Olefination with Sulfonyl Halides and Esters: E-Selective Synthesis of Alkenes from Semistabilized Carbanion Precursors

Article abstract of DOI:10.1002/ejoc.201701766

Carbanions of sulfonyl halides and activated sulfonates add to carbonyl compounds, and so-formed aldol-type adducts spontaneously fragment into olefins. This transformation mimics the one-pot Julia olefination with (hetero)aryl sulfones, but the mechanism of fragmentation involves a four-membered intermediate, typical for reactivity of phosphorus reagents. Moreover, in contrast to the reactions of sulfones, sulfonates of fluorinated alcohols (TFE and HFI) produce byproducts that are easily removed during workup. In our report, we focus on reactions of unstabilized and semistabilized carbanion precursors: alkylsulfonates, and allyl- and benzylsulfonates, respectively. In particular for semistabilized systems, olefins were synthesized as predominant E isomers in good yields. The presented studies reveal that optimal reaction conditions, including the type of base and alcohol groups of the sulfonates, are different depending on stabilization of the carbanion precursors and structure of the carbonyl substrates. The practical synthetic guide is supplemented with a discussion of the mechanism, based on reactivity studies of intermediates and identification of side-products.

Full text of DOI:10.1002/ejoc.201701766

A Journal of
Accepted Article
Title: Olefination with Sulfonyl Halides and Esters: E-Selective
Synthesis of Alkenes from Semistabilized Carbanion Precursors
Authors: Michał Barbasiewicz, Bartosz Górski, Dariusz Basiak, Alicja
Talko, Tymoteusz Basak, and Tomasz Mazurek
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10.1002/ejoc.201701766
European Journal of Organic Chemistry
FULL PAPER
DOI: ((will be filled in by the editorial staff))
Olefination with Sulfonyl Halides and Esters: E-Selective Synthesis of Alkenes from
Semistabilized Carbanion Precursors
Bartosz Górski,[a] Dariusz Basiak,[a,b] Alicja Talko,[a] Tymoteusz Basak,[a] Tomasz Mazurek,[a,b] and
Michał Barbasiewicz*[a]
Abstract: Carbanions of sulfonyl fluorinated alcohols (TFE and HFI) type of the base and alcohol groups of
halides and activated sulfonates add to produce byproducts, which are easily the sulfonates, are different depending
carbonyl compounds, and so-formed removed during workup. In our report on stabilization of the carbanion
aldol-type
fragment
adducts
into
spontaneously we focused on reactions of unstabilized precursors and structure of the carbonyl
olefins. This and semistabilized carbanion substrates. The practical synthetic guide
transformation mimics the one-pot Julia precursors: alkylsulfonates, and allyl- is supplemented with mechanistic
olefination with (hetero)aryl sulfones, and benzylsulfonates, respectively. In studies based on identification of
but mechanism of the fragmentation particular for semistabilized systems intermediates and side products.
consists of four-membered intermediate, olefins
were
synthesized
as
typical for reactivity of phosphorus predominant E isomers in good yields.
reagents. Moreover, in contrast to the The presented studies reveal that
reactions of sulfones, sulfonates of optimal reaction conditions, including
Keywords: olefination • alkenes •
sulfonates • carbanions • selectivity
Introduction
Olefination of carbonyl compounds is one of the key methods of
formation of the C=C bonds used in construction of the carbon
framework.[1] For this purpose heteroorganic reagents as silanes,[2]
phosphonium salts and phosphonates[3], and sulfones[4] are applied,
and after deprotonation so-formed nucleophilic species add to
carbonyl compounds with the formation of aldol-type adducts,
which transform into olefins. For sulfur-based processes, usually
named the one-pot Julia olefination, carbanions of alkyl (hetero)aryl
sulfones add to carbonyl compounds, and then spontaneously
undergo Smiles rearrangement via five-membered intermediate
Scheme 1. Example of the one-pot Julia olefination (top), and mechanism of olefination
with sulfonyl halides and esters, involving four-membered ring structure[6] (bottom).
[a]
B. Górski, D. Basiak, A. Talko, T. Basak, T. Mazurek, M. Barbasiewicz
Faculty of Chemistry, University of Warsaw,
Pasteura 1, 02-093 Warsaw, Poland
Fax: (+48) 22 822 59 96
E-mail: barbasiewicz@chem.uw.edu.pl
www.aromaticity.pl
(Scheme 1, top).[5] The mechanism considerably differs from
olefination with phosphorus reagents, where four-membered
oxaphosphetane fragments into olefins. Recently we demonstrated
that similar mechanism, involving four-membered intermediate, is
plausible for olefination based on reactions of sulfonyl halides and
esters (Scheme 1, bottom).[6] This kind of reactivity was described
for the first time by Hawkins, who tested reactions of series of
premetalated alkyl and aryl mesylates with benzophenone.[7] In
reactions of trifluoroethyl, phenyl and 2,6-diisopropylphenyl
mesylates expected 1,1-diphenylethylene was isolated in 56-73% of
yield, but analogous trifluoroethyl ethanesulfonate poorly reacted
ORCID (M. Barbasiewicz): 0000-0002-0907-7034
[b]
D. Basiak, T. Mazurek
Faculty of Chemistry, Warsaw University of Technology, Noakowskiego
3, 00-664 Warsaw, Poland
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejoc.xxxxxxxxx.
1
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10.1002/ejoc.201701766
European Journal of Organic Chemistry
with benzaldehyde, giving only 23% of alkene. To the best of our
knowledge the preliminary studies were never continued under
premetalated precursor conditions,[8] where deprotonation precedes
addition of the carbonyl compound. Further reports[6,9] based on a
similar concept utilized so-called Barbier conditions, where base is
added to a mixture of carbanion precursor and carbonyl compound,
limiting application of enolizable aldehydes and ketones. Reactions
of semistabilized benzylsulfonyl fluorides[9a] and methallylsulfonyl
fluoride[9b] utilized heterogenous carbonate base, while NEt3 was
applied to promote reactions with more acidic ethyl
fluorosulfonylacetate.[9c] In most cases olefins were isolated in
moderate to good yields as mixtures of isomers, but reactions of
aldehydes bearing acidic -protons were sluggish, giving lower
yields of alkenes. Recently similar approach was applied by us for
less acidic trifluoroethyl alkanesulfonates, which react with
nonenolizable aldehydes and ketones in the presence of tert-BuOLi,
giving various olefins isolated in good yields, as mixtures of
isomers.[6]
reaction with solvent, e.g. 4-methylbenzyl chloride (1b) led to the
mixture of sodium 4-methylbenzylsulfonate and 4-methylbenzyl
alcohol, which after chlorination gave 2b in diminished yield 29%.
Analogous two-step alkylation-chlorination procedure with
4-methoxybenzyl chloride (1a) led only to an intractable mixture of
products. In most cases application of PCl5 for chlorination of
sodium sulfonates was efficient, giving good yields of sulfonyl
chlorides. The process was carried out on crude mixtures of
intermediate sulfonates with NaCl (formed as a stoichiometric
byproduct of the alkylation). Interestingly, when similar reactions
were attempted using allyl bromide and ethyl bromoacetate,
presence of NaBr made the chlorination process unselective, and
resulted in diminished yields and purities of products. Finally, with
the prepared sulfonyl chlorides in hand we synthesized a series of
sulfonates (3-5) in high yields and purities, using procedures
described in our previous report.[6,10]
OLEFINATION UNDER BARBIER CONDITIONS
In the present report we describe further studies of the promising
olefination method, concerning control of the E/Z-selectivity, and
application of enolizable carbonyl compounds under premetalated
precursor conditions. After careful examination of the reaction
conditions we identified experimental procedures for olefination of
various carbonyl compounds, giving predominant E isomers of
alkenes. Moreover, detailed mechanistic studies and structure-
activity correlations of substrates enabled understanding of
elementary processes, which operate under these conditions.
Studies of olefination with sulfonyl halides and esters started
from screening of reactions of carbanion precursors, using
procedure described in our previous report for trifluoroethyl
alkanesulfonates. When equimolar amount of the precursor,
carbonyl compound and two equivalents of tert-BuOLi were
combined in THF at r.t. under argon for 16 h a series of olefins was
isolated in good yields, usually in range 60-85%, as mixtures of
isomers.[6] We expected that under similar conditions variation of
alcohol/phenol groups of the sulfonates can affect isomer ratio of the
produced alkenes, in particular for coordinating 8-hydroxyquinoline
and 2-hydroxypyridine derivatives (3h, 3i, 4h, and 4i), and sterically
demanding 2,6-disubstituted phenyl sulfonates[7] (3k-m, Figure
1).[11]
Results and Discussion
At the outset of our research we required a set of sulfonate
precursors for further tests with carbonyl compounds. Although
numerous alkanesulfonyl chlorides are available from commercial
sources, derivatives of allyl- and benzylsulfonyl chlorides are
usually expensive. Therefore, we synthesized them from
corresponding benzyl, allyl and methallyl chlorides (1a-f), and ethyl
chloroacetate (1g) by refluxing with Na2SO3 in aqueous ethanol,
evaporation and drying of the residue, and chlorination with PCl5 or
oxalyl chloride in DCM. Products were isolated by crystallization
(for arylmethanesulfonyl chlorides, 2b-d), or vaccum distillation
(for allyl, methallyl and acetate derivative, 2e-g) as presented at
Scheme 2.[10]
Scheme 2. Syntheses of selected sulfonyl chlorides used for preparation of carbanion
precursors. Molar reactant ratios were shown in parentheses.[10] a - High boiling point
N-methylformanilide was used as a catalyst to avoid contamination of the distilled
products; b - Oxalyl chloride was applied as a chlorinating agent.
Figure 1. Reactions of sulfonyl esters (3-5) with freshly distilled benzaldehyde and tert-
BuOLi. Olefins 6-8 were isolated by chromatography as mixtures of E/Z isomers
(isomer ratios were shown in parentheses). a - Data taken from ref.[6]; b - At Scheme
2 the same compound is denoted as 2g; c - Most of the carbanion precursor remained
unreacted; d - Reaction with 2,2,3,3,4,4,4-heptafluorobutyl 1-octanesulfonate 3n,
expectedly more electrophilic at the sulfur center than 3d, gave similar yield of alkene
(83% of 6, as a mixture of E/Z isomers 42:58).
We observed that donor-substituted benzyl chlorides refluxed
with aqueous alcoholic solution of Na2SO3 favoured competitive
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10.1002/ejoc.201701766
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Surprisingly, structure of the alcohol/phenol groups displayed
only little effect on the E/Z selectivity, but influenced the reaction
yield over a broad range. Following our previous findings,[6] good
leaving groups as chloride, fluoride and pentafluorophenoxide
favored fast competitive carbanion decomposition to sulfene that
resulted in high conversions of precursors and low olefin yields. In
turn stable neo-pentyl sulfonates (3f and 4f) formed aldol-type
adducts, which did not react further to alkenes. Between the two
extremes sulfonates of moderately nucleofugal trifluoroethanol
(TFE), hexafluoroisopropanol (HFI), and phenol, appeared to be
good olefinating reagents in selected cases. However, interesting
effects displayed substituents present on the carbanionic center:
alkyl chain (nC7H15) in nonstabilized 1-octanesulfonates (3), phenyl
ring in semistabilized benzylsulfonates (4), and ester group in
stabilized derivatives of ethyl sulfoacetate (5). When nonstabilized
alkanesulfonates produced ca. equimolar mixtures of isomers of
1-phenylnon-1-ene (6), semistabilized benzylsulfonates preferred
formation of E-stilbene (7), in some cases isolated as a single isomer
(99:1). At the same time stabilized ethyl sulfoacetates failed to
react, and precursors 5c,d, and f were recovered after the reaction in
high yields.
Figure 2. Reactions of diastereoisomeric aldol-type adducts 9 with 4-methylbenzalde-
hyde under standard olefination conditions.[10] Molar reactant ratios were shown in
parentheses. Provided that the fragmentation mechanism is stereospecific,[6] and no
aldol-type equilibration occurs 9a (top) should lead to Z-7, and 9b (bottom) to E-7.
In contrast to adducts of nonstabilized trifluoroethyl
1-octanesulfonate (3d), which differed in reactivity,[6] reactions of
isomeric intermediates 9a,b gave similar results. In both cases
alkenes were produced as ca. equimolar mixtures of stilbene 7 and
cross-product with 4-methylbenzaldehyde 10, formed as
predominant E-isomers. High contents of the cross-product, and
little difference between reactivity of the isomers supports the idea
of fast aldol equilibration of less nucleophilic carbanions derived
from semistabilized precursors 4. In effect kinetic preference toward
formation of E-alkenes, supposedly similar to those observed for
slowly equilibrating adducts of 3d, likely translate into high E
selectivities of stilbenes, as presented at Figure 1.
At the beginning of our studies origin of selectivities observed
for reactions of semistabilized carbanion precursors 4 was not
entirely clear, however we reckoned that it likely derives from the
reaction mechanism, as presented at Scheme 1, bottom. Previous
mechanistic studies[6] on nonstabilized sulfonate 3d revealed that in
the initial step of reaction with benzaldehyde intermediate aldol-type
adduct is formed as a mixture of two diastereoisomers (64:36), and
their rates of fragmentation to alkenes differ substantially. Under the
reaction conditions (r.t.) minor isomer immediately transforms into
E-alkene 6 in a stereospecific manner (>99:1), whereas major
isomer fragments more slowly giving mixture of E- and Z-6 (28:72).
At the same time in the latter case aldol-type equilibration operates,
as demonstrated by the formation of cross-product with another
aldehyde present in the reaction mixture. Therefore, fast
fragmentation of the minor isomer to E-6, and slow fragmentation of
the major isomer to Z-6, accompanied with partial equilibration of
the isomeric adduct, resulted in the formation of ca. equimolar
mixture of the alkene isomers. However, we expected that the
disadvantageous scheme may totally change when aldol
equilibration is significantly faster than formation of alkenes, and
product distribution is controlled by the relative rates of
fragmentation to isomeric alkenes, rather than by isomer ratio of the
intermediate adducts (the Curtin-Hammett principle).[12] In the
presented case more stabilized (and sterically demanding)
carbanions of benzylsulfonates 4 are expected to shift aldol
equilibrium to the left, as compared with 3, and thus fasten
equilibration of the adducts, favoring formation of kinetically
preferred E-stilbene. The hypothesis was consistent with the fact,
that stronger carbanion stabilization in derivatives of ethyl
sulfoacetate (5c,d, and f) caused the aldol-type addition virtually
ineffective, and led only to recovery of substrates.
To better understand processes, which run at lower temperatures,
in particular these related to deprotonation of precursors and
formation of intermediate adducts, we performed another set of
experiments with selected precursors, as shown at Figure 3.
To support the presented concept we synthesized adducts of
semistabilized precursor 4d by quenching reaction with
benzaldehyde at low temperature,[13] and independently subjected
both isomers of 9 to standard olefination conditions in the presence
of one equivalent of 4-methylbenzaldehyde (Figure 2).
Figure 3. Reactions of carbanion precursors, benzaldehyde, and one equivalent of alkali
metal tert-butoxides arrested after 30 min at -78 C. Precursors recovery yields were
shown in parentheses. a - Intermediate aldol-type adduct 11a,b was isolated (34-44%);
b - Olefin 12 was isolated (ca. 1%); c - Condensation product 13a,b was isolated
(13-20%).[10]
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10.1002/ejoc.201701766
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The experiments can be considered low temperature variants of
these presented at Figure 1, in which mixtures of carbanion
precursors and benzaldehyde (Barbier conditions) were treated with
one equivalent of base at -78 C for 30 min, instead of prolonged
exposition to the excess of base at rt. At -78 C lithium tert-butoxide
appeared to be a relatively weak base, and in many cases
conversions of carbanion precursors were low or negligible, in
particular for less acidic nonstabilized substrates 3b-d. Therefore,
we tested also potassium tert-butoxide as a more potent base. From
the obtained results several interesting conclusions can be drawn,
some of them being parallel to the previous findings shown at
Figure 1. First, sulfonyl chlorides (3a, 4a, and 5a) react with one
equivalent of base with high or total conversions, but alkene yields
remain low, in consistency with competitive fast elimination of the
chloride anion giving sulfene.[6,14] On the other hand carbanions of
trifluoroethyl sulfonates (3d and 4d) add to benzaldehyde, but
following fragmentation to alkenes is exceedingly slow at -78 C (in
contrast to r.t.), and intermediate adducts 11a,b can be isolated in
34-44% of yield. At the same time the least nucleophilic derivatives
of ethyl sulfoacetate (5c-d) can be recovered after quenching of the
reaction in high yields with no traces of addition and fragmentation
products. However, the most useful informations arise from
isolation and identification of byproducts formed exclusively in the
experiments carried out at low temperature. From the reaction
mixtures with trifluoroethyl benzylsulfonate (4d) we isolated
unreacted ester (4d, 66% and 15% for tert-BuOLi and tert-BuOK,
respectively) and intermediate aldol-type adducts 11b (34%, 60:40
and 42%, 14:86, respectively), in the latter case accompanied with
condensation product 13b (13%, one isomer). Analogously under
the same conditions with tert-BuOK nonstabilized trifluoroethyl
1-octanesulfonate 3d led to a mixture, which contained aldol-type
adduct (11a, 44%, 100:0), condensation product (13a, 20%, 71:29),
and only traces of unreacted 3d and alkene 6. Evidently, when
fragmentation to olefins runs slowly O-anions of intermediate aldol-
type adducts undergo proton transfer from the  position, followed
by expulsion of the hydroxide, to give condensation products 13a,b
with restored sulfonyl group (Scheme 3, top).
-position of the precursor, followed by second aldol-type addition,
giving after fragmentation functionalized olefin 12 (Scheme 3,
bottom).[15] Summarizing the mechanistic findings and differences
between reactions promoted with lithium and potassium bases we
reckon that effect of the alkali metal cation manifests mainly in
ability of the anionic aldol-type adduct to undergo proton transfer,
which makes formation of the condensation product faster than
fragmentation to olefins. The idea was supported further with results
of reactions between nonstabilized trifluoroethyl alkanesulfonates
(14, 17, and 19), and 2-naphthaldehyde (Scheme 4).
Scheme 4. Methylenation (top), isopropylidenation (center), and reaction of derivative
of camphorsulfonic acid 19 with 2-naphthaldehyde. Molar reactant ratios were shown in
parentheses.[10]
In a previous report[6] we observed that methylenation of
2-naphthaldehyde with trifluoroethyl mesylate 14a led to the
formation of 2-vinylnaphthalene (15) isolated in low yield (31%),
accompanied with unidentified by-products. Following the previous
findings we repeated the reaction, and after careful chromatographic
separation isolated aldol-type adduct 16a (22%), and condensation
product 16b (12%). When the same reaction was repeated at 65 °C
intermediate 16a was no longer observed in the mixture, but yields
of alkene 15 and condensation product 16b increased to 39% and
24%, respectively (Scheme 4, top). Considering that olefin yields
with carbanion precursors bearing longer alkyl chains (Et, Pr,
n-octyl) were much higher (73-85%),[6] less favored methylenation
process is likely related to the absence of alkyl group at the
-position of the intermediate 16a. Effect of the alkyl substituent
can act in two ways, by changing conformational preferences around
the newly formed C-C bond (so-called reactive rotamer effect
related to proximity of the reacting centers),[16] or by decrease of
rate of fragmentation to a less substituted alkene. To overcome the
difficulties we synthesized two other methylenating precursors
Scheme 3. Postulated mechanism of formation of the condensation products 13a,b (top),
and alkene 12 (bottom).
Even more striking process was traced from the formation of
byproduct isolated in reactions of benzyl precursors bearing good
leaving groups on the sulfonyl moiety: fluoride (4b) and
hexafluoroisopropoxide (4c). In both cases from reactions with tert-
BuOK we isolated small amount (ca. 1%) of olefin 12. To explain
mechanism of its formation in control experiments pure samples of
E- and Z-stilbene 7 were treated with base and benzaldehyde for 30
min at -78 C. In both cases we detected no traces of 12, so
unquestionably the product was formed prior to fragmentation to
alkene. Thus, remaining alternative consists of proton transfer from
2,2,3,3,4,4,4-heptafluorobutyl
mesylate
(14b,
CH3SO2OCH2CF2CF2CF3) and 1,1,1,3,3,3-hexafluoroisopropyl
mesylate (14c, CH3SO2OCH(CF3)2). In both cases alcoholic groups
were highly substituted with electron-acceptor fluorine atoms as
compared with trifluoroethyl mesylate (14a), that should fasten
nucleophilic cyclization of adducts similar to 16a. Unfortunately, in
both cases olefin yields in reactions carried out at r.t. were low (27%
and 1%, for 14b and 14c, respectively), and further attempts to
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10.1002/ejoc.201701766
European Journal of Organic Chemistry
improve the process have failed.[17] Interesting differences between
outcome of the reaction with lithium and potassium base appeared
also for trifluoroethyl 2-propanesulfonate 17 (Scheme 4, center). As
the precursor possesses only one acidic proton at the -position to
the sulfonyl group, proton transfer and formation of the
condensation product is not possible. Therefore, we expected that in
this case potassium base should lead to high yield of alkene 18.
However, changing of base from tert-BuOLi to tert-BuOK
decreased yield from 68% to 18%.[18] Another example, in which
main olefination reaction was disfavored, concerned highly
branched precursor derived from camphorsulfonic acid 19 (Scheme
4, bottom). Under standard olefination conditions with model 2-
naphthaldehyde and tert-BuOLi we isolated only condensation
product 20 in 68% of yield, as a single isomer. Evidently in this case
steric hindrance displayed by the substrates hampered fragmentation
to the olefin, and again proton transfer process, followed by
expulsion of the hydroxide gave the condensation product. In
summary, under olefination conditions (in particular with tert-
BuOLi as a base) formation of the condensation product is a slow
but competing process, which manifests, when main olefination
reaction is disfavored.
Figure 4. Optimization studies of reactions of allyl and benzylsulfonates 4c,d and 21a,b
with 2-naphthaldehyde and tert-BuOLi and DBU as bases. E/Z isomer ratios of alkenes
and molar reactant ratios were shown in parentheses. a - Reaction run unselectively; 1H
NMR spectrum suggested reaction at the -position of the precursor with the C=C bond
transposition.
benzyl), whereas for nonstabilized systems trifluoroethyl esters
seem to be the best choice. Effect of base was less clear, for
allylsulfonate 21b tert-BuOLi gave better results, whereas for
benzylsulfonate 4c DBU was superior. Next, under Barbier
conditions optimal for the synthesis of stilbenes we tested series of
benzylsulfonates substituted in the aromatic ring, and electronically-
tuned benzaldehydes. Results are presented at Figure 5.
Encouraged by high selectivities and yields of stilbene 7
synthesized from semistabilized hexafluoroisopropyl (4c),
trifluoroethyl (4d), and phenyl benzylsulfonate (4j) we focused on
optimization of the reaction conditions, and determining scope and
limitations of the process.[19] Separation of the reaction mixtures
with aryl sulfonates shown at Figure 1 revealed that after quenching
and aqueous workup phenols remain as byproducts in the reaction
mixtures, and require removal by chromatography. In turn esters of
fluorinated alcohols: trifluoroethanol (TFE; b.p.=77-80 °C) and
hexafluoroisopropanol (HFI; b.p.=59 °C) behave as ‘traceless
precursors’, that after fragmentation to alkenes release
stoichiometric byproducts, which 'vanish' during evaporation of the
organic solvent, or remain undetected in the aqueous phase after the
extraction. When model reaction between 4c and benzaldehyde was
1
repeated in THF-d8, H NMR spectrum of crude reaction mixture
revealed presence of multiplet at 4.52 ppm, which after addition of
HFI increased in intensity. Next, when rest of the mixture was
quenched with NH4Cl in D2O, and both phases were analyzed with
1H NMR again resonance attributed to HFI was observed in the
organic phase.[10] Based on the data we can conclude that for
precursors like 3c, and 4c,d fragmentation to alkenes releases only
an easily volatile fluorinated alcohol as
a stoichiometric
byproduct,[20] and therefore in the following studies trifluoroethyl
and hexafluoroisopropyl sulfonates were tested as olefinating
reagents.
Figure 5. Syntheses of stilbenes under Barbier condions with DBU as a base. E/Z
isomer ratios of alkenes and molar reactant ratios were shown in parentheses. a - 32%
of yield of 27 (100:0) was obtained with tert-BuOLi as a base. b - 93% of yield of 23
(90:10) was obtained with 1.2 equivalents of 4c.
For reactions of 2-naphthaldehyde with trifluoroethyl and
hexafluoroisopropyl allyl- and benzylsulfonates two different
Barbier-type conditions were applied, first using tert-BuOLi, and
second with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene)[21] as a
base. The results are shown at Figure 4. In all cases
hexafluoroisopropyl esters of semistabilized allyl- and
benzylsulfonates gave better yields than trifluoroethyl
sulfonates.[22] It is worth to stress that under the same conditions
Interestingly, for a broad palette of precursors and aldehydes
isolated products were formed in good to excellent yields. Only
strongly substituted benzaldehydes, bearing dimethylamino group
and pentafluorophenyl ring, failed to react (Figure 5, top), but at the
same time substituents present at the carbanion precursors displayed
only little effect (Figure 5, bottom). It is worth to stress that the
reactions gave higher yields and selectivities of alkenes than those
described by Kagabu for benzylsulfonyl fluorides.[9a] However,
reaction with enolizable hydrocinnamaldehyde led only to a
complicated mixture of products and poor mass recovery after
chromatography. Therefore we turned our attention to premetalated
with
tert-BuOLi
nonstabilized
hexafluoroisopropyl
1-octanesulfonate 3c poorly reacted with benzaldehyde (giving 11%
of 6), and trifluoroethyl ester 3d was an optimal olefinating reagent
(84% of 6). Therefore hexafluoroisopropyl group is recommended
for olefination with more acidic semistabilized sulfonates (allyl and
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10.1002/ejoc.201701766
European Journal of Organic Chemistry
intermediate aldol-type adducts. Presence of the intermediates
suggested that fragmentation to alkenes was not complete, and
higher yields of the olefins can be obtained under more vigorous
conditions. At the same time similar polar products were not
observed for 2-naphthaldehyde, for which olefin yields were higher.
Therefore, we tested also conditions, where after 30 min at rt the
mixture is warmed to 65 °C for further 30 min. Indeed, the last stage
of the procedure greatly improved yields of olefins 35 and 36
(Figure 6, bottom), whereas for reactions with 2-naphthaldehyde
resulted in only little effect (Figure 6, top). Interestingly, when
similar reactions of 4c and cyclohexanecarbaldehyde with LiHMDS
were arrested at rt, and at 65 C olefin yields were practically the
same (80% and 77%, respectively). Therefore, we reckoned that
faster fragmentation to alkenes 22 and 23 can be attributed to the
steric hindrance around the carbonyl group of the aldehyde, rather
than the absence of acidic protons at the -position, or electronic
effects.[16,25] Accordingly, sterically demanding 2-naphthaldehyde
and cyclohexanecarbaldehyde, branched at the -position, give high
yields of alkenes at r.t., whereas hydrocinnamaldehyde requires
heating to 65 C, in consistency with the reactive rotamer
concept.[16] It is worth to stress that under the optimized olefination
conditions yields of the allylation products 22 and 35 were
comparable or exceeded those reported in the literature for Wittig
and Horner-Wadsworth-Emmons reagents.[26] In the next step, the
optimized conditions were applied for reactions of semistabilized
carbanion precursors with various enolizable aldehydes and ketones
(Figure 7).
precursor conditions, to perform reactions with enolizable carbonyl
compounds, which usually deprotonate and self-condense under
Barbier conditions.
OLEFINATION UNDER PREMETALATED
PRECURSOR CONDITIONS
On the base of preliminary experiments with premetalated
precursors,[6] and results presented at Figure 4 and Figure 5 we
started optimization of the reaction conditions for olefination of
more challenging enolizable aldehydes and ketones. Semistabilized
hexafluoroisopropyl allylsulfonate 21b and benzylsulfonate 4c were
tested in reactions with 2-naphthaldehyde and hydrocinnamaldehyde
(3-phenylpropanal). In model experiments carbanions were
generated with lithium and sodium hexamethyldisilazanes
(LiHMDS and NaHMDS)[23] in THF at -78 °C under argon for 30
min.[24] Then, a solution of aldehyde was added, and after 30 min
cooling bath was removed and Schlenk flask was kept at rt for 30
min, when the reaction was quenched with aqueous solution of
NH4Cl. In contrast to the reactions carried out under Barbier
conditions, in which equimolar proportion of substrates was used,
under premetalated conditions carbanion precursors were used in
excess (1.3 equivalents) to improve conversion of carbonyl
compounds. Results of the optimization studies are shown at Figure
6.
Figure 6. Optimization studies of reactions of semistabilized hexafluoroisopropyl
benzyl- (4c) and allylsulfonate 21b with 2-naphthaldehyde (top) and hydrocinnamalde-
hyde (bottom). E/Z isomer ratios of alkenes and molar reactant ratios were shown in
parentheses.
Figure 7. Syntheses of olefins from semistabilized hexafluoroisopropyl alkylsulfonates
with NaHMDS as a base. E/Z isomer ratios of alkenes and molar reactant ratios were
shown in parentheses. a - Yield and selectivity of 38 obtained, when the reaction was
quenched after 30 min at r.t. b - Yields and selectivities of alkenes obtained with
LiHMDS as a base.
In general two important observations were made. First, in
reactions of semistabilized precursors 21b and 4c kept at r.t. for 30
min (Figure 6, column left) sodium base appeared to be more
efficient than lithium base, in striking contrast to the behaviour of
nonstabilized trifluoroethyl 1-octanesulfonate 3d, which favoured
elimination to the condensation product, when treated with tert-
BuOK. However, when reaction of 3d was repeated under the same
conditions (NaHMDS, -78 C, 30 min, then r.t. 30 min), alkene 6
was formed in only 29% (88:12).[22] Second important finding in
reactions with hydrocinnamaldehyde carried out for 30 min at rt was
isolation of polar fraction of byproducts, which likely contained
Reactions of enolizable aldehydes: hydrocinnamaldehyde,
cyclohexanecarbaldehyde and octanal with hexafluoroisopropyl
benzylsulfonate 4c gave olefins 36, 38, and 6 isolated in 62%, 80%,
and 66% of yield, respectively. Cyclohexanone and acetophenone
gave moderate yields of 39 and 40 (58%, and 28%, respectively),
but the process was improved with LiHMDS, as a base (yields of
alkenes raised to 72% and 67%, respectively). In this case presence
of lithium cations plausibly shifted equilibrium of the aldol-addition
to the right, by stabilization of the intermediate aldol-type adducts.
Finally stilbene 27 was formed as a predominant E-isomer (98:2) in
6
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201701766
European Journal of Organic Chemistry
79% of yield, much better than this obtained in reaction with DBU
(28%; cf. Figure 5).
excellent yields and selectivities of alkenes. However for enolizable
carbonyl compounds we recommend premetalation of the precursor
with LiHMDS (for ketones) or NaHMDS (for aldehydes), addition
of the carbonyl compound, and warming of the reaction mixture to
65 C (see figure below). Under these conditions olefins are formed
in good yields as predominant E-isomers.
In the last step we turned back to nonstabilized trifluoroethyl
1-octanesulfonate 3d, an example of nonstablized carbanion
precursor. Under the optimized conditions we applied LiHMDS as a
base that led to satisfactory results.[27] For a palette of aldehydes
(hydrocinnamaldehyde,
cyclohexanecarbaldehyde,
and
-cyclocitral), and ketones (cyclohexanone, acetophenone, and
benzil) alkenes 41-46 were formed in moderate to good yields (31-
90%), and moderate selectivities (Figure 8). However,
nonenolizable 2-naphthaldehyde with 3d gave lower yield of styrene
47, than produced under Barbier conditions with tert-BuOLi as a
base (85%).[6]
Experimental Section
Procedure of olefination with t-BuOLi or DBU as
a base (standard Barbier
conditions):[10] A 30 mL Schlenk flask was charged with sulfonyl ester (2.0 mmol),
carbonyl compound (2.0 mmol), and argonated. Then THF (8 mL) was added, and to
the resulted solution tert-BuOLi (4.0 mL; 4.0 mmol; 1.0 M solution in THF) or DBU
(0.6 ml; 4.0 mmol) was added dropwise with stirring at r.t. The stirring was continued
for 16 h, and aqueuos solution of NH4Cl (8 mL; 10% w/v) was added. Then, the mixture
was transferred to the separatory funnel, followed by addition of aqueuos solution of
NH4Cl (50 mL; 10% w/v), and extracted with ethyl acetate (350 mL). Combined
organic phases were washed with water (50 mL), brine (50 mL), and dried over
anhydrous MgSO4. Then, the mixture was filtered, evaporated, and residue was
separated with column chromatography on cyclohexane:ethyl acetate mixture to elute
off the olefinic product.
Procedure of olefination with Li/NaHMDS as
a base (standard premetalated
conditions):[10] A 30 mL Schlenk flask was charged with sulfonyl ester (2.6 mmol), and
argonated. Then THF (8 mL) was added, and the flask was placed in a cooling bath
at -78 C. To the resulted solution LiHMDS or NaHMDS (2.4 mL; 2.4 mmol; 1.0 M
solution in THF) was added dropwise with stirring. The stirring was continued for 30
min, and a solution of carbonyl compound (2.0 mmol) in THF (2 mL) was added
dropwise. After 30 min the cooling bath was removed and stirring was continued for 30
min at r.t., and 30 min at 65 C. Then, the mixture was cooled to r.t., aqueuos solution
of NH4Cl (8 mL; 10% w/v) was added, the mixture was transferred to the separatory
funnel, followed by addition of aqueuos solution of NH4Cl (50 mL; 10% w/v), and
extracted with ethyl acetate (350 mL). Combined organic phases were washed with
water (50 mL), brine (50 mL), and dried over anhydrous MgSO4. Then, the mixture was
filtered, evaporated, and residue was separated with column on cyclohexane:ethyl
acetate mixture to elute off the olefinic product.
Figure 8. Syntheses of olefins from unstabilized trifluoroethyl 1-octanesulfonate (3d)
with LiHMDS as a base. E/Z isomer ratios of alkenes and molar reactant ratios were
shown in parentheses. a - Yields of alkenes obtained with tert-BuOLi as a base (under
standard Barbier conditions).
Conclusion
The presented systematic studies of the olefination reaction,
pioneered many years ago by Hawkins[7] and followers,[9] deliver
new data about reactivity of sulfonyl halides and activated esters.
Their application as carbonyl olefinating reagents features easy
removal of stoichiometric byproducts, being less problematic than
for Wittig (Ph3PO) or one-pot Julia (ArOH) reactions. Although the
presented transformations required extensive optimization of the
reaction conditions, the results may serve as a practical guide for
both application and further development of the methodology. The
most important findings are presented below.
Characterization data of alkenes
6, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  7.41-7.29 (m,
4+4H), 7.28-7.19 (m, 1+1H), 6.48-6.37 (m, 1+1H), 6.26 (dt, J=15.8, 6.9 Hz, 1H), 5.71
(dt, J = 11.7, 7.3 Hz, 1H), 2.37 (qd, J=7.3, 1.8 Hz, 2H), 2.24 (qd, J=6.9, 1.4 Hz, 2H),
1.57-1.44 (m, 2+2H), 1.34 (m, 8+8H), 1.01-0.86 (m, 3+3H). 13C NMR (100 MHz,
CDCl3)  137.9, 137.8, 133.2, 131.2, 129.7, 128.72, 128.66, 128.41, 128.1, 126.7, 126.4,
125.9, 33.1, 31.87, 31.84, 30.0, 29.4, 29.3, 29.23 (ovl), 29.20, 28.7, 22.69, 22.66, 14.11,
14.09. The 1H NMR and 13C NMR spectra were consistent with those described in the
literature[28]
.
For nonstabilized carbanion precursors (alkylsulfonates,
except of mesylates) trifluoroethyl esters are precursors of choice,
and reaction conditions, depending on character of the carbonyl
compound, consist of lithium tert-butoxide (2 equivalents), THF, r.t.,
16 h, or (for more demanding substrates) LiHMDS premetalated
carbanions, subjected to the carbonyl compound and gradually
heated to 65 °C. No sodium or potassium bases are recommended.
Olefins are isolated in moderate to good yields, as mixtures of
isomers.
7, white crystals, E isomer, mp.: 118.5-121.5 C (Lit. 123-124 C; T. Matsuda, K.
Suzuki, N. Miura, Adv. Synth. Catal. 2013, 355, 3396-3400). 1H NMR (400 MHz,
CDCl3)  7.58-7.49 (m, 4H), 7.40-7.34 (m, 4H), 7.30-7.25 (m, 2H), 7.13 (s, 2H). 13C
NMR (100 MHz, CDCl3)  137.3, 128.66, 128.65, 127.6, 126.5. The 1H NMR and
13C NMR spectra were consistent with those described in the literature[6]
.
8, yellowish oil, E isomer. 1H NMR (400 MHz, CDCl3)  7.67 (d, J=16.0 Hz, 1H), 7.54-
7.47 (m, 2H), 7.41-7.33 (m, 3H), 6.42 (d, J=16.0 Hz, 1H), 4.25 (q, J=7.1 Hz, 2H), 1.32
(t, J=7.1 Hz, 3H). 13C NMR (100 MHz, CDCl3)  167.0, 144.6, 134.4, 130.2, 128.8,
128.0, 118.2, 60.5, 14.3. The 1H NMR and 13C NMR spectra were consistent with those
described in the literature[29]
.
For semistabilized precursors (allyl- and benzylsulfonates)
hexafluoroisopropyl esters give best results and for nonenolizable
substrates Barbier conditions with tert-BuOLi or DBU give good to
7
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10.1002/ejoc.201701766
European Journal of Organic Chemistry
10, white solid, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  7.62-7.57 (m,
2H), 7.53-7.48 (m, 2H), 7.48-7.41 (m, 2H), 7.40-7.28 (m, 2+2H), 7.27-7.24 (m, 2+2H),
7.19 (d, J=16.4 Hz, 1H), 7.16 (d, J=16.4 Hz, 1H), 7.14-7.11 (m, 1H), 6.66 (d, J=12.7 Hz,
1H), 6.62 (d, J=12.7 Hz, 1H), 2.45 (s, 3H), 2.40 (s, 3H). 13C NMR (100 MHz, CDCl3) 
137.46, 137.45, 137.41, 136.8, 134.5, 134.2, 130.2, 129.5, 129.3, 128.86, 128.80,
128.74, 128.61, 128.57, 128.1, 127.7, 127.3, 126.9, 126.39, 126.36, 21.21, 21.18. The
32, white crystals, predominant E isomer, mp. 120.5-121.5 C (Lit.[38] 124 C). 1H NMR
(400 MHz, CDCl3)  7.86-7.79 (m, 4H), 7.73-7.68 (m, 2H), 7.52-7.45 (m, 2H), 7.44 (dt,
J=7.5, 1.3 Hz, 1H), 7.40 (ddd, J=8.0, 1.9, 1.0 Hz, 1H), 7.28-7.20 (m, 2H), 7.12 (d,
J=16.3 Hz, 1H). 13C NMR (100 MHz, CDCl3)  139.5, 134.2, 133.6, 133.2, 130.4,
130.16, 130.14, 129.2, 128.4, 128.0, 127.7, 127.3, 127.0, 126.4, 126.1, 125.2, 123.3,
122.9.
1H and 13C NMR spectra were consistent with those described in the literature[30]
.
33, white solid, E isomer, mp.=174.5-175 C (Lit.[39] 170-173 C). 1H NMR (400 MHz,
CDCl3)  7.89-7.83 (m, 2H), 7.83-7.79 (m, 2H), 7.73 (dd, J=8.7, 1.7 Hz, 1H), 7.65-7.59
(m, 4H), 7.51-7.43 (m, 2H), 7.34 (d, J=16.3 Hz, 1H), 7.22 (d, J=16.3 Hz, 1H). 13C NMR
(100 MHz, CDCl3)  140.8, 134.1, 133.6, 133.3, 131.3, 129.25 (q, 2JC-F=31.2 Hz), 128.5,
18, colorless oil. 1H NMR (400 MHz, CDCl3)  7.90-7.83 (m, 3H), 7.75 (s, 1H), 7.55-
7.44 (m, 3H), 6.54-6.49 (m, 1H), 2.04 (d, J=1.6 Hz, 3H), 2.03 (d, J=1.4 Hz, 3H). 13C
NMR (100 MHz, CDCl3)  136.2, 136.0, 133.4, 131.8, 127.7, 127.5 (ovl), 127.4, 127.0,
125.9, 125.3, 125.2, 26.9, 19.5. The 1H and 13C NMR spectra were consistent with those
3
128.1, 127.7, 127.4, 127.3, 126.6, 126.5, 126.3, 125.6 (q, JC-F=4.0 Hz), 123.3
described in the literature[6]
.
(resonance of the CF3 group was not visible). 19F NMR (376 MHz, CDCl3)  -62.9. The
1H and 13C spectra were consistent with those described in the literature[39]
.
20, white solid, one isomer (stereochemistry was not established), mp.=110-110.5 C.
1H NMR (400 MHz, CDCl3)  7.96-7.89 (m, 1H), 7.89-7.77 (m, 3H), 7.57 (dd, J=8.6,
1.8 Hz, 1H), 7.55-7.48 (m, 2H), 7.47 (s, 1H), 4.78-4.53 (m, 2H), 3.81 (dd, J=15.1, 0.7
Hz, 1H), 3.25 (s, 1H), 3.24 (d, J=15.1 Hz, 1H), 2.55 (td, J=12.7, 3.2 Hz, 1H), 2.35 (tt,
J=12.1, 4.2 Hz, 1H), 1.92-1.73 (m, 2H), 1.16 (s, 3H), 0.86 (s, 3H). 13C NMR (100 MHz,
CDCl3)  203.2, 139.6, 133.3, 133.1, 132.3, 130.4, 130.0, 128.4, 128.3, 127.6, 127.1,
126.6, 126.2, 122.1 (q, JC-F=278 Hz), 64.6 (q, JC-F=38.0 Hz), 57.1, 48.9, 48.3, 48.1,
25.73, 25.68, 20.2, 18.7. 19F NMR (376 MHz, CDCl3)  -74.3 (t, 3JF-H=7.9 Hz). MS (EI,
m/z, relative intensity): 452 (M+•, 51), 289 (100), 271 (7), 261 (29), 247 (35), 245 (12),
233 (37), 219 (16), 217 (14), 207 (48), 205 (31), 191 (27), 179 (35), 165 (21), 152 (15),
141 (39). Elem anal, calcd for C23H23F3O4S: C, 61.05; H, 5.12; found: C, 60.92; H, 4.95.
34, yellow crystals, predominant E isomer, mp.=169-170 C (Lit.[39] 165-167 C). 1H
NMR (400 MHz, THF-d8)  8.25-8.20 (m, 2H), 7.98 (s br, 1H), 7.89-7.81 (m, 4H),
7.81-7.76 (m, 2H), 7.59 (d, J=16.3 Hz, 1H), 7.51-7.45 (m, 2H), 7.42 (d, J=16.3 Hz, 1H).
13C NMR (100 MHz, THF-d8)  147.8, 145.1, 135.2, 134.8, 134.6, 134.1, 129.3, 129.0,
128.7, 128.5, 127.9, 127.6, 127.3, 127.2, 124.7, 124.2. The 1H and 13C spectra were
1
2
consistent with those described in the literature[39]
.
35, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  7.37-7.28 (m,
2+2H), 7.28-7.19 (m, 3+3H), 6.66 (dddd, J= 16.9, 11.2, 10.2, 1.1 Hz, 1H), 6.36 (dtd,
J=16.9, 10.3, 0.7 Hz, 1H), 6.18- 6.03 (m, 1+1H), 5.79 (dtd, J=15.3, 6.9, 0.8 Hz, 1H),
5.54 (dtq, J=10.9, 7.5, 1.1 Hz, 1H), 5.24 (ddt, J=16.9, 1.8, 0.8 Hz, 1H), 5.19-5.10 (m,
1+1H), 5.03 (ddt, J=10.2, 1.5, 0.7 Hz, 1H), 2.80-2.72 (m, 2+2H), 2.60-2.52 (m, 2H),
2.50-2.42 (m, 2H). 13C NMR (100 MHz, CDCl3)  141.67, 141.62, 137.1, 134.2, 132.0,
131.5, 131.4, 129.7, 128.37, 128.36, 128.29, 128.28, 125.85, 125.82, 117.2, 115.1, 35.8,
35.6, 34.4, 29.6. The 1H and 13C spectra were consistent with those described in the
22, white solid, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  7.90-7.76 (m,
4+4H), 7.67 (dd, J=8.6, 1.8 Hz, 1H), 7.57-7.45 (m, 2+3H), 7.07 (dddd, J=16.9, 11.2,
10.1, 1.1 Hz, 1H), 6.98 (ddt, J=15.6, 10.4, 0.8 Hz, 1H), 6.77 (d, J=15.7 Hz, 1H), 6.70-
6.56 (m, 1+1H), 6.45-6.38 (m, 1H), 5.54-5.48 (m, 1H), 5.48-5.42 (m, 1H), 5.36-5.31 (m,
1H), 5.28 (ddt, J=10.0, 1.5, 0.7 Hz, 1H). 13C NMR (100 MHz, CDCl3)  137.2, 134.8,
134.6, 133.6, 133.24, 133.23, 132.97, 132.94, 132.4, 131.1, 130.4, 129.9, 128.2, 127.93,
127.86, 127.69, 127.62, 127.56, 127.1, 126.5, 126.2, 126.1, 125.89, 125.84, 123.4,
119.9, 117.7 (ovl). The 1H and 13C NMR spectra of E isomer were consistent with those
literature[26c,40]
.
36, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  7.48-7.37 (m,
6+6H), 7.37-7.28 (m, 4+4H), 6.61-6.50 (m, 1+1H), 6.38 (dt, J=15.8, 6.8 Hz, 1H), 5.83
(dt, J=11.8, 7.1 Hz, 1H), 2.94-2.86 (m, 2+2H), 2.84-2.75 (m, 2H), 2.65 (dtd, J=8.8, 7.0,
1.4 Hz, 2H). 13C NMR (100 MHz, CDCl3)  141.7, 141.6, 137.6, 137.5, 131.7, 130.3,
129.9, 129.4, 128.7, 128.42, 128.41, 128.3, 128.1, 126.9, 126.5, 125.94, 125.86, 125.83,
36.0, 35.8, 34.8, 30.4. The 1H and 13C spectra were consistent with those described in
described in the literature[31]
.
23, white crystals, E isomer, mp.: 147.8-148.2 C (Lit.[32] 149-151 C). 1H NMR (400
MHz, CDCl3)  7.89-7.81 (m, 4H), 7.76 (dd, J=8.6, 1.7 Hz, 1H), 7.61-7.56 (m, 2H),
7.53-7.44 (m, 2H), 7.44-7.38 (m, 2H), 7.34-7.29 (m, 1H), 7.28 (d, J=6.1 Hz, 2H). 13C
NMR (100 MHz, CDCl3)  137.3, 134.8, 133.7, 133.0, 129.0, 128.72, 128.69, 128.3,
128.0, 127.66, 127.64, 126.61, 126.5, 126.3, 125.9, 123.5. The 1H and 13C NMR spectra
the literature[41,42]
.
37, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  7.35- 7.27 (m,
2+2H), 7.25-7.18 (m, 3+3H), 6.22 (ddt, J=15.6, 1.9, 0.9 Hz, 1H), 5.89 (dq, J=11.8, 1.5
Hz, 1H), 5.74 (dt, J=15.6, 6.9 Hz, 1H), 5.48 (dt, J=11.7, 7.2 Hz, 1H), 4.99-4.94 (m, 1H),
4.93-4.88 (m, 2H), 4.87-4.82 (m, 1H), 2.79-2.70 (m, 2+2H), 2.67-2.59 (m, 2H), 2.51-
2.42 (m, 2H), 1.88 (d, J=1.4 Hz, 3H), 1.86 (t, J=1.1 Hz, 3H). 13C NMR (100 MHz,
CDCl3) 142.0, 141.84, 141.80, 141.68, 133.3, 131.3, 130.5, 129.8, 128.41, 128.38,
were consistent with those described in the literature[33]
.
25, white solid, predominant E isomer, mp.=129.5-130.5 C (Lit.[33] 128 C). 1H NMR
(400 MHz, CDCl3)  7.52-7.48 (m, 2H), 7.48-7.44 (m, 2H), 7.39-7.31 (m, 2H), 7.27-
7.21 (m, 1H), 7.08 (d, J=16.3 Hz, 1H), 6.98 (d, J=16.3 Hz, 1H), 6.93-6.88 (m, 2H), 3.83
(s, 3H). 13C NMR (100 MHz, CDCl3)  159.3, 137.6, 130.1, 128.6, 128.2, 127.7, 127.2,
126.6, 126.2, 114.1, 55.3. The 1H and 13C NMR spectra were consistent with those
128.28, 128.27, 125.81, 125.80, 115.2, 114.6, 36.3, 35.9, 34.6, 30.4, 23.3, 18.7. The 1
and 13C spectra were consistent with those described in the literature[43]
H
.
described in the literature[33]
.
38, colorless oil, predominant E isomer. 1H NMR (400 MHz, CDCl3)  (E isomer) 7.45-
7.39 (m, 2H), 7.39-7.27 (m, 2H), 7.27-7.21 (m, 1H), 6.42 (dd, J=16.0, 1.2 Hz, 1H), 6.25
(dd, J=16.0, 6.9 Hz, 1H), 2.26-2.13 (m, 1H), 1.94-1.71 (m, 5H), 1.47-1.18 (m, 5H); (Z
isomer, selected resonances) 5.56 (dd, J=11.7, 10.1 Hz, 1H), 2.73-2.61 (m, 1H). 13C
NMR (100 MHz, CDCl3)  (E isomer) 138.0, 136.7, 128.4, 127.2, 126.7, 125.9, 41.1,
32.9, 26.2, 26.0; (Z isomer) 138.9, 137.9, 128.6, 128.1, 126.8, 126.4, 36.9, 33.2, 26.0,
26, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  8.31-8.25 (m,
1H), 8.17-8.11 (m, 1H), 7.98-7.89 (m, 2+1H), 7.88-7.77 (m, 2+1H), 7.68-7.63 (m, 2H),
7.61-7.50 (m, 4+1H), 7.49-7.38 (m, 3H), 7.38-7.32 (m, 1H), 7.20 (d, J=16.0 Hz, 1H),
7.15-7.13 (m, 2H), 7.10 (dt, J=12.2, 0.9 Hz, 1H), 6.89 (d, J=12.2 Hz, 1H). 13C NMR
(100 MHz, CDCl3)  137.6, 136.7, 135.2, 135.0, 133.68, 133.64, 132.0, 131.7, 131.5,
131.4, 129.0, 128.7, 128.6, 128.44, 128.40, 128.0, 127.7, 127.5, 127.0, 126.7, 126.4,
126.1, 126.0, 125.9, 125.79, 125.76, 125.66, 125.56, 124.9, 123.7, 123.6. The 1H and
25.7. The 1H and 13C spectra were consistent with those described in the literature[44]
.
13C NMR spectra were consistent with those described in the literature[34]
.
39, colorless oil. 1H NMR (400 MHz, CDCl3)  7.37-7.30 (m, 2H), 7.27-7.17 (m, 3H),
6.28 (s br, 1H), 2.42 (ddd, J=7.1, 5.0, 1.2 Hz, 2H), 2.30 (ddd, J=6.7, 5.0, 1.3 Hz, 2H),
1.73-1.55 (m, 6H). 13C NMR (100 MHz, CDCl3)  143.4, 138.4, 128.9, 128.0, 125.7,
121.9, 37.6, 29.4, 28.6, 27.9, 26.7. The 1H and 13C spectra were consistent with those
27, white crystals, E isomer, mp. 132.5-133 C (Lit.[35] 133-134 C). 1H NMR (400
MHz, CDCl3)  7.63-7.60 (m, 2H), 7.60-7.56 (m, 2H), 7.56-7.51 (m, 2H), 7.42-7.36 (m,
2H), 7.34-7.28 (m, 1H), 7.19 (d, J=16.3 Hz, 1H), 7.11 (d, J=16.3 Hz, 1H). 13C NMR
described in the literature[45]
.
2
(100 MHz, CDCl3)  140.8 (q, JC-F=1.4 Hz), 136.6, 131.1, 129.2 (q, JC-F =32.3 Hz),
3
1
128.8, 128.3, 127.1, 126.7, 126.5, 125.6 (q, JC-F=3.9 Hz), 124.2 (q, JC-F=272 Hz). 19F
40, white solid, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  7.59-7.54 (m,
2H), 7.45-7.38 (m, 6+4H), 7.35-7.20 (m, 2+2H), 7.16-7.06 (m, 1+2H), 7.01-6.96 (m,
2H), 6.89 (q, J=1.3 Hz, 1H), 6.52 (dt, J=2.4, 1.3 Hz, 1H), 2.33 (d, J=1.4 Hz, 3H), 2.25
(d, J=1.5 Hz, 3H). 13C NMR (100 MHz, CDCl3)  143.9, 142.1, 138.7, 138.3, 137.6,
137.4, 129.1, 128.9, 128.4, 128.3, 128.14, 128.13, 127.8, 127.7, 127.2, 126.9, 126.5,
126.4, 126.0, 126.0, 27.1, 17.5. The 1H and 13C spectra were consistent with those
NMR (376 MHz, CDCl3)  -63.0. The 1H, 13C and 19F NMR spectra were consistent
with those described in the literature[36]
.
31, white solid, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  7.86-7.78 (m,
2H), 7.78-7.69 (m, 1H), 7.65 (d, J=8.5 Hz, 1H), 7.50-7.40 (m, 2H), 7.37 (dd, J= 8.5, 1.7
Hz, 1H), 7.23-7.15 (m, 2H), 7.04-7.00 (m, 2H), 6.71 (d, J=12.2 Hz, 1H), 6.64 (d, J=12.2
Hz, 1H), 2.37 (s, 3H), 2.31 (s, 3H). 13C NMR (100 MHz, CDCl3)  137.6, 137.0, 135.1,
135.0, 134.6, 134.2, 133.7, 133.5, 132.9, 132.5, 130.5, 129.4, 128.94, 128.90, 128.87,
128.2, 127.93, 127.90, 127.84, 127.75, 127.66, 127.58, 127.4, 127.0, 126.44, 126.36,
126.27, 125.9, 125.78, 125.75, 123.5, 21.27, 21.24. The 1H spectrum was consistent
with these described in the literature[37] for both isomers.
described in the literature[46]
.
41, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3) δ 7.42-7.32 (m,
2H+2H), 7.32-7.22 (m, 3H+3H), 5.56-5.52 (m, 2H, E), 5.52-5.48 (m, 2H, Z) 2.80-2.72
(m, 2H+2H), 2.51-2.35 (m, 2H+2H), 2.12-2.04 (m, 2H+2H), 1.54-1.30 (m, 10H+10H),
1.04-0.96 (m, 3H+3H). 13C NMR (100 MHz CDCl3) δ 142.14 (E), 142.11 (Z), 131.2 (E),
130.7 (Z), 129.3 (E), 128.6 (Z), 128.43 (E), 128.42 (Z) 128.21 (Z), 128.18 (E), 125.7 (Z),
125.6 (E), 36.2 (E), 36.1 (Z), 34.5 (E), 32.6 (E), 31.9 (ovl), 29.7(Z), 29.6 (E), 29.3 (Z),
8
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10.1002/ejoc.201701766
European Journal of Organic Chemistry
29.24 (Z), 29.22 (E), 29.20 (Z), 29.1 (E), 27.2 (Z), 22.70 (E), 22.69 (Z), 14.1 (ovl). The
[4]
a) P. R. Blakemore, J. Chem. Soc., Perkin Trans. 1 2002, 2563-2585. b) For
recent example, see: S. M. A. H. Siddiki, A. S. Touchy, K. Kon, K. Shimizu,
Chem. Eur. J. 2016, 22, 6111-6119.
1H and 13C NMR spectra were consistent with those described in the literature[47]
.
42, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3) δ 5.38-5.34 (m,
1H+1H), 5.32-5.16 (m, 1H+1H), 2.32-2.20 (m, 1H), 2.07-2.00 (m, 2H), 2.00-1.93 (m,
2H), 1.93-1.84 (m, 1H), 1.76-1.56 (m, 4H+4H), 1.39-0.99 (m, 16H+16H), 0.93-0.86 (m,
3H+3H). 13C NMR (100 MHz CDCl3) δ 136.4, 136.0, 128.0, 127.7, 40.7, 36.3, 33.4,
33.3, 32.7, 31.9, 30.0, 29.7, 29.3, 29.25, 29.22, 29.1, 27.4, 26.3, 26.2 (ovl), 26.1, 26.0,
22.71, 22.69, 14.1 (ovl). The 1H and 13C NMR spectra were consistent with those
[5]
[6]
[7]
[8]
C. Aïssa, Eur. J. Org. Chem. 2009, 2009, 1831-1844.
B. Górski, A. Talko, T. Basak, M. Barbasiewicz, Org. Lett. 2017, 19, 1756-1759.
J. M. Hawkins, T. A. Lewis, A. S. Raw, Tetrahedron Lett. 1990, 31, 981-984.
Precedents of similar reactivity, utilizing premetalated conditions, can be found
concealed in a more recent literature, as single examples of transformations: a)
M. Bera, A. Maji, S. K. Sahoo, D. Maiti, Angew. Chem. Int. Ed. 2015, 54, 8515-
8519; b) A. Maji, B. Bhaskararao, S. Singha, R. B. Sunoj, D. Maiti, Chem. Sci.
2016, 7, 3147-3153; c) G. Cheng, P. Wang, J.-Q. Yu, Angew. Chem. Int. Ed.
2017, 56, 8183-8186.
described in the literature[47]
.
43, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3) δ 5.88-5.79 (m,
1H+1H), 5.47 (dt, J=11.3, 7.0 Hz, 1H, Z), 5.35 (dt, J=15.8, 6.9 Hz, 1H, E), 2.11 (qd,
J=7.0, 1.5 Hz, 2H, E), 2.01-1.95 (m, 2H+2H), 1.86 (qd, J=7.0, 1.5 Hz, 2H, Z), 1.66 (s,
3H, E), 1.65-1.57 (m, 2H+2H), 1.51 (s, 3H, Z), 1.51-1.21 (m, 14H+14H), 0.98 (s, 6H,
E), 0.95 (s, 6H, Z), 0.94-0.87 (m, 3H+3H). 13C NMR (100 MHz CDCl3) δ 137.83,
135.51, 134.53, 132.70, 127.60, 127.50, 127.42, 126.83, 39.49, 39.26, 34.26, 33.94,
33.28, 32.69, 31.97, 31.95, 31.92, 29.75, 29.73, 29.38, 29.35, 29.25, 29.23, 28.98, 28.74,
28.45, 22.74, 22.72, 21.45, 21.23, 19.44, 19.41, 14.14, 14.13. MS (EI, m/z, relative
intensity): 248 (M+•, 91), 233 (100), 205 (10), 192 (12), 178 (9), 163 (25), 149 (28), 135
(31), 133 (17), 123 (23), 121 (31), 119 (14), 109 (24), 107 (44), 105 (26), 95 (34), 93
(50), 91 (33). Elem anal, calcd for C18H32: C, 87.02; H, 12.98; found: C, 86.99; H, 12.86.
[9]
a) S. Kagabu, K. Hara, J. Takahashi, J. Chem. Soc., Chem. Commun. 1991, 408-
410; b) S. R. Dubbaka, P. Vogel, Tetrahedron 2005, 61, 1523-1530; c) S.
Kagabu, C. Shimizu, J. Takahashi, K. Hara, M. Koketsu, M. Ishida, Bull. Soc.
Chim. Fr. 1992, 129, 435-439; d) B. S. Nader, J. A. Cordova, K. E. Reese, C. L.
Powell, J. Org. Chem. 1994, 59, 2898-2901.
[10] See the Supporting Information for details.
[11] Under these conditions precursors 3d and 3f failed to react with
diphenylacetylene.
44, colorless oil. 1H NMR (400 MHz, CDCl3) δ 5.1 (tt, J=7.3, 1.3 Hz, 1H), 2.17-2.03 (m,
4H), 2.01-1.94 (m, 2H), 1.59-1.45 (m, 6H), 1.38-1.25 (m, 10H), 0.94-0.85 (m, 3H). 13
C
[12] J. I. Seeman, J. Chem. Educ. 1986, 63, 42-48.
NMR (100 MHz CDCl3) δ 139.3, 121.5, 37.2, 31.9, 30.2, 29.27, 29.26, 28.73, 28.68,
27.9, 27.1, 27.0, 22.7, 14.1. The 1H and 13C NMR spectra were consistent with those
[13] Interestingly, attempts to trap aldol-type adducts of premetalated 4c to
benzaldehyde (LiHMDS, -78 C, 5 min) led only to stilbene 7.
described in the literature[48]
.
[14] Under Barbier conditions with tert-BuOLi as a base (1.0 equiv., THF, -78 °C)
attempts of reaction of 3a with benzaldehyde activated with stoichiometric
amount of Lewis acid (MgCl2, ZnCl2(THF)2, TiCl4, SnCl4, BF3OEt2) failed to
considerably improve yield of 6.
45, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3) δ 7.50-7.46 (m,
1H+1H), 7.44-7.36 (m, 2H+2H), 7.34-7.26 (m, 2H+2H), 5.90 (tq, J=7.2, 1.4 Hz, 1H, E),
5.57 (tq, J=7.3, 1.5 Hz, 1H, Z), 2.34-2.26 (m, 2H, E), 2.13 (s, 3H+3H), 2.11-2.04 (m,
2H, Z), 1.61-1.23 (m, 10H+10H), 1.04-0.95 (m, 3H+3H). 13C NMR (100 MHz CDCl3) δ
144.0, 142.3, 135.9, 134.5, 128.8, 128.1, 127.97, 127.96, 127.95, 126.4, 126.3, 125.6,
31.92, 31.86, 30.2, 29.7, 29.4, 29.3, 29.24, 29.20, 29.1, 28.8, 25.6, 22.71, 22.68, 15.7,
14.12, 14.09. MS (EI, m/z, relative intensity): 216 (M+•, 79), 201 (4), 145 (10), 131
(100), 129 (20), 118 (52), 115 (20), 105 (28), 103 (12), 91 (37). Elem anal, calcd for
C16H24: C, 88.82; H, 11.18; found: C, 88.61; H, 11.27.
[15] The postulated mechanism displays some similarities with α-functionalization of
phosphorus betaines, see for example: D. M. Hodgson, T. Arif, J. Am. Chem.
Soc. 2008, 130, 16500-16501. Interestingly, we observed also that with excess
of tert-BuOLi base (10 equiv.) both isomers of aldol-type adducts of sulfonate
3d to benzaldehyde favored formation of E-6, suggesting epimerization on the
course of the fragmentation process. However, the observation was difficult to
be applied for preparative purposes.[10]
46, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3) δ 8.05-7.93 (m,
2H, E), 7.83-7.79 (m, 2H, Z), 7.56-7.51 (m, 1H+1H), 7.46-7.40 (m, 2H+2H), 7.39-7.34
(m, 2H+2H), 7.33-7.27 (m, 2H+2H), 7.26-7.21 (m, 1H+1H), 6.50 (t, J=7.5 Hz, 1H, Z),
6.29 (t, J=7.8 Hz, 1H, E), 2.32-2.24 (m, 2H, Z), 2.16-2.08 (m, 2H, E), 1.53-1.40 (m,
2H+2H), 1.36-1.14 (m, 8H+8H), 0.98-0.79 (m, 3H+3H). 13C NMR (100 MHz CDCl3) δ
198.5, 197.2, 145.2, 141.5, 140.7, 138.4, 137.3, 136.8, 136.1, 133.4, 132.5, 131.8,
129.57, 129.55, 129.4, 128.60, 128.56, 128.1, 128.0, 127.5, 127.3, 125.9, 31.63, 31.61,
29.9, 29.5, 29.3, 29.2, 29.1, 29.0, 28.93, 28.91, 22.5, 14.0. The 1H NMR spectrum was
[16] M. E. Jung, G. Piizzi, Chem. Rev. 2005, 105, 1735-1766.
[17] Reaction of 14a and 2-naphthaldehyde with LiHMDS gradually warmed to 65
C (under conditions shown at Figure 8) gave 35% of 15. Under similar
conditions (-78 C, 30 min; r.t., 30 min) 14c and 2-naphthaldehyde with
NaHMDS as a base failed to give alkene.
[18] Reaction of 17 and 2-naphthaldehyde with LiHMDS gradually warmed to 65 C
(under conditions shown at Figure 8) gave only 2% of 18.
consistent with this described in the literature[49]
.
47, colorless oil, mixture of E/Z isomers. 1H NMR (400 MHz, CDCl3)  7.96-7.80 (m,
7H), 7.80-7.73 (m, 1H), 7.67 (dd, J=8.5, 1.8 Hz, 1H), 7.59-7.45 (m, 5H), 6.72-6.58 (m,
1+1H), 6.45 (dt, J=15.8, 6.9 Hz, 1H, isom E), 5.86 (dt, J=11.6, 7.3 Hz, 1H, isom Z),
2.53 (qd, J=7.3, 1.9 Hz, 2H), 2.41-2.30 (m, 2H), 1.67-1.53 (m, 4H), 1.53-1.31 (m,
8+8H), 1.07-0.94 (m, 3+3H). 13C NMR (100 MHz, CDCl3)  135.38, 135.35, 133.72,
133.68, 133.34, 132.62, 132.11, 131.62, 129.81, 128.71, 127.97, 127.87, 127.77, 127.57,
127.53, 127.49, 127.34, 127.24, 126.02, 125.93, 125.55, 125.33, 125.28, 123.53, 33.20,
31.87, 31.84, 30.02, 29.44, 29.33, 29.27, 29.25, 29.21, 28.76, 22.71, 22.66, 14.13, 14.10.
The 1H NMR and 13C NMR spectra were consistent with those described in the
[19] During optimization of the olefination method we tested also heterogenic
conditions with Cs2CO3/DMF system, inspired by work of Kagabu[9a]. In
reactions of nonstabilized 1-octanesulfonyl precursors: 3b (fluoride), 3c
(hexafluoroisopropyl ester) and 3d (trifluoroethyl ester), vigorously stirred at rt
overnight we observed limited conversions, and maximum 26% of alkene 6 (for
3d). In turn semistabilized benzylsulfonates 4 gave good yields of stilbene 7
(60-80%), but of lower selectivity than with DBU.
[20] We suppose that, when tert-BuOLi is used as a base, second stoichiometric
byproduct (SO3) forms an adduct with the alkoxide (tert-BuOSO3).
literature[6]
.
[21] Compare: D. Simoni, M. Rossi, R. Rondanin, A. Mazzali, R. Baruchello, C.
Malagutti, M. Roberti, F. P. Invidiata, Org. Lett. 2000, 24, 3765-3768.
Acknowledgements
[22] The key role of the alcohol group on the reactivity of the sulfonates can be
demonstrated on the following examples: Unstabilized hexafluoroisopropyl
1-octanesulfonate (3c) appeared to be much less reactive toward benzaldehyde
then trifluoroethyl 1-octanesulfonate (e.g. 3d), whereas semistabilized
benzylsulfonates of TFE and HFI (4c and 4d, respectively) displayed similar
properties (Figure 1). In turn unstabilized and semistabilized trichloroethyl
sulfonates 3e and 4e were both poorly reactive and were recovered after the
reaction in high yields (>50%), despite similar pKa values of CF3CH2OH=12.5
and CCl3CH2OH=12.2. The pKa data of the alcohols was taken from: A.
Fedotova, B. Crousse, I. Chataigner, J. Maddaluno, A. Yu. Rulev, J. Legros, J.
Org. Chem. 2015, 80, 10375-10379.
This work was financed by the SONATA BIS program of the National Science Centre,
Poland (NCN, Grant No. DEC-2013/10/E/ST5/00030). Authors thank Mr Michał
Jadwiszczak for technical assistance.
[1]
[2]
T. Takeda, Ed., Modern Carbonyl Olefination: Methods and Applications,
WILEY-VCH, Weinheim, 2006.
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[23] Reactions of precursors 21b and 4c with 2-naphthaldehyde and KHMDS as a
base (quenched after 30 min at rt) gave alkenes 22 (55%; 60:40), and 23 (80%,
91:9). Deprotonation of the precursors with n-BuLi under the same conditions
gave 19% and 12% of alkenes, respectively.
[3]
B. E. Maryanoff, A. B. Reitz, Chem. Rev. 1989, 89, 863-927.
9
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10.1002/ejoc.201701766
European Journal of Organic Chemistry
[24] Carbanions of 3d, 4c and 4d generated with LiHMDS in THF at -78 C are
stable at least for 30 min, but easily decompose, when warmed to r.t. Main
decomposition pathway consists of elimination to sulfene, followed by trapping
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10
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Entry for the Table of Contents
Organic synthesis

B. Górski, D. Basiak, A. Talko,
T. Basak, T. Mazurek,
M. Barbasiewicz* … Page – Page
Olefination with Sulfonyl Halides
and Esters: E-Selective Synthesis
of Alkenes from Semistabilized
Carbanion Precursors
Sulfur-based olefination with
Horner-Wadsworth-Emmons-type
mechanism is systematically studied. yields of olefins, and for the latter
Nonstabilized and semistabilized
carbanion precursors react with
carbonyl compounds giving good
reagents E isomers of alkenes
predominate.
11
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