γ-diphenylphosphinoxy carbanions: Slow reacting analogues of-halocarbanions

Article abstract of DOI:10.1080/10426500802715569

Carbanion of diphenylphosphinyl ester of 3-hydroxypropyl phenyl sulfone undergoes slow 1,3-intramolecular nucleophilic substitution to give substituted cyclopropane. It can be efficiently trapped by external electrophiles such as aldehydes to produce aldo

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Phosphorus, Sulfur, and Silicon
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γ-Diphenylphosphinoxy
Carbanions: Slow Reacting
Analogues of γ -Halocarbanions
Mieczysław Maąkosza a & Anna Wojtasiewicz a
a Institute of Organic Chemistry PAN , Warsaw,
Poland
Published online: 26 Mar 2009.
To cite this article: Mieczysław Maąkosza & Anna Wojtasiewicz (2009) γ-
Diphenylphosphinoxy Carbanions: Slow Reacting Analogues of γ -Halocarbanions,
Phosphorus, Sulfur, and Silicon and the Related Elements, 184:4, 857-864, DOI:
10.1080/10426500802715569
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Phosphorus, Sulfur, and Silicon, 184:857–864, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802715569
γ-Diphenylphosphinoxy Carbanions: Slow Reacting
Analogues of γ-Halocarbanions
Mieczyslꢀaw Makosza and Anna Wojtasiewicz
ꢀ
Institute of Organic Chemistry PAN, Warsaw, Poland
Carbanion of diphenylphosphinyl ester of 3-hydroxypropyl phenyl sulfone under-
goes slow 1,3-intramolecular nucleophilic substitution to give substituted cyclo-
propane. It can be efficiently trapped by external electrophiles such as aldehydes to
produce aldol type anions, which undergo 1,5-intramolecular substitution to give
substituted tetrahydrofurans.
Keywords Carbanions; diphenylphosphinates; sulfones tetrahydrofurans
INTRODUCTION
In our preceding articles, we have shown that albeit γ-chlorocarbanions
generated by deprotonation of 3-chloropropyl phenyl sulfone, t-butyl 4-
chlorobutyrate, 4-chloro-butyronitrile, etc., undergo rapid intramolecu-
lar 1,3-nucleophilic substitution—so called γ-elimination—to form sub-
stituted cyclopropanes; they can be trapped by active electrophiles
such as aromatic aldehydes. The resulting aldol-type anions enter in-
tramolecular 1,5-substitution giving substituted tetrahydrofurans.1,2
Due to the high rate of the γ-elimination, the reaction should be car-
ried out at low temperature by addition of a base, potassium t-butoxide,
to a solution of the carbanion precursor and the aldehyde in THF,
since treatment of the carbanion precursors with a base before the
addition of aldehydes resulted in exclusive formation of the cyclo-
propane. The former procedure, however, could not be applied to the
reaction with aliphatic aldehydes, which are stronger CH acids than
the carbanion precursors because of the competing aldol reaction. On
the other hand, generation of these γ-chlorocarbanions in the pres-
ence of imines and the Michael acceptors always gave cyclopropanes;
Received 21 December 2007; accepted 25 January 2008.
Dedicated to Professor Marian Mikolꢀajczyk from the CBMiM PAN in Lꢀ o´dz´, Poland,
on the occasion of his 70th birthday.
Address correspondence to Mieczyslꢀaw Makosza, Institute of Organic Chemistry PAN,
ꢀ
Kasprzaka 44/52, 01-224, Warsaw, Poland. E-mail: icho-s@icho.edu.pl
857

858
M. Makosza and A. Wojtasiewicz
ꢀ
intramolecular substitution was faster than addition to such moder-
ately active electrophiles. We supposed that competition between in-
tramolecular substitution in γ-chlorocarbanions and their addition to
external electrophiles to some extent can be controlled by variation of
the nucleophilicity of the sulfone carbanion. Indeed, the carbanion of 3-
chloropropyl pentachlorophenyl sulfone, albeit cyclized rapidly, reacted
with activated imines to produce substituted pyrrolidines3 and Michael
acceptors to give cyclopentanes.4 One should expect that this competi-
tion could be also controlled by variation of the leaving group. Whereas
γ-bromocarbanions cyclize faster than γ-chloro carbanions,2 the car-
banion of γ-fluoropropyl phenyl sulfone is completely inert in the sense
of substitution of fluorine. The trimethylammonium group was also in-
efficient in this respect. The carbanion of 3-trimethylammonium propyl
phenyl sulfone does not undergo 1,3-substitution, but relatively slow
decomposition via Hoffman-type elimination takes place. Its adducts to
aldehydes also do not cyclize to tetrahydrofuranes.5
In looking for a leaving group that could be replaced by nucleophiles
slower than chlorine, we took into consideration the diphenylphosphi-
noxy group, which, according to Noyce6 undergoes solvolysis via SN1
type reaction substantially (ca. 30 times) slower than chlorine. On the
other hand, reactions of amines with ethyl diphenylphosphinate do
not proceed via SN2 type substitution, but addition of the amines to
the phosphorus atom.7 Although we were unable to find examples of
intermolecular nucleophilic SN2-type replacement of this group, there
are numerous examples of intramolecular nucleophilic substitution
of diphenylphospinoxy group by carbanions and N-anions located
in γ-position, producing substituted cyclopropanes8 and aziridines.9
In order to test the possibility of using diphenylphosphinoxy group
as a slower reacting analogue of halogens in γ-halocarbanions, we
have choosen diphenylphosphinyl ester of 3-hydroxy propyl phenyl
sulfone 1.
RESULTS AND DISCUSSION
In our hands, the carbanion of this sulfone undergoes intramolecular
1,3-substitution of the diphenylphosphinoxy group to form phenyl-
sulfonyl cyclopropane, albeit substantially slower than analogous
substitution of chlorine. Thus treatment of 1 with t-BuOK in THF and
quenching with acid after 5 min leads to the conversion of 1 into 2 not
exceeding 10%, whereas under identical conditions, conversion of the
lithium salt of the anion of 1 generated by treatment of 1 with BuLi
was more than 50%. Nevertheless the potassium salt of the carbanion

γ-Diphenylphosphinoxy Carbanions
859
SCHEME 1 Reactions of 1 with base and aldehydes.
of 1 reacts with a series of aromatic aldehydes giving the expected
tetrahydrofurans (Scheme 1).
The reaction of 1 with aromatic aldehydes proceeded efficiently giv-
ing the expected substituted tetrahydrofurans with good yields exclu-
sively as the trans-isomers (Table I, entries 2–7). Most of these tetrahy-
drofurans 3a, 3b, 3d, and 3g were obtained earlier in an analogous re-
action of aldehydes with the carbanion of 3-chloropropyl phenyl sulfone
as trans-isomers. Physical properties of the tetrahydrofurans obtained
in this article are identical to those reported. Similarly, the reaction
with pivalic aldehyde gave the expected tetrahydrofuran with excel-
lent yield. Since aliphatic aldehydes are relatively strong CH acids,
procedure of the reaction with these aldehydes was changed. First
TABLE I Reactions of 1 with Base and
Aldehydes (Scheme 1)
Entry
R
Products, Yield
1
2
3
4
5
6
7
8
9
nonea
C6H5
p-MeC6H4
p-MeOC6H4
PhCH CH
3-Pyridyl
2-Furyl
2, 60%
3a, 80%b
3b, 76%b
3c, 79%
3d, 45%b
3e, 35%
3f, 51%
Me3C
3g, 89%b
CH3CH(CH3)c
CH3CH2CHc2
CHc3
2, 20%, 3h, 50%
2, 15%, 3i, 46%
2, 22%, 3j, 20%
10
11
aExperiment without aldehyde, BuLi, −75◦C to room
temperature, THF.
bPhysical and spectral data: see ref. [1].
cAldehyde was added 15 s after base.

860
M. Makosza and A. Wojtasiewicz
ꢀ
the carbanion was generated by treatment of 1 with base, followed by
addition of aldehydes. This procedure, which could not be applied for re-
actions of γ-chlorocarbanions, worked well for iso- and n-butyraldehyde.
Thus 2-isopropyl-, 2-n-propyl 3-phenylsulfonyl tetrahydrofurans could
be obtained in reasonable yields (Table I, entries 9–10).
The reaction of the anion of 1 with acetaldehyde was less efficient
(Table I, entry 11). It appears that due to high CH acidity of the alde-
hyde, proton exchange with the anion of 1 resulted in partial recovery
of 1 and consumption of the aldehyde.
Although we have not found examples of intermolecular SN2-type
nucleophilic substitution of the diphenylphosphinoxy group, a similar
process takes place readily when catalyzed by Lewis acids. For instance,
reaction of alkyl diphenyl phosphinates with alkoxytrimethylsilanes
catalyzed by trimethylsilyl triflate gave dialkyl esters,10 whereas their
reaction with trimethyl allyl silane resulted in C-allylation.11 To inves-
tigate the possibility of an intermolecular SN2 nucleophilic substitution
of the diphenyl phosphinoxy group, we reacted 1 with carbanion of 2-
phenylpropionitrile generated in advance. In the reaction mixture, we
found the starting compound 1, 3-hydroxy propyl phenyl sulfone, and
cyclopropyl phenyl sulfone; the expected product of an intermolecular
SN2-type substitution was not detected (Scheme 2).
SCHEME 2 Reaction of 1 with carbanion of 2-phenylpropionitrile.
Thus an intermolecular SN2 reaction with this active carbanion did
not take place; it appears that the main process was its addition to the
phosphorus atom followed by P O bond cleavage. Additionally, proton
exchange with 1 produced the anion of 1 and subsequently the cyclo-
propane.
CONCLUSION
We have shown that the diphenyl phosphinoxy group can act as
a leaving group in 1,3- and 1,5-intramolecular SN2-type substitu-
–
tion with the sulfonyl-stabilized carbanion and O anions. Thus 3-
diphenylphosphinoxy propyl phenyl sulfone can behave as a precursor
of the slow-reacting analogue of γ-halocarbanions.

γ-Diphenylphosphinoxy Carbanions
861
EXPERIMENTAL
All reactions were carried out under argon atmosphere in dried glass-
ware using standard Schlenk techniques. Tetrahydrofuran was dis-
tilled from potassium–benzophenone ketyl. Melting points are uncor-
1
rected. H NMR and 13C NMR spectra were recorded with CDCl3 as
standard (δ = 7.26 ppm and 77 ppm, respectively) with a Bruker 500
spectrometer. IR data were recorded on an FT-IR Perkin Elmer Spec-
trum 2000 using a film (for oils) or KBr pellets (for solids). Mass spec-
trometric data were obtained with an AMD 604 Intectra GmbH spec-
trometer in electron ionization mode or with a MarinerTM instrument
in electrospray mode. Microanalyses were performed by the analitical
laboratory of the Institute of Organic Chemistry, Polish Academy of
Sciences.
DIPHENYLPHOSPHINYL ESTER OF
3-HYDROXYPROPYLPHENYL SULFONE (1)
To a solution of 3-hydroxypropylphenyl sulfone (5.00 g, 25.0 mmol) and
triethylamine (3.80 g, 37.5 mmol) in benzene (50 mL), diphenylphos-
phinic chloride (5.60 g, 25.0 mmol) in 10 mL of benzene was added drop-
wise, and the mixture was refluxed for 2 h. The mixture was washed
with water (50 mL), with diluted HCl (50 mL), concentrated NaHCO3,
and with brine. The solvent was evaporated, and the residue was puri-
fied by passing through silica gel (hexane/ethyl acetate) giving 1 (yield
7.50 g, 79 %). Mp 71–73◦C (EtOH). IR (film CH2Cl2, νmax/cm−1): 3452,
3059, 2961, 1591, 1483, 1439, 1307, 1225, 1145, 1131, 1113, 1087, 1071,
1
1019, 997, 953, 822. 789, 754, 730, 694, 597, 559, 534. H NMR (500
MHz, CDCl3): δ = 2.12–2.19 (m, 2H), 3.24–3.28 (m, 2H), 4.06–4.11 (m,
2H), 7.42–7.47 (m, 4H), 7.51–7.58 (m, 4H), 7.63–7.67 (m, 1H), 7.73–7.78
(m, 4H), 7.88–7.91 (m, 2H); 13C NMR (125 MHz, CDCl3): δ = 24.2, 52.9,
62.5, 128.0, 128.6, 128.7, 129.3, 130.4, 131.45, 131.53, 132.3, 132.4,
133.8, 138.9. MS (EI 70 eV) m/z (%): 400 (M+, <1), 259 (100), 231 (34),
219 (34), 201 (81), 141 (42), 118 (80), 91 (1), 77 (56), 51 (13), 41 (17).
HRMS (EI): Calcd. for: C21H21O4PS 400.0898, found: 400.0882; Anal.
Calcd. for C21H21O4PS: C 62.99, H 5.29, S 8.01, found C 62.74, H 5.22,
S 8.22%.
Reaction of Diphenylphosphinyl Ester of 3-Hydroxypropyl-
phenyl Sulfone (1) with Aldehydes: General Procedure
To a solution of 1 (200 mg, 0.5 mmol) and aldehyde (0.75 mmol) in THF
(2 mL) at –75◦C under argon, t-BuOK (112 mg, 1 mmol, in 1 mL of THF)

862
M. Makosza and A. Wojtasiewicz
ꢀ
was added dropwise. After 30 min at –75◦C, the mixture was warmed to
room temperature and kept for 60 min. After that, a solution of NH4Cl
was added, the mixture was extracted with CH2Cl2 (3 × 25 mL), and
the extracts were washed with brine and dried over MgSO4. Column
chromatography with hexane–EtOAc gave the substituted tetrahydro-
furans.
trans-2-(4-Metoxyphenyl)-3-phenylsulfonyl Tetrahydrofuran
(3c)
◦
Mp 75–77 C (EtOH); IR (film KBr, νmax/cm−1): 3006, 2972, 2880,
2838, 1610, 1584, 1512, 1445, 1304, 1293, 1249, 1147, 1080, 1028, 956,
1
827, 781, 746, 723, 688, 637, 625, 580, 534, 517. H NMR (500 MHz,
3
CDCl3): δ = 2.25–2.34 (m, 1H), 2.50–2.56 (m, 1H), 3.66 (ddd, J(H,H)
3
= 4.2, 5.5, 9.6 Hz, 1H), 3.77 (s, 3H), 3.98 (ddd, J(H,H) = 6.7, 8.5, 8.5
3
3
Hz, 1H), 4.15 (ddd, J(H,H) = 3.6, 8.5, 8.5 Hz, 1H), 5.24 (d, J(H,H) =
5.5 Hz, 1H), 6.75–6.79 (m, 2H), 7.04–7.07 (m, 2H), 7.51–7.55 (m, 2H),
7.62–7.66 (m, 1H), 7.86–7.89 (m, 2H). 13C NMR (125 MHz, CDCl3):
δ = 28.6, 55.3, 68.2, 71.0, 80.0, 113.9, 127.1, 128.6, 129.3, 132.2, 133.9,
138.3, 159.4. MS (EI 70 eV) m/z (%): 318 (M+, <1), 176 (100), 135 (66),
77 (13). HRMS (EI): Calcd. for C17H18O4S: 318.0926, found 318.0938;
Anal. Calcd. for C17H18O4S: C 64.13, H 5.70, S 10.07, found C 64.21, H
5.59, S 10.26%.
trans-2-(Pyridin-3-yl)-3-phenylsulfonyl Tetrahydrofuran (3e)
Oil, IR (film CH2Cl2, νmax/cm−1): 3061, 2954, 2882, 1580, 1480, 1447,
1
1429, 1306, 1148, 1086, 1072, 1025, 750, 721, 689, 616, 601, 561. H
NMR (500 MHz, CDCl3): δ = 2.23–2.32 (m, 1H), 2.49–2.56 (m, 1H), 3.65
(ddd, 3J(H,H) = 4.2, 5.6, 9.7 Hz, 1H), 4.01 (ddd, 3J(H,H) = 6.7, 8.5, 8.5
3
3
Hz, 1H), 4.16 (ddd, J(H,H) = 3.7, 8.5, 8.5 Hz, 1H), 5.32 (d, J(H,H) =
3
5.6 Hz, 1H), 7.19 (dd, J(H,H) = 4.8, 7.9 Hz, 1H), 7.51–7.57 (m, 3H),
3
7.63–7.67 (m, 1H), 7.85–7.89 (m, 2H), 8.37 (s, 1H), 8.48 (d, J(H,H) =
4.85 Hz, 1H). 13C NMR (125 MHz, CDCl3): δ = 28.7, 68.5, 70.8, 78.2,
123.3, 128.5, 129.5, 133.7, 134.2, 135.8, 138.0, 147.6, 149.3. MS (EI 70
eV) m/z (%): 147 (100), 117 (14), 106 (81), 91 (12), 77 (40), 65 (14), 51
(31), 39 (19). HRMS (ESI): Calcd. for C15H15NO3SNa: 312.0665, found:
312.0669.
trans-2-(Fur-2-yl)-3-phenylsulfonyl Tetrahydrofuran (3f)
Mp 79–80 ◦C (EtOH). IR (film CH2Cl2, νmax/cm−1): 3145, 3120, 3064,
2975, 2897, 2876, 1585, 1506, 1444, 1298, 1147, 1086, 1060, 1011, 958,
1
920, 882, 815, 748, 716, 685, 618, 599, 569, 538. H NMR (500 MHz,
CDCl3): δ = 2.38–2.46 (m, 1H), 2.56–2.63 (m, 1H), 3.95–4.10 (m, 3H),

γ-Diphenylphosphinoxy Carbanions
863
3
3
5.22 (d, J(H,H) = 6.0 Hz, 1H), 6.06 (d, J(H,H) = 3.2 Hz, 1H), 6.18
3
(dd, J(H,H) = 1.8, 3.2 Hz, 1H), 7.23–7.25 (m, 1H), 7.48–7.53 (m, 2H),
7.58–7.63 (m, 1H), 7.83–7.87 (m, 2H). 13C NMR (125 MHz, CDCl3): δ =
28.0, 67.0, 68.0, 74.1, 108.6, 110.3, 128.4, 129.2, 133.9, 138.0, 142.8,
151.1. MS (EI 70 eV) m/z (%): 136 (100), 95 (61), 77 (18). HRMS (ESI):
Calcd. for C14H14O4SNa: 301.0505, found: 301.0492; Anal. Calcd. for
C14H14O4S: C 60.42, H 5.07, S 11.52, found: C 60.47, H 5.00, S 11.69 %.
Reaction of 1 with Aliphatic Aldehydes, Synthesis of 3h, 3i,
and 3j: General Procedure
◦
To a solution of 1 (200 mg, 0.5 mmol) in THF (2 mL) at –75 C under
argon, t−BuOK (112 mg, 1 mmol, in 1 mL of THF) was added dropwise
and then, after 15 sec, the aldehyde (0.75 mmol) was added. After 30
min at –75 ◦C the mixture was warmed to room temperature and kept
for 60 min. After that, the solution of NH4Cl was added, the mixture was
extracted with CH2Cl2 (3 × 25 mL), and the extract was washed with
brine and dried over MgSO4. Column chromatography with hexane–
EtOAc gave the substituted tetrahydrofurans.
trans-2-Propyl-3-phenylsulfonyl Tetrahydrofuran (3h)
Oil; IR (film CH2Cl2, νmax/cm−1): 3065, 2960, 2874, 1585, 1447, 1304,
1145, 1086, 1046, 949, 929, 837, 752, 720, 691, 602, 547. 1H NMR (500
3
MHz, CDCl3): δ = 0.83 (t, J(H,H) = 7.1 Hz, 3H), 1.23–1.48 (m, 4H),
2.06–2.16 (m, 1H), 2.33–2.40 (m, 1H), 3.29–3.35 (m, 1H), 3.74 (ddd,
3
3J(H,H) = 7.0, 8.5, 8.5 Hz, 1H), 3.88 (ddd, J(H,H) = 4.1, 7.7, 8.5 Hz,
1H), 4.23 (ddd, 3J(H,H) = 3.3, 6.0, 8.5 Hz, 1H), 7.55–7.60 (m, 2H),
7.64–7.68 (m, 1H), 7.88–7.92 (m, 2H). 13C NMR (125 MHz, CDCl3): δ =
13.7, 18.9, 28.5, 37.2, 67.1, 68.3, 78.5, 128.5, 129.3, 133.9, 138.4. MS
(EI 70 eV) m/z (%): 211 (39), 147 (17), 141 (51), 125 (11), 112 (81), 84
(100), 77 (85), 69 (23), 55 (22), 51 (29), 41 (51). HRMS (ESI): Calcd. for
C13H18O3SNa: 277.0869, found: 277.0871. Anal. Calcd. for C13H18O3S:
C 61.39, H 7.13, S 12.61, found: C 61.44, H 7.30, S 12.73 %.
trans-2-Isopropyl-3-phenylsulfonyl Tetrahydrofuran (3i)
Oil; IR (film CH2Cl2, νmax/cm−1): 2962, 2877, 1468, 1447, 1306, 1148,
1
1086, 934, 749, 720, 691, 581, 548. H NMR (500 MHz, CDCl3): δ =
3
0.84 (t, J(H,H) = 6.6 Hz, 6H), 1.60–1.68 (m, 1H), 2.04–2.13 (m, 1H),
2.36–2.43 (m, 1H), 3.45 (ddd, 3J(H,H) = 3.5, 5.0, 9.5 Hz, 1H), 3.79 (ddd,
3
3J(H,H) = 6.5, 8.4, 8.4 Hz, 1H), 3.90 (ddd, J(H,H) = 3.6, 8.4, 8.4 Hz,
3
1H), 4.15 (t, J(H,H) = 5.0 Hz, 1H), 7.57–7.61 (m, 2H), 7.66–7.70 (m,
1H), 7.91–7.95 (m, 2H). 13C NMR (125 MHz, CDCl3): δ = 16.8, 18.9,

864
M. Makosza and A. Wojtasiewicz
ꢀ
28.8, 32.0, 66.4, 67.5, 83.3, 128.8, 129.4, 133.9, 138.4. HRMS (ESI):
Calcd. for C13H18O3SNa: 277.0869, found 277.0880.
trans-2-Methyl-3-phenylsulfonyl Tetrahydrofuran (3j)
Oil; IR (film CH2Cl2, νmax/cm−1): 3069, 2977, 2892, 2871, 1585, 1477,
1384, 1304, 1292, 1258, 1146, 1103, 1088, 1026, 997, 940, 897, 870, 749,
719, 692, 642, 603, 583, 545, 442. 1H NMR (500 MHz, CDCl3): δ = 1.20
3
(d, J(H,H) = 6.2 Hz, 3H), 2.13–2.22 (m, 1H), 2.37–2.40 (m, 1H), 3.28
3
(ddd, J(H,H) = 5.2, 6.7, 10.1 Hz, 1H), 3.71–3.77 (m, 1H), 3.93 (ddd,
3
3J(H,H) = 3.9, 7.8, 8.6 Hz, 1H), 4.31 (quintet, J(H,H) = 6.3 Hz, 1H),
7.57–7.62 (m, 2H), 7.66–7.70 (m, 1H), 7.90–7.94 (m, 2H). 13C NMR (125
MHz, CDCl3): δ = 20.6, 28.7, 67.1, 69.6, 75.3, 128.6, 129.4, 134.0, 138.5;
MS (EI 70 eV) m/z (%): 141 (12), 84 (100), 77 (41), 55 (17), 51 (24), 43
(83). HRMS (ESI): Calcd. for C11H14O3SNa: 249.0556, found: 249.0550.
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