Observation of intermediates in Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton containing Group 15 elements with benzaldehyde

Article abstract of DOI:10.1080/10426507.2018.1521410

The heteroatom effect of Group 15 elements (P, As, Sb and Bi) has been investigated on stereochemical drift in the Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton with benzaldehyde. 1,2-Oxaphosphetanes were observed as intermediates and the isomerization from cis-form to trans-form, the origin of stereochemical drift, was detected between ?90 °C and 25 °C by VT-³¹P{¹H} NMR spectroscopy. The isomerization was found to start at lower temperatures as the raw number of heavier period elements. Cross experiments showed that the isomerization occurred through equilibrium between 1,2-oxaphosphetanes and phosphonium ylides-benzaldehyde.GRAPHICAL ABSTRACT (Figure presented.).

Full text of DOI:10.1080/10426507.2018.1521410

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Observation of intermediates in Wittig reactions
of non-stabilized phosphonium ylides bearing a
phosphaheteratriptycene skeleton containing
Group 15 elements with benzaldehyde
Yosuke Uchiyama, Suguru Kuniya, Ryo Watanabe & Takemaru Ohtsuki
To cite this article: Yosuke Uchiyama, Suguru Kuniya, Ryo Watanabe & Takemaru Ohtsuki
(2019): Observation of intermediates in Wittig reactions of non-stabilized phosphonium ylides
bearing a phosphaheteratriptycene skeleton containing Group 15 elements with benzaldehyde,
Phosphorus, Sulfur, and Silicon and the Related Elements, DOI: 10.1080/10426507.2018.1521410
To link to this article: https://doi.org/10.1080/10426507.2018.1521410
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PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
https://doi.org/10.1080/10426507.2018.1521410
SHORT COMMUNICATION
Observation of intermediates in Wittig reactions of non-stabilized phosphonium
ylides bearing a phosphaheteratriptycene skeleton containing Group 15
elements with benzaldehyde
Yosuke Uchiyama , Suguru Kuniya, Ryo Watanabe, and Takemaru Ohtsuki
Department of Chemistry, School of Science, Kitasato University, Sagamihara, Japan
ABSTRACT
ARTICLE HISTORY
The heteroatom effect of Group 15 elements (P, As, Sb and Bi) has been investigated on stereo-
chemical drift in the Wittig reactions of non-stabilized phosphonium ylides bearing a phosphahe-
teratriptycene skeleton with benzaldehyde. 1,2-Oxaphosphetanes were observed as intermediates
and the isomerization from cis-form to trans-form, the origin of stereochemical drift, was detected
between ꢀ90 C and 25 C by VT- P{ H} NMR spectroscopy. The isomerization was found to start
at lower temperatures as the raw number of heavier period elements. Cross experiments showed
that the isomerization occurred through equilibrium between 1,2-oxaphosphetanes and phos-
phonium ylides-benzaldehyde.
Received 19 July 2018
Accepted 26 August 2018
KEYWORDS
ꢁ
ꢁ
31
1
Heteroatom effect; 1,2-
Oxaphosphetane; stereo-
chemical drift;
isomerization; phosphahe-
teratriptycene skeleton
GRAPHICAL ABSTRACT
Introduction
Results and discussion
Non-stabilized triphenylphosphonium ylides are well-known Synthesis of ethylphosphonium iodides bearing a
to be reacted with benzaldehydes to give (Z)-olefins as a phosphaheteratriptycene skeleton
[
1]
major product in the Wittig reaction. On the other hand,
the reaction of non-stabilized tri(n-butyl)phosphonium
ylides with benzaldehydes was reported to give (E)-olefins as
a major product. The selectivity of (E)- and (Z)-olefins is
considered to the substituent groups on the phosphorus
atom of the ylides, which affect the stereochemical drift of
the intermediates. We have recently reported (E)-selective
Wittig reactions of non-stabilized phosphonium ylides bear-
Ethylphosphonium iodides 1, 2 and 4 bearing a phosphahe-
teratriptycene skeleton containing Group 15 elements (P, As
and Bi) were synthesized by the similar method of phosphas-
[
2]
[3–5]
tibatriptycene derivative 3 (M ¼ Sb).
The reaction of
tris(2-bromo-4,5-dimethylphenyl)phosphine with t-BuLi fol-
lowed by the addition of a THF solution of MCl (M ¼ P, As
3
and Bi) afforded diphosphatriptycene 5, phosphaarsatripty-
cene 6 and phosphabismatriptycene 8 in 7%, 6% and 10%
yields as reported for phosphastibatriptycene 7 (Scheme 1).
ing
hydes.
a
phosphastibatriptycene skeleton with benzalde-
The results showed that the tridentate ligand in
[
3–5]
Phosphaheteratriptycenes 5, 6 and 8 reacted with ethyl iodide
the 1,2-oxaphosphetanes bearing the phosphastibatriptycene
skeleton has the similar substituent effects with n-butyl
groups on the phosphorus atom of 1,2-oxaphosphetanes.
Herein, we will report about the heteroatom effect of Group
ꢁ
in CHCl at 70 C to afford ethylphosphonium iodides 1, 2
3
and 4 in 75%, 93% and 80% yields, respectively. Phosphorus-
3
1 signals of each ethylphosphonium iodide were observed at
lower field than those of phosphaheteratriptycenes. Proton
1
5 elements in a phosphaheteratriptycene skeleton on the
signals of CH CH group showed reasonable P–H coupling
3
2
isomerization from cis-1,2-oxaphosphetanes to trans-forms
in Wittig reactions of non-stabilized phosphonium ylides
with benzaldehyde.
and the integral ratio. The NMR spectra indicated successful
ethylation at the phosphorus atom.
CONTACT Yosuke Uchiyama
yosuke@kitasato-u.ac.jp
ß 2019 Taylor & Francis Group, LLC

2
Y. UCHIYAMA ET AL.
Scheme 1. Synthetic route of ethylphosphonium iodides bearing a phosphaheteratriptycene skeleton.
Scheme 2. Wittig reactions of non-stabilized phosphonium ylides with benzaldehyde.
Scheme 3. Observation of isomerization between cis- and trans-1,2-oxaphosphetanes.
Wittig reactions of non-stabilized phosphonium ylides
with benzaldehyde
case of phosphastibatriptycene derivative and its mechanism
was revealed to be not a pathway through Schlosser type
intermediate but that via equilibrium between 1,2-oxa-
phosphetanes and a phosphonium ylide-benzaldehydes,
[
6]
Non-stabilized phosphonium ylides 9–12 were generated in a
J-Young NMR tube by the reactions of ethylphosphonium
which was revealed by exchange reaction of benzaldehyde
ꢁ
iodides 1–4 with TMS NNa in THF at 0 C for 10min
(
[3–5]
2
units in 1,2-oxaphosphetanes.
In order to investigate
3
1
Scheme 2). In the P NMR spectra, phosphorus-31 signals of
heteroatom effects at the other bridgehead position of a
phosphaheteratriptycene in the equilibrium, Wittig reactions
of non-stabilized phosphonium ylides 9–12 with benzalde-
9
1
–12 were observed at significant upper field than those of
–4. Wittig reactions of 9–12 with benzaldehyde gave (E)- and
(
Z)-olefins in 15%, 32%, 87% and 42% yields together with
phosphine oxides 13–16, respectively. The ratio of (E)- and
Z)-olefins was almost 1:1 in the case of diphosphatriptycene
ꢁ
hyde were conducted at ꢀ90 C and intermediates were
ꢁ
ꢁ
observed at temperatures between ꢀ90 C and 25 C by
(
31
1
VT- P{ H} NMR spectroscopy. The isomerization from
cis-1,2-oxaphosphetanes to trans-forms was detected at 0 C
derivative and (E)-olefin was obtained as a major product in
the cases of phosphaarsatriptycene, phosphastibatriptycene and
phosphabismatriptycene derivatives (Scheme 2).
ꢁ
ꢁ
ꢁ
ꢁ
for 17, ꢀ20 C for 18, ꢀ40 C for 19 or ꢀ60 C for 20
(
Scheme 3, Figure 1). The results showed that the isomer-
ization occurred at lower temperature as the raw number
of heavier period elements increases. The selectivity of (E)-
and (Z)-olefins depended on the isomerization, the origin
of stereochemical drift, based on the heteroatom effect in
Observation of intermediates by Variable Temperature
31
1
(VT)- P{ H} NMR spectroscopy
The trialkylphosphonium ylide systems showed the isomer- the equilibrium between 1,2-oxaphosphetanes and phos-
ization between cis- and trans-1,2-oxaphosphetanes, which phonium ylides-benzaldehyde. The equilibrium was attrib-
[
2]
is considered as the origin of stereochemical drift.
uted to electronegativity, 2.19 for P, 2.18 for As, 2.05 for
ꢁ
[7]
Similarly, the isomerization was observed at ꢀ40 C in the Sb and 2.02 for Bi.

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
3
3
1
1
Figure 1. VT- P{ H} NMR spectra of isomerization between cis- and trans-1,2-oxaphosphetanes.
Scheme 4. Mechanism of the Wittig reactions of non-stabilized phosphonium ylides 9-12 bearing a phosphaheteratriptycene skeleton with benzaldehyde.
Mechanism of the Wittig reactions depending on
isomerization of intermediates
the (E)-selective Wittig reaction of a non-stabilized tri(n-
[
2]
butyl)phosphonium ylide with benzaldehyde. The isomer-
ization has also been revealed to proceed via an equilibrium
of 1,2-oxaphosphetanes and phosphonium ylides-benzalde-
hyde based on the reported exchange reaction of benzalde-
Wittig reactions of non-stabilized phosphonium ylides 9–12
bearing
a
phosphaheteratriptycene skeleton containing
Group 15 elements with benzaldehyde gave (E)- and (Z)-ole-
fins as final products in the ratios, which depended on a
phosphaheteratriptycene skeleton, together with phosphine
oxides 13–16. The stereospecific olefin formation was
considered to proceed via the isomerization from cis-1,2-
oxaphosphetanes to trans-forms because cis-1,2-oxaphosphe-
tanes 17a–20a were observed as a kinetic product at the first
hydes in the deprotonation of b-hydroxyalkyl phosphonium
[3,4]
salt with TMS NNa.
A tridentate ligand in this system is
2
constructed by three aryl groups, so that the reactivities of
,2-oxaphosphetanes bearing a phosphaheteratriptycene con-
1
taining Group 15 elements should be similar to those of 1,2-
oxaphosphetanes formed from non-stabilized triphenylphos-
[1]
phonium ylides rather than those of non-stabilized tribu-
3
1
1
[2]
stage by VT- P{ H} NMR spectroscopy and trans-forms
tylphosphonium ylides. However, the result was reverse.
17b–20b were detected at different temperatures depending Therefore, heteroatom at the other bridgehead position of a
on a phosphaheteratriptycene skeleton containing Group 15 phosphaheteratriptycene skeleton affects the equilibrium
elements. The isomerization is regarded as the origin of rather than thermodynamic stability of 1,2-oxaphosphetanes.
stereochemical drift, which was reported for the first time in The isomerization from cis-1,2-oxaphosphetanes to trans-

4
Y. UCHIYAMA ET AL.
forms occurred more easily, as the raw number of heavier No.18750037) from the Ministry of Education, Culture, Sports, Science,
and Technology of Japan and Kitasato University Research Grant for
Young Researchers. The authors thank Emeritus Prof. Takayuki
Kawashima for useful advices.
elements increases. The reason was why the heteroatom
effect derived from electronegativity induced polarization
of M–C bonds to stable non-stabilized phosphonium ylides
[
7]
bearing
a
phosphaheteratriptycene skeleton containing
Group 15 elements, from which the equilibrium inclined to ORCID
the right hand.
Yosuke Uchiyama
http://orcid.org/0000-0002-9513-1147
Conclusions
References
The heteroatom effect of Group 15 elements in a phospha-
heteratriptycene skeleton on the equilibrium between 1,2-
oxaphosphetanes and phosphonium ylides-benzaldehyde in
the isomerization from cis-1,2-oxaphosphetanes to trans-
forms has been investigated in Wittig reactions of non-stabi-
lized phosphonium ylides 9-12 with benzaldehyde. The het-
[1] Maryanoff, B. E.; Reitz, A. B. The Wittig Olefination Reaction
and Modifications Involving Phosphoryl-Stabilized Carbanions.
Stereochemistry, Mechanism, and Selected Synthetic Aspects.
Chem. Rev. 1989, 89, 863–927.
[
2] Maryanoff, B. E.; Reitz, A. B.; Mutter, M. S.; Inners, R. R.;
Almond, H. R.; Jr., Whittle, R. R.; Olofson, R. A.
Stereochemistry and Mechanism of the Wittig Reaction.
Diasteromeric Reaction Intermediates and Analysis of the
Reaction Course. J. Am. Chem. Soc. 1986, 108, 7664–7678.
eroatom at the other bridgehead position of
a
phosphaheteratriptycene skeleton affected the isomerization
temperature to start observing trans-forms, which became
lower as the raw number of heavier elements increases,
showing the selectivity of (E)- and (Z)-olefins under the
same reaction condition. However, we could not reveal
whether the equilibrium occurred via a betaine intermediate
or the direct retro [2 þ 2] cycloaddition-reconstruction. The
investigation on the reaction mechanism is in progress.
[3] Uchiyama, Y.; Ohtsuki, T.; Murakami, R.; Shibata, M.;
Sugimoto, J. (E)-Selective Wittig Reactions between
Nonstabilized Phosphonium Ylide Bearing
a
a
Phosphastibatriptycene Skeleton and Benzaldehydes. Eur. J. Org.
Chem. 2017, 2017, 159–174.
[
4] Uchiyama, Y.; Ohtsuki, T.; Murakami, R.; Shibata, M.;
Sugimoto, J. E-Selective Wittig Reactions Using a Nonstabilized
Phosphonium Ylide Bearing a Phosphastibatriptycene Skeleton
with Benzaldehydes under Salt-Free Conditions. Phosphorus
Sulfur Silicon Relat. Elem. 2016, 191, 1523–1526.
Disclosure statement
[
[
5] Uchiyama, Y.; Ohtsuki, T.; Murakami, R.; Sugimoto, J. Wittig
Reactions
of
Phosphonium
Ylides
Bearing
the
No potential conflict of interest was reported by the authors.
Phosphastibatriptycene Skeleton with Carbonyl Compounds.
Phosphorus Sulfur Silicon Relat. Elem. 2015, 190, 633–637.
6] Schlosser, M.; Christmann, K. F. Trans-Selective Olefin
Syntheses. Angew. Chem. Int. Ed. Engl. 1966, 5, 126.
Acknowledgements and thanks
This study was partially supported by
a
Grant-in-Aid for
[7] Emsley, J. The Elements, 3 ed.; Oxford University Press: New
Encouragement of Young Scientists (B) to Y. U. (No.16750041 and
York, 1998. pp 22–23, 26–27, 36–37, 152–153.