The C-OH/P-H dehydrative cross-coupling for the construction of the P-C bond under metal-free conditions

Article abstract of DOI:10.1039/c7gc00882a

Herein, we report an atom-economical and environmentally benign approach for P-C bond construction via C-OH/P-H dehydrative cross-coupling reaction. This reaction was carried out under metal-free conditions, proceeds in the absence of any solvent and deli

Full text of DOI:10.1039/c7gc00882a

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The C-OH/P-H Dehydrative Cross-Coupling for the Construction
of P-C Bond under Metal-free Conditions
Peizhong Xie,*a Jinyu Wang, a Jing Fan, a Yanan Liu, a Xiangyang Wo a and Teck-Peng Loh*a,b,c
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Herein, we report an atom-economical and environmentally progress, 6f,6g impeded the wide application of these methods.
benign approach for P-C bond construction via C-OH/P-H Hence, the developments of simple, convenient especially
dehydrative cross-coupling reaction. This reaction was carried out metal-free methods for the construction of P-C bond in a
under metal-free conditions, proceeds in the absence of any green manner are still highly appealing and essential.
solvent and delivered allylic phosphorus compounds in high yields
Transition-metal-catalyzed Cross-Coupling for P-C Bond Construction (Pr evious work)
with wide functional group tolerance.
M = Pd, Ni, Rh, Ru, Cu, Ag etc; L = Ligand
O
rganophosphorus compounds play important roles in
[C]
H
[C] FG
M/L
material science, pharmaceuticals and are ubiquitous building
blocks or ligands in organic synthesis.1 Recently, it has also
been shown to function as efficient directing group for C-H
bond activation.2 Therefore, the development of convenient
and efficient methods for the construction of P-C bond is
highly desirable.1a,3 Since the pioneering work of Hirao in 1981,
(M/L,[O] )
[P]
H
[P]
[C]
[P]
[C]
(Oxidative/Radical)-
Cross Coupling
Cross Coupling
(FG = X (Br, I), OR, CN, COOR, etc.)
Environmentally Benign C-OH/P-H Dehydrative Cross-Coupling (This wor k)
R2
R2
OH
4
O
P
transition-metal catalyzed cross-coupling reactions of P-H
O
P
catalyst free
neat
R4
H2O
+
R4
R3
+
species with organohalides or other counterparts have been
established as efficient methods for the construction of P-C
H
EWG
R3
EWG
EWG = COOR, CN
bonds.3c,5 Other methods such as oxidative or radical/radical
6
7
Scheme 1. Cross-coupling strategies for P-C bond formation involving P-H
species.
C-H/P-H cross-coupling and P-H species addition to
3,8
unsaturated bonds
are also efficient and direct versions
among those reactions (Scheme 1, top). However, the need for
strict anhydrous conditions, use of expensive metals, low atom
efficiency or/and hazardous conditions besides poor functional
group tolerance encourage researchers to continue to search
for more practical method for the construction of
organophosphorus compounds.1a,1h,3a Furthermore, drawbacks
associated with quantitative oxidants requirement and strong
coordinating character of phosphorus to metal hampering the
We envisage that the dehydrative coupling of alcohols with
phosphorus based reagents as nucleophiles will be an
attractive method for the construction of carbon-phosphorus
bonds. This is because alcohols are inexpensive and
abundantly available. Furthermore, this reaction is atom-
economical and environmentally benign since water is the only
byproduct (Scheme 1, bottom). Although the dehydrative
coupling with many different nucleophiles (NuH) to deliver C-C
9
10
and C-X (X = N,O,) have been widely studied, the direct
dehydrative cross-coupling between C-OH and P-H species
remains as an unsolved problem,11 probably due to the poor
leaving ability of hydroxyl group and strong coordinating
character of phosphorus to metal.6 Stimulated by Li’s
impressive dehydrative coupling between allylic alcohol and
terminal alkynes for making C-C bond,12 we embarked on the
development of phosphorylation of allylic alcohol as a novel
method for the synthesis of allylic phosphorus compounds,
which are extremely valuable synthetic intermediates in
pharmaceutical chemistry, agrochemicals, chiral phosphine
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a Experimental conditions see General method. b Reactions performed at 60 oC.
and selectivity. The allylic alcohol with tert-butyl ester was
suitable substrate for gram scale reaction (Scheme 3).
Subsequently, we examined the scope of the phosphine oxides
using coupling partner 1a and the results are listed in Table 3.
Typical diarylphosphine oxides with electron-donating and
electron-withdrawing substituents on aryl were well tolerated
OH
CO2R
60 o
neat, 24h
C
affording corresponding 3t-3v in high yield with high
CO2R
Ar
Ar
+
Ph2P(O)H
selectivity. In addition, phosphine oxides with multi-
substituents worked well and 3w can be obtained in moderate
yield which might be attributed to the steric hindrances effect.
Dialkylphosphine oxide was also proved to be the suitable
substrate for transformation (3x).
P(O)Ph2
Ar = Ph
OH
3a: R = Et, 65% yield (8.8g)
3aa: R = Me, 72% yield (10.8g)
CO2But
CO2But
90 o
Ar
C
Ar
Ph2P(O)H
+
Table 3. Substrate scope for phosphine oxidants a
neat
36h
3j
P(O)Ph2
Ar = 4-BrC6H4
73% yield (1.1g)
Ph
Ph
OH
O
P
O
P
Scheme 3. The grams scale reactions and synthetic application of allylic
phosphorus.
neat
90 o
R3
R3
R3
R3
H2O
+
+
H
EtOOC
C
EtOOC
3
2
With attempt to gain further insight into the mechanism
involved, Density functional theory (DFT) calculations were
conducted at a B3LYP/6-31+G(d) level. We proposed the
1
19
transformation might occur through two pathways: direct
dehydrative coupling through a formal concerted process
(Path A) or stepwise process via a Michael addition then
followed by dehydration reaction of alcohol (Path B). We
selected dimethylphosphine oxide
2 as model for the
mechanism study. According to the substantial agreement
among chemists, dimethylphosphine oxide undergoes
dimethylphosphine oxide (
tautomerism. 3,20 The compounds almost existed entirely in the
form of former isomer under neutral conditions, while the
2)–hydroxydimethylphosphine (2’)
2
later version 2’ is reactive and believed to be the actual
nucleophilic species in the bond formation step. 20b
H
O
P
O
P
b
Reactions performed under the standard conditions. DMSO (2.0 mL) as the
solvent.
(1)
H
2'
2
hydroxy-
dimethylphosphine
dimethylphosphine
oxide
It should be noted that these secondary phosphine oxides are
readily available from reactions between diethyl phosphonate
and the corresponding organolithium or Grignard reagents. 17
Theoretically, a variety of phosphorus functionalities have the
potential to be incorporated into allylic framework
As it’s shown in Figure 1, the reaction is triggered by
nucleophilic addition of hydroxydimethylphosphine 2’ to the
active double bond of allylic alcohol. In path A, calculations
indicated that “mutual aid effect” occurred between allylic
conveniently by using this method. For example, the P- alcohol and phosphine oxides. The hydrogen bond between
stereogenic (RP)-(-)-Menthylphosphine oxide18 was successfully
the hydroxyl group of alcohol and hydroxydimethylphosphine
favored the existence of 2’ and accelerated the following
nucleophilic addition with a free energy of activation of 15.7
kcal mol-1
(TS1). At the same time, the C-O bond in alcohol was
introduced into allylic skeleton with high yield and Z/E
selectivity (Scheme 2). The configuration of phosphorus was
stable and maintained (RP/SP > 99/1), no isomerization process
was detected.
greatly activated by hydrogen bond with the generation of
zwitterionic intermediate IM1, which was followed by a
barrier-less process (TS2) to give the desired product with Z
selectivity and H2O. Thus, that was a formal concerted process
and is favourable thermodynamically releasing 23.5 kcal/mol.
Theoretically, the dehydrative coupling might also proceeded
stepwise (path B). Initially, the hydrogen bond between ester
group and hydroxydimethylphosphine 2’ could promote the
nucleophilic addition. The computed activation free energy of
this addition process from starting materials to IM1’ is 16.3
Ph
O
P
Ph
OH
O
P
Ph
neat
Men-(-) 90 o
Ph
H
+
EtO2C
C
Men-(-)
EtO2C
3z, 91%, Z/E > 95/5
(-)-Men = L-(-)-Menthyl
Scheme 2. Incorporating P-stereogenic phosphine oxide into allylic skeleton.
The C-OH/P-H dehydrative cross-coupling reaction also can be
performed well even in 10 grams scales with comparable yield
kcal/mol, which is slightly higher than TS1. IM1 then
isomerized to IM2’. Finally, the rate-determining step from
IM2’ to E-3 occurred with 19.5 kcal/mol computed activation
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1
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free energy. Compared with path B, path A is favoured in
activation free energy. Moreover, Z-selectivity for path A is in
accordance with the result of X-ray analysis (3j)
.
Figure 1. DFT computed energy surface for the dehydrative cross-coupling.
B3LYP/6-31+G(d) level. Path A: (TS1-IM1-TS2); Path B: (TS1’-IM1’-IM2’-TS2’).
H
H
O
O
P
O
H
MeO
O
P
P
Ph
COOMe
O
O
H
[
G298 ]
H298
OH
OMe
IM1
Ph
kcal / mol
HO
TS1'
[16.3]
2.5
Ph
H
H
TS2'
O
2
3
O
P
[19.5]
5.3
Ph
CO2Me
TS2
IM1
TS1
[15.7]
2.2
[10.2]
-3.6
[10.1]
-4.7
O
H
P
(a) D. Zhao, R. Wang, Chem. Soc. Rev., 2012, 41, 2095; (b) Ł.
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Chem., 2011, 696, 130.
IM2'
[0.0]
0.0
OH
[-1.6]
-15.4
[2.2]
-10.5
Ph
1 + 2
IM1'
COOMe
4
5
T. Hirao, T. Masunaga, Y. Ohshiro and T. Agawa, Synthesis,
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H
O
MeO
O
P
[-15.7]
-17.5
O
P
O
OMe
OH
H
(E)-3
OH
IM2'
IM1'
Ph
[-23.5]
-24.8
Ph
(Z)-3
6
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In conclusion, we developed the first C-OH/P-H dehydrative
cross-coupling reaction between MBH alcohol and phosphine
oxides. This is an atom-economical and environmentally
benign approach for P-C bond construction with water as the
only by-product. This reaction proceeded smoothly without
any catalyst and additive in solvent-free manner to deliver the
desired product with wide tolerance. A variety of allylic
phosphorus compounds can be obtained in good to excellent
yields with high Z-selectivity. DFT calculation indicated that the
direct dehydrative coupling through a formal concerted
process. In the key transition state, the intermolecular
hydrogen bond stabilize hydroxydiaryl(alkyl)phosphine,
accelerate nucleophilic addition, and active C-O bond.
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7
8
We greatly acknowledge financial support by the Natural
Science Foundation of Jiangsu Province, China (Grant No.
BK20160977), and the financial support by SCIAM Fellowship
by Jiangsu National Synergetic Innovation Center for Advanced
Material. Prof. Dr. Zhixiang Yu (Peking University) and Prof. Dr.
Qiang Wang (Nanjing Tech University) are kindly
acknowledged for helpful mechanism discussions. Dr. Qinggao
Hou (Beijing Institute of Technologe) is thanked for single
crystal X-ray diffraction analysis. Manuscript revision by Dr.
Maraswami Manikantha (Nanyang Technological University)
and Dr. Zhishuai Geng (Georgia Institute of Technology) are
also gratefully acknowledged.
9
For selected review see: (a) R. Kumar and E. V. Van der
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Notes and references
4 | J. Name., 2012, 00, 1-3
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W. Shurtleff and D. W. C. MacMillan, Nature, 2015, 524, 330;
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11 The first formal C-OH/P-H dehydrative cross-coupling was
developed by Montchamp in 2008. This reaction processed
via the Fischer-like esterification of allylic alcohol with H-
phosphinic acids and followed by
a
Pd-catalyzed
isomerization to give allylic phosphinic acids. L. Coudray, K.
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16 CCDC-1484668
(3j)
contains
the
supplementary
crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac. ac.uk/data_request/cif.
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,
19 All of the DFT calculations were performed with the Gaussian
09 program package. The geometry optimization of all the
minima and transition states involved were performed at the
B3LYP levels of theory with the 6-31+G(d) basis set used. The
vibrational frequencies were computed at the same level of
theory to check whether each optimized structure is an
energy minimum or a transition state and to evaluate its
zero-point vibrational energy (ZPVE). For the DFT
calculations involving the addition of phosphines to active
alkenes see selected example: Y.. Xia, Y. Liang, Y. Chen, M.
Wang, L. Jiao, F. Huang, S. Liu, Y. Li and Z.-X. Yu, J. Am. Chem.
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