),
= 0.34 (PE/EA 80/20) H NMR (300 MHz, CDCl3, 298 K): 7.28−
3
4
3
7.24 (m, 4H), 7.20−7.08 (m, 6H), 5.27−5.18 (m, 1H), 2.49 (d, 4JHH
=
6.70 (dd, JHH = 8.4 Hz, JHH = 1.9 Hz, 1H), 6.63 (d, JHH = 8.4 Hz,
1H), 6.50 (d, 4JHH = 1.9 Hz, 1H), 4.64 (br s, 2H), 4.17 (d, 4JHH = 2.3
Hz, 2H), 3.79 (s, 3H), 3.61 (s, 3H), 2.46 (t, 4JHH = 2.3 Hz, 1H), 2.40
2.1 Hz, 1H), 1.50 (d, JHH = 6.62 Hz, 3H). 13C NMR (75 MHz,
CDCl3, 298 K): 150.6 (d, JPC = 7.6 Hz), 150.5 (d, JPC = 7.3 Hz), 129.9
(d, JPC = 0.9 Hz), 129.8 (d, JPC = 0.9 Hz), 125.5 (d, JPC = 1.5 Hz),
125.5 (d, JPC = 1.3 Hz), 120.3 (d, JPC = 4.9 Hz, 2C), 120.3 (d, JPC = 4.8
Hz), 81.2 (d, JPC = 6.0 Hz), 75.1 (s), 65.9 (d, JPC = 5.6 Hz), 23.3 (d,
JPC = 6.1 Hz). 31P NMR (120 MHz, CDCl3, 298 K): −12.8 (s). IR
(ATR) (cm−1): νmax 3282, 2126, 1718, 1593, 1492, 1457, 1291, 1220,
1196, 1168, 1092, 1029, 999, 967, 916, 781, 693, 656, 617. MS EI:
302.0 (100), 292.9 (22), 251.0 (25), 250.0 (84), 249.0 (79), 209.0
(67), 170.0 (41), 145.0 (14), 129.0 (15), 128.0 (55), 94.0 (89).
HRMS (EI+): m/z calculated for [M]+ [C16H15O4P]+ 302.0708, found
302.0692.
3
(t, JHH = 2.4 Hz, 1H), 2.28 (s, ca. 1.2H, tol). 11B NMR (160 MHz,
4
CDCl3, 298 K): 0.5 (br s). 19F NMR (283 MHz, CDCl3, 298 K):
3
3
−133.6 (d, JFF = 20.6 Hz, 2F, o-F), −157.5 (t, JFF = 20.5 Hz, 1F, p-
F), −164.1 (m, 2F, m-F). The product could not be fully characterized
in solution, as subsequent dissociation of boron from the amide
oxygen atom followed by cyclization to yield 8a occurs. Anal. Calcd for
C33H15BF15NO3: C, 51.52; H, 1.97; N, 1.82. Found: C, 51.49; H, 1.85;
N, 1.82. IR (cm−1): νmax 2359, 2340, 2322, 1647, 1560, 1560, 1516,
1464, 1456, 1273, 1258, 1240, 1099, 978.
Synthesis of 7b. 3-Methyl-N,N-di(prop-2-yn-1-yl)but-2-enamide
(1b; 36 mg, 0.2 mmol) was dissolved in toluene (ca. 2 mL) and added
to B(C6F5)3 (102 mg, 0.2 mmol) to give a yellow solution. The
reaction mixture was left at room temperature without stirring for 30
min. Slow evaporation of the solvent yielded large colorless blocks of
the product which could be characterized by X-ray diffraction. The
remaining solvent was decanted off and the product washed with
petroleum ether (3 × 3 mL) and dried in vacuo to give pure 7b. Yield:
Characterization Data for 6b. Yield: 1.65 g, 5.0 mmol, quant. Rf =
0.43 (PE/EA 80/20). 1H NMR (300 MHz, CDCl3, 298 K): 7.15−6.94
3
5
(m, 10H), 5.14−5.05 (m, 1H), 1.94 (qd, JHH = 6.6 Hz, JHH = 1.95
Hz, 2H), 1.33 (d, 3JHH = 7.5 Hz, 3H), 0.86 (t, 3JHH = 6.6 Hz, 3H). 13
C
NMR (75 MHz, CDCl3, 298 K): 150.7 (d, JPC = 7.5 Hz), 150.6 (d, JPC
= 7.4 Hz), 129.8 (d, JPC = 0.5 Hz), 129.7 (d, JPC = 0.5 Hz), 125.4 (d,
JPC = 1.2 Hz), 125.3 (dd, JPC = 1.3 Hz), 120.3 (dd, JPC = 3.8 Hz), 120.3
(d, JPC = 3.8 Hz), 89.3 (s), 77.3 (d, JPC = 5.6 Hz), 67.0 (d, JPC = 5.7
Hz), 23.8 (d, JPC = 6.4 Hz), 13.5 (s), 12.4 (s). 31P NMR (120 MHz,
CDCl3, 298 K): −12.8 (s). IR (cm−1): νmax 2976, 2937, 2878, 2247,
1694, 1592, 1490, 1437, 1370, 1346, 13178, 1286, 1221, 1192, 1163,
1133, 1105, 1071, 1058, 1047, 1010, 989, 956, 901, 802, 769, 689, 616.
MS EI: 330.1 (56), 252.0 (14), 251.0 (100), 250.0 (76), 249.0 (38),
238.0 (6), 237.0 (48), 170.0 (20), 161.9 (6), 150.9 (7), 94.0 (39), 81.0
(7), 80.0 (9), 79.0 (15), 77.0 (15). HRMS (EI+): m/z calculated for
[M]+ [C18H19O4P]+ 330.1021, found 330.1019.
1
57 mg, 0.08 mmol, 41%. H NMR (400 MHz, CDCl3, 298 K): 7.12−
6.95 (m, ca. 2H, tol), 5.32 (br s, 1H), 4.49 (d, 4JHH = 2.2 Hz, 2H), 4.28
(d, 4JHH = 2.2 Hz, 2H), 2.38 (t, 4JHH = 2.2 Hz, 1H), 2.24 (t, 4JHH = 2.2
Hz, 1H), 2.19 (s, ca. 1.4H, tol), 1.48 (s, 3H), 1.24 (s, 3H). 11B NMR
(160 MHz, CDCl3, 298 K): −0.5 (br s). 19F NMR (283 MHz, CDCl3,
298 K): −134.1 (d, 3JFF = 20.1 Hz, 2F, o-F), −157.4 (t, 3JFF = 20.5 Hz,
1F, p-F), −164.0 (m, 2F, m-F). The product could not be fully
characterized in solution, as subsequent dissociation of boron from the
amide oxygen atom followed by cyclization to yield 8b occurs. Anal.
Calcd for C29H13BF15NO: C, 50.68; H, 1.91; N, 2.04. Found: C, 50.83;
H, 1.82; N, 2.11. IR (cm−1): νmax 2361, 2340, 2322, 1647, 1559, 1516,
1456, 1281, 1257, 1092, 980, 868, 806, 766, 729, 690, 682.
Characterization Data for 6c. Yield: 0.81 g, 3.0 mmol, quant. Rf =
0.32 (PE/EA 50:50). 1H NMR (300 MHz, CDCl3, 298 K): 7.89−7.76
(m, 4H), 7.53−7.38 (m, 6H), 5.20−5.10 (m, 1H), 2.43 (d, 4JHH = 2.1
Synthesis of 8a. 3,4-Dimethoxy-N,N-di(prop-2-yn-1-yl)-
benzamide (1a; 52 mg, 0.2 mmol) was dissolved in toluene (8 mL)
and added to B(C6F5)3 (102 mg, 0.2 mmol) to give a yellow solution.
The reaction mixture was heated to 45 °C for 2 days without stirring,
whereupon CH2Cl2 (ca. 0.5 mL) was added. Upon cooling small
colorless crystals of the product formed. The remaining solvent was
decanted off, and the crystals were washed with petroleum ether (3 ×
3 mL) and then dried under vacuum to give colorless crystals of the
3
Hz, 1H), 1.62 (d, JHH = 6.6 Hz, 3H). 13C NMR (75 MHz, CDCl3,
298 K): 132.3 (d, JPC = 58.2 Hz), 132.3 (d, JPC = 2.9 Hz), 132.2 (d, JPC
= 2.8 Hz), 132.1 (dd, JPC = 10.4 Hz), 131.4 (d, JPC = 2.9 Hz), 130.6 (d,
JPC = 52.6 Hz), 128.6 (d, JPC = 13.4 Hz), 128.4 (d, JPC = 13.2 Hz), 82.5
(d, JPC = 6.1 Hz), 74.0 (s), 61.7 (d, JPC = 5.2 Hz), 24.2 (d, JPC = 3.8
Hz). 31P NMR (120 MHz, CDCl3, 298 K): 32.7 (s). IR ATR (cm−1):
υmax= 3392, 3067, 2981, 2936, 2245, 1593, 1440, 1375, 1343, 1321,
1231, 1167, 1131, 1115, 1072, 1053, 1007, 967, 926, 798, 758, 734,
704, 674, 641, 629, 617. MS EI: 270.0 (100), 269.0 (9), 241.0 (12),
217.0 (12), 203.0 (16), 202.0 (41), 201.0 (63), 199.0 (14), 155.0 (7),
146.0 (7), 141.0 (7), 129.0 (11), 77.0 (30). HRMS (EI+) m/z
calculated for [M]+ [C16H15O2P]+: 270.0810, found: 270.0805.
Characterization Data for 6d. Yield: 0.92 g, 3.0 mmol, quant. Rf =
1
pure product. Yield: 89 mg, 0.12 mmol, 58%. H NMR (500 MHz,
CDCl3, 298 K): 7.59 (dd, 3JHH = 8.6 Hz, 4JHH = 2.2 Hz, 1H), 7.35 (d,
4JHH = 2.2 Hz, 1H), 7.10 (d, 3JHH = 8.6 Hz, 1H), 6.64 (br s, 1H), 4.54
(d, 4JHH = 2.6 Hz, 2H), 4.38 (d, 4JHH = 2.6 Hz, 2H), 4.04 (s, 3H), 3.98
(s, 3H), 2.75 (t, 4JHH = 2.2 Hz, 1H). 11B NMR (160 MHz, CDCl3, 298
K): −16.9 (s). 19F NMR (283 MHz, CDCl3, 298 K): −132.7 (d, 3JFF
=
1
22.4 Hz, 2F, o-F), −160.8 (t, 3JFF = 20.8 Hz, 1F, p-F), −165.0 (m, 2F,
m-F). Anal. Calcd for C33H15BF15NO3: C, 51.52; H, 1.97; N, 1.82.
Found: C, 51.50; H, 1.89; N, 1.91. IR (cm−1): νmax 2357, 2342, 1613,
1597, 1512, 1458, 1437, 1396, 1348, 1284, 1271, 1080, 961, 810, 768.
Synthesis of 8b. 3-Methyl-N,N-di(prop-2-yn-1-yl)but-2-enamide
(1b; 36 mg, 0.2 mmol) was dissolved in toluene (8 mL) and added to
B(C6F5)3 (102 mg, 0.2 mmol) to give a yellow solution. The reaction
mixture was heated to 45 °C for 2 days without stirring, giving an
orange solution. Upon cooling small colorless acicular crystals of the
product formed. The remaining solvent was decanted off, and the
crystals were washed with petroleum ether (3 × 3 mL) and dried
under vacuum to give colorless crystals of the pure product. Yield: 79
mg, 0.11 mmol, 57%. 1H NMR (500 MHz, CDCl3, 298 K): 6.53 (br s,
0.33 (PE:EE = 50/50). H NMR (300 MHz, CDCl3, 298 K): 7.92−
7.76 (m, 4H), 7.54−7.39 (m, 6H), 5.24−5.14 (m, 1H), 2.05 (qd, 3JHH
5
3
= 7.5 Hz, JHH = 1.92 Hz, 2H), 1.58 (d, JHH = 6.5 Hz, 3H), 0.98 (t,
3JHH = 7.5 Hz, 3H). 13C NMR (75 MHz, CDCl3, 298 K): 132.4 (d, JPC
= 58.2 Hz), 132.2 (d, JPC = 10.4 Hz), 132.0 (d, JPC = 2.6 Hz), 132.0 (d,
JPC = 2.8 Hz), 131.3 (d, JPC = 10.3 Hz), 130.1 (d, JPC = 51.4 Hz), 128.4
(d, JPC = 13.3 Hz), 128.3 (d, JPC = 13.1 Hz), 88.3 (s), 78.4 (d, JPC = 5.3
Hz), 62.5 (d, JPC = 5.4 Hz), 24.5 (d, JPC = 4.5 Hz), 13.4 (s), 12.3 (s).
31P NMR (120 MHz, CDCl3, 298 K): 31.9 (s). IR ATR (cm−1): νmax
3299, 3194, 2993, 2115, 1594, 1487, 1455, 1436, 1375, 1352, 1310,
1211, 1179, 1162, 1132, 1114, 1087, 1013, 970, 854, 787, 756, 728,
695, 675. MS (EI): 298.1 (100), 283.0 (62), 269.0 (12), 219.0 (91),
202.0 (43), 201.0 (65), 143.0 (17), 141.0 (16), 77.0 (28). HRMS
I
DOI: 10.1021/acs.organomet.5b00753
Organometallics XXXX, XXX, XXX−XXX

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Article
2H), 5.96 (br s, 1H), 4.32 (d, 4JHH = 2.4 Hz, 2H), 4.15 (d, 4JHH = 2.4
vacuo, leaving a white solid, which was recrystallized from hexane with
a drop of toluene at −40 °C to give colorless crystals of 9b. Yield: 43
mg, 0.06 mmol, 31%. Mp: 182−190 °C. 1H NMR (500 MHz, DMSO-
d6, 298 K): 10.11 (br s, 1H, NH), 7.39−7.30 (m, 5H, Ph-H), 5.90 (br
s, 1H, NH), 5.74 (s, 1H, CH), 4.43 (br s, 2H, CH2), 3.65 (br s, 2H,
CH2). 11B NMR (160 MHz, DMSO-d6, 298 K): −16.9 (br s). 19F
NMR (283 MHz, DMSO-d6, 298 K): −132.1 (d, 3JFF = 21.3 Hz, 2F, o-
F), −161.1 (t, 3JFF = 21.0 Hz, 1F, p-F), −165.1 (t, 3JFF = 21.0 Hz, 2F,
m-F). IR (cm−1): νmax 3088, 3062, 3029, 2923, 2783, 1944, 1865, 1808,
1648, 1605, 1519, 1495, 1469, 1380, 1287, 1101, 1067, 1032, 981, 872,
819, 771, 733, 695, 616. HRMS (ES−): m/z calculated for [M − H]−
[C29H11BN2OF15]− 698.0761, found 698.0790.
4
Hz, 2H), 2.62 (t, JHH = 2.5 Hz, 1H), 2.39 (s, 3H), 2.27 (s, 3H). 11B
NMR (160 MHz, CDCl3, 298 K): −16.9 (s). 19F NMR (283 MHz,
CDCl3, 298 K): −132.7 (d, 3JFF = 21.9 Hz, 2F, o-F), −160.9 (t, 3JFF
=
20.8 Hz, 1F, p-F), −165.1 (m, 2F, m-F). HRMS (EI+): m/z calculated
for [M − H]− [C29H12BF15NO]− 686.0772, found 686.0799. IR
(cm−1): νmax 2359, 2334, 2322, 1636, 1512, 1456, 1271, 1262, 1080,
974, 963, 806.
Synthesis of 8c. 4-Nitro-N,N-di(prop-2-yn-1-yl)benzamide (1c;
48 mg, 0.2 mmol) was dissolved in toluene (3 mL) and was added to
B(C6F5)3 (102 mg, 0.2 mmol) to give a yellow solution. The reaction
mixture was left at room temperature for 1 h, CH2Cl2 (ca. 1 mL) was
added, and the solvent was allowed to evaporate slowly to give small
acicular colorless crystals of the product which were suitable for X-ray
diffraction. The remaining solvent was decanted off, and the crystals
were washed with petroleum ether (3 × 3 mL) and then dried under
vacuum to give colorless crystals of the pure product. Yield: 130 mg,
Synthesis of 10a. Prop-3-yn-2-yldiisopropylcarbamate (3a; 18.3
mg, 0.1 mmol) and B(C6F5)3 (51.2 mg, 0.1 mmol) were dissolved in
0.6 mL of CD2Cl2, and the mixture was left for 24 h. The progress of
1
the reaction was monitored by H, 11B, and 19F NMR spectroscopy.
The solution was concentrated and, when the reaction was complete,
layered with pentane and stored at −20 °C, whereby the product
crystallized out. The remaining solution was decanted off and the
resulting solid washed with cold pentane (3 × 2 mL). Drying in vacuo
afforded the product as a white crystalline solid. Yield: 44.5 mg, 0.06
0.17 mmol, 86%. 1H NMR (500 MHz, CDCl3, 298 K): 8.51 (d, 3JHH
=
3
8.9 Hz, 2H), 8.08 (d, JHH = 8.9 Hz, 2H), 6.69 (s, 1H, CH), 5.23 (s,
4
4
2H), 4.47 (br d, JHH = 2.4 Hz, 2H), 2.78 (t, JHH = 2.4 Hz, 1H). 11B
NMR (160 MHz, CDCl3, 298 K): −16.9 (s). 19F NMR (283 MHz,
CDCl3, 298 K): −132.7 (d, 3JFF = 22.5 Hz, 2F, o-F), −160.3 (t, 3JFF
=
mmol, 64%. H NMR (500 MHz, CD2Cl2, 298 K): 6.46 (s, 1H, CH),
1
4
3
21.1 Hz, 1F, p-F), −164.7 (m, 2F, m-F). Anal. Calcd for
C31H10BF15N2O3: C, 49.37; H, 1.34; N, 3.7. Found: C, 52.50; H,
1.64; N, 3.52. IR (cm−1): νmax 2361, 2341, 1653, 1636, 1597, 1533,
1512, 1456, 1445, 1400, 1358, 1296, 1267, 1258, 1084, 978, 961, 928,
891, 866, 808, 770, 739, 716, 692, 669.
4.85 (d, JHH = 2.1 Hz, 2H), 4.22 (sept., JHH = 6.9 Hz, 1H), 4.07
(sept., 3JHH = 6.9 Hz, 1H), 1.39 (d, 3JHH = 6.9 Hz, 6H), 1.36 (d, 3JHH
=
6.9 Hz, 6H). 11B NMR (96 MHz, CD2Cl2, 298 K): −17.0 (s). 19F
3
NMR (282 MHz, CD2Cl2, 298 K): −133.0 (d, JFF = 22 Hz, 6F, o-F
B(C6F5)3), −161.9 (t, 3JFF = 20 Hz, 3F, p-F B(C6F5)3), −166.2 (m, 6F,
m-F B(C6F5)3). 13C NMR (125 MHz, CD2Cl2, 298 K): 160.9 (s),
148.7 (dm), 140.5 (m), 139.1 (dm), 137.2 (dm), 123.4 (br s), 119.4
(q), 74.1 (s), 71.6 (s), 53.0 (s), 51.7 (s), 20.2 (s), 20.2 (s). IR (ATR)
(cm−1): νmax 1716, 1663, 1643, 1512, 1457, 1442, 1404, 1379, 1363,
1264, 1144, 1079, 1066, 978, 959, 902, 867, 844, 804, 763, 747, 736,
704, 675, 658, 642, 607. MS-DART: 696.1 (30), 684.2 (25), 681.4
(28), 680.4(64), 610.1,(35), 563.1 (28), 550.5 (24), 546.1 (58), 536.1
(26), 528.1 (58). HRMS-DART: (+) m/z calculated for [M + H]+
[C28H18BF15NO2]+ 696.1191, found 696.1183.
Synthesis of 8d. N,N-Di(prop-2-yn-1-yl)cyclohexanecarboxamide
(1d; 40 mg, 0.2 mmol) was dissolved in toluene (2 mL) and added to
B(C6F5)3 (102 mg, 0.2 mmol) to give a cloudy yellow solution.
Leaving the solution to stand for 10 min resulted in the formation of a
white precipitate, which was redissolved by gentle heating with the
addition of a few drops of CH2Cl2. The reaction mixture was left for 2
days, and then the solvent was allowed to evaporate slowly to give
colorless crystals of the product which were suitable for X-ray
diffraction. The remaining solvent was decanted off, and the crystals
were washed with petroleum ether (3 × 3 mL) and then dried under
vacuum to give colorless crystals of the pure product. Yield: 114 mg,
0.15 mmol, 80%. 1H NMR (400 MHz, DMSO-d6, 298 K): 6.31 (s, 1H,
CH), 4.51 (s, 2H, CH2), 4.06 (s, 2H, CH2), 2.78 (t, 4JHH = 2.5 Hz,
1H, CH), 1.90−1.68 (m, 5H, CH), 1.53−1.45 (m, 2H, CH), 1.33−
1.17 (m, 4H, CH). 11B NMR (160 MHz, CDCl3, 298 K): −17.0 (s).
19F NMR (283 MHz, CDCl3, 298 K): −132.8 (d, 3JFF = 22.4 Hz, 2F, o-
Synthesis of 10c. Prop-2-yn-1-yldiphenylcarbamate (3c; 50 mg,
0.2 mmol) and B(C6F5)3 (102 g, 0.2 mmol) were dissolved in 2 mL of
toluene to give a clear colorless solution. This was immediately cooled
to −40 °C and left for 5 days to give a crop of small pale yellow
crystals suitable for X-ray diffraction. The solution was decanted, and
the solid was washed with hexane (3 × 2 mL) and dried in vacuo to
afford the product as a white solid. Yield: 91 mg, 0.12 mmol, 60%. Mp:
65−72 °C. 1H NMR (500 MHz, CDCl3, 298 K): 7.46−7.25 (m, 10H,
Ph-H), 6.43 (s, 1H, CH), 4.9 (s, 2H, CH2). 13C NMR (126 MHz,
CDCl3, 298 K): 162.3 (s), 149.2 (m), 147.3 (m), 139.9 (m), 140.3 (s),
147.3 (m), 139.9 (m), 137.9 (m), 135.9 (m), 130.1 (s), 129.9 (s),
126.7 (m), 126.6 (m), 110.2 (s), 73.0 (s). 11B NMR (160 MHz,
CDCl3, 298 K), −17.1 (s). 19F NMR (282 MHz, CDCl3, 298 K):
3
F), −160.9 (t, JFF = 20.4 Hz, 1F, p-F), −165.3 (m, 2F, m-F). Anal.
Calcd for C31H17BF15NO: C, 52.06; H, 2.40; N, 1.96. Found: C, 51.94;
H, 2.24; N, 1.94. HRMS (EI+): m/z calculated for [M]+
[C31H16BF15NO]+ 714.1085, found 714.1079. IR (cm−1): νmax 2363,
2342, 2322, 1630, 1512, 1454, 1437, 1304, 1260, 1233, 1180, 1138,
1113, 1078, 978, 961, 883, 841, 818, 806, 768, 669.
3
3
−132.6 (d, JFF = 21.3 Hz, 2F, o-F), −160.5 (t, JFF = 21.2 Hz, 1F, p-
Synthesis of 9a. B(C6F5)3 (51 mg, 0.1 mmol) was dissolved in
CDCl3 (ca. 0.5 mL) and added to 1,3-di(prop-2-yn-1-yl)urea 2a (14
mg, 0.1 mmol). The reaction mixture was heated at 50 °C for 7 days to
give a yellow solution and a crop of needle-shaped crystals which were
suitable for X-ray diffraction. The remaining solvent was decanted off,
and the product was washed with hexane (4 × 2 mL) and dried in
vacuo to give pure 9a. Yield: 20 mg, 0.03 mmol, 31%. Mp: 178−184
F), −164.9 (t, JFF = 21.2 Hz, 2F, m-F). IR (cm−1): νmax 3088, 3046,
3
3016, 2915, 2873, 2739, 1946, 1861, 1806, 1737, 1616, 1584, 1518,
1476, 1381, 1319, 1287, 1251, 1212, 1179, 1101, 1088, 1029, 973, 898,
774, 739, 719, 702, 689. HRMS (EI−): m/z calculated for [M − H]−
[C34H12BNO2F15]− 761.0785, found 761.0775.
Synthesis of 11a. Prop-3-yn-2-yldiisopropylcarbamate (3a; 18 mg,
0.1 mmol) and B(C6F5)3 (51 mg, 0.1 mmol) were dissolved in 0.6 mL
of C6D6, and the reaction mixture was left at 60 °C for 15.5 h. The
1
°C. H NMR (500 MHz, DMSO-d6, 298 K): 10.01 (br s, 1H, NH),
4
5.91 (s, 1H, NH), 5.65 (s, 1H, CH), 4.07 (d, JHH = 2.0 Hz, 2H,
1
progress of the reaction was monitored by H, 11B, and 19F NMR
CH2), 3.64 (s, 2H, CH2), 3.30 (br s, 1H, CH). 11B NMR (160 MHz,
DMSO-d6, 298 K): −17.0 (s). 19F NMR (283 MHz, DMSO-d6, 298
K): 132.1 (d, 3JFF = 22.2 Hz, 2F, o-F), 161.3 (t, 3JFF = 22.2 Hz, 1F, p-
spectroscopy. The solution was concentrated when the reaction was
complete and layered with pentane and then stored at −20 °C,
whereby the product crystallized out. The remaining solution was
decanted off and the resulting solid washed with cold pentane (3× 2
mL). Drying in vacuo afforded the product as a white crystalline solid.
3
F), 165.2 (t, JFF = 22.2 Hz, 2F, m-F). IR (cm−1): νmax 3085, 3061,
3029, 2922, 2876, 1708, 1672, 1643, 1607, 1572, 1545, 1514, 1495,
1460, 1380, 1280, 1082, 1030, 977, 729, 695. HRMS (ES−): m/z
calculated for [M − H]− [C25H7BN2OF15]− 646.0448, found
646.0445.
Synthesis of 9b. B(C6F5)3 (51 mg, 0.1 mmol) was dissolved in
CDCl3 (ca. 0.5 mL) and added to 1-benzyl-3-(prop-2-yn-1-yl)urea
(2b; 19 mg, 0.1 mmol). The reaction mixture was heated to 50 °C for
14 days to give a pale yellow solution. The solvent was removed in
1
Yield: 50.4 mg, 0.07 mmol, 72%. H NMR (600 MHz, C6D6 298 K):
4
4.68 (s, 1H), 4.55 (d, JHH = 2.6 Hz, 1H), 4.48 (br s, 1H), 4.38 (d,
4JHH = 2.6 Hz, 1H), 3.06 (br s, 1H), 0.89 (d, 3JHH = 6.8 Hz, 3H), 0.86
(d, 3JHH = 6.6 Hz, 3H), 0.83 (d, 3JHH = 6.8 Hz, 3H), 0.80 (d, 3JHH = 6.8
Hz, 3H). 11B NMR (96 MHz, C6D6, 298 K): 0.8 (br s). 19F NMR (282
MHz, C6D6, 298 K): −134.8 (br d, 2F, o-F, B(C6F5)2), −136.0 (m, 2F,
J
DOI: 10.1021/acs.organomet.5b00753
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o-F, B(C6F5)2), −143.0 (m, 2F, o-F C6F5), −156.8 (m, 2F, p-F,
B(C6F5)2), −157.6 (t, 3JFF = 21.7 Hz, 1F, p-F, C6F5), −162.9 (br s, 2F,
m-F, C6F5), −163.4 (m, 2F, m-F, B(C6F5)2), −163.7 (m, 2F, m-F
B(C6F5)2). 13C NMR (150 MHz, C6D6, 298 K): 156.4 (s), 155.8 (s),
148.4 (dm), 147.9 (dm), 145.3 (dm), 140.38 (dm), 139.3 (dm), 137.7
(dm), 118.9 (br s, C−B), 117.7 (t), 98.9 (s), 49.7 (s), 47.3 (s), 29.0
(br s), 20.6 (s), 20.1 (s), 19.0 (s), 18.9 (s).
(br s), 141.3 (m), 139.3 (m), 138.2 (m), 136.2 (m), 108.8 (s), 53.6
(s), 11.2 (s). 11B NMR (160 MHz, CDCl3, 298 K): 0.7 (br s). 19F
NMR (282 MHz, CDCl3, 298 K): −134.7 (m, 2F, o-F), −156.8 (m,
1F, p-F), −163.7 (s, 2F, m-F). IR (cm−1): 3380, 3088, 3062, 3028,
2922, 2873, 1943, 1863, 1806, 1731, 1697, 1674, 1648, 1604, 1519,
1496, 1470, 1379, 1291, 1105, 1085, 1033, 979, 774, 736, 725, 697,
625. HRMS (EI−): m/z calculated for [M − H]− [C22H4BNO2F15]−
609.0132, found 609.0142.
Synthesis of 11b. But-3-yn-2-yldiisopropylcarbamate (3b; 19.7
mg, 0.1 mmol) and B(C6F5)3 (51.2 mg, 0.1 mmol) were dissolved in
0.6 mL of CD2Cl2, and the reaction mixture was left for 24 h. The
Synthesis of 13. Ethyl pent-1-yn-3-ylcarbonate (5a; 15.6 mg, 0.1
mmol) and B(C6F5)3 (51.2 mg, 0.1 mmol) were dissolved in 0.6 mL of
CD2Cl2, and the mixture was left for 66 h at room temperature. The
1
completion of the reaction was monitored by H, 11B, and 19F NMR
1
completion of the reaction was monitored by H, 11B, and 19F NMR
spectroscopy. The solution was concentrated when the reaction was
complete and layered with pentane and stored at −20 °C, resulting in
crystallization of the product. The remaining solution was decanted
off, and the solid was washed with cold pentane (3 × 2 mL). Drying in
vacuo afforded the product as a white crystalline solid. Yield: 54.7 mg,
spectroscopy. Removal of the solvent in vacuo afforded the crude
product as a brown solid. The product was recrystallized by slow
evaporation of toluene to yield a small crop of colorless plates. Yield:
53.9 mg, 0.08 mmol, 81%. 1H NMR (400 MHz, CD2Cl2, 298 K): 5.20
3
3
4
1
3
(t, JHH = 7.5 Hz, 1H), 4.80 (dq, JHH = 7.1 Hz, JHH = 1.4 Hz, 2H),
4.48 (s, 1H), 2.23−2.04 (m, 2H), 1.55 (t, 3JHH = 7.1 Hz, 3H), 0.93 (t,
3JHH = 7.5 Hz, 3H); 11B NMR (96 MHz, CD2Cl2, 298 K): −0.9 (br s).
19F NMR (282 MHz, CD2Cl2, 298 K): −139.2 (m, 2F, o-F, B(C6F5)2),
−139.8 (m, 2F, o-F B(C6F5)2), −147.0 (br s, 2F, o-F C6F5), −161.2 (t,
0.08 mmol, 75%. H NMR (300 MHz, CD2Cl2, 298 K): 5.04 (q, JHH
= 6.9 Hz, 1H, CH), 4.68−4.64 (m, 1H, CH), 4.34 (s, 1H, CH),
4.00−3.91 (m, 1H, CH), 1.70 (d, 3JHH = 6.9 Hz, 3H, CH3), 1.44−1.30
(m, 12H, CH3). 13C NMR (125 MHz, CD2Cl2, 298 K): 156.7 (s),
149.1 (m), 148.4 (dm), 147.8 (dm), 145.4 (dm), 140.4 (dm), 140.1
(dm), 139.3 (dm) 137.9 (dm), 137.6 (dm), 137.3 (dm), 119.0 (t),
118.4 (br m), 110.2 (s), 50.1 (s), 48.1 (s), 29.4 (br s), 21.1 (s), 20.5
(s), 20.0 (s), 19.8 (s), 11.0 (s). 11B NMR (96 MHz, CD2Cl2, 298 K):
0.0 (br s). 19F NMR (282 MHz, CD2Cl2, 298 K): −135.0 (br s, 2F, o-F
3
3JFF = 20.2 Hz, 1F, p-F B(C6F5)2), −161.7 (t, JFF = 20.6 Hz, 1F, p-F
B(C6F5)2), −162.2 (t, 3JFF = 20.6 Hz, 1F, p-F C6F5), −166.7 (br m, 2F,
m-F C6F5), −168.2 (m, 4F, m-F B(C6F5)2). 13C NMR (100 MHz,
CD2Cl2, 298 K): 159.4 (s), 148.5 (dm), 147.8 (dm), 145.5 (dm),
140.9 (dm), 140.6 (dm), 139.8 (dm), 138.3 (dm), 138.1 (dm), 137.7
(dm,), 120.6 (s), 117.6 (t), 117.1 (m), 71.8 (s), 27.9 (br s), 18.8 (s),
14.2 (s), 13.6 (s). IR (reflection) (cm−1): νmax 3293, 2979, 2940, 2882,
2358, 2125, 1756, 1515, 1465, 1396, 1373, 1342, 1302, 1275, 1177,
1094, 1062, 1007, 948, 939, 893, 857, 7901, 670.
3
B(C6F5)2), −136.3 (m, 2F, o-F B(C6F5)2), −143.1 (d, JFF = 20.6 Hz,
2F, o-F C6F5), −158.7 (t, 3JFF = 20.7 Hz, 1F, p-F B(C6F5)2), −159.0 (t,
3
3JFF = 20.0 Hz, 1F, p-F B(C6F5)2), −159.7 (t, JFF = 20.8 Hz, 1F, p-F
C6F5), −163.9 (m, 2F, m-F C6F5), −164.8 (m, 2F, m-F B(C6F5)2),
−165.0 (m, 2F, m-F B(C6F5)2), all C6F5 rings are inequivalent. IR
(ATR) (cm−1): νmax 2993, 2978, 1702, 1644, 1614, 1517, 1494, 1464,
1393, 1374, 1284, 1250, 1215, 1182, 1157, 1091, 1068, 1039, 993, 974,
956, 934, 904, 873, 860, 824, 777, 751, 737, 720, 699, 686, 663, 629,
617. MS-DART: 728.1 (26), 727.1 (85), 726.1 (20), 680.4 (30), 610.1
(18), 577.1 (23), 560.1 (31), 559.1 (34), 543.1 (24), 542.1 (100),
541.1 (25), 536.1 (19). HRMS-DART: (+) m/z calculated for [M +
NH4]+ [C29H23BF15N2O2]+ 727.1613, found 727.1601.
Crystallographic Studies. Crystallographic studies were under-
taken on single crystals mounted inParatone and studied on an Agilent
SuperNova Dual three-circle diffractometer using Cu Kα or Mο Kα
radiation and a CCD detector. Measurements were typically made at
150(1) K with temperatures maintained using an Oxford Cryostream.
Data were collected, integrated, and corrected for absorption using a
numerical absorption correction based on Gaussian integration over a
multifaceted crystal model within CrysAlisPro.29 The structures were
solved by direct methods and refined against F2 within SHELXL-
2013.30 A summary of crystallographic data are available as Supporting
Information, and the structures have been deposited with the
Cambridge Structural Database (CCDC deposition numbers
(1413179−1413189 and 1429175).
Synthesis of 11c. Prop-2-yn-1-yldiphenylcarbamate (3c; 50 mg,
0.2 mmol) and B(C6F5)3 (102 mg, 0.2 mmol) were dissolved in 2 mL
of toluene to give a clear colorless solution. After 5 days at room
temperature a few drops of CH2Cl2 were added and the solvent was
left to evaporate to give large pale yellow blocks suitable for X-ray
diffraction. The solution was decanted and the solid washed with
hexane (3 × 2 mL). This was then dried in vacuo to yield the pure
product as a white solid. Yield: 101 mg, 0.13 mmol, 66%. Mp: 137−
ASSOCIATED CONTENT
1
■
146 °C. H NMR (500 MHz, CDCl3, 298 K): 7.50−7.35 (m, 10H,
Ar−H), 4.73 (d, 2JHH = 2.5 Hz, 1H, C−H), 4.66 (d, 2JHH = 2.5 Hz,
1H, C−H), 4.39 (s, 1H, B−C−H). 13C NMR (126 MHz, CDCl3,
298 K): 157.2 (s), 155.6 (s), 130.1 (s), 129.9 (s), 129.4 (s), 129. (s),
* Supporting Information
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00753.
126.7 (s), 126.6 (s), 100.5 (s). 11B NMR (160 MHz, CDCl3, 298 K)
3
1.4 (br s). 19F NMR (282 MHz, CDCl3, 298 K): −134.0 (d, JFF
=
3
21.5 Hz, 2F, o-F B(C6F5)2), −135.5 (d, JFF = 21.5 Hz, 2F, o-F
NMR spectra and crystallographic data (PDF)
Crystallographic data (CIF)
B(C6F5)2), −141.4 (br s, 1F, o-F C6F5), −143.2 (br s, 1F, o-F C6F5),
3
3
−156.6 (t, JFF = 21.2 Hz, 1F, p-F B(C6F5)2), −157.0 (t, JFF = 21.2
Hz, 2F, p-F B(C6F5)2), −161.2 (br s, 1F, m-F C6F5), −162.0 (br s, 1F,
m-F C6F5), −163.0 (m, 2F, m-F B(C6F5)2) −163.8 (m, 2F, m-F
B(C6F5)2. All C6F5 rings are inequivalent. IR (cm−1): νmax 3055, 2987,
2686, 2359, 2307, 1673, 1647, 1618, 1582, 1519, 1496, 1487, 1465,
1423, 1384, 1289, 1273, 1260, 1209, 1161, 1107, 1092, 1026, 998, 972,
896, 759, 738, 717, 699. HRMS (EI+): m/z calculated for [M + Na]+
[C34H13BF15NO2Na]+ 785.0734, found 785.0711.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail for M.M.H.: mhansmann@ucsd.edu.
*E-mail for R.L.M.: MelenR@cardiff.ac.uk.
Notes
Synthesis of 12. Under less anhydrous conditions, benzylprop-2-
yn-1-ylcarbamate (4a; 38 mg, 0.2 mmol) was added to B(C6F5)3 (102
mg, 0.2 mmol) in 2 mL of toluene to give a slightly yellow solution.
After reaction for 4 days at room temperature the solution was
concentrated in vacuo, layered with hexane, and left at −40 °C to
produce yellow-orange blocks suitable for X-ray diffraction. Yield: 55
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
M.M.H. is grateful to the Fonds der Chemischen Industrie for a
Chemiefonds scholarship and the Studienstiftung des deut-
schen Volkes. We thank W.R. Grace for the kind donation of
B(C6F5)3.
1
mg, 0.09 mmol, 45%. Mp: 95−102 °C. H NMR (500 MHz, CDCl3,
298 K): 8.29 (br s, 1H, NH), 6.56 (s, 1H, CH), 2.18 (s, 3H, CH3).
13C NMR (126 MHz, CDCl3, 298 K): 157.9 (s), 148.0 (br s), 147.1
K
DOI: 10.1021/acs.organomet.5b00753
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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Hansmann, M. M.; Rominger, F.; Boone, M. P.; Stephan, D. W.;
Hashmi, A. S. K. Organometallics 2014, 33, 4461−4470.
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DOI: 10.1021/acs.organomet.5b00753
Organometallics XXXX, XXX, XXX−XXX