Preparation of tetraoxadiphosphadibo-rocane-2,6-diones

Article abstract of DOI:10.1080/00397911.2010.535238

Cyclization of aryl/alkyl phosphonic dichlorides (2a-f) with phenylboronic acid/K₂CO₃/I₂ in dry toluene at 60-70° C afforded 2,6-diaryl/alkyl-4,8-diphenyl-1,3,5,7,2λ⁵, 6λ⁵,4,8-tetraoxadiphosphadiborocane-2,6-diones (3a-f). Taylor & Francis Group, LLC.

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Preparation of
Tetraoxadiphosphadiborocane-2,6-diones
K. R. Kishore Kumar Reddy a , M. Veera Narayana Reddy a , K. Reddi
Mohan Naidu a , G. Chandra Sekhar Reddy a & C. Suresh Reddy a
a Department of Chemistry , Sri Venkateswara University , Tirupati ,
India
Accepted author version posted online: 06 Sep 2011.Published
online: 16 Dec 2011.
To cite this article: K. R. Kishore Kumar Reddy , M. Veera Narayana Reddy , K. Reddi Mohan Naidu ,
G. Chandra Sekhar Reddy & C. Suresh Reddy (2012) Preparation of Tetraoxadiphosphadiborocane-2,6-
diones, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 42:7, 1026-1032, DOI: 10.1080/00397911.2010.535238
To link to this article: http://dx.doi.org/10.1080/00397911.2010.535238
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Synthetic Communications1, 42: 1026–1032, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.535238
PREPARATION OF TETRAOXADIPHOSPHADIBO-
ROCANE-2,6-DIONES
K. R. Kishore Kumar Reddy, M. Veera Narayana Reddy,
K. Reddi Mohan Naidu, G. Chandra Sekhar Reddy, and
C. Suresh Reddy
Department of Chemistry, Sri Venkateswara University, Tirupati, India
GRAPHICAL ABSTRACT
Abstract Cyclization of aryl/alkyl phosphonic dichlorides (2a–f) with phenylboronic
acid=K2CO3=I2 in dry toluene at 60–70 ꢀC afforded 2,6-diaryl=alkyl-4,8-diphenyl-1,3,5,7,
2k5,6k5,4,8-tetraoxadiphosphadiborocane-2,6-diones (3a–f).
Keywords Akyl=aryl phosphorous dichlorides; phenylboronic acid; 1-phenylboryl
(1-phenylboryl)phenylphosphinate; tetraoxadiphosphadiborocane-2,6-diones
INTRODUCTION
Phosphorus-containing macrocycles are interesting molecules with potential
application in supramolecular and synthetic organic chemistry.[1–3] Past and present
research has led to the construction of phosphorane macrocycles with large preorga-
nized macrocyclic cavities bearing concave functionalities.[4–6] Being phosphorus
analogs of crown ethers with potential catalytic activity and ion-carrying ability,[7–11]
they have become important molecules in the field of host–guest complexation.[12,13]
Similarly, interest in the synthesis and characterization of organoboron
macrocycles is evident from applications as anticancer agents and in boron neutron
capture therapy (BNCT).[14] They also have a wide range of other uses as
fluorescent,[15] electro- and nonlinear optical materials,[16,17] and as reagents in
organic synthesis.[18,19] Recently, several dimeric boron complexes found application
in host–guest chemistry.[20,21]
Received August 17, 2010.
Address correspondence to C. Suresh Reddy, Department of Chemistry, Sri Venkateswara
University, Tirupati 517 502, India. E-mail: csrsvu@gmail.com
1026

TETRAOXADIPHOSPHADIBOROCANE-2,6-DIONES
1027
Scheme 1. Synthesis of tetraoxadiphosphadiborocane-2,6-diones (3a–j).
Macrocycles were prepared by reacting dithiols with 1,4-dibromobutane in the
presence of K2CO3 at room temperature.[22] Direct addition of dichlorophenylpho-
sphine to tetraethylene glycol bis(2-lithiophenyl) ether or its reaction with the diso-
dium salt of ethylene glycol ditosylates[3] led to the monophospha-crown ethers.
New spiro and ansa phosphazene derivatives were formed by the reaction of
sodium [2,2-methylenebis (4-chlorophenoxide)] and hexachlorocyclotriphospha-
zene.[23] No report exists on phosphorus–boron macrocycles with a C–B–O–P–C
bond system, which may have several interesting applications. The eight-membered
tetraoxadiphosphoadiborocane ring system in 3a–f with two phosphoryl oxygens,
being rich in electron density, can serve as a trap for heavy-metal cations, catalyst
for electrophilic substituents, and molecular capsule for drugs. In this context,
several of them (3a–f) have been synthesized by simple cyclization of aryl=alkyl
phosphonic dichlorides (2a–f) with phenylboronic acid=K2CO3=I2 in dry toluene
at 60–70 ꢀC (Scheme 1).
RESULTS AND DISCUSSION
Phenylboronic acid (1) reaction with K2CO3 converts it into its potassium salt. O-
Phosphorylation of potassium salt of phenylboronate with phosphonic dichlorides 2a–f
at 60–70 ꢀC in toluene in the presence of stoichiometric amount of I2 led to formation of
macrocycles 3a–f with P–O–B–O bond system. The Lewis acidic nature of boronic acid
=
helps to close the molecules by formation of a coordinate bond from the P O lone pair
electron to boron. Iodine was found to be essential for phosphorylation of PhB(OK)2
at a faster rate and for completion of the reaction to form the products 3a–f in relatively
pure state in moderate yield. Iodine, by virtue of its affinity to potassium and chlorine
atoms, weakens O–K and P–Cl bonds and facilitates nucleophlic attack of oxygen
atoms on phosphorus with the formation of the macrocyclic ring (Scheme 1).
During the reaction of dichlorophenyl phosphine (4) with trivalent phosphorus
with dipotassium salt of phenylboronic acid, we observed formation of acylic
1-phenylboryl (1-phenylboryl) phenylphosphinate (6), through the intermediate phe-
nylphosphaboronic acid (5) rather then the expected cyclic product (7). Formation of

1028
K. R. KISHORE KUMAR REDDY ET AL.
Scheme 2. Conformation test for the formation of acylic 1-phenylboryl (1-phenylboryl) phenyl-
phosphinate.
6 was further confirmed by its esterfication with ethanol and MgSO4 in dry toluene
at 40–45 ꢀC and isolation of the corresponding 1-ethoxy-1-phenylboryl (1-ethoxy-1-
phenylboryl)phenylphosphinate (8) (Scheme 2).
In the conversion of 4 to 6 through the intermediate 5, the trivalent phosphorus
=
of the P–O–B bonds is rearranged to pentavalent phosphorus as O P–B bond system.
Phenyl boronic acids, when reacted with same dichloride in the presence of
NaH and I2 in toluene at reflux temperature, gave poor product yields with long
reaction time. When carried out without catalyst in dry toluene, the expected
products were not formed.
The obtained crude products (3a–f) were purified by dissolving the crude pro-
duct mixture of sodium salt of phenylboronic acid and liquid phosphoric dichloride
in water and keeping it for 30 min, followed by extraction with diethyl ether. Evap-
oration of ether afforded pure products. They were fully characterized by elemental
1
analysis; infrared (IR), H, 11B, 13C, and 31P–NMR, and mass spectral data.
A multiplet in the region d 8.30–6.84 for aromatic protons and a broad singlet at
d 3.16–2.29 for phosphorus-linked aliphatic group protons is observed in the 1H NMR.
The presence of 31P and 11B NMR chemical shifts at d 4.13–9.52[24] and d 18.12–
24.35[25] respectively is in good agreement with the proposed structures for 3a–f.
EXPERIMENTAL
2,6-Diaryl/alkyl-4,8-diphenyl-1,3,5,7,2k5,6k5,4,8-tetraoxa-
diphosphadi-borocane-2,6-dione[24](3a–f)
A solution of aryl=alkyl phosphonic dichloride (4 mmol) in 10 mL of dry tolu-
ene was added dropwise to a stirred solution of dipotassium salt of phenylboronic
acid (4 mmol) in 40 mL of dry toluene at 0 ꢀC for 20 min. A stoichiometric amount
of iodine[26,27] was added to the mixture, and its temperature was increased to

TETRAOXADIPHOSPHADIBOROCANE-2,6-DIONES
1029
60–70 ꢀC with stirring for 40–50 h. When thin-layer chromatographic (TLC) analysis
indicated completion of the reaction, the reaction mixture was filtered. The filtrate
was concentrated under reduced pressure, washed with water, and extracted
with diethyl ether (3 ꢁ 20 mL). The combined organic layer was concentrated in vac-
uum, and the residue was washed with hexane repeatedly to remove any residual
impurities and recrystallized from diethyl ether to yield pure 2,6-diaryl=alkyl-4,8-
diphenyl-1,3,5,7,2k5,6k5,4,8-tetraoxadiphosphadiborocane-2,6-diones (3a–f).
2,6-Dimethyl-4,8-diphenyl-1,3,5,7,2k5,6k5,4,8-tetraoxadiphosphadi-
borocane-2,6-dione (3a). Molecular formula (MF): C14H16B2O6P2; yield: 49%;
mp: 159–161 ꢀC. Anal. calcd. (%): C, 46.22; H, 4.43. Found: C, 46.15; H, 4.35, IR
(KBr) (nmax cmꢂ1): 1217 (P O), 1094 (P-O); 31P NMR (121 MHz, CDCl3): d 4.13;
=
11B-NMR (64 MHz, CDCl3): d 22.82; H-NMR (400 MHz, CDCl3): d 7.62–7.16
1
(10H, m, Ar-H), 2.29–2.20 (6H, br, P-CH); 13C NMR (75 MHz, CDCl3): d 135.63,
132.68, 127.98, 23.08; LCMS: m=z (%): 362 (29), [M ꢂ Hþ], 360 (47), 314 (32), 270
(44), 226 (100), 156 (17), 112 (88).
2,6-Diethyl-4,8-diphenyl-1,3,5,7,2k5,6k5,4,8-tetraoxadiphospha-
diborocane-2,6-dione (3b). MF: C16H20B2O6P2; yield: 63%; mp: 228–230 ꢀC.
Anal. calcd. (%): C, 49.04; H, 5.14. Found: C, 48.99; H, 5.12, IR (KBr) (nmax cmꢂ1):
1222 (P O), 1027 (P-O); 31P NMR (121 MHz, CDCl3): d 6.87; 11B NMR (64 MHz,
=
1
CDCl3): d 22.78; H NMR (400 MHz, CDCl3): d 7.75–7.17 (10H, m, Ar-H), 2.97
(4H, br, P-CH), 1.07 (6H, br, P-CH-CH); 13C NMR (75 MHz, CDCl3): d 135.52,
128.02, 127.95, 40.02, 22.16; LCMS: m=z (%): 391 (23) [Mþ], 390 [M ꢂ Hþ] (47), 344
(53), 298 (50), 265 (59), 229 (100), 183 (61), 160 (51).
4,8-Diphenyl-2,6-dipropyl-1,3,5,7,2k5,6k5,4,8-tetraoxadiphosphadi-
borocane-2,6-dione (3c). MF: C18H24B2O6P2; yield: 71%; mp: 241–243 ꢀC. Anal.
calcd. (%): C, 51.48; H, 5.76. Found: C, 51.43; H, 5.81, IR (KBr) (nmax cmꢂ1): 1218
(P O), 1098 (P-O); 31P NMR (121 MHz, DMSO-d6): d 9.52; 11B NMR (64 MHz,
=
DMSO-d6): d 22.89; 1H NMR (400 MHz, DMSO-d6): d 7.65, 7.36 (10H, brs,
Ar-H), 3.16 (4H, br, P-CH), 1.35 (4H, br, P-C-CH), 0.93 (6H, br, P-C-C-CH); 13C
NMR (75 MHz, DMSO-d6): 129.88 (C-2, C-6), 129.18 (C-3, C-5), 128.18 (C-4),
49.30 (C-10), 20.55 (C-20), 14.18 (C-30); LCMS: m=z (%): 419 (47) [Mþ], 396 (25),
354 (15), 295 (57), 242 (100), 219 (15).
2,4,6,8-Tetraphenyl-1,3,5,7,2k5,6k5,4,8-tetraoxadiphosphadiboro-cane-
2,6-dione (3d). MF: C24H20B2O6P2; yield: 59%; mp: 190–192 ꢀC. Anal. calcd. (%):
C, 59.07; H, 4.13. Found: C, 59.12; H, 4.21, IR (KBr) (nmax cmꢂ1): 1216 (P O), 1092
=
(P-O); 31P NMR (121 MHz, DMSO-d6): d 4.91; 11B NMR (64 MHz, DMSO-d6): d
1
24.95; H NMR (400 MHz, DMSO-d6): d 7.65–6.84 (20H, br, Ar-H); 13C NMR
(75 MHz, CDCl3): d 137.73, 134.88, 130.48, 130.26, 124.82, 122.75; LCMS: m=z
(%): 487 (89) [Mþ], 473 (76), 441 (64), 419 (68), 396 (62), 373 (100).
2,6-Di(2-chlorophenyl)-4,8-diphenyl-1,3,5,7,2k5,6k5,4,8-tetraoxadiphos-
phadi-borocane-2,6-dione (3e). MF: C24H18B2Cl2O6P2; yield: 64%; mp:
218–220 ꢀC. Anal. calcd. (%): C, 51.76; H, 3.26. Found: C, 51.72; H, 3.31, IR
(KBr) (nmax cmꢂ1): 1216 (P O), 1097 (P-O); 31P NMR (121 MHz, CDCl3): d 6.63;
=
11B NMR (64 MHz, CDCl3): d 23.01; H NMR (400 MHz, CDCl3): d 8.04–7.30
1

1030
K. R. KISHORE KUMAR REDDY ET AL.
13
(18H, m, Ar-H); C NMR (75 MHz, CDCl3): 127.9 (C-3 and C-5), 131.0 (C-40),
132.5 (C-2 and C-6), 133.5 (C-20 and C-60), 134.7(C-4), 135.5 (C-30 and C-50); LCMS:
m=z (%): 557 (87) [M þ Hþ], 488 (74), 443 (69), 420 (81), 374 (45), 338 (84), 296 (56),
273 (62), 181 (59), 135 (58), 112 (100).
2,6-Di(4-nitrophenyl)-4,8-diphenyl-1,3,5,7,2k5,6k5,4,8-tetraoxadiphos-
phadi-borocane-2,6-dione (3f). MF: C24H18B2N2O10P2; yield: 53%; mp:
255–256 ꢀC. Anal. calcd. (%): C, 49.87; H, 3.14. Found: C, 49.84; H, 3.21, IR
(KBr) (nmax cmꢂ1): 1225 (P O), 1091 (P-O); 31P NMR (121 MHz, CDCl3): d 6.85;
=
11B NMR (64 MHz, CDCl3): d 28.24; H NMR (400 MHz, CDCl3): d 8.30–7.22
1
(18H, m, Ar-H); 13C NMR (75 MHz, CDCl3): d 152.92, 143.39, 142.40, 140.54,
139.88, 136.39, 125.78, 123.84; LCMS: m=z (%): 599 (38) [MHþ þ 23], 569 (42),
558 (63), 476 (77), 429 (64), 384 (51), 307 (100).
1-Ethoxy-1-phenylboryl(1-ethoxy-1-phenylboryl)phenyl-
phosphinate[24] (3)
A solution of dichlorophenyl phosphine (4, 4 mmol) in 10 mL of dry toluene was
added dropwise to a stirred solution of phenylboronic acid (1, 4 mmol) in 40 mL of
[26,27]
dry toluene, and K2CO3 (8 mmol) and stoichiometric amount amount of I2
at
0 ꢀC for a period of 20 min. Later the temperature was increased to 60 ꢀC, and stirring
was continued for 3–4 h to complete the formation of corresponding 1-phenylboryl
(1-phenylboryl)phenylphosphinate 6 as indicated by TLC analysis. Triethylamine
hydrochloride was separated from the reaction mixture by filtration. The filtrate
containing 6 was used for further reactions.
The filtrate containing 6 was cooled before addition of ethanol (4 mmol), dry
toluene (40 mL), and a catalytic amount of MgSO4. It was stirred and allowed to
warm up to room temperature. Stirring was continued for an additional 3–4 h at
40–45 ꢀC. When TLC analysis indicated the consumption of the starting material,
the solid formed was separated by filtration, and the filtrate was concentrated under
reduced pressure. The residue was washed with water and recrystallized from diethyl
ether to yield the required pure 1-ethoxy-1-phenylboryl (1-ethoxy-1-phenylboryl)-
phenylphosphinate (8).
1-Phenylboryl,1-phenylboryl phenylphosphinate (6). MF: C18H17B2O4P;
yield: 78%; mp: 181–183 ꢀC, Anal. calcd. (%): C, 61.78; H, 4.90. Found: C, 61.81; H,
4.99, IR (KBr) (nmax cmꢂ1): 3336 (O-H), 1299 (P O), 703 (P-B); 31P NMR (121 MHz,
=
CDCl3): d 19.06; 11B NMR (64 MHz, CDCl3): d 24.52, 30.14; H NMR (400 MHz,
1
CDCl3): d 7.72–7.39 (11H, t, Ar-H), 7.25 (4H, m, Ar-H); LCMS: m=z (%): 350 (34)
[Mþ], 309 (40), 257 (37), 238 (78), 197 (21), 141 (43), 120 (50), 83 (100).
1-Ethoxy-1-phenylboryl(1-ethoxy-1-phenylboryl phenylphosphinate (8).
MF: C22H25B2O4P; yield: 72%; mp: 168–170 ꢀC. Anal. calcd. (%): C, 65.08; H, 6.21.
Found: C, 65.19; H, 6.34, IR (KBr) (nmax cmꢂ1): 1308 (P O), 701 (P-B); 31P NMR
=
(121 MHz, CDCl3): d 19.76; 11B NMR (64 MHz, CDCl3): d 24.68, 30.45; H NMR
1
(400 MHz, CDCl3): d 7.85–7.80 (4H, t, Ar-H), 7.45–7.34 (6H, m, Ar-H), 6.66 (4H, s,
Ar-H), 4.29 (2H, d, J ¼ 10.4, P-O-B-OCH2) and d 3.97 (2H, dd, J ¼ 10.8, J ¼ 28.4 Hz,
P-B-OCH2), 1.33 (3H, d, J ¼ 4.8 Hz, CH3) and 0.91 (3H, d, J ¼ 4.4, CH3); 13C NMR

TETRAOXADIPHOSPHADIBOROCANE-2,6-DIONES
1031
(75 MHz, CDCl3): d 135.5 (C-1, C-6), 134.8 (C-4), 133.5 (C-20, C-60), 132.5 (C-200,
C-600), 131.0 (C-40), 127.9 (C-30, C-300, C-50 and C-500), 78.8 (P-O-B-O-C), 78.6
(P-B-O-C), 22.1 (P-O-B-O-C-C), 20.5 (P-B-O-C-C); LCMS: m=z (%): 407 (25)
[MHþ], 399 (35), 388 (18), 373 (25), 350 (17), 288 (61), 115 (29), 102 (100).
ACKNOWLEDGMENT
The authors thank the Council of Scientific and Industrial Research, Human
Resources Development Group, Government of India, New Delhi, for providing
financial assistance (01=2347=09=EMR-II).
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