Domino Meyer-Schuster/Arylation Reaction of Alkynols or Alkynyl Hydroperoxides with Diazonium Salts Promoted by Visible Light under Dual Gold and Ruthenium Catalysis

Article abstract of DOI:10.1002/adsc.201600158

A method for the arylative coupling of alkynols or alkynyl hydroperoxides using equimolar amounts of diazonium salts at room temperature has been achieved through application of a gold/photoredox dual catalytic system. The excess of external reagents (oxi

Full text of DOI:10.1002/adsc.201600158

UPDATES
DOI: 10.1002/adsc.201600158
Domino Meyer–Schuster/Arylation Reaction of Alkynols or
Alkynyl Hydroperoxides with Diazonium Salts Promoted by
Visible Light under Dual Gold and Ruthenium Catalysis
Benito Alcaide,a,* Pedro Almendros,b,* Eduardo Busto,a and Amparo Lunaa
a
Grupo de Lactamas y Heterociclos Bioactivos, Departamento de Química Orgµnica I, Unidad Asociada al CSIC, Facultad
de Química, Universidad Complutense de Madrid, 28040 Madrid, Spain
Fax: (+34)-91-3944103; e-mail: alcaideb@quim.ucm.es
Instituto de Química Orgµnica General, Consejo Superior de Investigaciones Científicas, IQOG-CSIC, Juan de la Cierva
b
3, 28006 Madrid, Spain
Fax: (+34)-91-5644853; e-mail: Palmendros@iqog.csic.es
Received: February 5, 2016; Revised: March 2, 2016; Published online: April 27, 2016
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201600158.
Abstract: A method for the arylative coupling of al-
kynols or alkynyl hydroperoxides using equimolar
amounts of diazonium salts at room temperature
has been achieved through application of a gold/
photoredox dual catalytic system. The excess of ex-
ternal reagents (oxidant or base) and high tempera-
tures required by previous arylative Meyer–Schus-
ter rearrangement protocols are avoided by exploi-
tation of a visible light-mediated process.
ral products, as well as its usefulness as precursor for
the construction of more complex structures.[5] Tradi-
tional procedures for the preparation of enones, such
as aldol condensation and olefination reactions pres-
ent serious limitations. The synthesis of a,b-unsaturat-
ed ketones from propargylic alcohols through the
Meyer–Schuster rearrangement (Scheme 1a), which
consists in a formal 1,3-hydroxy shift followed by tau-
tomerization, represents a tremendous advance in this
area.[6] The alkynol rearrangement associated to an
extra arylation should provide competitive advantag-
es, because it could afford conjugated enones with in-
ternal substitution. However, previous efforts in the
arylative Meyer–Schuster rearrangement have been
limited to two independent reports, namely, the gold-
catalyzed oxidative cross-coupling of propargylic ace-
Keywords: alcohols; alkynes; diazo compounds;
gold; photocatalysis
In recent years, gold-catalyzed reactions have experi- tates with arylboronic acids (Scheme 1b),[7] and the
enced considerable progress in the field of synthetic copper-catalyzed rearrangement of propargylic alco-
organic chemistry.[1] Unfortunately, gold catalysis has hols using diaryliodonium salts (Scheme 1c).[8]
A
not been conveniently exploited in domino function- major shortcoming of both methodologies is the poor
alization/coupling sequences because of the high atom economy. Moreover, excess of external reagents
redox potential Au(I)/Au(III).[2] Although the inclu- (oxidant or base) are employed, thus generating addi-
sion of strong oxidants in the reaction medium has tional waste. Furthermore, the use of heat is required
provided access to Au(I)/Au(III) cycles in coupling in both protocols. With the aim of overcoming theses
protocols,[3] the need to add two-fold molar amounts defects, we suppose that the incorporation of diazoni-
of environmentally unfriendly oxidants [Selectfluor, um salts in this sequence could be a great advantage
N-fluorobenzenesulfonimide, or (diacetoxyiodo)ben- for the area. The arylation step is associated with the
zene] is a serious drawback of this strategy. Recently, concerted elimination of N2 which preserves our envi-
the seminal works of the groups of Glorius and Toste ronment because it is free of waste, thus rendering di-
employed a gold-photoredox co-catalysis that allowed azonium salts as a green and low-cost source of struc-
Au(I)/Au(III) catalytic cycles by stepwise one-elec- tural diversity.[9] Besides, a vast array of diverse arene-
tron transfers.[4]
diazonium salts are easily prepared from cheap ani-
On the other hand, the development of efficient lines. Visible light photocatalysis has appeared as
synthetic approaches for the a,b-unsaturated ketone a very convenient tool in redox processes.[10] The im-
structural motif is of great importance because of its plementation of the visible light-mediated arylative
presence in a large number of biologically active natu- Meyer–Schuster rearrangement at room temperature
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Domino Meyer–Schuster/Arylation Reaction of Alkynols
Scheme 1. State of the art for the arylative Meyer–Schuster rearrangement.
is a challenge due to its sustainable aspects. Herein,
Table 1. Optimization of the reaction conditions for the ary-
we disclose the application of diazonium salts as aryl
transfer reagents in the gold-photoredox co-catalyzed
reaction with alkynols or alkynyl hydroperoxides to
lative Meyer–Schuster rearrangement of alkynol 1a under
gold-photoredox co-catalysis.[a]
the
valuable
a,b-unsaturated
ketone
motif
(Scheme 1d).[11]
To test the reactivity of the alkynol or alkynyl hy-
droperoxide moieties, several conditions were
screened. Alkynol 1a and diazonium salt 2a were
chosen as model substrates for the optimization of the
reaction parameters. Initially, we tried the arylative
Meyer–Schuster rearrangement in the presence of
Gagoszꢁ catalyst [(Ph3P)AuNTf2], and the photoactive
ruthenium complex [Ru(bpy)3](PF6)2 (bpy=2,2’-bipyr-
idine), in the presence of visible light (entry 1,
Table 1). Fortunately, the proposed reaction between
1a and 2a did occur to afford the aryl-substituted a,b-
unsaturated ketone 3a in reasonable yield without
traces of the non-arylated a,b-unsaturated ketone
counterpart. However, the excess (4 equiv.) of diazo-
nium salt used in previous gold-photoredox processes
was not benefitial in our case due to the formation of
1,2-diaryldiazene side products. In an attempt to im-
prove the reaction efficiency, smaller amounts of di-
azonium salt 2a were tested in the reaction (entries 2
and 3, Table 1). To our delight, the results showed
that the use of equimolecular amounts of diazonium
salt 2a has a dramatic effect on the reaction, sharply
improving its cleanliness with the subsequent associat-
ed yield increase, under otherwise identical conditions
(entry 3, Table 1). A screening of pure and mixed sol-
vents revealed that a mixture methanol/acetonitrile
(3:1) was the best reaction medium. A low gold cata-
lyst loading (5 mol%) did not affect the selectivity but
Entry
Gold salt
2a (equiv.)
Yield [%][b]
1
2
3
4
5
6
7
8
[(Ph3P)AuNTf2]
[(Ph3P)AuNTf2]
[(Ph3P)AuNTf2]
[(Ph3P)AuNTf2][c]
[(Ph3P)AuNTf2][d]
[AuClIPr]
4
2
1
1
1
1
1
1
1
1
1
50
62
80
80
68
5
59
41
34
0
Ph3PAuCl
[(Ph3P)AuNTf2][e]
[(Ph3P)AuNTf2][f]
–
9
10
11
[(Ph3P)AuNTf2][g]
0
[a]
Unless otherwise noted, the reaction was carried out
using 1a (1.0 mmol), Au precatalyst (0.01 mmol), [Ru(b-
py)3](PF6)2 (0.0025 mmol) in MeOH/MeCN (3:1) at
room temperature using
(365 nm) as the light source.
a fluoresecent light lamp
[b]
Yield of pure, isolated product 2a after silica gel chroma-
tography with correct analytical and spectral data.
Au precatalyst (0.02 mmol) was used.
Au precatalyst (0.005 mmol) was used.
[Ir(ppy)2(dtbbpy)](PF6)2] was used.
Fluorescein was used.
The reaction was conducted in the absence of both visi-
ble light as well as [Ru(bpy)3](PF6)2 catalyst.
[c]
[d]
[e]
[f]
[g]
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Benito Alcaide et al.
slightly decreased the yield (entry 5, Table 1). Com-
pared with the standard conditions, poor or moderate
yields of the product were achieved from the reaction
system when [AuClIPr] [IPr=1,3-bis(2,6-diisopropyl-
phenyl)imidazol-2-ylidene] or Ph3PAuCl were used to
replace [(Ph3P)AuNTf2] (entries 6 and 7, Table 1).
[Ru(bpy)3](PF6)2 was the best photoredox catalyst
compared with [Ir(ppy)2(dtbbpy)](PF6)2] (ppy=2-phe-
nylpyridine; dtbbpy=4,4’-di-tert-butyl-2,2’-bipyridine)
or fluorescein (entries 8 and 9, Table 1). As anticipat-
ed, the gold salt was indispensable for this transfor-
mation (entry 10, Table 1). Not unexpectedly, we did
not obtain product 3a while both photoredox catalyst
and visible-light were absent in the reaction mixture
(stirred in the dark) (entry 11, Table 1).
With the reaction conditions optimized, we then ex-
amined the scope of this sequence with respect to the
aryldiazonium component. Worthy of note, the chal-
lenging primary propargylic alcohol 1a was prone to
react with different arylating partners. As demonstrat-
ed in Scheme 2, a series of aryldiazonium salts 2b–g
with substituents on the aryl ring were smoothly con-
verted into the corresponding a-arylated a,b-unsatu-
rated ketones 3b–g in reasonable yields (up to 77%).
It was found that electron-withdrawing substituents
Scheme 3. Synthesis of aryl-substituted a,b-unsaturated ke-
tones 3h–n through gold-photoredox co-catalyzed arylative
Meyer–Schuster rearrangement of secondary alkynols 1b–e.
normally gave reasonable yields while strongly elec- The reaction worked well with both aliphatic and aro-
tron-donating groups (MeO) resulted in failure (3d). matic substituents, such as in secondary alkynols 1b–e,
In order to explore the generality of this reaction, giving rise to alkenes 3h–n with excellent diastereose-
a wide range of complex alkynols were also tested. lectivities (>95:5, E/Z) (Scheme 3). Gratifyingly, the
The reaction was found not to be significantly affect- dialkyl-substituted alkynol 1d smoothly afforded the
ed by the electronic nature of the alkynol substituents. corresponding products 3k and 3l in fair yields. To fur-
ther demonstrate the scope of the arylative rearrange-
ment, thiophene derivative 1e was then applied in the
reaction, generating 3m and 3n in a competent
manner. Clearly, this tandem sequence could be appli-
cable to alkynols bearing a heterocyclic moiety. To
show the potential of the methodology, a gram-scale
synthesis of 3i was carried out. It is remarkable that
the yield was not decreased when the reaction was
scaled-up (1 gram of alkynol 1c) and the loading of
gold catalyst was reduced from 10 mol% to 5 mol%.
The steric hindrance at the contiguous positions of
the alkynol precursors affected the reaction greatly.
When 9-ethynyl-9H-fluoren-9-ol 4a was employed,
only a trace amount of the desired product 5a was ob-
tained. The major product (62% yield) was the classi-
cal (non-arylative) Meyer–Schuster adduct, which in-
dicates that the bulkiness of the substituents has a neg-
ative effect on the arlyation. Gratifyingly, the use of
excess of diazonium salt provided aryl-substituted
a,b-unsaturated ketones 5a and 5b in reasonable
yields (57–70%) under otherwise the same reactions
conditions (Scheme 4). Compounds 5 can be consid-
ered as hybrid scaffolds as a combination of the val-
uable a,b-unsaturated ketone and fluorene[12] frame-
works. It was observed that the arylative Meyer–
Schuster rearrangement of heterocycle-containing ter-
Scheme 2. Synthesis of aryl-substituted a,b-unsaturated ke-
tones 3b–g through gold-photoredox co-catalyzed arylative
Meyer–Schuster rearrangement of primary alkynol 1a.
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Domino Meyer–Schuster/Arylation Reaction of Alkynols
Scheme 5. Synthesis of aryl-substituted a,b-unsaturated ke-
tones 3a and 3b through gold-photoredox co-catalyzed ary-
lative Meyer–Schuster rearrangement of alkynyl hydroper-
oxide 9.
A plausible mechanism for the gold-photoredox co-
catalyzed formation of a,b-unsaturated ketones 3, 5,
and 7 from alkynols 1, 4, and 6 or alkynyl hydroper-
oxide 9 and diazonium salts 2 is presented in
Scheme 6. The cationic organogold(III) intermediate
11, which may be considered as a robust electrophile,
should be formed through photoredox oxidation.
Next, arylgold(III) species 11 should interact with the
alkynol or alkynyl hydroperoxide moiety with a final
aryl group transfer. A catalytic cycle was postulated
based on the use of a Ru(II) species as a strong re-
Scheme 4. Synthesis of aryl-substituted a,b-unsaturated ke- ductant for the generation of an aryl radical from di-
tones 5 and 7 through gold-photoredox co-catalyzed aryla-
tive Meyer–Schuster rearrangement of tertiary alkynols 4a
and 6a.
azonium salts 2. Initially, Ru(II) complexes are rever-
sibly promoted to their excited state, [*Ru(II)]+,
under visible light exposure. Consecutive transfer of
an electron to diazonium salt 2 may generate the cor-
responding aryl radical, that should be spontaneously
tiary alkynols was equally efficient (Scheme 4). For paired with the gold(I) salt to form unstable organo-
instance, the relevant[13] 3-acylidene-2-oxindole deriv- gold(II) intermediate 10. Subsequent oxidation by
ative 7a could be smoothly afforded in reasonable Ru(III) produces arylgold(III) species 11 which, fol-
yield and with total Z diastereoselectivity starting lowed by reductive elimination, liberates phosphoni-
from
3-ethynyl-3-hydroxyindolin-2-one
6a um derivative [Ph3PAr]+,[16] releasing the rutheniu-
(Scheme 4).[14] Curiously, adducts 7b and 7c, initially m(II) photoredox catalyst into the first catalytic cycle
obtained as their corresponding hemiacetals by 1,2- (Scheme 6, right catalytic cycle). Next, alkynols 1, 4,
addition reaction of methanol to the a,b-unsaturated and 6 or alkynyl hydroperoxide 9 enter the second
ketone moiety, evolves through protonation, dehydra- catalytic cycle, which is gold-catalyzed, furnishing
tion, and final hydration to oxindole-tethered tetra- complex 1, 4, 6, 9-Au(III) through coordination of the
substituted olefins 8b and 8c. The stereochemistry of gold salt to the triple bond. Species 1, 4, 6, 9-Au(III)
products 8 was unambiguously determined by the evolves through a 1,3-hydroxide (hydroperoxide)
NOE analysis of enol ether 8c. Noticeably, the forma- transposition to intermediate 12. Regioselective nu-
tion of the arylative Meyer–Schuster rearrangement cleophilic addition of water in gold-allenyl complex
adducts can be disturbed by some substituent factors 12 to give intermediate 13, followed by loss of water
(presence of EWG) in the diazonium salt. Notably, or hydrogen peroxide, provides the alkenylgold(III)
Scheme 4 shows how the mild conditions of the gold/ 14. Reductive elimination linked to proton release lib-
photoredox dual catalysis allow the selective forma- erates a,b-unsaturated ketones 3, 5, and 7 with con-
tion of functionalized indolin-2-one derivatives with- comitant regeneration of the gold(I) catalyst, closing
out harming the sensitive oxindole ring.
the second catalytic cycle (Scheme 6, left catalytic
We next turned our attention to the employment of cycle).
alkynyl hydroperoxides, an under explored kind of
The mechanism proposed in Scheme 6 is fully con-
substrates in gold catalysis.[15] Indeed, under opti- sistent with the recent theoretical study of the visible
mized standard reaction conditions, the arylative rear- light-mediated gold-catalyzed oxyarylation reaction of
rangement proceeded. Thus, the reactions of hydro- alkenes,[17] in which the favorable gold catalytic cycle
peroxide 9 led to aryl-substituted a,b-unsaturated ke- is the sequence of radical addition, single electron
tones 3a and 3b (Scheme 5), but with diminished transfer, coordination, cyclization, and reductive elim-
yields in comparation to alkynols.
ination.
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Benito Alcaide et al.
Scheme 6. Mechanistic explanation for the gold-photoredox co-catalyzed preparation of a,b-unsaturated ketones 3, 5, and 7
from alkynols 1, 4, and 6 or alkynyl hydroperoxide 9 and diazonium salts 2.
tially added to a solution of diazonium salt 2 (1.0 equiv.)
and the appropriate alkynol 1 or alkynyl hydroperoxide 9
coupling of alkynols or alkynyl hydroperoxides using (1.0 mmol) in a mixture of MeOH/MeCN (3:1, 7.5 mL). The
In conclusion, the direct rearrangement/arylative
reaction mixture was then warmed to room temperature
and stirred under irradiation from visible light source (21W
fluorescent light bulb installed in a tool box). After comple-
tion (TLC), diethyl ether was added and the mixture was fil-
tered though a pad of silica gel. The solvent of the filtrate
was removed under reduced pressure. Chromatography of
the residue using hexanes/ethyl acetate mixtures gave ana-
lytically pure compounds. Spectroscopic and analytical data
for pure forms of compounds 3, 5, 7 and 8 follow.
Aryl-substituted a,b-unsaturated ketone 3a: From 40 mg
(0.30 mmol) of alkynol 1a, and after chromatography of the
residue using hexanes/ethyl acetate (4:1) as eluent, gave
compound 3a as a colorless oil; yield: 80 mg (80%).
1H NMR (300 MHz, CDCl3, 258C): d=7.68 (m, 2H), 7.36
(d, J=7.3 Hz, 1H), 7.26 (m, 4H), 7.10 (d, J=8.6 Hz, 2H),
5.89 (s, 1H), 5.48 (s, 1H); 13C NMR (75 MHz, CDCl3,
258C): d=196.9, 147.0, 136.8, 135.8, 133.2, 131.7 (2C), 129.9
(2C), 128.7 (2C), 128.4 (2C), 122.6, 121.9; IR (CHCl3): n=
1681, 1589 cmÀ1; HR-MS (ES): m/z=287.0079, calcd. for
C15H12BrO [M+H]+: 287.0072.
equimolar amounts of diazonium salts at room tem-
perature to afford aryl-substituted a,b-unsaturated ke-
tones has been achieved through application of
a gold/photoredox dual catalytic system.
Experimental Section
General Methods
1H NMR and 13C NMR spectra were recorded on Bruker
AMX-500, Bruker Avance-300, or Varian VRX-300S spec-
trometers. NMR spectra were recorded in CDCl3 solutions,
except where otherwise stated. Chemical shifts are given in
ppm relative to TMS (1H, 0.0 ppm), or CDCl3 (13C,
77.0 ppm). Low and high resolution mass spectra were taken
on an AGILENT 6520 Accurate-Mass QTOF LC/MS spec-
trometer using the electrospray mode (ES) unless otherwise
stated. IR spectra were recorded on a Bruker Tensor 27
spectrometer. All commercially available compounds were
used without further purification.
Aryl-substituted a,b-unsaturated ketone 3b: From 26 mg
(0.20 mmol) of alkynol 1a, and after chromatography of the
residue using toluene as eluent, gave compound 3b as a col-
Typical Procedure for the Arylative Meyer–Schuster
Rearrangement of Alkynols or Alkynyl Hydroper-
oxides using Gold/Photoredox Catalysis
1
orless oil yield: 23 mg (55%). H NMR (300 MHz, CDCl3,
258C): d= 7.91 (m, 2H), 7.56 (m, 1H), 7.43 (m, 4H), 7.35
(m, 3H), 6.08 (s, 1H), 5.65 (s, 1H); 13C NMR (75 MHz,
CDCl3, 258C): d=197.5, 148.2, 137.0, 136.9, 133.0, 129.9,
128.6 (3C), 128.3 (2C), 127.0 (2C), 120.9 (2C); IR (CHCl3):
In a flask in the absence of light at À788C, [(Ph3P)AuNTf2]
(10 mol%) and [Ru(bpy)3](PF6)2 (2.5 mol%) were sequen-
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Domino Meyer–Schuster/Arylation Reaction of Alkynols
n=1650, 1597 cmÀ1; HR-MS (ES): m/z=209.0967, calcd. for
C15H13O [M+H]+: 209.0966.
Aryl-substituted a,b-unsaturated ketone 3c: From 40 mg
(0.30 mmol) of alkynol 1a, and after chromatography of the
residue using hexanes/ethyl acetate (4:1) as eluent, gave
258C): d=7.78 (d, J=7.0 Hz, 1H), 7.38 (m, 8H), 6.61 (q,
J=7.1 Hz, 1H), 1.90 (d, J=7.1 Hz, 2H); 13C NMR (75 MHz,
CDCl3, 258C): d=197.2, 142.7, 139.7, 138.3, 135.7, 131.8,
129.5 (4C), 128.2 (2C), 128.0 (2C), 127.4, 15.5; IR (CHCl3):
n=1730, 1684, 1091 cmÀ1; HR-MS (ES): m/z=223.1117,
calcd. for C16H15O [M+H]+: 223.1123.
compound 3c as
a colorless oil; yield: 36 mg (51%).
1H NMR (300 MHz, CDCl3, 258C): d=7.90 (m, 2H), 7.57
(m, 1H), 7.44 (m, 4H), 7.05 (t, J=8.7 Hz, 2H), 6.05 (s, 1H),
5.65 (s, 1H); 13C NMR (75 MHz, CDCl3, 258C): d=197.3,
162.8 (d, J=248.2 Hz), 147.0, 136.9, 133.1, 129.9 (2C), 128.9,
(d, J=8.2 Hz, 2C), 128.4 (2C), 121.3, 115.5 (d, J=21.7 Hz,
2C); IR (CHCl3): n=1667, 1509 cmÀ1; HR-MS (ES): m/z=
227.0870, calcd. for C15H12FO [M+H]+: 227.0872.
Aryl-substituted a,b-unsaturated ketone 3j: From 29 mg
(0.20 mmol) of alkynol 1c, and after chromatography of the
residue using toluene as eluent, gave compound 3j as a color-
less oil; yield: 41 mg (67%). 1H NMR (300 MHz, CDCl3,
258C): d=7.74 (m, 2H), 7.52 (m, 2H), 7.43 (m, 3H), 7.15
(d, J=8.4 Hz, 2H), 6.63 (q, J=7.1 Hz, 1H), 1.87 (d, J=
7.1 Hz, 2H); 13C NMR (75 MHz, CDCl3, 258C): d=196.7,
141.7, 140.6, 138.1, 134.6, 131.9, 131.4 (2C), 131.3 (2C),
129.5 (2C), 128.2 (2C), 121.6, 15.6; IR (CHCl3): n=1658,
Aryl-substituted a,b-unsaturated ketone 3e: From 40 mg
(0.30 mmol) of alkynol 1a, and after chromatography of the
residue using hexanes/thyl acetate (5:1) as eluent, gave com-
1269 cmÀ1
;
HR-MS (ES): m/z=301.0228, calcd. for
1
C16H14BrO [M+H]+: 301.0228.
pound 3e as a colorless oil; yield: 53 mg (70%). H NMR
(300 MHz, CDCl3, 258C): d=8.22 (d, J=8.9 Hz, 2H), 7.89
(m, 2H), 7.61 (m, 3H), 7.48 (t, J=7.5 Hz, 2H), 6.27 (s, 1H),
5.89 (s, 1H); 13C NMR (75 MHz, CDCl3, 258C): d=196.1,
147.6, 146.2, 143.3, 136.6, 133.5, 129.9 (2C), 128.6 (2C),
128.1 (2C), 125.0, 123.8 (2C); IR (CHCl3): n=1663,
Aryl-substituted a,b-unsaturated ketone 3k: From 19 mg
(0.20 mmol) of alkynol 1d, and after chromatography of the
residue using toluene as eluent, gave compound 3k as a col-
1
orless oil; yield: 20 mg (58%). H NMR (300 MHz, CDCl3,
258C): d=7.36 (m, 3H), 7.11 (d, J=8.0, 1.5 Hz, 2H), 6.99
(q, J=7.1 Hz, 1H), 2.55 (q, J=7.3 Hz, 1H), 1.71 (d, J=
7.1 Hz, 1H), 1.06 (t, J=7.3 Hz, 1H); 13C NMR (75 MHz,
CDCl3, 258C): d=201.4, 143.5, 137.4, 136.1, 129.6 (2C),
128.2 (2C), 127.3, 32.8, 15.4, 8.3; IR (CHCl3): n=1681,
1625 cmÀ1; HR-MS (ES): m/z=175.1123, calcd. for C12H15O
[M+H]+: 175.1123.
Aryl-substituted a,b-unsaturated ketone 3l: From 19 mg
(0.20 mmol) of alkynol 1d, and after chromatography of the
residue using hexanes/ethyl acetate (20:1) as eluent, gave
1515 cmÀ1
;
HR-MS (ES): m/z=253.0742, calcd. for
C15H11NO3 [M]+: 253.0739.
Aryl-substituted a,b-unsaturated ketone 3f: From 40 mg
(0.30 mmol) of alkynol 1a, and after chromatography of the
residue using hexanes/ethyl acetate (5:1) as eluent, gave
compound 3f as
a colorless oil; yield: 63 mg (77%).
1H NMR (300 MHz, CDCl3, 258C): d=7.91 (m, 2H), 7.59
(m, 5H), 7.47 (m, 2H), 6.19 (s, 1H), 5.80 (s, 1H); 13C NMR
(75 MHz, CDCl3, 258C): d=196.7, 146.9, 140.5, 136.8, 133.3,
129.8 (2C), 128.5 (2C), 127.5 (2C), 125.5 (q, J=3.7 Hz, 2C),
123.9 (q, J=272.2 Hz, CF3), 123.6; IR (CHCl3): n=1665,
compound 3l as
a colorless oil; yield: 28 mg (64%).
1H NMR (300 MHz, CDCl3, 258C): d=7.07 (m, 4H), 7.00
(q, J=7.1 Hz, 1H), 2.59 (q, J=7.3 Hz, 2H), 1.72 (d, J=
7.1 Hz, 3H), 1.07 (t, J=7.3 Hz, 3H); 13C NMR (75 MHz,
CDCl3, 258C): d=201.1, 162.1 (d, J=246.2 Hz), 142.7, 138.2,
131.7, (d, J=3.4 Hz), 131.3, (d, J=8.0 Hz, 2C), 115.2 (d, J=
1325 cmÀ1
; HR-MS (ES): m/z=276.0759, calcd. for
C16H11F3O [M]+: 276.0762.
Aryl-substituted a,b-unsaturated ketone 3g: From 40 mg
(0.30 mmol) of alkynol 1a, and after chromatography of the
residue using hexanes/ethyl acetate (7:1) as eluent, gave
compound 3g as a colorless oil; yield: 47 mg (57%).
1H NMR (300 MHz, CDCl3, 258C): d=8.14 (d, J=8.5 Hz,
1H), 8.02 (m, 2H), 7.89 (m, 2H), 7.69 (d, J=8.5 Hz, 1H),
7.49 (m, 3H), 6.17 (s, 1H), 5.77 (s, 1H), 4.38 (q, J=7.1 Hz,
2H), 1.39 (t, J=7.1 Hz, 3H); 13C NMR (75 MHz, CDCl3,
258C): d=196.8, 166.1, 147.5, 141.2, 136.8, 133.2, 129.9 (2C),
129.8 (2C), 128.4 (2C), 127.0 (2C), 125.2, 122.8, 61.0, 14.2;
8.0 Hz, 2C), 32.4, 15.5, 8.4; IR (CHCl3): n=1679, 1511 cmÀ1
;
HR-MS (ES): m/z=193.1015, calcd. for C12H14FO [M+H]+:
193.1029.
Aryl-substituted a,b-unsaturated ketone 3m: From 43 mg
(0.20 mmol) of alkynol 1e, and after chromatography of the
residue using toluene as eluent, gave compound 3m as a col-
1
orless oil; yield: 53 mg (90%). H NMR (300 MHz, CDCl3,
IR (CHCl3): n=1714, 1684 cmÀ1
; HR-MS (ES): m/z=
258C): d=7.82 (m, 1H), 7.50 (m, 7H), 7.37 (m, 2H), 7.27
(m, 1H), 7.09 (m, 1H), 6.94 (dd, J=5.1, 3.7 Hz, 1H);
13C NMR (75 MHz, CDCl3, 258C): d=196.4, 138.5 (2C),
137.7, 135.8, 135.5, 133.3, 131.6, 130.7, 129.9 (2C), 129.3
(2C), 129.1 (2C), 128.4, 128.2 (2C), 126.7; IR (CHCl3): n=
1641, 1600 cmÀ1; HR-MS (ES): m/z=291.0842, calcd. for
C19H15OS [M+H]+: 291.0844.
Aryl-substituted a,b-unsaturated ketone 3n: From 43 mg
(0.20 mmol) of alkynol 1e, and after chromatography of the
residue using hexanes/ethyl acetate (10:1) as eluent, gave
compound 3n as a colorless oil; yields: 63 mg (85%).
1H NMR (300 MHz, CDCl3, 258C): d=7.70 (m, 2H), 7.54
(d, J=8.4 Hz, 2H), 7.47 (m, 2H), 7.39(m, 2H), 7.23 (d, J=
5.0 Hz, 1H), 7.15 (d, J=8.4 Hz, 2H), 7.02 (m, 1H), 6.88 (dd,
J=5.1, 3.7 Hz, 1H); 13C NMR (75 MHz, CDCl3, 258C): d=
196.1, 138.3, 138.1, 136.4, 136.0, 134.7, 133.7, 132.4 (2C),
131.8 (2C), 131.7, 131.0, 129.3 (2C), 128.3 (2C), 126.9,
280.1107, calcd for C18H16O3 [M ]+: 280.1099.
Aryl-substituted a,b-unsaturated ketone 3h: From 42 mg
(0.20 mmol) of alkynol 1b, and after chromatography of the
residue using toluene as eluent, gave compound 3h as a col-
orless solid; yield: 44 mg (77%); mp 99–1018C. 1H NMR
(300 MHz, CDCl3, 258C): d=7.89 (m, 2H), 7.50 (m, 3H),
7.29 (m, 9H), 7.12 (m, 2H); 13C NMR (75 MHz, CDCl3,
258C): d=197.6, 140.7, 140.1, 138.1, 136.4, 134.7, 132.1,
130.3 (2C), 129.7 (2C), 129.6 (2C), 128.9, 128.7 (2C), 128.2
(2C), 128.1 (2C), 127.9; IR (CHCl3): n=1652, 1266 cmÀ1
;
HR-MS (ES): m/z=285.1275, calcd. for C21H17O [M+H]+:
285.1279.
Aryl-substituted a,b-unsaturated ketone 3i: From 29 mg
(0.20 mmol) of alkynol 1c, and after chromatography of the
residue using toluene as eluent, gave compound 3i as a color-
less oil; yield: (40 mg (92%). 1H NMR (300 MHz, CDCl3,
Adv. Synth. Catal. 2016, 358, 1526 – 1533
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1531

UPDATES
Benito Alcaide et al.
122.9; IR (CHCl3): n=1643, 1601 cmÀ1; HR-MS (ES): m/z=
367.9872, calcd. for C19H13BrOS [M]+: 367.9870.
122.9, 122.8, 108.2, 77.0, 57.0, 26.2; IR (CHCl3): n=3357,
1704, 1605 , cmÀ1; HR-MS (ES): m/z=439.1389, calcd. for
C25H20F3NO3 [M]+: 439.1395.
Aryl-substituted a,b-unsaturated ketone 5a: From 56 mg
(0.20 mmol) of alkynol 4a, and after chromatography of the
residue using toluene as eluent, gave compound 5a as
1
a yellow solid; yield: 41 mg (57%); mp 174–1768C. H NMR
Acknowledgements
(300 MHz, CDCl3, 258C): d=8.19 (d, J=7.5 Hz, 2H), 7.70
(d, J=7.4 Hz, 2H), 7.57 (m, 3H), 7.46 (m, 5H), 7.31 (m,
3H), 7.04 (d, J=8.0 Hz, 1H), 6.97 (t, J=8.0 Hz, 1H), 6.72
(d, J=7.9 Hz, 1H); 13C NMR (75 MHz, CDCl3, 258C): d=
197.4, 140.9, 140.5, 140.4, 137.0, 136.3, 136.0, 135.1, 134.7,
134.0, 130.0 (2C), 129.2 (2C), 129.0 (4C), 128.8, 128.7, 128.6,
127.1, 126.8, 125.3, 124.8, 119.5, 119.4; IR (CHCl3): n=1646,
1596 cmÀ1; HR-MS (ES): m/z=358.1352, calcd. for C27H18O
[M]+: 358.1358.
Support for this work by MINECO and FEDER (Projects
CTQ2012-33664-C02-01, CTQ2012-33664-C02-02, CTQ2015-
65060-C2-1-P, and CTQ2015-65060-C2-2-P) is gratefully ac-
knowledged. E. B. thanks MINECO for a postdoctoral con-
tract.
Aryl-substituted a,b-unsaturated ketone 5b: From 56 mg
(0.20 mmol) of alkynol 4a, and after chromatography of the
residue using toluene as eluent, gave compound 5b as
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a yellow solid; yield: 61 mg (70%); mp 198–2008C. H NMR
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213–2158C; H NMR (300 MHz, CDCl3, 258C): d=8.03 (m,
2H), 7.54 (m, 7H), 7.30 (m, 1H), 7.02 (d, J=7.6 Hz, 1H),
6.85 (m, 2H), 3.17 (s, 3H); 13C NMR (75 MHz, CDCl3,
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(2C), 130.5, 129.8 (2C), 128.9 (2C), 128.8 (2C), 126.5, 124.2,
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residue using hexanes/ethyl acetate (3:1) as eluent, gave
compound 8b as a yellow solid; yield: 54 mg (65%); mp 95–
978C; 1H NMR (300 MHz, CDCl3, 258C): d=7.96 (d, J=
8.7 Hz, 2H), 7.28 (m, 4H), 7.14 (m, 3H), 7.03 (m, 3H), 6.85
(d, J=7.8 Hz, 1H), 4.08 (s, 1H), 3.24 (s, 3H), 3.13 (s, 3H);
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(ES): m/z=416.1368, calcd. for C24H20N2O5 [M]+: 416.1372.
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compound 8c as a yellow solid; yield: 48 mg (55%); mp
1
195–1978C. H NMR (300 MHz, CDCl3, 258C): d=7.33 (m,
6H), 7.08 (m, 6H), 6.84 (d, J=7.7 Hz, 1H), 3.26 (s, 1H),
3.25 (s, 3H), 3.12 (s, 3H); 13C NMR (75 MHz, CDCl3,
258C): d=177.1, 155.1, 143.8, 139.8, 132.7, 132.5 (2C), 131.5,
129.9 (2C), 129.5, 128.8 (q, J=32.4 Hz), 128.4, 127.9 (2C),
124.3 (q, J=3.7 Hz, 2C), 124.0 (q, J=272.3 Hz, CF3), 123.8,
1532
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Adv. Synth. Catal. 2016, 358, 1526 – 1533

UPDATES
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