Photoinduced hydrophosphinylation of alkenes with diphenylphosphine oxide

Article abstract of DOI:10.1016/j.tetlet.2008.11.079

Photoinduced hydrophosphinylation of alkenes with diphenylphosphine oxide took place regioselectively affording the corresponding phosphine oxide in good yields. This hydrophosphinylation is of simple operation and widely tolerant to a variety of the functionalities.

Full text of DOI:10.1016/j.tetlet.2008.11.079

Tetrahedron Letters 50 (2009) 624–626
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Photoinduced hydrophosphinylation of alkenes with diphenylphosphine oxide
*
Shin-ichi Kawaguchi, Akihiro Nomoto, Motohiro Sonoda, Akiya Ogawa
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Photoinduced hydrophosphinylation of alkenes with diphenylphosphine oxide took place regioselec-
tively affording the corresponding phosphine oxide in good yields. This hydrophosphinylation is of sim-
ple operation and widely tolerant to a variety of the functionalities.
Received 22 September 2008
Revised 11 November 2008
Accepted 17 November 2008
Available online 27 November 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Because of the wide applications of organophosphorus com-
pounds1 in coordination chemistry, agrochemicals, and polymer
science, the development of highly selective and environment-
friendly synthetic methods of phosphorus compounds has been
of current interest. In this Letter, we wish to report a solvent-free,
atom-economical, and highly efficient synthesis of organophos-
phorus compounds by the photoinduced hydrophosphinylation of
alkenes with diphenylphosphine oxide. Thus, for example, the
hydrophosphinylation of 1-octene with Ph2P(O)H can be con-
ducted at room temperature upon irradiating a mixture of 1-octene
and Ph2P(O)H with a xenon lamp through Pyrex (Eq. 1):
When a mixture of 1-octene (1.0 mmol) and diphenylphosphine
oxide (0.2 mmol) in a sealed NMR tube (u = 4 mm, Pyrex) under N2
atmosphere was irradiated with a xenon lamp at room tempera-
ture, a regioselective hydrophosphinylation took place to give
diphenyloctylphosphine oxide (1a) in excellent yield (Table 1, en-
try 1).11 This reaction also proceeded efficiently in a larger scale
(entry 2). The hydrophosphinylation did not take place without
photoirradiation (entry 3). When the hydrophosphinylation reac-
tions were performed using various olefins bearing chloro, cyano,
hydroxyl, phenyl, phenoxy, or amino groups, the corresponding
products 1b–g were obtained in good to excellent yields without
affecting these functional groups (entries 4–9). Moreover, internal
alkenes were also found to be good substrates for the reaction (en-
tries 10 and 11). 3,4-Dihydro-2H-pyrane reacted with diphenyl-
phosphine oxide regioselectively affording the corresponding
hydrophosphinylation product 1i. The hydrophosphinylation also
took place successfully even with a bulky vinyltrimethylsilane (en-
try 12).
A similar hydrophosphinylation, however, proceeded slowly in
solvents such as THF, benzene, chloroform, and ethanol, affording
the adducts in low yields. Interestingly, we found that the addition
of pyridine to the mixture can accelerate the reaction (Table 2).
Thus, when a mixture of 1-octene (0.1 mmol), diphenyphosphine
oxide (0.3 mmol), and pyridine (0.3 mmol) in chloroform-d
(0.6 mL) was irradiated, 1a was obtained in 91% yield (entry 1).
Noted that the yield of 1f and 1j from allyl phenyl ether and
vinylsilane, respectively, were dramatically improved compared
to those in the absence of pyridine (entries 2 and 4).
O
PPh2
ν
h
(> 300 nm)
R
Ph2P(O)H
0.2 mmol
ð1Þ
+
R
r.t., neat
1
1.0 mmol
The addition of P(X)–H bonds (X = lone pair, O, or S) to carbon–
carbon unsaturated bonds is one of the most straightforward
methods for the synthesis of organophosphorus compounds. This
hydrophosphinylation is known as ‘Pudovik reaction’.2 The Pudo-
vik reaction can proceed via a radical and/or ionic mechanism. In
the cases of carbon–carbon unsaturated compounds activated by
an electron-withdrawing group, the reaction proceeds via ionic
mechanism.3 When inactive olefins and organophosphorus com-
pounds such as R2P(O)–H are employed, this addition prefers a rad-
ical pathway.2b Recently, the hydrophosphinylations of alkenes
with R2P(O)–H using radical initiator4–6 or microwave7 were re-
ported. Photoirradiation8,9 is thought to be one of the simplest
methods; however, such a photoinduced hydrophosphinylation
of alkenes with diphenylphosphine oxide has not been investi-
gated in detail.10,5b
To clarify the reaction mechanism, a mixture of 1,6-heptadiene
and diphenylphosphine oxide was irradiated under solvent-free
condition (condition A) or in CDCl3 in the presence of pyridine as
an additive (condition B) (Scheme 1). Under both conditions, the
reaction proceeded via cyclization, affording the five-membered
ring compound5a in good yields. These result indicates that this
hydrophosphinylation in the presence or absence of pyridine pro-
ceeds via a radical mechanism.
* Corresponding author. Tel./fax: +81 72 254 9290.
E-mail address: ogawa@chem.osakafu-u.ac.jp (A. Ogawa).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.11.079

S.-i. Kawaguchi et al. / Tetrahedron Letters 50 (2009) 624–626
625
Table 1
Photoinduced hydrophosphinylation of alkenes with Ph2P(O)H
O
PPh2
h
ν
R
+
Ph2P(O)H
0.2 mmol
R
r.t., no solvent
1.0 mmol
1
Entry
Alkene
Time (h)
Product
Yielda (%)
O
nC6H13
1
18
18
18
1a12
99
93
0
PPh2
nC6H13
2b
3c
O
4
16
1b13
1c14
99
Cl
PPh2
Cl
O
NC
5
15
96
NC
PPh2
O
6
18
1d15
92
HO
PPh2
HO
O
7
8
16
18
1e16
1f17
90
70
Ph
PPh2
Ph
O
PhO
PhO
PPh2
O
H2N
9
16
16
1g18
57 (81)
(71)
H2N
PPh2
O
PPh2
10
1h19
O
PPh2
O
11
45
27
1i20
99
O
O
12
1j21
48 (58)
TMS
PPh2
TMS
a
Isolated yield (1H NMR yield).
Reactions were performed using alkene 7.0 mmol, Ph2P(O)H 1.4 mmol.
Without photoirradiation.
b
c
Table 2
O
Photoinduced hydrophosphinylation of alkenes with Ph2P(O)H in the presence of
pyridine
PPh2
h
ν
Ph2P(O)H
+
O
PPh2
ν
h
condition A or B
R
Ph2P(O)H
0.3 mmol
+
R
r.t., CDCl3
A: cis
B: cis
:
:
trans = 4.6:1 83%
trans = 6.4:1 86%
1
pyridine 0.3 mmol
0.1 mmol
Scheme 1. Condition A: 1,6-heptadiene (0.1 mmol), Ph2P(O)H (0.2 mmol), C6D6
(0.6 mL); B: 1,6-heptadiene (0.1 mmol), Ph2P(O)H (0.3 mmol), pyridine (0.3 mmol),
CDCl3 (0.6 mL).
Entry
1
Alkene
Time (h)
Product
Yielda (%)
91
O
nC6H13
18
18
1a
PPh2
nC6H13
PhO
A possible pathway for this hydrophosphinylation is shown in
Scheme 2. Upon photoirradiation, diphenylphosphine oxide gener-
ates a phosphinoyl radical. A phosphinoyl radical selectively attacks
theterminal carbonof an alkene, affordingthe corresponding radical
intermediate (A). This intermediate (A) abstracts a hydrogen of
diphenylphosphine oxide, affording the hydrophosphinylation
product with generation of another phosphinoyl radical.
In summary, we have developed a photoinduced hydrophosph-
inylation of alkenes with diphenylphosphine oxide, which is
widely tolerant to a variety of functionalities, giving high yields
of the corresponding adducts regioselectively.
O
PhO
2
3
1f
93
PPh2
O
PPh2
35
12
1h
1j
(66)
(74)
O
4
TMS
PPh2
TMS
a
Isolated yield (1H NMR yield).

626
S.-i. Kawaguchi et al. / Tetrahedron Letters 50 (2009) 624–626
548, 511 cmꢀ1
;
1H NMR (CDCl3) d 0.85 (t, J = 6.9 Hz, 3H), 1.12–1.44 (m, 10H)
h
ν
O
1.54–1.68 (m, 2H) 2.19–2.30 (m, 2H), 7.40–7.54 (m, 6H), 7.70–7.85 (m, 4H); 13C
NMR (CDCl3) d 14.0, 21.4, 21.6, 22.6, 29.0, 29.7 (d, JC–P = 71.7 Hz), 30.9 (d,
JC–P = 15.1 Hz), 31.7, 128.6 (d, JC–P = 11.3 Hz), 130.8 (d, JC–P = 9.0 Hz), 131.6,
133.2 (d, JC–P = 96.6 Hz); 31P NMR (CDCl3) d 33.2; HRMS (EI) calcd for C20H27OP:
314.1800, found: 314.1804; Anal. Calcd for C20H27OP: C, 76.40; H, 8.66. Found:
C, 76.48; H, 8.58.
Ph2P(O)H
+
PPh2
R
R
Ph2P
O
h
ν
13. For the spectral and analytical data of (6-chlorohexyl)diphenylphosphine oxide
(1b): colorless oil; IR (NaCl) 3418, 3055, 2933, 2862, 1636, 1591, 1485, 1437,
Ph2P(O)H
R
1309, 1180, 1121, 1072, 1028, 997, 945, 748, 721, 696, 648, 550, 515 cmꢀ1 1H
;
NMR (CDCl3) d 1.41–1.72 (m, 8H), 2.23–2.29 (m, 2H) 3.48 (t, J = 6.4 Hz, 2H),
7.45–7.53 (m, 6H), 7.71–7.75 (m, 4H); 13C NMR (CDCl3) d 21.2, 26.2, 29.6 (d,
JC–P = 98.4 Hz), 29.9 (d, JC–P = 13.0 Hz), 32.1, 44.8, 128.6 (d, JC–P = 11.0 Hz), 130.6
(d, JC–P = 8.0 Hz), 131.6, 132.9 (d, JC–P = 98.4 Hz); 31P NMR (CDCl3) d 33.0; HRMS
(EI) calcd for C18H22ClOP: 320.1097, found: 320.1095.
h
ν
R
O
Ph2P
O
Ph2POH
PPh2
(A)
14. For the spectral and analytical data of (5-cyanopentyl)diphenylphosphine
oxide (1c): pale yellow oil; IR (NaCl) 3418, 3057, 2934, 2868, 2245, 1734, 1645,
1437, 1177, 1121, 1072, 1028, 997, 748, 721, 698, 544, 513 cmꢀ1 1H NMR
;
Scheme 2. A possible pathway of photoinduced hydrophosphinylation.
(CDCl3) d 1.51–1.67 (m, 6H), 2.21–2.32 (m, 4H), 7.44–7.60 (m, 6H), 7.66–7.81
(m, 4H); 13C NMR (CDCl3) d 16.7, 20.7, 24.8, 29.2 (d, JC–P = 66.3 Hz), 29.7 (d,
JC–P = 10.0 Hz), 119.3, 128.6 (d, JC–P = 11.0 Hz), 130.6 (d, JC–P = 8.0 Hz), 131.7,
Acknowledgments
132.7 (d, JC–P = 97.4 Hz); 31P NMR (CDCl3)
d 32.7; HRMS (EI) calcd for
C18H20NOP: 297.1283, found: 297.1284.
15. For the spectral and analytical data of diphenyl-(6-hydroxyhexyl)phosphine
This work is supported by Grant-in-Aid for Scientific Research
on Priority Areas (Area 444, No. 19020061) and Scientific Research
(B, 19350095), from the Ministry of Education, Culture, Sports, Sci-
ence and Technology, Japan.
oxide (1d): colorless oil; IR (NaCl) 3366, 3057, 2930, 2858, 1437, 1173, 1121,
1057, 1028, 997, 748, 721, 696, 548, 511 cmꢀ1 1H NMR (CDCl3) d 1.31–1.65 (m,
;
8H), 2.25 (dt, J = 11.0, 8.2 Hz, 2H) 3.07 (s, 1H) 3.54–3.58 (m, 2H), 7.43–7.52 (m,
6H), 7.70–7.78 (m, 4H); 13C NMR (CDCl3) d 21.3, 25.1, 29.4 (d, JC–P = 72.3 Hz),
30.4 (d, JC–P = 15.1 Hz), 32.3, 62.2, 128.5 (d, JC–P = 11.0 Hz), 130.6 (d,
JC–P = 8.0 Hz), 131.6, 132.9 (d, JC–P = 97.4 Hz); 31P NMR (CDCl3) d 33.8; HRMS
(EI) calcd for [M+H+] C18H24O2P: 303.1514, found: 303.1512.
References and notes
16. For the spectral and analytical data of diphenyl-(4-phenylbutyl)phosphine
oxide (1e): pale yellow oil; IR (NaCl) 3413, 3026, 2934, 2860, 1489, 1456, 1435,
1. (a) Quin, L. D. A Guide to Organophosphorus Chemistry; Wiley-Interscience: New
York, 2000; (b) Kolodiazhnyi, O. I. Phosphorus Ylides; Wiley-VCH: Weinheim,
1999.
2. (a) Pudovik, A. N.; Konovalova, I. V. Synthesis 1979, 81; (b) Semenzin, D.;
Etemad-Moghadam, G.; Albouy, D.; Diallo, O.; Koenig, M. J. Org. Chem. 1997, 62,
2414.
3. (a) Bell, A.; Davidson, A. H.; Earnshaw, C.; Norrish, H. K.; Torr, R. S.; Trowbridge,
D. B.; Warren, S. J. Chem. Soc., Perkin Trans. 1 1983, 2879; (b) Khachatryan, R. A.;
Sayadyan, S. V.; Grigoryan, N. Y. J. Gen. Chem. USSR (Engl. Transl.), 1989, 58,
2197; (c) Hall, C. D.; Lowther, N.; Tweedy, B. R. J.; Hall, A. C.; Shaw, G. J. Chem.
1184, 1121, 1028, 997, 932, 744, 696, 517 cmꢀ1 1H NMR (CDCl3) d 1.67–1.77
;
(m, 4H), 2.24–2.32 (m, 2H), 2.59 (t, J = 7.6 Hz, 2H), 7.10–7.26 (m, 5H), 7.44–7.50
(m, 6H), 7.69–7.74 (m, 4H); 13C NMR (CDCl3) d 21.3, 29.7 (d, JC–P = 71.0 Hz),
32.8 (d, JC–P = 14.4 Hz), 35.5, 128.4, 128.7 (d, JC–P = 11.5 Hz), 128.8, 130.8, 130.9
(d, JC–P = 8.6 Hz), 132.3 (d, JC–P = 122.8 Hz), 133.7, 142.0; 31P NMR (CDCl3) d
33.1; HRMS (EI) calcd for C22H23OP: 334.1487, found: 334.1489.
17. For the spectral and analytical data of diphenyl-(3-phenoxypropyl)phosphine
oxide (1f): colorless oil; IR (NaCl) 3420, 3057, 2932, 1585, 1497, 1437, 1389,
1290, 1244, 1182, 1121, 997, 908, 808, 754, 719, 694, 544, 513 cmꢀ1 1H NMR
;
Soc., Perkin Trans.
2
1998, 2047; (d) Bunlaksananusorn, T.; Knochel, P.
(CDCl3) d 2.05–2.15 (m, 2H), 2.41–2.51 (m, 2H), 4.00 (t, J = 6.0 Hz, 2H), 6.81–
Tetrahedron Lett. 2002, 43, 5817.
6.88 (m, 2H), 6.90–6.95 (m, 1H), 7.21–7.28 (m, 2H) 7.40–7.55 (m, 6H), 7.71–
4. For the radical initiated hydrophosphinylation of alkene, see: (a) Rey, P.;
Taillades, J.; Rossi, J. C.; Gros, G. Tetrahedron Lett. 2003, 44, 6169; (b) Han, L.-B.;
Zhao, C.-Q. J. Org. Chem. 2005, 70, 10121; (c) Jessop, C. M.; Parsons, A. F.;
Routledge, A.; Irvine, D. J. Eur. J. Org. Chem. 2006, 1547; (d) Hirai, T.; Han, L.-B.
Org. Lett. 2007, 9, 53.
7.79 (m, 4H); 13C NMR (CDCl3) d 21.8, 26.4 (d, JC–P = 72.7 Hz), 67.4 (d, JC–P
=
14.1 Hz), 114.4, 120.8, 128.7 (d, JC–P = 11.5 Hz), 129.4, 130.7 (d, JC–P = 9.5 Hz),
131.8, 132.8 (d, JC–P = 98.7 Hz), 158.6; 31P NMR (CDCl3) d 33.4; HRMS (EI) calcd
for C21H21O2P: 336.1279, found: 336.1275; Anal. Calcd for C21H21O2P: C, 74.99;
H, 6.29. Found: C, 74.13; H, 6.10.
5. For the addition reaction involving phosphorous centered radical, see: (a)
Jessop, C. M.; Parsons, A. F.; Routledge, A.; Irvine, D. Tetrahedron Lett. 2003, 44,
479; (b) Tayama, O.; Nakano, A.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. J. Org.
Chem. 2004, 69, 5494; (c) Carta, P.; Puljic, N.; Robert, C.; Dhimane, A.-L.;
Fensterbank, L.; Lacôte, E.; Malacria, M. Org. Lett. 2007, 9, 1061.
6. For reviews concerning phosphorous centered radicals, see, for example: (a)
Leca, D.; Fensterbank, L.; Lacôte, E.; Malacria, M. Chem. Soc. Rev. 2005, 34, 858;
(b) Marque, S.; Tordo, P. Top. Curr. Chem. 2005, 250, 43.
18. For the spectral and analytical data of (3-aminopropyl)diphenylphosphine
oxide (1g): yellow oil; IR (NaCl) 3389, 2359, 2340, 1437, 1317, 1159, 1123, 719,
696, 667, 548 cmꢀ1 1H NMR (CDCl3) d 1.72–1.79 (m, 2H), 2.00 (br s, 2H), 2.30–
;
2.37 (m, 2H), 2.77 (t, J = 6.5 Hz, 2H), 7.40–7.55 (m, 6H), 7.72–7.79 (m, 4H); 13C
NMR (CDCl3) d 25.1, 27.0 (d, JC–P = 72.3 Hz), 42.6 (d, JC–P = 15.1 Hz), 128.6 (d,
JC–P = 11.0 Hz), 130.7 (d, JC–P = 10.0 Hz), 131.7, 132.8 (d, JC–P = 97.4 Hz); 31P
NMR (CDCl3) d 33.4; HRMS (EI) calcd for [M+H+] C15H18NOP: 260.1204, found:
260.1209.
7. Stockland, R. A., Jr.; Taylor, R. I.; Thompson, L. E.; Patel, P. B. Org. Lett. 2005, 7,
851.
8. For the photoinduced bisphosphination and thiophosphination of alkyne, see:
(a) Kawaguchi, S.-i.; Nagata, S.; Shirai, T.; Tsuchii, K.; Nomoto, A.; Ogawa, A.
Tetrahedron Lett. 2006, 47, 3919; (b) Shirai, T.; Kawaguchi, S.-i.; Nomoto, A.;
Ogawa, A. Tetrahedron Lett. 2008, 49, 4043.
9. For the photoinduced addition of R2PH to carbon–carbon unsaturated bond,
see: (a) Stiles, A. R.; Rust, F. F.; Vaughan, W. E. J. Am. Chem. Soc. 1952, 74, 3282;
(b) Mitchell, T. N.; Heesche, K. J. Organomet. Chem. 1991, 409, 163; (c) Mitchell,
T. N.; Heesche-Wagner, K. J. Organomet. Chem. 1992, 436, 43; (d) Ellis, D.;
Farrugia, L. J.; Hickman, D. T.; Lovatt, P. A.; Peacock, R. D. J. Chem. Soc., Chem.
Commun. 1996, 1817.
19. For the spectral and analytical data of cyclohexyldiphenylphosphine oxide
(1h): white solid; mp 146–148 °C; IR (KBr) 2930, 2853, 2363, 1437, 1178, 1119,
721, 693, 559, 543 cmꢀ1 1H NMR (CDCl3) d 1.20–1.81 (m, 10H), 2.19–2.28 (m,
;
1H), 7.28–7.50 (m, 6H), 7.73–7.85 (m, 4H); 13C NMR (CDCl3) d 24.7, 25.7, 26.3
(d, JC–P = 13.1 Hz), 37.1 (d, JC–P = 73.3 Hz), 128.5 (d, JC–P = 10.0 Hz), 131.0 (d,
JC–P = 10.0 Hz), 131.4, 131.9 (d, JC–P = 102.4 Hz); 31P NMR (CDCl3) d 35.0; HRMS
(EI) calcd for C18H21OP: 284.1330, found: 284.1331.
20. For the spectral and analytical data of diphenyl(tetrahydropyran-3-
yl)phosphine oxide (1i): white solid; mp 148–151 °C; IR (KBr) 3053, 2947,
2845, 1439, 1178, 1119, 1097, 1074, 1028, 995, 951, 904, 883, 856, 839, 752,
721, 700, 569, 534 cmꢀ1 1H NMR (CDCl3) d 1.64–1.97 (m, 4H), 2.59–2.66 (m,
;
1H), 3.39 (td, J = 11.5, 3.7 Hz, 1H), 3.67 (td, J = 11.5, 2.7 Hz, 1H), 3.91–3.95 (m,
2H), 7.48–7.56 (m, 6H), 7.75–7.86 (m, 4H); 13C NMR (CDCl3) d 21.8, 25.8 (d,
JC–P = 10.6 Hz), 36.6 (d, JC–P = 71.0 Hz), 66.9, 68.1, 128.8 (d, JC–P = 8.6 Hz), 126.9
(d, JC–P = 10.6 Hz), 130.9 (d, JC–P = 7.7 Hz), 130.9 (d, JC–P = 7.7 Hz), 131.7, 131.8,
131.9, 132.0; 31P NMR (CDCl3) d 30.9; HRMS (EI) calcd for C17H19O2P: 286.1123,
found: 286.1127.
10. For
the
transition
metal-catalyzed
hydrophosphinylation
and
hydrophosphination of alkene, see: (a) Shulyupin, M. O.; Kazankova, M. A.;
Beletskaya, I. P. Org. Lett. 2002, 4, 761; (b) Allen, A., Jr.; Ma, L.; Lin, W.
Tetrahedron Lett. 2002, 43, 3707; (c) Takaki, K.; Koshoji, G.; Komeyama, K.;
Takeda, M.; Shishido, T.; Kitani, A.; Takehira, K. J. Org. Chem. 2003, 68, 6554; (d)
Dobashi, N.; Fuse, K.; Hoshino, T.; Kanada, J.; Kashiwabara, T.; Kobata, C.; Nune,
S. K.; Tanaka, M. Tetrahedron Lett. 2007, 48, 4669.
21. For the spectral and analytical data of diphenyl-[2-(trimethylsilyl)ethyl]-
phosphine oxide (1j): colorless oil; IR (NaCl) 3433, 3055, 2951, 2897, 1437,
11. When tBu2P(O)H was also employed as
a
dialkylphosphine oxide, the
1412, 1250, 1184, 1155, 1121, 841, 721, 698, 532, 511 cmꢀ1 1H NMR (CDCl3) d
;
corresponding hydrophosphinylation product was obtained in 37% yield by
0.00 (s, 9H), 0.72–0.75 (m, 2H), 2.14–2.16 (m, 2H), 7.45–7.55 (m, 6H), 7.68–
the irradiation through quartz tube with high pressure mercury lamp (h
m
7.73 (m, 4H); 13C NMR (CDCl3)
d
ꢀ2.1, 6.9 (d, JC–P = 7.7 Hz), 23.9 (d,
>200 nm).
JC–P = 70.1 Hz), 128.7 (d, JC–P = 11.5 Hz), 131.0 (d, JC–P = 9.6 Hz), 131.7, 132.8
(d, JC–P = 97.4 Hz); 31P NMR (CDCl3) d 35.0; HRMS (EI) calcd for C22H23OP:
334.1487, found: 334.1489.
12. For the spectral and analytical data of diphenyloctylphosphine oxide (1a):
white solid; mp 48–50 °C; IR (KBr) 2928, 2855, 1437, 1182, 1121, 718, 694,