Reactivity and utility of allenylphosphonates: Formation of a novel hydroperoxide and propargylic alcohol and facile thiol addition under catalyst-free, solvent-free conditions

Article abstract of DOI:10.1055/s-2007-990794

2-(Propa-1,2-dienyl)-, 2-(buta-1,2-dienyl)-, and 2-(3-methylbuta-1,2- dienyl)-substituted 5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxides 1a-c react readily upon heating with thiols under catalyst-free, base-free, and solvent-free conditions to give sulfanyl

Full text of DOI:10.1055/s-2007-990794

PAPER
3171
Reactivity and Utility of Allenylphosphonates: Formation of a Novel
Hydroperoxide and Propargylic Alcohol and Facile Thiol Addition under
Catalyst-Free, Solvent-Free Conditions
Reactivity and
U
tility o
a
f
A
llenylp
n
School of Chemistry, University of Hyderabad, Hyderabad 500046, AP, India
Fax +91(40)23012460; E-mail: kckssc@uohyd.ernet.in
Received 19 June 2007
vinyl and/or allylphosphonates of types 4 or 5 where at-
tack takes place at the b-carbon.4,5 The reactions with
amines can be extended to those with nucleobases as well
as gaseous ammonia and in our previous work we have
Abstract: 2-(Propa-1,2-dienyl)-, 2-(buta-1,2-dienyl)-, and 2-(3-
methylbuta-1,2-dienyl)-substituted 5,5-dimethyl-1,3,2-dioxaphos-
phinane 2-oxides 1a–c react readily upon heating with thiols under
catalyst-free, base-free, and solvent-free conditions to give sulfa-
nyl-substituted phosphonates. The reaction undergoes to essential shown that the precursor 7 gives both trans-vinyl and allyl
completion within 15 minutes under microwave radiation. While
products 8–10 , but in the case of ammonia, cis-vinylphos-
phonate 11 is preferentially formed (Scheme 2).5 Attack
1a,b react with 4-chlorothiophenol to afford both 2-[2-(4-chlo-
rophenylsulfanyl)prop-1-enyl]- 12 and 2-[2-(4-chlorophenylsulfa-
at the g-carbon (umpolung addition) takes place with phe-
nyl)prop-2-enyl]-5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxides
nols for the phosphine-catalyzed reactions.6 The addition
13, 1c gives 2-[2-(4-chlorophenylsulfanyl)-3-methylbut-2-enyl]-
of thiols to allenes is a well-known protocol for the prep-
aration of vinylic and allylic sulfides; these reactions were
conducted using UV radiation or palladium catalysis.7
Earlier, reactions of thiols with phosphorylated allenes
were performed in the presence of a base (e.g., NaOEt)
and a solvent (e.g., EtOH).3a,8
5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide (13d) regioselective-
ly. Molecular oxygen undergoes a novel reaction with the allene 1c
to give propargylic alcohol 2-(3-hydroxy-3-methylbut-1-ynyl)-5,5-
dimethyl-1,3,2-dioxaphosphinane 2-oxide (16) via the correspond-
ing hydroperoxide; the structures of these were confirmed by X-ray
crystallography. The synthetic utility of the sulfanyl-substituted al-
lyphosphonate 13d in the Horner–Wadsworth–Emmons reaction to
afford synthetically valuable sulfanyl-substituted buta-1,3-dienes
and a conjugated triene is demonstrated.
R1
H
P
γ
C
α
C
β
C
R1, R2 = H
[1a; δ(P) 8.8]
O
O
R
1 = H, R2 = Me [1b; δ(P) 8.9]
Key words: allenes, thiol addition, oxygenation, Horner–
Wadsworth–Emmons reaction, allenylphosphonates
R2
R1, R2 = Me
[1c; δ(P) 9.9]
O
H
C
Nu
R1
α-attack
β-attack
Allenes or 1,2-dienes are potential precursors for a variety
of molecules of industrial and pharmaceutical impor-
tance.1,2 Among these, allenylphosphonates (phosphory-
lated allenes) 1a–c constitute a readily accessible family
of allenes that can be used as versatile building blocks in
organic synthesis.3 Since in substituted allenes, phospho-
rus can impart a different electronic constraint relative to
a carbon or hydrogen on the intermediates, the stere-
ochemistry of the products in the reactions using alle-
nylphosphonates and phenyl-substituted allenes may be
the result of different pathways. In addition, the experi-
mental conditions also could influence the final outcome
of the reaction. As an example, in the simple addition re-
action of allene 2 with a nucleophile shown in Scheme 1,
the incoming nucleophile can, in principle, attack any of
the three carbon centers, a, b, or g depending upon the
substituents present and the conditions used. Although the
resulting primary products 3–6 are all alkenes, geometri-
cal isomerism is also possible.
C
C
Y
R2
H
3
4
H
H
R1
R2
H
R1
R2
C
H
Y
R1
R2
γ
C
C
H
Y
α
C
β
C
Nu-H
Y
C
C
C
C
C
Nu
Nu
R1
2
5
Nu
R2
H
Y
C
C
γ-attack
H
6
Scheme 1
By keeping the above reactions in mind and in continua-
tion of our investigations on organophosphorus chemis-
try,3j,5,9 we report herein the direct addition of thiols with
the inexpensive phosphorylated allenes 1a–c under envi-
ronmentally benign, catalyst-free, and solvent-free condi-
tions. While doing so, we have observed a novel reaction
of 1c with dioxygen in which the first formed hydroperox-
ide leads to a phosphono-propargylic alcohol, as shown
by X-ray crystallography. We also report the successful
utilization of the sulfanyl-substituted allylphosphonate
products to afford synthetically useful 3-sulfanyl-substi-
The simple reactions of allenes are those with nucleo-
philes like amines, alcohols, phenols, or thiols leading to
SYNTHESIS 2007, No. 20, pp 3171–3178
x
x.
x
x
.
2
0
0
7
Advanced online publication: 21.09.2007
DOI: 10.1055/s-2007-990794; Art ID: P07707SS
© Georg Thieme Verlag Stuttgart · New York

3172
M. Chakravarty, K. C. Kumara Swamy
PAPER
Me
H2N
N
N
H
Me
H
O
N
N
N
N
P
R = H
adenine
R = Me
adenine
N
H
OH
O
N
H
H
O
O
H
R
C
R
8
N
H
P
C
C
O
O
H
Me
10
P
O
H
H
7
Me
O
O
O
adenine
R = Me
H
H
ammonia
R = H
N
P
N
N
H
H
O
O
N
P
H2N
O
NH2
9
O
11
Scheme 2
tuted trans-buta-1,3-dienes via Horner–Wadsworth–
Table 1 Formation of 12 and 13
Emmons (HWE) reaction.
R1
H
R2
H
R3
Product Yielda (%) 31P NMR, d
The various vinyl 12a–c and allyl products 13a,b,d,e iso-
lated from the reaction of 1a–c with thiols are shown in
Scheme 3 and Table 1. Treatment of 1a with 4-chloro-
thiophenol without solvent at 100 °C for 4–6 hours afford-
ed an isomeric mixture of 12a and 13a (combined yield
80%) in ~2:3 ratio by 31P NMR, thus showing that a cata-
lyst or base is unnecessary for this reaction. It should be
noted that in the final reaction mixture, only one vi-
nylphosphonate isomer is present for which we assign E-
stereochemistry (tentative). We also performed the same
reaction using palladium(II) acetate in tetrahydrofuran,
but the product ratio remained unchanged; under micro-
wave conditions also the essentially the same ratio was
maintained but the reaction was essentially complete in 15
minutes. The product distribution, however, is distinctly
different from that of the palladium(II) acetate catalyzed
addition of benzenethiol in tetrahydrofuran to phenylal-
lene (wherein a mixture of three isomers was obtained) or
tert-butyl- or cyclohexylallene (RCH=C=CH2 where
R = t-Bu, Cy) in which the products RCH2C(SPh)=CH2
are formed regioselectively.7b
4-ClC6H4
12a
13a
34
45
12.9
20.5
Me
H
4-ClC6H4
12b
13b
23
12.9
21.5, 21.9
(ratio 9:1)
41b
H
H
Cy
12c
13d
20
80
70
13.7
22.3
23.9
Me
Me
Me
Me
4-ClC6H4
CH2CH2OH 13e
a Isolated yield.
b E/Z Isomeric mixture.
and found that the allyl product 13a [d(P) 20.5] is not
formed. The mixture contains only the vinyl product 12a
[d(P) 12.9], precursor 1a [d(P) 8.8], and an unknown spe-
cies [d(P) 13.9]. Upon further heating, the allyl derivative
13a begins to develop at the cost of the intermediate
product with d(P) 13.9 (Figure 1).10 At present we cannot
assign a structure to the intermediate, but based on
31P NMR it appears to contain the (5,5-dimethyl-2-
We have checked the 31P NMR spectrum of the reaction
mixture after heating 1a with 4-chlorothiophenol at 70–80
°C for 15 minutes without solvent (or with CHCl3, 6 h)
oxo-1,3,2-dioxaphosphinan-2-yl)methylene
group
[(OCH2CMe2CH2O)P(O)CH=]. It is possible that the
peak at d(P) 13.9 is due to the b-ketophosphonate 5,5-
dimethyl-2-(2-oxopropyl)-1,3,2-dioxaphosphinane 2-ox-
ide [(OCH2CMe2CH2O)P(O)CH2COCH3], but a pure
sample of this compound did not react with 4-chlo-
rothiophenol upon heating at 100 °C for 48 hours.
O
O
R1
R2
P
O
R3SH
+
H
1a–c
The ratio of the vinyl to allyl phosphonates 12/13 depends
on the substituents present on the allene as well as on the
thiol. In the case of 1b, a regioisomeric mixture (12b and
13b) was obtained in 1:2 ratio (by 31P NMR spectrum of
the reaction mixture) and for 1c, a regioselective product
13d was obtained in 80% yield. We used mainly 4-chlo-
rothiophenol as it is a solid and gives less stench com-
pared to other thiols. While treatment of 1a with
neat, 90–110 °C
4–6 h
O
O
O
O
SR3
O
P
O
CHR1R2
SR3
P
H
R1
R2
+
H
H
12
13
Scheme 3
Synthesis 2007, No. 20, 3171–3178 © Thieme Stuttgart · New York

PAPER
Reactivity and Utility of Allenylphosphonates
3173
Figure 1 31P NMR spectra of the reaction mixture of 1a with 4-
chlorothiophenol: (a) CHCl3, reflux, 6 h (a similar spectrum was ob-
tained neat, 70–80 °C, 15 min) and (b) neat, microwave heating, 15
min (a similar spectrum was obtained, neat, 100 °C, 12 h).
Figure 2 The structure and ORTEP diagram of compound 14 [P–
C(6) 1.786(3); C(6)–C(7) 1.325(4) Å. H-bond parameters: O(4)–
H(4)⋅⋅⋅O(3¢) 0.75(3), 2.14(4), 2.886(4) Å, 177(4)°; symmetry code: x,
–1 + y, z].
cyclohexanethiol gave a mixture of three phosphonates
[d(P) 12.0, 13.1, 14.8] from which 12c [d(P) 12.0] was
isolated in 20% yield, that with 2-sulfanylethanol afforded
the allyl product 13e [d(P) 23.9; isolated yield 70%] ste-
reoselectively.
Me
Me
H
P
C
O
C
C
O
O
What is perhaps more interesting in terms of reactivity is
that when we used an old sample of 1c in reaction with 4-
chlorothiophenol, we isolated the unexpected product 14
reproducibly in about 10% yield. This compound showed
an IR band at 3380 cm–1 and hence an X-ray crystal struc-
ture (Figure 2) was determined. As is evident, the hydroxy
group could not have entered from either of the expected
precursors, and hence we examined the original sample.
This sample had some viscous liquid present along with
solid and the 31P NMR spectrum showed peaks at d –12.2
and –11.4 (1:5) in addition to that expected for 1c (d 9.9).
Careful chromatography [Rf ~ 0.58 for both (EtOAc–hex-
ane, 1:1)] followed by crystallization afforded the com-
pounds 15 and 16 (Scheme 4).11 We then found that
exposure of 1c to air for ~30 days leads to its conversion
into 16 (50%) along with a small quantity of 15 (ca. 5%).
Both of these compounds were characterized by single-
crystal X-ray crystallography (Figure 3). It is likely that
compound 14 is formed by the cis addition of 4-chlo-
rothiophenol to 16.
1c
H
O
O
O
H
Me
O
2 (atmospheric)
Me
C
Me
C
Me
C
C
C
O
C
O
O
∆
O
O
P
P
O
15 [δ(P) –12.2; (X-ray)]
16 [δ(P) –11.4; (X-ray)]
Scheme 4
5,5-Diethyl-2-(3-methylbuta-1,2-dienyl)-1,3,2-dioxaphos-
phinane 2-oxide (dP 10.9) also reacts with molecular oxy-
gen and the propargylic alcohol 17 could be isolated
readily (Figure 4).12 This result shows that reaction of al-
lenylphosphonates containing terminal =CMe2 groups
with molecular oxygen is general.
Compound 16 is less reactive towards 4-chlorothiophenol
compared to 1c. A better route to 16 is to expose 1c to air
for ~30 days and then use chromatography to separate 16
(ca. 50% yield). Although slow oxidation (autoxidation)
is common for many unsaturated compounds in light/air
over a long period,13 and compound 1c has been known in
the literature for a long time, there has been no report on
its stability when exposed to air. We could distill it at 180
°C/9 mbar and could keep it under water for 48 hours with
Figure 3 PLATON drawings of (a) 15 [P–C(6) 1.740(2), C(6)–C(7)
1.184(2), O(4)–O(5) 1.436(3) Å. H-bond parameters: O(5)–
H(5O)⋅⋅⋅O(3¢) 0.93(3), 1.89(3), 2.782(4) Å, 160(3)°; symmetry code:
x – 1, y, z)] and (b) 16 [P–C(6) 1.732(2), C(6)–C(7) 1.195(3) Å. H-
bond parameters: O(4)–H(4)⋅⋅⋅O(3¢) 0.82, 1.93, 2.750(2) Å, 173.8°;
symmetry code: 1 – x, 1 – y, 2 – z]. Note: In 15, the oxygen atoms O4
and O5 are disordered and only one of the two positions is shown in
the drawing.
Synthesis 2007, No. 20, 3171–3178 © Thieme Stuttgart · New York

3174
M. Chakravarty, K. C. Kumara Swamy
PAPER
H
O
Me
Me
C
C
C
O
O
Et
Et
P
O
17 [δ(P) –12.3]
Figure 4
<5% decomposition (to 15 and 16). Upon treatment with
hydrogen peroxide, 1c gave a mixture with 15 and 16 as
the major products (~50%).
Figure 5 An ORTEP drawing of 18a.
It may be noted that the sulfanyl-substituted allylphospho-
nates 13a,b,d,e have a PCH2 group from which deproto-
nation can easily be effected and utilized in HWE reaction
with aldehydes to afford buta-1,3-dienes. In the present
work we have utilized the easily synthesized 13d as the
precursor for the HWE reaction (Scheme 5). Reactions
with aldehydes were performed in the presence of the in-
expensive base sodium hydride at room temperature for
6–10 hours using tetrahydrofuran as solvent. The trans-
buta-1,3-dienes 18, conjugated trans-triene 19,14 and the
bis(trans-buta-1,3-diene) 20 were isolated in good yields;
refluxing temperature was required in the synthesis of 20.
The stereochemistry of these dienes is confirmed by
checking the single-crystal X-ray crystal structure for 18a
(Figure 5). It should be noted that earlier 2-(phenylsulfa-
nyl)-substituted 1,3-dienes were prepared by Zhijie and
Padwa using tetrakis(triphenylphosphine)palladium(0)-
catalyzed cross-coupling of a-allenyl acetates
CH2=CH=C(SPh)CR1R2(OAc) with several terminal
alkynes.15 These sulfur containing buta-1,3-dienes hold
potential for the synthesis of new cyclic ring systems.16
However, in their case a cis-butadiene structure was pro-
posed while our route gives trans-buta-1,3-dienes as
shown by the X-ray crystal structure of 18a.
The synthetic potential of the thiol addition reaction pre-
sented here is further illustrated in the case of benzamido
heterocyclic phosphonate 13f (Figure 6). We also have
obtained the nucleobase appended phosphonate 13g [1H
and 31P NMR], but the sample could be obtained only in
~90% purity.17
OH
OH
OH
O
N
N
O
N
N
O
O
O
S
O
P
O
O
S
N
Me
P
H
H
Me
H
Me
H
Me
13g [δ(P) 23.7]
13f [δ(P) 22.5]
Figure 6
In summary, we have synthesized the sulfanyl-substituted
allylphosphonates by the direct addition of thiols with
phosphorylated allenes under nonbasic, catalyst-free, and
solvent-free conditions. The reactions are complete within
Cl
H
Ar
Me
Me
H
O
S
O
O
S
Me
Me
NaH, THF
r.t., 6–10 h
P
+
Ar-CHO
Cl
13d
18a Ar = 4-MeC6H4 76% (X-ray)
18b Ar = 4-MeOC6H4 73%
Cl
Me
H
H
Me
H
H
H
Me
Me
H
S
S
H
H
S
Me
Me
Cl
Cl
19 (67%)
20 (56%)
Scheme 5
Synthesis 2007, No. 20, 3171–3178 © Thieme Stuttgart · New York

PAPER
Reactivity and Utility of Allenylphosphonates
3175
Hz, OCH2), 118.5 (d, J = 10.0 Hz, =CH2), 129.6, 130.8, 134.3 (d,
J = 10.0 Hz, =CSAr), 134.6, 134.7.
5,5-diethyl analogue), to lead to the propargylic alcohols 31P NMR (160 MHz, CDCl3): d = 20.5 (s).
15 minutes under microwave radiation. Molecular oxy-
gen undergoes a novel reaction with the allenes 1c (and its
16 via the hydroperoxide 15; the structures of these were
confirmed by X-ray crystallography. Utilization of sulfa-
nyl-substituted allyphosphonates in the HWE reaction to
afford synthetically valuable sulfanyl-substituted buta-
1,3-dienes and a conjugated triene is demonstrated.
Anal. Calcd for C14H18ClO3PS: C, 50.53; H, 5.41; S, 9.62. Found:
C, 50.53; H, 5.43; S, 9.56
GC-MS: m/z = 332 [M]+, 334 [M + 2]+.
2-[2-(4-Chlorophenylsulfanyl)but-1-enyl]-5,5-dimethyl-1,3,2-
dioxaphosphinane 2-Oxide (12b) and 2-[2-(4-Chlorophenylsul-
fanyl)but-2-enyl]-5,5-dimethyl-1,3,2-dioxaphosphinane
2-Oxide (13b)
Following the procedure for 12a/13a using allene 1b (0.30 g, 1.5
mmol) and the thiol, these compounds were synthesized.
Chemicals were purified when required according to standard pro-
cedures.18All reactions, unless stated otherwise, were performed in
a dry N2 atmosphere. 1H, 13C and 31P{H} NMR spectra were record-
ed using a 200 MHz or a 400 MHz spectrometer in CDCl3 (unless
stated otherwise) with shifts referenced to TMS (d = 0) or 85%
H3PO4 (d = 0). IR spectra were recorded on an FT/IR spectropho-
tometer. Melting points were determined by using a local hot-stage
melting point apparatus and are uncorrected. Microanalyses were
performed using a CHNS analyzer. Mass spectra were recorded us-
ing a GCMS-QP2010 and LCMS 2010A.
2-[2-(4-Chlorophenylsulfanyl)but-1-enyl] Derivative 12b
Yield: 0.12 g (23%); mp 90–92 °C.
IR (KBr): 1588, 1474, 1373, 1240, 1059, 1011 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.00, 1.04 (2 s, 6 H, 2 CH3), 1.30
(t, J = 7.2 Hz, 3 H, CH2CH3), 2.81 (q, J ~7.2 Hz, 2 H, CH2CH3),
3.70 [dd (app t), J = 11.2, 11.2 Hz, 2 H, OCH2], 4.11 [dd (app t),
J = 11.2, 11.2 Hz, 2 H, OCH2], 4.88 (d, J = 14.3 Hz, 1 H, =CH),
7.44 (br, 4 H, Ar-H).
13C NMR (50 MHz, CDCl3): d = 14.6 (s, CH2CH3), 21.5 (s, 2 CH3,
merged together), 28.4 (d,J = 6.1 Hz, CH2CH3), 32.5 (d, J = 5.0 Hz,
CMe2), 75.3 (d, J = 6.1 Hz, OCH2), 101.7 (d, J = 190.4 Hz, PCH),
128.2, 130.1, 136.5, 137.0, 169.8 (d, J = 13.3 Hz, =CCH2CH3).
Precursors 5,5-dimethyl-2-(propa-1,2-dienyl)-1,3,2-dioxaphosphi-
nane 2-oxide (1a), 2-(buta-1,2-dienyl)-5,5-dimethyl-1,3,2-dioxa-
phosphinane 2-oxide (1b), and 5,5-dimethyl-2-(3-methylbuta-1,2-
dienyl)-1,3,2-dioxaphosphinane 2-oxide (1c) were prepared using
literature procedures.19 5,5-Diethyl-2-(3-methylbuta-1,2-dienyl)-
1,3,2-dioxaphosphinane 2-oxide was prepared in a manner similar
to 1c as a liquid; 1H NMR: d = 0.90–1.00 (m), 1.20–1.40 (m), 1.76
(br m), 3.92–4.19 (m), 5.16(m); 31P NMR: d = 10.9.
31P NMR (160 MHz, CDCl3): d = 12.9 (s).
Anal. Calcd for C15H20ClO3PS: C, 51.95; H, 5.81; S, 9.25. Found:
C, 51.98; H, 5.80; S, 9.13.
GC-MS: m/z = 346 [M]+, 348 [M + 2]+.
2-[2-(4-Chlorophenylsulfanyl)prop-1-enyl]-5,5-dimethyl-1,3,2-
dioxaphosphinane 2-Oxide (12a) and 2-[2-(4-Chlorophenylsul-
fanyl)prop-2-enyl]-5,5-dimethyl-1,3,2-dioxaphosphinane 2-Ox-
ide (13a); Typical Procedure
A mixture of 1a (0.30 g, 1.6 mmol) and 4-chlorothiophenol (0.28 g,
1.9 mmol) was heated neat at 90–100 °C in a 10-mL round bot-
tomed flask for 4–6 h. The products formed were separated by col-
umn chromatography (silica gel, EtOAc–hexane, 2:3) to give
initially 12a and then 13a.
2-[2-(4-Chlorophenylsulfanyl)but-2-enyl] Derivative 13b
Yield: 0.21 g (41%); mp 78–80 °C.
IR (KBr): 1476, 1267, 1092, 1055, 1005 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.02, 1.08 (2 s, 6 H, 2 CH3), 1.84–
1.85 (m, 3 H, =CCH3), 2.87 (d, J = 21.2 Hz, 2 H, PCH2), 3.81–4.21
(m, 4 H, OCH2), 6.17–6.20 (m, 1 H, =CH), 7.24–7.28 (m, 4 H, Ar-
H).
2-[2-(4-Chlorophenylsulfanyl)prop-1-enyl] Derivative 12a
Yield: 0.18 g (34%); mp 92–94 °C.
IR (KBr): 1582, 1474, 1391, 1244, 1092, 1053, 1007 cm–1.
13C NMR (100 MHz, CDCl3): d = 15.7 (d, J = 3.1 Hz, =CCH3), 21.5
and 21.6 (2 s, 2 CH3), 28.6 (d, J = 136.0 Hz, PCH2), 32.6 (d, J = 6.6
Hz, CMe2), 75.3 (d, J = 6.4 Hz, OCH2), 123.2 (d, J = 11.0
Hz, =CMeH), 129.2, 129.3, 130.9, 131.7, 136.4 (d, J = 13.0
Hz, =CSAr)
1H NMR (400 MHz, CDCl3): d = 1.01, 1.06 (2 s, 6 H, 2 CH3), 2.40
(d, J = 2.4 Hz, 3 H, =CCH3), 3.70 [dd (app t), J = 11.5, 11.5 Hz, 2
H, OCH2], 4.12 [dd (app t), J = 11.5, 11.5 Hz, 2 H, OCH2], 4.98 (d,
J = 14.4 Hz, 1 H, PCH), 7.44 (br, 4 H, Ar-H).
13C NMR (100 MHz, CDCl3): d = 20.9 [d, J = 6.5 Hz, =C(CH3)],
21.5 and 21.6 (2 s, 2 CH3), 32.4 [d, J = 5.6 Hz, C(CH3)2], 75.2 (d,
J = 6.0 Hz, OCH2), 104.3 (d, J = 189.8 Hz, PCH), 128.1, 130.1,
136.6, 136.9, 163.0 (weak signal, not well resolved).
31P NMR (160 MHz, CDCl3): d = 21.5 (br s).
Anal. Calcd for C15H20ClO3PSCl C, 51.95; H, 5.81; S, 9.25. Found:
C, 51.94; H, 5.80; S, 10.14.
GC-MS: m/z = 346 [M]+, 348 [M + 2]+.
A peak was present at d 21.7 (ca 5%) in the 31P NMR and very low
intensity peaks buried in the major signals in the 1H NMR due to the
other isomer.
31P NMR (160 MHz, CDCl3): d = 12.9 (s).
Anal. Calcd for C14H18ClO3PS: C, 50.53; H, 5.41; S, 9.62. Found:
C, 50.59; H, 5.43; S, 9.59.
2-[2-(4-Chlorophenylsulfanyl)prop-2-enyl] Derivative 13a
Yield: 0.24 g (45%); mp 117–119 °C.
2-[2-(Cyclohexylsulfanyl)prop-1-enyl]-5,5-dimethyl-1,3,2-di-
oxaphosphinane 2-Oxide (12c)
Following the typical procedure using the same molar quantities of
the allene 1a and the thiol gave 12c; yield: 0.097 g (20%); mp 94–
96 °C.
IR (KBr): 1574, 1472, 1372, 1263, 1059, 1007 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.01 (s, merged with another CH3
signal, 6 H, 2 CH3), 1.28–1.95 (m, 10 H, C6H10), 2.25 (d, J = 2.4 Hz,
IR (KBr): 1613, 1476, 1372, 1267, 1057, 1009 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.04, 1.10 (2 s, 6 H, 2 CH3), 2.87
(d, J = 21.2 Hz, 2 H, PCH2), 3.83–4.23 (m, 4 H, OCH2), 5.16 and
5.51 (2 d, 2 H, J = 4.8 Hz, =CH2), 7.27–7.43 (m, 4 H, Ar-H).
13C NMR (100 MHz, CDCl3): d = 21.5 and 21.6 (2 s, 2 CH3), 32.4
(d, J = 135.0 Hz, PCH2), 32.7 (d, J = 6.0 Hz, CMe2), 75.5 (d, J = 6.0
Synthesis 2007, No. 20, 3171–3178 © Thieme Stuttgart · New York

3176
M. Chakravarty, K. C. Kumara Swamy
PAPER
3 H, =CCH3), 2.91–3.14 (m, 1 H, SCH), 3.71–4.12 (m, 4 H, OCH2),
5.17 (d, J = 14.4 Hz, 1 H, =CH).
13C NMR (50 MHz, CDCl3): d = 21.5 and 21.7 (2 s, 2 CH3), 21.9,
25.7, 32.2, 32.4, 32.6, 43.7 (SCH), 75.2 (d, J = 6.4 Hz, OCH2),
101.7 (d, J = 191.7 Hz, PCH), 161.6 (d, J = 11.3 Hz, =CCH3).
31P NMR (160 MHz, CDCl3): d = 10.0 (s).
Anal. Calcd for C16H22ClO4PS: C, 50.99; H, 5.88. Found: C, 50.97;
H, 5.88.
An X-ray crystal structure was determined for this sample.
31P NMR (160 MHz, CDCl3): d = 12.0 (s).
2-(3-Hydroperoxy-3-methylbut-1-ynyl)-5,5-dimethyl-1,3,2-di-
oxaphosphinane 2-Oxide (15) and 2-(3-Hydroxy-3-methylbut-
1-ynyl)-5,5-dimethyl-1,3,2-dioxaphosphinane 2-Oxide (16);
Typical Procedure
Anal. Calcd for C14H25O3PS: C, 55.24; H, 8.27. Found: C, 55.43; H,
8.26.
These two compounds were obtained by simply exposing the allene
1c (ca. 0.50 g, 2.3 mmol) to air for 30 d in an Erlenmeyer flask and
they were separated by column chromatography (hexane–EtOAc,
1:1).
2-[2-(4-Chlorophenylsulfanyl)-3-methylbut-2-enyl]-5,5-di-
methyl-1,3,2-dioxaphosphinane 2-Oxide (13d)
Following the typical procedure using allene 1c (0.30 g, 1.4 mmol)
and the thiol gave 13d; yield: 0.40 g (80%); mp 116–117 °C.
IR (KBr): 1574, 1472, 1262, 1182, 1071, 1017 cm–1.
2-(3-Hydroperoxy-3-methylbut-1-ynyl) Derivative 15
1H NMR (400 MHz, CDCl3): d = 1.04, 1.07 (2 s, 6 H, 2 CH3), 2.01
and 2.05 [2 d, 6 H, J ~5.0 Hz, =C(CH3)2], 2.96 (d, J = 21.1 Hz, 2 H,
PCH2), 3.79–4.17 (m, 4 H, OCH2), 7.11–7.25 (m, 4 H, Ar-H).
Yield: 0.028 g (5%); Rf = 0.58 (hexane–EtOAc, 1:1); mp 120–122
°C.
IR (KBr): 3262, 2224, 2197, 1258, 1057, 1003 cm–1.
13C NMR (100 MHz, CDCl3): d = 21.4 and 21.5 (2 s, 2 CH3), 22.3
(d, J = 2.9 Hz, =CH3), 23.7 (d, J = 2.9 Hz, =CH3), 31.0 (d,
J = 135.5 Hz, PCH2), 32.5 (d, J = 5.8 Hz, CMe2), 75.3 (d, J = 6.4
Hz, OCH2), 114.7 (d, J = 13.2 Hz, =CSAr), 129.2, 129.3, 129.4,
131.6, 134.6, 147.0 (d, J = 1.2 Hz, =CMe2).
1H NMR (200 MHz, CDCl3): d = 0.90, 1.30 [2 s, 6 H, C(CH3)2],
1.59 [s, 6 H, C(OH)(CH3)2], 3.91–4.20 (m, 4 H, OCH2), 8.92 (br, O-
OH).
13C NMR (100 MHz, CDCl3): d = 20.4 and 22.0 (2 s), 25.7, 32.4,
77.4, 103.5 (the acetylenic carbon signals were too low in intensity
due to the small amount).
31P NMR (160 MHz, CDCl3): d = 22.3 (s).
31P NMR (160 MHz, CDCl3): d = –12.2 (s).
Anal. Calcd for C16H22ClO3PS: C, 53.21; H, 6.09, S, 8.86. Found:
C, 53.31; H, 5.99; S, 8.92.
GC-MS: m/z = 360 [M]+, 362 [M + 2]+.
An X-ray crystal structure was determined for this sample.
2-(3-Hydroxy-3-methylbut-1-ynyl) Derivative 16
Yield: 0.26 g (50%); Rf = 0.56 (hexane–EtOAc, 1:1); mp 98–100
°C.
2-[(2-Hydroxyethyl)sulfanyl]-3-methylbut-2-enyl]-5,5-dimeth-
yl-1,3,2-dioxaphosphinane 2-Oxide (13e)
Following the typical procedure using allene 1c (0.30 g, 1.4 mmol)
and the thiol gave 13e as a gummy liquid; yield: 0.286 g (70%).
IR (KBr): 3385 (br), 1649 (br), 1474, 1267, 1063, 1007 cm–1.
1H NMR (400 MHz, CDCl3): d = 0.98, 1.15 (2 s, 6 H, 2 CH3), 1.89
and 2.05 [d, J ~5.8 Hz, 6 H, =C(CH3)2], 2.88 (t, J ~5.0 Hz, 2 H,
SCH2), 3.08 (d, J = 21.6 Hz, 2 H, PCH2), 3.70 (t, J ~5.8 Hz, 2 H,
CH2OH), 3.80–4.28 (m, 4 H, OCH2).
13C NMR (100 MHz, CDCl3): d = 21.3 and 21.5 (2 s, 2 CH3), 22.1
(d, J = 3.0 Hz, =CH3), 23.7 (d, J = 3.0 Hz, =CH3), 31.8 (d,
J = 136.1 Hz, PCH2), 32.5 (d, J = 6.0 Hz, CMe2), 36.4 (s, -SCH2),
60.9 (s, CH2OH), 75.1 (d, J = 6.3 Hz, OCH2), 115.2 (d, J = 12.9
Hz, =CSAr), 143.5 (d, J = 12.0 Hz, =CMe2).
IR (KBr): 3364, 2205, 1478, 1464, 1377, 1275, 1182, 1138, 1051,
999 cm–1.
1H NMR (400 MHz, CDCl3): d = 0.90, 1.28 [2 s, 6 H, C(CH3)2],
1.58 [s, 6 H, C(OH)(CH3)2], 3.87–4.20 (m, 4 H, OCH2).
13C NMR (100 MHz, CDCl3): d = 20.3 and 22.0 [2 s, C(CH3)2], 30.5
[s, C(OH)(CH3)2], 32.3 (d, J = 6.0 Hz, CMe2), 64.6 [d, J = 3.7 Hz,
C(OH)], 68.9 (d, J = 286.0 Hz, PC≡C), 76.7 (br, OCH2), 108.1 (d,
J = 46.6 Hz, PC≡C).
31P NMR (160 MHz, CDCl3): d = –11.4 (s).
Anal. Calcd for C10H17O4P: C, 51.79; H, 7.34. Found: C, 51.72; H,
7.38.
31P NMR (160 MHz, CDCl3): d = 23.9 (s).
An X-ray crystal structure was determined for this sample.
Anal. Calcd for C12H23O4PS: C, 48.97; H, 7.82, S, 10.88. Found: C,
48.92; H, 7.84; S, 10.91
5,5-Diethyl-2-(3-hydroxy-3-methylbut-1-ynyl)-1,3,2-dioxaphos-
phinane 2-Oxide (17)
Following the typical procedure for 15/16; yield: 0.28 g (53%); mp
The reaction mixture showed a small quantity (ca. 10%) of the vinyl
product also.
69–71 °C.
IR (KBr): 3368, 2199, 1462, 1279, 1177, 1074, 1028, 1003 cm–1.
2-[2-(4-Chlorophenylsulfanyl)-3-hydroxy-3-methylbut-1-enyl]-
5,5-dimethyl-1,3,2-dioxaphosphinane 2-Oxide (14)
This compound was obtained when an old sample of 1c (0.36 g, 1.7
mmol) was treated with 4-chlorothiophenol (0.24 g, 1.7 mmol) in
THF under reflux for 24 h; yield: 0.063 g (10%); mp 190–192 °C.
1H NMR (400 MHz, CDCl3): d = 0.88 and 0.93 (2 t, J ~7.5 Hz, 6 H,
2 CH2CH3), 1.25 (q, J ~7.5 Hz, 2 H, CH2CH3), 1.62 [s, 6 H,
C(CH3)2], 1.77 (q, J ~7.5 Hz, 2 H, CH2CH3), 3.98–4.14 (m, 4 H,
2 OCH2).
IR (KBr): 3380, 1588, 1480, 1242, 1094, 1055, 1001 cm–1.
13C NMR (100 MHz, CDCl3): d = 7.0 and 7.2 (CH2CH3), 22.0 and
23.1 (2 s, 2CH2), 30.6 [s, C(CH3)2], 37.2 (d, J = 5.1 Hz, CEt2), 64.8
[d, J = 3.7 Hz, C(OH)], 68.9 (d, J = 286.0 Hz, PC≡C), 78.6 (d,
J = 6.0 Hz, OCH2), 107.4 (d, J = 46.6 Hz, PC≡C).
1H NMR (400 MHz, CDCl3): d = 1.02, 1.13 [2 s, 6 H, C(CH3)2],
1.40 [s, 6 H, C(CH3)2OH], 3.09 (br, OH), 3.86–4.07 (m, 4 H,
OCH2), 6.81 (d, 1 H, J = 16.9 Hz, =CH), 7.25–7.42 (m, 4 H, Ar-H).
13C NMR (50 MHz, CDCl3): d = 21.5 and 21.7 (2 s, 2 CH3), 29.8 (s,
2 CH3), 32.6 (d, J = 6.1 Hz, CMe2), 75.9 (d, J = 6.1 Hz, OCH2),
122.6 (d, J = 190.2 Hz, PC), 129.2, 131.8, 132.0, 133.4, 164.5.
31P NMR (80 MHz, CDCl3): d = –12.3 (s).
Anal. Calcd For C12H21O4P: C, 55.38; H, 8.13. Found: C, 55.34; H,
8.17.
Synthesis 2007, No. 20, 3171–3178 © Thieme Stuttgart · New York

PAPER
Reactivity and Utility of Allenylphosphonates
3177
3-(4-Chlorophenylsulfanyl)-4-methyl-1-(4-tolyl)penta-1,3-di-
ene (18a); Typical Procedure
1,4-Bis[3-(4-chlorophenylsulfanyl)-4-methylpenta-1,3-di-
enyl]benzene (20)
Following the typical procedure for 18a but in this case the mixture
was heated under reflux for 6 h; yield: 0.08 g (56%); mp 190–192
°C (became reddish in color).
IR (KBr): 1610 (vw), 1474, 1092, 1011, 953, 808 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.19 [s, 12 H, 2 (CH3)2], 6.96 (d,
J ~15.3 Hz, 2 H, =CH), 7.07–7.31 (m, 16 H, =CH, Ar-H).
The phosphonate 13d (0.20 g, 0.55 mmol) was dissolved in THF
(10 mL) and slowly added to a suspension of NaH (0.05 g, 2.2
mmol) in THF (20 mL) at 0 °C over 5 min; the mixture was stirred
at this temperature for 0.5 h. Then, 4-methylbenzaldehyde (0.06 g,
0.49 mmol) was added and the mixture stirred at r.t. for 6 h. H2O (5
mL) was added and the aqueous layer extracted with Et2O (3 × 10
mL). The organic layer was collected, dried (Na2SO4), and filtered.
The solvent was removed from the filtrate to give a residue that was
purified by column chromatography (hexane–EtOAc) to give 18a;
yield: 0.12 g (76%, based on the aldehyde used); mp 106–108 °C.
13C NMR (100 MHz, CDCl3): d = 21.7 and 24.9 (2 s, 2CH3), 124.5,
124.9, 126.8, 127.4, 128.9, 130.4, 131.1, 136.3, 136.8, 147.1.
Anal. Calcd for C30H28ClS2: C, 68.81; H, 5.39; S, 12.24. Found: C,
68.82; H, 5.39; S, 12.86.
IR (KBr): 1576, 1472, 1092, 959 cm–1.
1H NMR (200 MHz, CDCl3): d = 2.18 (s, 6 H, 2 CH3), 2.34 (s, 3 H,
Ar-CH3), 7.01 (d, J = 15.6 Hz, 1 H, =CH), 7.08–7.32 (m, 9 H, Ar-
H, =CH).
13C NMR (50 MHz, CDCl3): d = 21.2 and 21.7 (2 s, 2 CH3), 24.8 (s,
Ar-CH3), 124.3, 124.6, 126.6, 127.6, 128.9, 129.3, 130.5, 131.6,
134.9, 136.6, 137.4, 146.3.
2-[2-(Benzoxazol-2-ylsulfanyl)-3-methylbut-2-enyl)-5,5-di-
methyl-1,3,2-dioxaphosphinane 2-Oxide (13f)
Following the typical procedure for 12a/13a using allene 1c (0.50
g, 2.3 mmol) and benzoxazole-2-thiol (0.42 g, 2.8 mmol) and heat-
ing for 20 h; yield: 0.542 g (64%); mp 82–84 °C.
IR (KBr): 1784, 1599, 1503, 1453, 1372, 1262, 1063, 1007 cm–1.
Anal. Calcd for C19H19ClS: C, 72.47; H, 6.08; S, 10.18. Found: C,
72.62; H, 6.02; S, 10.92.
GC-MS: m/z = 314 [M]+, 316 [M + 2]+.
1H NMR (400 MHz, CDCl3): d = 0.99, 1.05 (2 s, 6 H, 2CH3), 2.07
and 2.13 [2 d, 6 H, J ~5.0 Hz, =C(CH3)2], 3.34 (d, J = 20.0 Hz, 2 H,
PCH2), 3.78–4.20 (m, 4 H, OCH2), 7.25–7.62 (m, 4 H, Ar-H).
An X-ray crystal structure was determined for this compound.
13C NMR (100 MHz, CDCl3): d = 21.4 and 21.5 (2 s, 2 CH3), 22.6
(d, J = 3.0 Hz, =CH3), 24.2 (d, J = 3.0 Hz, =CH3), 31.6 (d,
J = 130.5 Hz, PCH2), 32.6 (d, J = 5.9 Hz, CMe2), 75.1 (d, J = 6.4
Hz, OCH2), 110.0, 110.4 (d, J = 13.6 Hz, =CSAr), 118.7, 124.0,
124.3, 142.0, 150.2 (d, J = 11.0 Hz, =CMe2), 151.9, 163.6.
3-(4-Chlorophenylsulfanyl)-1-(4-methoxyphenyl)-4-methyl-
penta-1,3-diene (18b)
Following the typical procedure for 18a using the same molar quan-
tities of 13d and 4-methoxybenzaldehyde; yield: 0.12 g (73%, based
on the aldehyde used); mp 112–114 °C.
31P NMR (160 MHz, CDCl3): d = 22.5 (s).
IR (KBr): 1605, 1510, 1474, 1248, 1094, 968 cm–1.
Anal. Calcd for C17H22O4NSP: C, 55.57; H, 6.03, N, 3.81; S, 8.72.
Found: C, 55.64; H, 6.03; N, 4.00; S, 9.02.
LC-MS: m/z = 369 [M + 2]+.
1H NMR (400 MHz, CDCl3): d = 2.17 and 2.19 (2 s, 6 H, 2 CH3),
3.82 (s, 3 H, OCH3), 6.84 (d, J = 8.8 Hz, 2 H, Ar-H), 6.95 (d,
J = 15.6 Hz, 1 H, =CH), 7.08–7.35 (m, 9 H, Ar-H, =CH).
13C NMR (100 MHz, CDCl3): d = 21.6 and 24.8 (2 s, 2 CH3), 55.3
(s, OCH3), 113.9, 114.0, 123.1, 128.0, 128.8, 129.6, 130.3, 130.9,
136.5, 145.8.
X-ray Crystallography: Single-crystal X-ray data were collected on
an Enraf-Nonius MACH3 or on a Bruker AXS-SMART diffracto-
meter, using Mo-Ka (l = 0.71073 Å) radiation. The structures were
solved by direct methods and refined by full-matrix least squares
method using standard procedures.20 Absorption corrections were
done using SADABS program, where applicable. In some cases, the
terminal carbon atoms of the tert-butyl groups showed high ther-
mals and hence were refined using a suitable disorder model. All
non-hydrogen atoms were refined anisotropically; hydrogen atoms
were fixed by geometry or located by a difference Fourier map and
refined isotropically. Crystal data are available as SI as well as CIF
files. CCDC reference numbers are 642268–642271.
Anal. Calcd for C19H19ClOS: C, 68.97; H, 5.78. Found: C, 68.94; H,
5.81.
GC-MS: m/z = 330 [M]+, 332 [M + 2]+.
5-(4-Chlorophenylsulfanyl)-6-methyl-1-phenylhepta-1,3,5-
triene (19)
Following the typical procedure for 18a using 13d (0.10 g, 0.27
mmol) and cinnamaldehyde (0.036 g, 0.25 mmol); yield: 0.06 g
(67%); mp 116–118 °C.
Compound 14: C16H22ClO4PS, M = 376.82, orthorhombic, space
group Pca21, a = 17.577(2), b = 6.0938(9), c = 17.136(2) Å,
V = 1835.5(4) Å3, Z = 4, m = 0.424 mm–1, data/restraints/parame-
ters: 3221/1/216, R indices [I > 2s(I)]: R1 = 0.0406, wR2 (all
data) = 0.0869. Flack parameter: 0.07(7). Compound 15:
C10H17O5P, M = 248.21, monoclinic, space group P21/n,
a = 6.3065(19), b = 17.718(5), c = 11.427(4) Å, V = 1276.1(7) Å3,
Z = 4, m = 0.219 mm–1, data/restraints/parameters: 3018/0/167, R
indices [I > 2s(I)]: R1 = 0.0502, wR2 (all data) = 0.1289.
IR (KBr): 1576, 1472, 1389, 1090, 980 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.14 and 2.17 (2 s, 6 H, 2 CH3),
6.54 (d, J = 15.0 Hz, 1 H, =CH), 6.84–6.90 (m, 2 H, Ar-H), 7.07 (d,
J = 8.6 Hz, 2 H, Ar-H), 7.19–7.40 (m, 8 H, Ar-H).
13C NMR (100 MHz, CDCl3): d = 21.6 and 24.8 (2 s, 2 CH3), 124.4,
126.3, 127.3, 127.4, 128.6, 128.9, 129.1, 129.4, 130.4, 132.1, 133.0,
136.4, 137.4, 146.9.
Compound 16: C10H17O4P, M = 232.21, monoclinic, space group
P21/n, a = 6.7771(6), b = 16.9531(14), c = 11.0444(9) Å,
V = 1257.16(18) Å3, Z = 4, m = 0.212 mm–1, data/restraints/para-
meters: 2202/0/141, R indices [I > 2s(I)]: R1 = 0.0427, wR2 (all
data) = 0.1213. Compound 18a: C19H19SCl, M = 314.85, monoclin-
ic, space group C2, a = 19.741(6), b = 6.0068(17), c = 14.558(4) Å,
V = 1686.5(8) Å3, Z = 4, m = 0.342 mm–1, data/restraints/parame-
ters: 3322/1/193, R indices [I > 2s(I)]: R1 = 0.0411, wR2 (all
data) = 0.0984. Flack parameter: 0.00(7).
Anal. Calcd for C20H19ClS: C, 73.48; H, 5.85; S, 9.80. Found: C,
73.50; H, 5.82; S, 9.92.
GC-MS: m/z = 326 [M]+, 328 [M + 2]+.
Synthesis 2007, No. 20, 3171–3178 © Thieme Stuttgart · New York

3178
M. Chakravarty, K. C. Kumara Swamy
PAPER
Efremov, Y. Y.; Sharafutdinova, D. R.; Cherkasov, R. A.
Russ. Chem. Bull. (Engl. Transl.) 2004, 53, 2253.
(c) Khusainova, N. G.; Mostovaya, O. A.; Berdnikov, E. A.;
Cherkasov, R. A. Russ. Chem. Bull. (Engl. Transl.) 2003, 52,
1033.
Acknowledgment
We thank DST (New Delhi) for financial support and for Single
Crystal X-ray diffractometer facility at the University of Hydera-
bad, and UGC (New Delhi) for equipment under UPE and CAS pro-
grams. M.C. thanks CSIR for a fellowship.
(9) (a) Muthiah, C.; Praveen Kumar, K.; Aruna Mani, C.;
Kumara Swamy, K. C. J. Org. Chem. 2000, 65, 3733.
(b) Muthiah, C.; Senthil Kumar, K.; Vittal, J. J.; Kumara
Swamy, K. C. Synlett 2002, 1787. (c) Kumaraswamy, S.;
Kommana, P.; Satish Kumar, N.; Kumara Swamy, K. C.
Chem. Commun. 2002, 40. (d) Chakravarty, M.; Srinivas,
B.; Muthiah, C.; Kumara Swamy, K. C. Synthesis 2003,
2368. (e) Balaraman, E.; Kumara Swamy, K. C. Synthesis
2004, 3037. (f) Satish Kumar, N.; Praveen Kumar, K.;
Pavan Kumar, K. V. P.; Kommana, P.; Vittal, J. J.; Kumara
Swamy, K. C. J. Org. Chem. 2004, 69, 1880. (g) Kumara
Swamy, K. C.; Kumaraswamy, S.; Senthil Kumar, K.;
Muthiah, C. Tetrahedron Lett. 2005, 46, 3347. (h) Kumara
Swamy, K. C.; Praveen Kumar, K.; Bhuvan Kumar, N. N. J.
Org. Chem. 2006, 71, 1002. (i) Kumara Swamy, K. C.;
Satish Kumar, N. Acc. Chem. Res. 2006, 39, 324.
(j) Bhuvan Kumar, N. N.; Chakravarty, M.; Kumara Swamy,
K. C. New J. Chem. 2006, 30, 1614.
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(d) Chang Wu, M.-S.; Rayabarapu, D. K.; Cheng, C. H. J.
Am. Chem. Soc. 2003, 125, 12426. (e) Oh, C. H.; Ahn, T.
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(10) The 1H NMR spectrum of this mixture showed peaks at d =
3.40 (d, J = 22.0 Hz), in addition to those for 12a and 1a.
There was also an additional minor peak in the initial stages
in the 31P NMR at d = 23.9 (unassigned).
(11) Compound 15 was more difficult to obtain in a pure form,
probably because of conversion into 16.
(12) When we tried to separate this compound from 5,5-diethyl-
2-(3-methylbuta-1,2-dienyl)-1,3,2-dioxaphosphinane 2-
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fractions.
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Synthesis 2007, No. 20, 3171–3178 © Thieme Stuttgart · New York