Synthesis and properties of four-membered phosphorus heterocycles-2-Fluoro-1,2λ5-Oxaphosphetanes

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Phosphorus, Sulfur, and Silicon and the Related

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Synthesis and Properties of Four-Membered

Phosphorus Heterocycles - 2-Fluoro-1,2Λ⁵-

Oxaphosphetanes

Anastasia O. Kolodiazhna^a& Oleg I. Kolodiazhnyi^a

^aInstitute of Bioorganic Chemistry and Petrochemistry of National Academy of Sciences of

Ukraine, Ukraine, Kiev, 02094, Murmanska Street, 1

Accepted author version posted online: 08 Jun 2015.

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To cite this article: Anastasia O. Kolodiazhna & Oleg I. Kolodiazhnyi (2015): Synthesis and Properties of Four-Membered

Phosphorus Heterocycles - 2-Fluoro-1,2Λ⁵-Oxaphosphetanes, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:

10.1080/10426507.2015.1054485

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ACCEPTED MANUSCRIPT

SYNTHESIS AND PROPERTIES OF FOUR-MEMBERED PHOSPHORUS

HETEROCYCLES - 2-FLUORO-1,⁵-OXAPHOSPHETANES

Anastasia О. Kolodiazhna, Oleg I. Kolodiazhnyi*

Institute of Bioorganic Chemistry and Petrochemistry of National Academy of Sciences of

Ukraine, Ukraine, 02094, Kiev, Murmanska Street, 1

^*Address correspondence to Institute of Bioorganic Chemistry and Petrochemistry, National

Academy of Sciences of Ukraine, Murmanskaia 1, Kyiv 02094, Ukraine. e-mail:

olegkol321@rambler.ru

Received x xxx 2015; accepted xx xxx 2015.

Dedicated to Editor-in-Chief Emeritus of this Journal Professor Robert R. Holmes.

Abstract

The

preparation

of

four-membered

phosphorus(V)-heterocycles,

2-fluoro-1,⁵-

oxaphosphetanes, by reaction of P-fluoroylides with carbonyl compounds is described. The

reaction is stereoselective and leads preferentially to the formation of threo-1,2^-

oxaphosphetanes. Oxaphosphetanes were isolated as individual compounds and their structures

1

were confirmed by Н, ¹³C, and ³¹Р NMR spectra. The fluoro-1,⁵-oxaphosphetanes may be

1

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easily converted to various alkenylphosphonates: allyl- or vinylphosphonates. This reaction

represents a good method for the preparation of phosphorylated alkenes

Keywords

1,2⁵-Oxaphosphetanes, phosphoranes, allylphosphonates, vinylphosphonates, P-fluoroylides

2

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INTRODUCTION

One of the most interesting and intriguing classes of organophosphorus compounds is 1,2-

oxaphosphetanes – four-membered heterocycles containing pentacoordinated phosphorus.^1-3

The reaction of phosphorus ylides with carbonyl compounds, leading to the formation of olefins,

is one of the major reaction in synthetic organic chemistry.⁴Extensive experimental^5,6and

theoretical work^7,8has been devoted to clarify the reaction mechanism. A variety of different

species, betaines,⁸diradicals, and 1,2-oxaphosphetanes,^1-3were proposed as possible reactive

intermediates. However, only 1,2-oxaphosphetanes were fully identified and some of them (А-

С) were isolated (Scheme 1).^9-11Among the stable oxaphosphetanes the biggest interest is in the

2-halogen-1,2-oxaphosphetanes D, which possess relatively high stability and various

reactivity.^12-15

DISCUSSION

The available methods for the synthesis of 2-fluoro-1,2⁵-oxaphosphetanes can be used for

investigation of the reaction mechanism of phosphorus ylides with carbonyl compounds as well

as for preparing stable oxaphosphetanes thats can be used as initial reactants for organic

synthesis. The 2-fluoro-1,2⁵-oxaphosphetanes are the most stable representatives of this type of

compounds. They can be purified by distillation under vacuum and stored in a refrigerator. At

the same time they possess interesting chemical properties and enter to various chemical

transformations.

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The 2-fluoro-1,2⁵-oxaphosphetanes were prepared by reaction of P-fluoroylides with carbonyl

compounds. Earlier we developed convenient methods for the synthesis of P-fluoroylides. For

example, they can be obtained in high yields by dehydrofluorination of

alkyltrifluorophosphoranes.^13-15

In the present article we have studied 2-fluoro-1,2⁵-oxaphosphetanes 2a-h which were prepared

by reaction of P-fluoroylides 1a-d with aldehydes and ketones leading to the formation of [2+2]-

cycloaddition products 2a-h in very high yields (Scheme 2). The 2-fluorooxaphosphetanes 2 are

stable compounds at room temperature, which were isolated and studied by means of NMR

spectroscopy. The 2-fluoro-3-silyl-1,2⁵-oxaphosphetanes 2a-j, containing С-3 and С-4-

19

31

asymmetric atoms, exist as mixture of erythro- and threo-diastereomers. The F and Р NMR

spectra for compounds 2a-j showed two sets of signals in the ratio ~4: 1 for the diastereomers.

The ³¹P NMR chemical shifts of 2-fluorooxaphosphetanes were found at -37 to -43 ppm as

1

doublets with a large constant J_PF~750-780 Hz and the values _Fwere found out at -45 ppm,

1

doublets with the constant J_PF750-780 Hz. In H NMR spectra were found signals of Me₃Si

3

group, C(3)H proton at 4.80-5.0 ppm, double doublet with ²J_PH~14 and J_HF~7.5 Hz; OC(4)H

13

at 5.2  5.4 ppm. In the C NMR spectra, the signal _Cof С-4 was found at +80 ppm and the

1

2

signal of С-2 at +30 ppm as double doublets, J_PC~130 Hz, and J_FC~50 Hz, correspondingly.

The spectroscopic data of 2-fluorooxaphosphetanes 2a-h are typical for pentacoordinated

phosphorus compounds.¹⁶

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The transformations of 2-fluoro-1,2⁵-oxaphosphetanes proceeded without Р—С bond cleavage

leading to

a

number of interesting organophosphorus compounds. Thus, 2-

fluorooxaphosphetanes 2a-h hydrolyze with formation of 2-hydroxyphosphonates 3, which were

isolated as crystalline compounds. The treatment of 2-fluorooxaphosphetanes 2a-h with an ether

solution of HCl led to the formation of 2-chlorooxaphosphetanes 4. In contrast to 2,2,2-

triphenyloxaphosphetanes, upon heating, the decyclization of 2-fluorooxaphosphetanes 2

occurred, leading to the formation of phosphorylated alkenes – allyl- or vinylphosphonates. The

direction of reaction depends on substituents R²and R³at CandC of oxaphosphetane

cycle. The 2-fluorooxaphosphetanes bearing R²=H, Alk, Аr, at C-3 and R³=Alkyl at C-4

proceeded with HF elimination to give allylphosphonates 5a,b.^16cThe reaction was catalyzed by

boron trifluoride etherate. The 2-fluorooxaphosphetanes bearing R=Me₃Si substituent at C-3

eliminated Me₃SiF to afford vinylphosphonates 6a-l (Table 1). This reaction is a convenient

method for the preparation of phosphorylated alkenes that are versatile building blocks for

organic synthesis.¹⁷

Upon heating to 60 to 80 °С, the 2-fluoro-3-silyloxaphosphetanes 2a-h converted into

vinylphosphonates 6 in high yields. The reaction is regioselective and afforded pure trans-

vinylphosphonates 6a-m, without inclusion of allylphosphonates 5. The trans-geometric

configuration of vinylphosphonates 6a-m was proven by NMR spectra which have disclosed

3

2

signals, of two double doublets of olefin protons at 6-8 ppm with J_HH=~16-18 Hz and J_PH

3

=~17-20 Hz. It is known that J_HHof cis-vinylphosphonates are 11 – 14 Hz, and J_PHare

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approximately 40-57 Hz.^15-18The trans-vinylphosphonates 6a-c were synthesized earlier, their

spectroscopic data were identical with those previously reported.^13,18

The most stable were 2-fluoro-3-silyloxaphosphetanes 2g, bearing CF₃group at С-4. Upon

heating to +100 °С the oxaphosphetanes 2g eliminated Me₃SiF affording a mixture of E- and Z-

vinylphosphonates 6k in the ratio 2:1. However the slow conversion of 2g at +20 °С over several

days provided almost pure E-vinylphosphonates E-6k, containing only 2-3% of Z-isomer.

Probably, this effect can be explained by formation of carbocation intermediate G and rotation of

substituents around the C-C bond (Scheme 5). In addition, the initial 2-fluorooxaphosphetanes

2a-h exist as mixture of threo- and erythro-diastereomers, but they converted into pure E-

vinylphosphonates. We suppose that the 2-fluorooxaphosphetanes under condition of acid

catalysis (with HF or BF₃) via the formation of an oxonium intermediate F, convert to

carbocation intermediate G which has a planar configuration. The removal of a proton from

the carbocation intermediate G depends on electronic effects of the substituents. Alkyl

groups possessing the +I-effect and the effect of hyperconjugation stabilize the positive charge

and reduce the energy of activated state. Therefore, the activated state G' is energetically more

favorable than the activated state, leading to the formation of vinylphosphonate. However, the

presence of Me₃Si at С-3 in G' leads to the elimination of Me₃SiF, which has a high energy of

formation, that creates a preference for the formation of vinylphosphonates (Scheme 5).³

The formation of carbocation intermediate G was experimentally confirmed (Scheme 6). The

treatment of 2-hydroxyphosphonate with trifluoracetic acid and refluxing for several hours,

generated the carbocation intermediate G, as a result of acid-catalyzed dehydration of alcohol 3.⁹

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Then the intermediate G converted into allylphosphonate 5a, which is identical to the one

obtained from 2-fluorooxaphosphetane 2i.

The reaction of ylides 1 with carbonyl compounds proceeded with an equimolecular ratio of

reagents upon cooling in diethyl ether. The reaction can be carried out in one-pot without

isolation of oxaphosphetanes. In the reaction flask at low temperature, was placed the ether

solution of P-fluoroylide and carbonyl compound. Next solvent was evaporated and the residue

o

was heated to 60 to 100 C. The course of reaction was monitored by TLC and by emission of

gaseous Me₃SiF. The vinylphosphonates 6 were purified by distillation under vacuum or by

column chromatography and obtained in good yields. The reaction of ylides 1a-c with

unsaturated aldehydes led to the formation of dienophosphonates 6i,j. The IR spectra of these

dienes contained intensive absorption bands of 1560 and 1620 cm^-1corresponding to

unsymmetrical and symmetrical valence vibrations of trans-С=С—С=С bonds, and also bands

З010, 3030, 3090 – 3100 for valence vibration-frequencies and 930 – 940 cm^-1for the

1

deformation frequencies of vinyl groups. In the H NMR spectrum the signal assigned to four

diene protons was observed in the field of 6-8 ppm.^19-21

The reaction of ylides with aldehydes is regioselective. For example, the reaction of ylide 1c

with terephthalic aldehyde in the 2:1 ratio of initial reagents led to formation of a 1,4-bis-

vinylphosphonobenzene 6m and in the 1:1 ratio afforded phosphonovinylbenzaldehyde 6l,

which are interesting as starting reagents for organic synthesis. The reaction was performed at

+20 °С in THF. Elemental analysis and spectroscopic data of phosphonovinylbenzaldehyde 6l

responded to the structure. IR spectra contained absorbtions at 2700 (СН) and 1690 cm^-1(С=O),

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showing the presence of an aldehyde group, and also bands at 1550 (С=С), 1205, 1215 cm^-1

1

(Р=O). The H NMR spectra of compound revealed the singlet of an aldehyde proton at 11.5

ppm, double doublets of vinyl protons at 6.5 ppm (РСН=С) and 7.7 ppm (РС=СH) with

coupling constants ³J_HH17 HZ, ³J_PH19 Hz and ²J_PH17.5 Hz. There was also a double doublet of

ortho-protons for the 1,4-disubstituted benzene ring.

CONCLUSION

In conclusion, we have studied the reaction of P-fluoroylides with aldehydes and ketones

leading to the formation of 2-fluoro-1,2^-oxaphosphetanes, that could be converted into

phosphorylated alkenes by heating. The structure of the alkenes depended upon the nature of

substituents at С-3 and С-4 atoms in a four-membered cycle. The 2-fluorooxaphosphetanes,

bearing alkyl groups at the С-4 atom, as a result of 1,4-elimination of hydrogen fluoride,

afforded allylphosphonates. The 2-fluorooxaphosphetanes bearing the trimethylsilyl group at the

С-3-atom, through 1,2-elimination of trimethylsilylfluoride afforded E-vinylphosphonates. The

conversion of 2-fluorooxaphosphetanes into alkenphosphonates proceeded via the formation of

a carbenium ion intermediate.

EXPERIMENTAL

IR spectra were obtained in KBr pellets and recorded with a Vertex 70 IR Fourier

13

spectrophotometer. The mass spectra were recorded on an AEIMS-902 model. The ¹H, C, and

³¹P NMR spectra were measured in C₆D₆and CDCl₃solution with TMS as internal or 85%

H₃PO₄as an external standard with Varian VXR-300 and Gemini 2000 (400 MHz)

spectrometers. Chemical shifts (δ) are reported in parts per million. Coupling constants (J) are

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reported in Hz. Solvents were preliminarily distilled in an inert atmosphere: diethyl ether,

hexane, benzene, and carbon tetrachloride over phosphorus pentoxide, methanol and

triethylamine over sodium, and ethyl acetate over calcium chloride. All commercially available

reagents were used without further purification. Melting points are uncorrected. The P-

fluoroylides 1a-d were prepared by reaction of trifluroalkylphosphonates with butyllithium using

methods earlier reported by us.^12,15Other reagents were purchased from Merck (Germany), Fluka

(Buchs, Switzerland), and Acros and were used without further purification. TLC was performed

on plates coated with silica gel 60 with an F₂₅₄indicator; column chromatography was carried

out on silica gel 60 (230–240 mesh).

2,2-Bis(diethylamino)-2-fluoro-3-(trimethylsilyl)-4-phenyl-1,2-⁵-oxaphosphetane

(Typical experiment)

(2a)

To a solution of ylide 1c (0.02 moles) in 5 mL of diethyl ether at 0 °C was added 0.022 moles of

benzaldehyde. The reaction mixture was left for 3 – 4 h at +20 °C. Then the solvent was

evaporated under reduced pressure. The product is unstable, therefore was used without

purification. Colorless liquid. Yield 95 %.

¹H NMR (CDCl₃):  0.18 d (³J_PH1.0 Hz, 9H, Me₃Si); 1.21, t (³J_PH7 Hz, 6H, CH₃); 1.33 t (³J_PH

3

7 Hz, 6H, CH₃); 3.21 m (8H, CH₂N); 4.80, d.d (²J_PH14 Hz, J_FH7.5 Hz, 1H, PCH); 5.23 d.d

(³J_PH5 Hz, ³J_HH7.5 Hz, 1H, OCH); 7.5 m; 7.73 m; 8.07 m (5H, C₆H₅) (major diastereomer). ¹³C

3

NMR (C₆H₆): _C1.81, dd (³J_CP8 Hz, ⁴J_CF2 Hz, Me₃Si); 15.73, dd (²J_CP8 Hz, J_CF3 Hz, CH₃);

9

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2

3

29.1, d.d (¹J_CP130 Hz, J_CF28 Hz, PCH); 37.9 dd (²J_CP7 Hz, J_CF6 Hz, NCH₂); 82; 124.29;

125.93; 127.08; 148.2 (major diastereomer).

³¹Р NMR (CDCl₃): _P= 39.18, d, ¹J_PF780 Hz; 38.53, d, ¹J_PF762 Hz. ¹⁹F NMR (CDCl₃): _F=

1

41.0, d, J_PF780 Hz, _F= 39.6, d, J_PF760 Hz (4:1). Anal. Calcd. for C₁₉H₃₆FN₂OPSi: P,

8.01%. Found: P, 8.00%.

Other 2-fluoro-oxaphosphetanes 2b-h were prepared analogously to compound 2a. These

compounds were used for further synthesis without purification. Parameters of ^l9F and ³¹Р

spectra are presented below in the Table 2.

2,2-Вis(diethylamino)-2-fluoro-4-spiro-cyclohexane-1,2⁵-oxaphosphetane (2i)

To a solution of ylide 1d (0.02 moles) in 5 mL of diethyl ether at 0 °С was added 0.022 moles of

cyclohexanone. The reaction mixture was left for 3 – 4 h at +20 °С. Then the solvent was

evaporated and the residue was distilled under vacuum. Colorless liquid. Yield 90 %. Bp 110 ^oC

(0.02 mmHg).

¹H NMR (CDCl₃):  1.1 t (³J_HH7 Hz, 12H, СН₃СН₂); 1.48 m (10H, С₅Н₁₀); 2.90 m (8H, CH₂N);

13

5.5 d (²J_HP25 Hz, 2H, РСН₂). C NMR (C₆H₆): _C13.78; 22.27; 23.84; 37.15 d (³J_CP8.5 Hz,

3

2

С₅Н₁₀); 40.43 dd (²J_CP7.5 Hz, J_CF7 Hz, CN); 51.16 d.d (¹J_CP139 Hz, J_CF51, PC); 66.0 d.d

3

31

(²Jср 20 Hz, J_CF9 (ОС). Р NMR (C₆D₆): _P= -44.0, d (¹J_PF756 Hz); _F-42.2, d (¹J_PF756).

MS (m/e): 306 (M⁺) M 306.40. Anal. Calcd. for C₁₅H₃₂FN₂OP: N 9.14; Р 10.11. Found: N 9.02;

Р 10.02.

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2,2-Bis(diethylamino)-2-fluoro-4,4-dimethyl-1,2⁵-oxaphosphetane (2j)

Preparation was analogous to 2a. Yield 70%. Bp 70-75 ^oC(0.02 mmHg).

¹H NMR (CDCl₃):  1.08 t (³J_HH7 Hz, 12H, CH₃); 1.31 s; 1.34 s [(CH₃)₂C]; 2.78 t (²J_HP15.5

Hz,1H, PCH^a); 3.08 t (²J_PH15.5 Hz, 1H, PCH^b); 3.19 m; 3.25 m (8H, CH₂N).

¹³C NMR (C₆H₆): _C13.6 (CH₃); 27.5 d (³J_CP9 Hz); 30.6 d [³J_CP9 Hz, (CH₃)₂C]; 36.6 m

(CH₂N); 42.05 dd (¹J_PC130 Hz, ³J_FC50 Hz, CH₂); 66.5 (CMe₂).

³¹Р NMR (C₆D₆): _P= -47.5, d (¹J_PH765 Hz). ¹⁹F NMR (C₆D₆): _F= -45.95 Hz, d (¹J_PH765 Hz).

MS (m/e) 266 (M+), M=266.34.

Anal. Calcd. for C₁₂H₂₈FN₂OP: C 54.12; H 10.60. Found: C 54.02; H 10.42%.

[(1-Hydroxycyclohexyl)methyl]-phosphonic bis(diethylamide) (3)

¹H NMR (CDCl₃): 1.07 t (⁴J_HH7 Hz, 12H, CH₃) 1.3-1.6 m (10H, CH₂); 2.1 d (2H, ²J_PH19 Hz,

PCH₂); 2.9 m (8H, CH₂N). ³¹Р NMR (C₆D₆): _P= 29.28. MS (m/e): 304 (M⁺) (M 304.23).

Anal. Calcd. for C₁₅H₃₃N₂O₂P: C, 59.18; H, 10. Found: C, 59.61; H, 11.15%.

2-Chloro-2-phenylethylphosphonic bis(diethylamide) (4)

To a solution of 2-fluoroxaphosphetane (0.01 mol) in 5 mL of ether at -70 °С was added ether

solution of hydrogen chloride (0.01 mol). The temperature was raised to room temperature. The

precipitate of the hydrochloride of phosphonate 4 was filtered off and treated with triethylamine

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in ether. A product dissolved on ether, was combined with a mother solution. The solvent was

evaporated; the residue was recrystallized in pentane (-70 °С). Yield 70%, mp 42-43 °С.

¹H NMR (CDCl₃):  0.8 t (³J_HH7 Hz, 6H, CH₃CH₂); 1.08, t (³J_HH7 Hz, 6H, СН₃СН₂); 2.56 d.d

(³J_HH7 Hz, ²J_НР13.0 Hz, 1H, PCH); 2.59 dd (³J_HH6.5 Hz, ²J_НР13 Hz, 1H, РСН’); 2.63 m; 2.97

3

m (8H, NCH₂); 5.31 dt (³Jнн 7 Hz, J_HP8.5 Hz, 1H, СНС1); 7.27 m (5H, С₆Н₅). ³¹Р NMR

(C₆D₆): _P= 29.28 ppm.

Anal. Calcd. for С₁₆Н₂₈СlN₂ОР; Сl 10.72; N 8.47; Р 9.36. Found: Cl 11.07; N 8.46; Р 8.98%.

1-Cyclohexen-1-yl-methylphosphonic bis(diethylamide) (5a)

a)

The 2-fluoro-1,2⁵-oxaphosphetanes (0.015 moles) was heated carefully to 120 – 140 °С

and gaseous hydrogen fluoride emission was observed .Then the reaction mixture was distilled

under vacuum.

Bp 145 ^oC (0.08 mmHg). Yield 85 %.

b)

To 2-fluorooxaphosphetane 2 (0.015 mol.) was added several drops of boron trifluoride

etherate. The reaction mixture was left for several hours at ambient temperature or at weak

heating. Gaseous hydrogen fluoride emission was observed. Then the reaction mixture was

distilled under vacuum. Bp 145 ^oC (0.08 mmHg). Yield 80 %.

c)

A solution of bis(diethylamide) - [(1-hydroxycyclohexyl)methyl]-phosphonate 3 (0.015

mol) in trifluoroacetic acid (10 mL) was heated for 2 h. Then the solution was evaporated under

pressure reduced (10 mmHg) and residue was distilled under vacuum (0.06 mmHg). Yield 50%.

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Bp 140 ^oC (0.06 mmHg). The product was additionally purified by column chromatography

with silica gel (eluent ethyl acetate/hexane).

¹H NMR (CDCl₃):  1.02 t (³Jнн 7 Hz, 12H, CH₃CH₂); 1.53, m; 1.94 m; 2.11 m [(СН₂)₄]; 2.35 d

(²Jнр 16.6 Hz, 2H, РСН₂); 2.93 dq ( ³J_HP10 Hz, 8H, NCH₂); 5.39 m (СН=С).

¹³C NMR (C₆H₆), _C12.73; 20.5; 21.34; 23.89; 28.01; 34.08 d (¹J_CP109, PC); 37.35; 123.34 d

(²J_CP12 Hz, РСС=С); 129.28.

³¹Р NMR (C₆D₆): _P= 32.6 ppm. m/z 286 (M+) (M 286.39).

Anal. Calcd. for C₁₅H₃₁N₂OP: C 62.91, H 10.91, P 10.82%. Found: C 62.60, H 10.72, P

10.99%.

(2-Methyl-2-propenyl)-phosphonic bis(diethylamide) (5b)

Was prepared analogously to 5a. Yield 50%, bp 100 ^oC (0.08 mmHg).

¹H NMR (CDCl₃):  1.01 t (³Jнн 7 Hz, 12H, CH₃CH₂); 1.81 s (3H, СН₃C=C); 2.42 d (²J_HP16.6

Hz, 2H, РСН₂); 2.93 dq ( ³J_HP10 Hz, 8H, NCH₂); 4.7 d (⁴J_HP2 Hz, 1H, СН^a=С); 4.9 d (⁴J_HP

Hz, 1H, СН^b=С); ³¹Р NMR (C₆D₆): _P= 31.74. MS (m/e) 246 (M+) (M 246.33).

2

Anal. Calcd. for C₁₂H₂₇N₂OP. C 58.51; H 11.05; P 12.57%. Found: C 59.21; H 11.55; P 12.26%.

Vinylphosphonates 6a-m (general method).

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2-Fluorooxaphosphetanes 2a-h were heated to 80 – 100 °С. The evolution of gaseous Me₃SiF

was observed. The reaction mixture was then crystallized in hexane or heptane, and distilled

under vacuum or chromatographed on column with silica gel

Di-tert–butyl(2-phenylethenyl)phosphine oxide (6a)

The ylide 1b (0.01 mol) was mixed with benzaldehyde (0.01 mol) and the mixture was heated at

150 °С for 30 – 40 min to the end of Me₃SiF emission. The residue was cooled and recrystallized

from heptane. Yield 80 %, mp 138 °С.¹³

2

¹Н NMR (CDCl₃):  1.53 d (³J_HH13.7 Hz, 9H,CH₃C); 7.08 d.d (³J_HH18 Hz, J_PH22.5 Hz, 1H,

PCH=C); 7.95 dd (³J_HH18 Hz, 1H, C=CH); 7.8 m (5H, C₆H₅). ³¹Р NMR (CDCl₃):  50 ppm.

Diphenyl(2-phenylethenyl)phosphine oxide (6b).

To a stirring solution of ylide 1a (0.01 mole) in ether (10 mL) at -70 ^oC was added benzaldehyde

(0.011 mol). Then the temperature of reaction mixture was raised to +20 ^oC and the mixture was

left for 12 hr. The course of reaction was monitored by ³¹P NMR. The ³¹Р NMR spectrum

showed the full conversion of ylide 1a into 2-fluoroxaphosphetane 2c in several hours: _Р-43.5

ppm, doublet, ¹J_PF620 Hz. The solvent was evaporated under vacuum and the residue was

heated up to 80 – 100 °С, then the reaction mixture was treated with water and separated by

column chromatography on silica gel with ethyl acetate as an eluent. Yield 40%, m.p. 165 °С

that corresponds to the published data.¹⁸

14

ACCEPTED MANUSCRIPT

¹H NMR (CDCl₃):  6.35, d.d (³J_HH17.0 Hz, ²J_HP24.0 Hz, 1H, РСН=С); 7.3 m; 7.75 m (16H,

РС=СН+ С₆Н₅). ³¹Р NMR (C₆D₆): _P= 22.0 ppm.

E-(2-Phenylethenyl)phosphonic bis(diethylamide) (6c)

o

To a solution of ylide 1c (0.01 mol) at -70 C was added benzaldehyde (0.015 mol), the

temperature was raised to room and the mixture was stirred for 14 h. The reaction mixture was

evaporated under pressure reduced (10 mmHg) at +20 ^oC, then the residue was heated at 100 °С

for 15 min. under vacuum (0.05 mm Hg) and the residue was recrystallized in hexane. Yield

80%, mp 103.5 °С.

3

¹Н NMR (CDCl₃):  1.38 t (³Jнн 7 Hz, 12Н, СН₃СН₂); 3.38 dq (³Jнн 7 Hz, Jрн 11 Hz, 8H,

3

CH₂N); 6.60 d.d (³J_HH17.2 Hz, J_PH18 Hz, 1Н, РСН=С); 7.75 d.d (³J_НН17.5, J_РН19, 1Н,

С=СН); 7.65 m (5Н, С₆Н₅). ¹³C NMR (C₆D₆):  13.70; 41.85; 114.50, d (¹J_PC152.0 Hz,

PCH=C); 128.70; 131.66 d (²J_PC24.0 Hz, РC=С), 144.17, 161.90 d (³J_PC30 Hz). ³¹Р NMR

(CDCl₃): _P24.50 ppm.

1E-1-propenyl]-phosphonic bis (diethylamide) (6d)

Preparation was analogous to 6c.Yield 72%. Bp 80^oC (0.05 mmHg).

15

ACCEPTED MANUSCRIPT

¹H NMR (CDCl₃):  0.92 t (³J_HH7.7 Hz, 12H, CH₃); 1.85 d (⁴J_PH8 Hz, 3H, CH₃); 2.98 dq (³J_HH

7 Hz, ³J_PH10 Hz, 8H, CH₂N); 5.66 d.d (²J_PH20 Hz, ³J_HH16 Hz, 1H, PCH=C); 6.61 ddq (³Jнр 18

Hz, ³Jнн 16 Hz, ³Jнн 6 Hz, 1H, РС=СН). ³¹Р NMR (C₆D₆): _P24.7 ppm.

Anal. Calcd. for C₁₁H₂₅N₂OP. P, 13.33%. Found: P, 13.43%

1E-1-Pentenylphosphonic bis(diethylamide) (6e)

was prepared analogously to 6c. Yield 70%, bp 110^oC (0.05 mmHg).

¹H NMR (CDCl₃): _0.86 t (³J_HH7.7 Hz, 3H, CH₃); 1.03 t (³Jнн 7 Hz, 12H, CH₃CH₂N); 1.42m

(2H, CH₂); 2.13 d.t (³Jнн 7 Hz, ³J_PH7 Hz, 2H, СН₂); 3.08 dq (³J_HH7 Hz, ³J_PH10 Hz, 8H,

CH₂N); 5.65 d.d.t (²J_PH20 Hz, ³J_HH16 Hz, ⁴J_HH, 1.4 Hz, 1H, PCH=C); 6.65 d.d.t (³J_HP18 Hz,

³Jнн 16 Hz, ³Jнн 6 Hz, 1H, РС=СН). ³¹Р NMR (C₆D₆): _P24.2 ppm.

1E-1-Hhexenylphosphonic bis(diethylamide) (6f)

was prepared analogously to 6c. Yield 68%, bp 120-123 ^oC(0.04 mmHg).

¹H NMR (CDCl₃):  0.83 t (³Jнн 7 Hz, 3H, CH₃); 1.01 t (³Jнн 6.8 Hz, 12H, СН₃СН₂N); 1.20-

1.40 m (4H, CH₂); 2.16 d.t (³J_HH6.8 Hz, 2H, СН₂); 2.98 dq (³J_HH7 Hz, ³J_HP12 Hz, 8H, NCH₂);

5.63, d.d.t (³J_HH16.8 Hz, ²J_HP21 Hz, ⁴J_HH1.5 Hz, 1H, РСН=С); 6.61 d.d.t (³J_HP19 Hz, ³J_HH16.8

Hz, ³J_HH6.7 Hz, 1H, РС=СН). ³¹Р NMR (C₆D₆): _P23.95 ppm.

16

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1E-1-octenylphosphonic bis(diethylamide) (6g)

Was prepared analogously to 6c.Yield 80%, bp 135 (0.06 mmHg).

¹H NMR (CDCl₃):  0.83 t (³Jнн 7 Hz, 3H, CH₃), 1.02 t (³Jнн 6.9 Hz, 12H, CH₃CH₂N); 1.22 m

(8H, CH₂); 2.15 d.t (³Jнн 6 Hz, ³Jнн 6.8 Hz, 2H, СН₂C=); 2.97 ddq (³Jнн 7.8 Hz, ³J_HP11.7 Hz,

3

4

8H, NCH₂); 5.61 d.d.t (²J_HP21.3 Hz, Jнн 16.8 Hz, J_НP1.5 Hz, 1H, PCH=C); 6.61 d.d.t (³J_НP

3

4

19.3 Hz, Jнн 16.8 Hz, J_HH6.7 Hz, 1H, РС=СH). ¹³C NMR (CDCl₃): 12.17; 12.15; 20.68;

26.17; 26.85; 28.70; 32.22 d (³J_CP18.9 Hz, PC=CC); 119.1 d (¹J_CP153.14 Hz, PC=); 148.36.

³¹Р NMR (C₆D₆): _P= 24.1 ppm. m/z 302 (M+) M= 302.436.

Anal. Calcd. for C₁₆H₃₅N₂OP: C, 63.54; H, 11.66; P, 10.24%. Found: C, 63.66; H, 11.72; P,

10.04%.

(1E)-1-Decenylphosphonic bis(diethylamide) (6h)

Preparation was analogous to 6c. Yield 79%, bp 145-150 ^oC (0.05 mmHg).

¹H NMR (CDCl₃):  0.81, t (³J_HH7 Hz, 3H, CH₃), 1.01 t (³J_HH7 Hz, 12H, CH₃CH₂N); 1.20 м

10H, CH₂); 2.13 d.t (³Jнн 7 Hz, ³J_HH7 Hz, 2H, CH₂C=); 2.98 dq (³Jнр 10.5 Hz, 8H, NCH₂);

5.64 d.d.t (²J_HP20.5 Hz, ³J_HP16.8 Hz, ⁴J_HH1.5 Hz, 1H, PCH=С); 6.61 d.d.t (³J_HP19 Hz, ³J_НН

16.8 Hz, ³Jнн 6.5 Hz, 1H, РС=СН). ³¹Р NMR (C₆D₆): _P= 24.1 ppm.

Anal. Calcd. for C₁₈H₃₉N₂OP: C, 65.42; H 11.89; P, 9.37%. Found: C, 66.12; H 12.09; P, 9.01%

4-Phenyl-(1Е,3Е)-butadienylphosphonic bis(diethylamide) (6i)

17

ACCEPTED MANUSCRIPT

To a solution of 1a (0.02 mol) in diethyl ether (10 mL) was added cinnamic aldehyde (0.02 mol)

at 0 – +5^oC. The mixture was left for 18 h at room temperature and then was evaporated under

pressure reduced. The residue was distilled under vacuum

1

Yield 70 %, b. p.170-175 °С (0.06 mmHg). H NMR (CDCl₃):  1.4 t (³J_НН7 Hz, 12H, CH₃);

3.30 dq (³J_PH10 Hz, 8H, CH₂N); 6.30 m (1H, CH=C); 7.30 m (3Н, C=CH+СН=СН); 7.80 m

(5Н, C₆Н₅).

³¹Р NMR (CDCl₃): _P23.30 ppm.

Anal. Calcd. for С₁₈Н₂₉N₂ОР: C, 67.47; H, 9.12; P, 9.67%. Found: C, 67.77; H, 9.20; Р, 9.66%.

1E,3E-4,8-Dimethyl-1,3,7-nonatrienylphosphonic bis(diethylamide) (6j)

Yield 40%, bp 160 ^oC (0.08 mmHg). _H1.04 t (³J_HH7 Hz, CH₃CH₂N); 1.60 m (3H, CH₃); 1.70 m

(3H, CH₃); 1.81 m (3H, CH₃); 2.1 m (4H, CH₂); 3.0 m (8H, CH₂N); 5.11 t (³J_PH8 Hz, 1H,

CH=CMe₂); 5.49 t ( ³J_HP17 Hz, 1H, C=CHP); 5.9 d (³J_HP12Hz, 1H, C=CH); 6.6 m (1H, C=CH)

MS (m/e)= 340 (M+) M 340.48

Anal. Calcd. for C₁₉H₃₇N₂OP. C, 67.02; H, 10.95; P, 9.10%. Found: C, 67.57; H, 10.20; Р,

9.46%.

3,3,3-Trifluoro-2-phenylpropenephosphonic bis(diethylamide) (6k)

a)

The 2-fluorooxaphosphetanes 2g (0.02 mol) was heated to 80 – 100 °С. The evolution of

gaseous Me₃SiF was observed. The reaction mixture was then distilled under vacuum or

18

ACCEPTED MANUSCRIPT

o

chromatographed on column with silica gel. Yield 70 %, bp 150 С (0.07 mmHg ). The mixture

of E- and Z-isomers in ratio 2:1 was obtained. We assume that the major isomer is E-alkene 6k,

because _Hof vinyl proton and _Pof this compound are shifted to down field relative to those of

minor Z-isomer. In earlier reported ³¹P NMR spectra of vinylphosphonates, the signals of Z-

isomers appeared at higher field than the ones of E-isomers.^{20, 22,23a-c}

b)

The 2-fluorooxaphosphetanes 2g (0.02 mol) was left at 20 °С for a week. The reaction

o

mixture was then distilled under vacuum. Yield 75 %, b. p.150 С (0.07 mmHg ). The almost

pure E-isomer was obtained.

(E-isomer): ¹Н NMR (CDCl₃):  1.38 t (³J_НН7 Hz, 12H, CH₃); 3.27 dq (³J_PH10 Hz, 8H, CH₂N);

4

31

6.80 dq (²J_PH12 Hz, J_HF1.5 Hz, 1Н, С=СН); 7.60 m (5Н, C₆Н₅). Р NMR (CDCl₃):  23.50

ppm ¹⁹F NMR (CDCl₃), _F68.11

(Z-isomer): ¹H NMR (CDCl₃):  1.28 t ( ³Jнн 7 Hz, СН₃СН₂); 3.27 m (СН₂N); 6.4 d (²J_HР9 Hz,

С=СН); 7.6 m (С₆Н₅). ³¹Р NMR (CDCl₃):  18.20 ppm

Anal. Calcd. for C₁₇H₂₆F₃N₂OP. C, 56.35; H, 7.23; P, 8.55%. Found: C, 56.15; H, 7.03; P,

8.10%.

1E-4-Formylphenylethenylphosphonic bis(diethylamide) (6l)

A solution of ylide 1c (0.02 mol) in 10 mL of diethyl ether was added to 0.025 mol of

terephthalic aldehyde in THF (3 mL) at 0 °С. The reaction mixture was left for a night. Then the

solvent was evaporated under reduced pressure (10 mmHg). The residue was recrystallized in a

19

ACCEPTED MANUSCRIPT

mixture of ether/pentane at 0 °С. Yield 50 %, mp 92.5 – 94 °С. After second recrystallization in

1

hexane, mp 98 °С. Н NMR (CDCl₃):  1.40 t (³Jнн 7 Hz, 12Н, СНзСН₂); 3.41 d.d (³Jнн 7 Hz,

2

³J_PH10.5 Hz, 8Н, СН₂N); 8.10 d.d (4Н, С₆Н₄); 6.80 d.d (³J_HH17.5 Hz, J_РН17.5 Hz, 1Н,

3

РСН=С); 7.85, d.d (³Jнн 17.5 Hz, J_PH19 Hz, 1Н, С=СН); 8.00 d; 8.10 d (⁴J_HH9 Hz, 4Н,

С₆Н₄); 10.30 s (1Н, С(О)Н). ¹³C NMR (CDCl₃):  14.01; 41.7 d, J 6; 105.2 d (¹J_PC160 Hz);

130.1; 131.5; 136.0; 142.5; 154.2 d (²J_PC32); 191.5. ³¹Р NMR (CDCl₃), _P: 23.7 ppm.

Anal. Calcd. for С₁₇Н₂₇N₂O₂Р: С 63.34; Н 8.44; Р 9.61%. Found: С 63.13; Н 8.41; Р 9.52 %:

Bis(1E, 1’E)-(2-tetraethyldiamidophosphonoethenyl)benzene (6m)

To a solution of ylide 1c (0.025 mol) in diethyl ether (10 mL) was added dropwise a solution of

terephthalic aldehyde (0.01 mol) in THF at -70 ^oC. The temperature was raised to a room and the

reaction mixture was left for a night. The solvent was evaporated, the residue was recrystallized

in heptane to give a yellow crystalline product, yield 50%. After second recrystallization in

1

heptane m.p. 188.5-190 °С. Н NMR (CDCl₃):  1.05 t (³Jнн 7 Hz, 24H, СНзСН,); 3.03 dq

3

2

(³Jнн 7 Hz, J_PH11 Hz, 16Н, NСН₂); 6.33 d.d (³Jнн 17 Hz, J_PH17 Hz, 2Н, РСН=С); 7.30 d.d

3

13

(³J_НН17 Hz, J_РН19 Hz, 2Н, С=СН); 7.44 m (4Н, С₆Н₄). C NMR (CDCl₃):  14.00 d (³J_PC

8

Hz); 41.80; 105.70 (¹J_PC180 Hz, PCH=); 129.80; 137.70; 154.20 (²J_PC32 Hz). ³¹Р NMR

(CDCl₃): _P24.80 ppm.

Anal. Calcd. for С₂₀Н₄₈Н₂О₂Р₂: С 61.16; Н 9.47; N 10.97%. Found С 61.31; Н 9.66; N10.85%.

20

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Table 1 Vinylphosphonates 6a-m

Yield,%^a)

Comp- R¹

d

R³

R⁴

bp ^oC (p

_P,

mmHg)/

ppm

mp ^oC (solvent)

138 (heptane)

t-Bu

H

Ph

50

40

85

80

72

68

80

79

60

35.0

22.0

24.7

24.3

23.95

24.1

23.30

25.0

6a

6b

6c

6d

6e

6f

Ph

165 (heptane)

103.5 (hexane)

120 (0.05)

Et₂N

Ph

Me

Pr

120 (0.05)

Bu

120-123 (0.04)

135 (0.06)

C₆H₁₃

C₈H₁₇

PhCH=CH-

6g

6h

6i

145-150 (0.05)

170 (0.06)

Me₂C=CHCH₂CH₂C(Me)CH= 35

C-

160 (0.08)

6j

Et₂N

CF₃Ph

74

140 (0.03)

17.0;

18.7^b)

23.7

6k

Et₂N

H

-C₆H₄CHO-4

-C₆H₄CH=CHP(O)(NEt₂)₂

50

98 (hexane)

6l

190 (heptane)

24.8

6m

^a)yield of the isolated product; ^b)mixture of E/Z-diastereomers in 97:3 ratio

24

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.Table 2. 2-Fluoro-3-Silyl-1,2⁵-oxaphosphetanes 2a-h

№

comp-d

2a

R¹

R²

H

R³

Ph

J_PF,Hz Threo/Erythro

_P, ppm

_F, ppm

Et₂N

—39.18 —40.89

—38.83 —39.54

670

3 : 2

t-Bu

Ph

H

Ph

Pr

-

768

670

768

763

777

774

4 : 1

-

2b

2c

2d

11.0

—43.50 —29.5

—39.27 —43.71

—42.11 —42.61

—39.22 —43.71

—42.32 —42.61

Et₂N

4 : 1

Et₂N

H

Bu

4 : 1

3 : 1

4 : 1

3 : 1

2e

2f

H

C₆H₁₃—39 .20 —43.71

—42.10 —42.61

H

C₈H₁₇—39 .88 —42.85

—42.20 —42.07

2g

2h

CF₃

Ph

—38.60 —41.11

—37 .45 —49.01

25

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Scheme 1. Examples of stable oxaphosphetanes

26

ACCEPTED MANUSCRIPT

R¹=Ph, R²=Me₃Si (1a); R¹=t-Bu, R²=Me₃Si (1b); R¹=Et₂N, R²=Me₃Si (1c); R¹=Et₂N, R²=H

(1d);

R¹=Et₂N, R²=Me₃Si, R³=Ph, R⁴=H (2a); R¹=t-Bu, R²=Me₃Si, R³=Ph, R⁴=H (2b); R¹=Ph,

R²=Me₃Si, R³=Ph, R⁴=H, (2c); R¹=Et₂N, R²=Me₃Si, R³=Pr, R⁴=H (2d); R¹= Et₂N, R²=Me₃Si,

R³=Bu, R⁴=H (2e); R¹= Et₂N, R²=Me₃Si, R³=C₆H₁₃, R⁴=H (2f); R¹= Et₂N, R²=Me₃Si, R³=C₈H₁₇,

R⁴=H (2g), R¹=Ph, R²=Me₃Si, R³=Ph, R⁴=CF₃(2h); R¹=Et₂N, R²=H, R³+R⁴=(CH₂)₅(2i);

R¹=Et₂N, R²=H, R³=R⁴=Me, (2j);

Scheme 2. Synthesis of 2-fluoro-1,2⁵-oxaphosphetanes 2a-j

27

ACCEPTED MANUSCRIPT

.

a=H₂O (-HF); b=HCl, ether (-HF); c=100-120^oC, ~0.5 hr (-HF) or BF₃Et₂O,+20^oC, 168

hr; d=60-80^oC (-Me₃SiF)

Scheme 3. Chemical properties of 2-fluoro-1,2⁵-oxaphosphetanes 2a-i

28

ACCEPTED MANUSCRIPT

Scheme 4 Effect of temperature on the stereoselectivity of 2-fluoro-1,2⁵-oxaphosphetane 2g

conversion into vinylphosphonates 6k

29

ACCEPTED MANUSCRIPT

Article Doi

Synthesis and properties of four-membered phosphorus heterocycles-2-Fluoro-1,2λ5-Oxaphosphetanes

DOI: 10.1080/10426507.2015.1054485

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Authors:

Article abstract of DOI:10.1080/10426507.2015.1054485

Full text of DOI:10.1080/10426507.2015.1054485

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