Diethyl [(2RS,5RS)-5-iso­propyl-2,3,3-tri­methylpyrrolidin-2-yl]­phos­phon­ate

The cis or trans conformation of the title compound (C₁₄H₃₀NO₃P) is difficult to predict because of its dependancy on experimental conditions. X-ray analysis shows a trans stereochemistry of the methyl and iso­propyl groups in [alpha] positions with respect to the N atom.

S1. Comment

Nitroxide radicals are becoming an increasingly important aspect of chemical applications due to the enormous need of materials enjoying new or improved physical and chemical properties. After being used in ESR as spin probes (Zhdanov, 1992; Keana, 1984; Berliner, 1976), they have also been applied as contrast-enhancing agents for magnetic resonance imaging (Kuppusamy et al., 1995). Recently, stable nitroxide radicals found a successful application in the field of Living Free Radical Polymerization (Hawker, 1997; Grimaldi et al., 1997). The concept of using stable free radicals, such as pyrrolidine derived from β-phosphorylated nitroxides, has been extensively developed in our laboratory. These nitroxides are prepared by oxidation of the corresponding α-phosphorylated pyrrolidines (Roubaud et al., 1994, 1996). However, mixtures of cis and trans isomers were obtained by using this method. Recently, we have reported the cyclization of β-allenic aminophosphonates into α-phosphorylated pyrrolines (Amedjkouh et al., 1997). Its reduction with NaBH₄ leads only to the cis isomer, thus a series of (2,3,5-alkylpyrrolidin-2-yl)diethylphosphonates was prepared. In the present paper, we report the structure of diethyl [(2RS,5RS)-5-isopropyl-2,3,3-trimethylpyrrolidin-2-yl]phosphonate, (I).

As a precursor for a new serie of pyrrolidinyl nitroxides, the title compound was obtained using our new procedure. The crystallographic conformation of the pyrrolidinyl ring is ³T₄ [the puckering parameters (Cremer & Pople, 1975) are: q = 0.374 (3) Å and ϕ = 85.1 (5)°] as it is usually observed for this kind of molecules. The methyl and isopropyl moities borne by C₅ and C₆, respectively, are in trans positions. The diethoxyphosphoryl group occupies the axial position on C₅ [the angle between the bond C—P and the normal of the ring mean plane is 14.3 (2)°]. The crystal packing is assumed by N1—H30···O3(3/2 − x, y − 1/2, 3/2 − z) hydrogen bond with H30···O3 2.30 (3) Å and N1—H30···O3(3/2 − x, y − 1/2, 3/2 − z) 152 (3)°, and usual van der Waals interactions of which the shortest distance is C14···H10(C8)(x − 1/2, 1/2 − y, z − 1/2) 3.09 (19) Å.

S2. Experimental

(5-Isopropyl-2,3,3-trimethylpyrrolidin-2-yl)diethylphosphonate was synthesized by reduction of the corresponding pyrroline (Amedjkouh et al., 1997, 2000) with sodium borohydride. Suitable colorless prisms for X-ray analysis were grown in pentane solution in the fridge or at room temperature by slow evaporation.

S3. Refinement

All the H atoms were theoretically located except for the H₃₀ atom borne by the N atom, which was refined.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: BEGIN SDP (Frenz, 1985); program(s) used to solve structure: MULTAN80 (Main et al., 1980); program(s) used to refine structure: LSFM SDP (Frenz, 1985); software used to prepare material for publication: CIF VAX MolEN (Fair, 1990).

(I)

Crystal data

C14H30NO3P	F(000) = 640
Mr = 291.37	Dx = 1.10 Mg m^−3 Dm = 1.11 (2) Mg m^−3 Dm measured by flotation
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 9.552 (3) Å	Cell parameters from 25 reflections
b = 11.853 (7) Å	θ = 10–16°
c = 15.615 (4) Å	µ = 0.16 mm^−1
β = 96.47 (2)°	T = 294 K
V = 1757 (2) Å^3	Prism, colorless
Z = 4	0.50 × 0.40 × 0.30 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	θmax = 24.7°, θmin = 2.2°
θ/2θ scans	h = −10→10
3018 measured reflections	k = 0→13
2744 independent reflections	l = 0→17
1861 reflections with I > 3σ(I)	2 standard reflections every 60 min
Rint = 0.030	intensity decay: −9.6%

Refinement

Refinement on F	0 restraints
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.049	w = 4Fo^2/[σ^2(Fo^2) + 0.0025Fo^4]
wR(F^2) = 0.069	(Δ/σ)max = 0.003
S = 1.17	Δρmax = 0.37 e Å^−3
1861 reflections	Δρmin = −0.20 e Å^−3
173 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
P	0.88259 (9)	0.11005 (7)	0.83161 (5)	0.0500 (2)
O1	1.0475 (2)	0.1212 (2)	0.8532 (1)	0.0657 (7)
O2	0.8394 (2)	0.0554 (2)	0.9170 (1)	0.0685 (7)
O3	0.8077 (2)	0.2156 (2)	0.8097 (2)	0.0648 (7)
N	0.7149 (2)	−0.0366 (2)	0.7492 (2)	0.0496 (7)
C1	1.1089 (4)	0.1940 (4)	0.9214 (3)	0.082 (1)
C2	0.8640 (3)	−0.0011 (2)	0.7501 (2)	0.0481 (8)
C3	0.8749 (3)	0.0415 (3)	0.6561 (2)	0.0533 (9)
C4	0.7266 (3)	0.0885 (3)	0.6322 (2)	0.0545 (9)
C5	0.6292 (3)	0.0080 (3)	0.6722 (2)	0.0488 (8)
C6	1.2599 (4)	0.2126 (4)	0.9098 (3)	0.104 (2)
C7	0.6958 (5)	0.0674 (4)	0.9410 (3)	0.094 (1)
C8	0.6995 (6)	0.1201 (5)	1.0244 (3)	0.120 (2)
C9	0.9628 (4)	−0.0979 (3)	0.7811 (2)	0.067 (1)
C10	0.9907 (4)	0.1298 (4)	0.6483 (2)	0.073 (1)
C11	0.8983 (4)	−0.0583 (4)	0.5970 (3)	0.082 (1)
C12	0.4930 (3)	0.0621 (3)	0.6952 (2)	0.060 (1)
C13	0.4058 (4)	−0.0214 (4)	0.7407 (3)	0.083 (1)
C14	0.4080 (4)	0.1110 (4)	0.6149 (3)	0.100 (2)
H1	1.1022	0.1584	0.9765	0.1011*
H2	1.0575	0.2635	0.9208	0.1011*
H3	1.3028	0.2621	0.9531	0.1275*
H4	1.3088	0.1446	0.9101	0.1275*
H5	1.2641	0.2497	0.8544	0.1275*
H6	0.6535	−0.0059	0.9443	0.1140*
H7	0.6394	0.1111	0.8995	0.1140*
H8	0.6069	0.1276	1.0393	0.1477*
H9	0.7549	0.0762	1.0655	0.1477*
H10	0.7408	0.1931	1.0207	0.1477*
H11	0.5966	−0.0497	0.6322	0.0638*
H12	0.7187	0.1626	0.6541	0.0697*
H13	0.7046	0.0902	0.5708	0.0697*
H14	0.9488	−0.1179	0.8383	0.0828*
H15	0.9447	−0.1616	0.7444	0.0828*
H16	1.0584	−0.0748	0.7798	0.0828*
H17	1.0684	0.0973	0.6267	0.0907*
H18	0.9531	0.1894	0.6107	0.0907*
H19	1.0186	0.1625	0.7039	0.0907*
H20	0.8289	−0.1142	0.6010	0.0999*
H21	0.8944	−0.0327	0.5387	0.0999*
H22	0.9896	−0.0903	0.6132	0.0999*
H23	0.5186	0.1222	0.7341	0.0754*
H24	0.3209	0.0156	0.7547	0.1036*
H25	0.3800	−0.0836	0.7048	0.1036*
H26	0.4570	−0.0460	0.7930	0.1036*
H27	0.3234	0.1440	0.6304	0.1256*
H28	0.4617	0.1660	0.5897	0.1256*
H29	0.3838	0.0517	0.5744	0.1256*
H30	0.711 (3)	−0.108 (3)	0.752 (2)	0.0507*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P	0.0492 (4)	0.0440 (4)	0.0561 (4)	0.0006 (4)	0.0022 (4)	−0.0000 (4)
O1	0.050 (1)	0.069 (1)	0.076 (1)	−0.006 (1)	−0.004 (1)	−0.015 (1)
O2	0.067 (1)	0.082 (2)	0.056 (1)	−0.002 (1)	0.005 (1)	0.007 (1)
O3	0.072 (1)	0.043 (1)	0.078 (1)	0.010 (1)	0.005 (1)	−0.002 (1)
N	0.046 (1)	0.042 (1)	0.061 (1)	−0.005 (1)	0.006 (1)	0.006 (1)
C1	0.070 (2)	0.080 (3)	0.091 (3)	−0.006 (2)	−0.011 (2)	−0.022 (2)
C2	0.040 (1)	0.041 (2)	0.063 (2)	0.002 (1)	0.006 (1)	−0.000 (2)
C3	0.048 (2)	0.056 (2)	0.058 (2)	−0.004 (2)	0.014 (1)	−0.003 (2)
C4	0.050 (2)	0.062 (2)	0.051 (2)	−0.004 (2)	0.001 (1)	0.007 (2)
C5	0.044 (2)	0.049 (2)	0.053 (2)	−0.004 (1)	0.003 (1)	−0.000 (2)
C6	0.070 (3)	0.091 (3)	0.144 (4)	−0.016 (2)	−0.021 (3)	−0.027 (3)
C7	0.087 (3)	0.127 (4)	0.069 (2)	−0.010 (3)	0.012 (2)	0.003 (3)
C8	0.144 (4)	0.133 (4)	0.086 (3)	−0.001 (4)	0.023 (3)	−0.023 (3)
C9	0.059 (2)	0.048 (2)	0.092 (2)	0.014 (2)	−0.002 (2)	0.000 (2)
C10	0.056 (2)	0.085 (2)	0.081 (2)	−0.015 (2)	0.018 (2)	0.007 (2)
C11	0.079 (2)	0.090 (3)	0.079 (2)	0.004 (2)	0.024 (2)	−0.022 (2)
C12	0.045 (2)	0.065 (2)	0.069 (2)	−0.001 (2)	0.003 (2)	0.002 (2)
C13	0.055 (2)	0.093 (3)	0.107 (3)	−0.010 (2)	0.028 (2)	−0.001 (2)
C14	0.056 (2)	0.129 (4)	0.112 (3)	0.012 (3)	−0.008 (2)	0.033 (3)

Geometric parameters (Å, º)

P—O1	1.579 (2)	C2—C9	1.529 (4)
P—O2	1.578 (3)	C3—C4	1.528 (4)
P—O3	1.463 (2)	C3—C10	1.537 (5)
P—C2	1.827 (3)	C4—C5	1.515 (4)
O1—C1	1.442 (5)	C5—C12	1.528 (4)
O2—C7	1.469 (5)	C7—C8	1.441 (6)
N—C2	1.484 (4)	C3—C11	1.533 (5)
N—C5	1.474 (4)	C12—C13	1.521 (5)
C1—C6	1.490 (6)	C12—C14	1.529 (5)
C2—C3	1.566 (5)
O1—P—O2	101.7 (1)	N—C2—C9	110.3 (2)
O1—P—O3	115.4 (1)	C3—C2—C9	115.8 (3)
O1—P—C2	103.0 (1)	N—C5—C4	104.6 (2)
O2—P—O3	112.4 (1)	N—C5—C12	111.6 (3)
O2—P—C2	106.2 (1)	C4—C5—C12	114.3 (3)
O3—P—C2	116.5 (1)	C5—C4—C3	105.4 (3)
P—O1—C1	121.4 (2)	C2—C3—C4	100.9 (2)
P—O2—C7	121.1 (2)	C2—C3—C10	114.7 (3)
C2—N—C5	110.5 (2)	C2—C3—C11	110.2 (3)
O1—C1—C6	108.5 (4)	C4—C3—C10	112.8 (3)
O2—C7—C8	110.1 (4)	C4—C3—C11	109.2 (3)
P—C2—N	103.3 (2)	C10—C3—C11	108.8 (3)
P—C2—C3	114.1 (2)	C5—C12—C13	111.2 (3)
P—C2—C9	108.2 (2)	C5—C12—C14	110.8 (3)
N—C2—C3	104.4 (2)	C13—C12—C14	111.2 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N—H30···O3^i	0.85 (4)	2.30 (3)	3.078 (4)	152 (3)

Symmetry code: (i) −x+3/2, y−1/2, −z+3/2.