trans-(1R,2R)-1-Benzyl-2-phenyl­cyclo­propane­carboxylic acid

The cyclo­propane ring of the title compound, C₁₇H₁₆O₂, shows a high level of substituent-induced bond-length asymmetry. The carboxyl group adopts a conformation that prompts electron-density transfer from the ring towards the carbonyl π system.

S1. Comment

Cyclopropanes are interesting building blocks often used in modern organic synthesis (de Meijere et al., 2006). In particular, cyclopropanecarboxylate groups are found in a number of biologically active species. Their synthesis is mostly based on a classical homologues Wittig reaction (Tombo & Bellus, 1991; Donaldson, 2001). Recently, we proposed a novel method based on transformation of the substituted α-phosphono-γ-lactones into the corresponding ethyl cyclopropanecarboxylates by treatment with sodium ethoxide in boiling THF (Krawczyk et al., 2005, 2007). The title compound, (I), is a key product of this synthesis. Morever, cyclopropane is an obvious example of a simple chemical system characterized by a substantial ring strain energy. Its molecular orbitals are prone to interactions with the exocyclic π electrons (Cameron et al., 1990). Spectroscopic and chemical studies have shown that the cyclopropyl group is similar to a double bond in many respects (Lauher & Ibers, 1975; Jason & Ibers, 1977).

A view of (I) with the atom-numbering scheme is shown in Fig. 1. The endocyclic C—C bonds show a distinctive bond-length asymmetry. The shortest bond (C1—C2; Table 1) is located opposite the carboxyl and benzyl substituents, while the longest (C2—C3) is positioned in front of the unsubstituted endocyclic C1 atom. C1—C3 is a distal bond for the phenyl substituent. Substituent-induced bond-length asymmetry in cyclopropanes was studied in a very systematic way by Allen (1980). He demonstrated that interactions of the Walsh (1947, 1949) orbitals with a π system of the substituent are responsible for the bond-length differences. In particular, for the carboxylate group, the maximum overlap occurs if the torsion angle τ (X_n,_m—C—C═O) is 0 or 180° (X_n,_m is the mid-point of the distal C_n—C_m bond). For the title compound, the value is -164.6 (2)° (the trans–gauche conformation) and indicates the high level of orbital interactions. For the phenyl substituent Allen suggests to calculate τ as an average of the two torsion angles X_C1,C3—C2—C12—C13 and X_C1,C3—C2—C12—C17; these angles should be normalized to the range 〈-90, 90°〉. The value calculated for (I) [τ = 63.4 (4)°] indicates that the phenyl ring adopts a conformation intermediate between gauche and perpendicular. The vicinal C3—C4 and C2—C12 bond lengths are very close to the model values (1.476 and 1.502 Å) as specified by Allen for the carboxylate and phenyl substituents, respectively.

The trans–gauche conformation of the carboxylic acid substituent fragment prompts electronic interactions involving the bonding σ,π and antibonding σ*,π* orbitals. The most important interactions (Table 2 and Fig. 2) were computed by the Weinhold natural bond orbitals deletion procedure (Glendening et al., 1992) for the wavefunctions calculated with GAUSSIAN03 (Frisch et al., 2004) at the B3LYP/6–311++G(d,p) level of theory for the X-ray-determined coordinates.

In particular, the endocyclic C1—C3 and C2—C3 bonds participate in the electron density transfer towards the carbonyl group in the σ–π* fashion (Graczyk & Mikołajczyk, 1994) (28.5 and 11.6 kJ mol^-1, respectively), while the reverse back–donation is much weaker (1.8 and 6.6 kJ mol^-1, respectively). In comparison to the above effect, interaction of the phenyl ring with the cyclopropane ring has a more complex character and involves significant mutual σ–π* and σ*–π interactions (19.7 and 13.1 kJ mol^-1, respectively).

In the crystal structure, molecules form centrosymmetric dimers connected by strong hydrogen bonds linking carboxylate groups of both monomers. In terms of graph-set terminology (Etter et al., 1990; Bernstein et al., 1995), this system can be described as R²₂(8).

Related literature

For related literature, see: Allen (1980); Bernstein et al. (1995); Cameron et al. (1990); Donaldson (2001); Etter et al. (1990); Frisch et al. (2004); Glendening et al. (1992); Graczyk & Mikołajczyk (1994); Jason & Ibers (1977); Krawczyk et al. (2005, 2007); Lauher & Ibers (1975); Meijere et al. (2006); Tombo & Bellus (1991); Walsh (1947, 1949).

S2. Experimental

To a suspension of sodium hydride (6.0 mmol) and α-diethoxyphosphoryl-α-benzyl-γ-phenyl-γ-butyrolactone (6.0 mmol) in tetrahydrofuran (15 ml) was added dropwise under argon atmosphere at room temperature a solution of ethanol (0.40 ml) in tetrahydrofuran (15 ml). The reaction mixture was stirred for 0.5 h and then heated at reflux for 8 h. After cooling to room temperature, saturated NaCl solution (5 ml) was added, and tetrahydrofuran was evaporated under reduced pressure. The residue was extracted with dichloromethane (3 × 15 ml) and dried (Na₂SO₄). After evaporation, the crude product was purified by column chromatography and subsequently hydrolized to give (I). Good quality single crystals were selected from the reaction mixture (Krawczyk et al., 2007).

S3. Refinement

H atoms were located in a difference Fourier map. Those bonded to C atoms were refined as riding. The hydroxy atom H1 was refined without constraints.

Computing details

Data collection: SMART (Bruker, 2003); cell refinement: SAINT-Plus (Bruker, 2003); data reduction: SAINT-Plus (Bruker, 2003); program(s) used to solve structure: SHELXTL (Bruker, 2003); program(s) used to refine structure: SHELXTL (Bruker, 2003); molecular graphics: SHELXTL (Bruker, 2003); software used to prepare material for publication: SHELXTL (Bruker, 2003) and publCIF (Westrip, 2007).

Figures

	Fig. 1. The molecule of the title compound. Displacement elipsoids are drawn at the 50% probability level.
	Fig. 2. Natural bond orbitals, as in (I), involved in the electron density transfer from the vicinal (a) C1—C3 and (b) C2—C3 bonds to the carbonyl group C4═O2, accompanied by the orbitals describing the major cyclopropyl–phenyl interactions (c).

rac-trans-(1R,2R)-1-Benzyl-2-phenylcyclopropanecarboxylic acid

Crystal data

C17H16O2	Z = 2
Mr = 252.30	F(000) = 268
Triclinic, P1	Dx = 1.252 Mg m^−3
a = 5.9983 (2) Å	Mo Kα radiation, λ = 0.71073 Å
b = 9.5439 (4) Å	Cell parameters from 5353 reflections
c = 12.7293 (5) Å	θ = 2.3–28.1°
α = 111.330 (1)°	µ = 0.08 mm^−1
β = 92.188 (1)°	T = 293 K
γ = 97.965 (1)°	Prism, colourless
V = 669.15 (4) Å^3	0.50 × 0.20 × 0.15 mm

Data collection

Bruker SMART APEX diffractometer	2348 independent reflections
Radiation source: fine-focus sealed tube	2270 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.021
ω scans	θmax = 25.0°, θmin = 1.7°
Absorption correction: multi-scan (SHELXTL; Bruker, 2003)	h = −7→7
Tmin = 0.872, Tmax = 0.988	k = −11→11
9804 measured reflections	l = −15→15

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.112	H atoms treated by a mixture of independent and constrained refinement
S = 1.07	w = 1/[σ^2(Fo^2) + (0.051P)^2 + 0.1541P] where P = (Fo^2 + 2Fc^2)/3
2348 reflections	(Δ/σ)max < 0.001
176 parameters	Δρmax = 0.16 e Å^−3
0 restraints	Δρmin = −0.14 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq
O1	0.7410 (2)	0.89897 (14)	0.01402 (10)	0.0689 (4)
H1	0.819 (4)	0.951 (3)	−0.036 (2)	0.121 (8)*
O2	1.06628 (18)	0.98230 (13)	0.12336 (9)	0.0604 (3)
C1	0.5162 (3)	0.79975 (19)	0.16732 (14)	0.0584 (4)
H11	0.4460	0.8013	0.2351	0.070*
H12	0.4299	0.8336	0.1177	0.070*
C2	0.6461 (2)	0.67518 (17)	0.11376 (12)	0.0511 (4)
H3	0.6393	0.6413	0.0310	0.061*
C3	0.7705 (2)	0.83928 (16)	0.17714 (11)	0.0449 (3)
C4	0.8697 (2)	0.91330 (16)	0.10207 (12)	0.0471 (3)
C5	0.9050 (2)	0.87711 (16)	0.28991 (12)	0.0459 (3)
H51	0.8406	0.8071	0.3243	0.055*
H52	1.0588	0.8603	0.2761	0.055*
C6	0.9119 (2)	1.03798 (16)	0.37287 (11)	0.0449 (3)
C7	0.7264 (3)	1.08002 (18)	0.43037 (13)	0.0574 (4)
H71	0.5951	1.0088	0.4158	0.069*
C8	0.7314 (3)	1.2252 (2)	0.50892 (15)	0.0690 (5)
H81	0.6039	1.2512	0.5460	0.083*
C9	0.9231 (4)	1.3310 (2)	0.53248 (15)	0.0703 (5)
H91	0.9275	1.4287	0.5860	0.084*
C10	1.1086 (3)	1.2917 (2)	0.47644 (15)	0.0694 (5)
H101	1.2397	1.3633	0.4921	0.083*
C11	1.1032 (3)	1.14665 (18)	0.39682 (14)	0.0573 (4)
H111	1.2304	1.1220	0.3589	0.069*
C12	0.6673 (3)	0.55238 (16)	0.15805 (12)	0.0500 (4)
C13	0.5043 (3)	0.50666 (19)	0.21760 (15)	0.0634 (4)
H131	0.3794	0.5560	0.2338	0.076*
C14	0.5247 (4)	0.3881 (2)	0.25345 (17)	0.0789 (6)
H141	0.4135	0.3589	0.2938	0.095*
C15	0.7056 (4)	0.3136 (2)	0.23042 (17)	0.0783 (6)
H151	0.7180	0.2339	0.2546	0.094*
C16	0.8681 (4)	0.3572 (2)	0.17148 (17)	0.0766 (5)
H161	0.9919	0.3067	0.1552	0.092*
C17	0.8500 (3)	0.47578 (19)	0.13597 (15)	0.0649 (4)
H171	0.9629	0.5048	0.0964	0.078*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0753 (8)	0.0827 (8)	0.0588 (7)	−0.0017 (6)	−0.0085 (6)	0.0449 (7)
O2	0.0594 (7)	0.0729 (7)	0.0585 (7)	0.0039 (6)	0.0052 (5)	0.0383 (6)
C1	0.0511 (9)	0.0707 (10)	0.0632 (10)	0.0143 (7)	0.0056 (7)	0.0349 (8)
C2	0.0555 (9)	0.0543 (8)	0.0429 (8)	0.0030 (7)	0.0021 (6)	0.0201 (7)
C3	0.0495 (8)	0.0469 (8)	0.0438 (7)	0.0114 (6)	0.0066 (6)	0.0218 (6)
C4	0.0544 (9)	0.0465 (8)	0.0453 (8)	0.0130 (6)	0.0039 (6)	0.0212 (6)
C5	0.0522 (8)	0.0477 (8)	0.0459 (8)	0.0113 (6)	0.0066 (6)	0.0255 (6)
C6	0.0542 (8)	0.0478 (8)	0.0406 (7)	0.0090 (6)	0.0031 (6)	0.0256 (6)
C7	0.0633 (10)	0.0568 (9)	0.0524 (9)	0.0066 (7)	0.0125 (7)	0.0212 (7)
C8	0.0863 (12)	0.0655 (11)	0.0567 (10)	0.0222 (9)	0.0177 (9)	0.0201 (8)
C9	0.1087 (15)	0.0495 (9)	0.0507 (9)	0.0138 (9)	0.0014 (9)	0.0167 (7)
C10	0.0828 (12)	0.0574 (10)	0.0638 (10)	−0.0098 (9)	−0.0095 (9)	0.0269 (9)
C11	0.0580 (9)	0.0603 (9)	0.0562 (9)	0.0042 (7)	0.0016 (7)	0.0269 (8)
C12	0.0593 (9)	0.0461 (8)	0.0400 (7)	−0.0008 (6)	0.0019 (6)	0.0141 (6)
C13	0.0661 (10)	0.0619 (10)	0.0639 (10)	0.0022 (8)	0.0126 (8)	0.0277 (8)
C14	0.0967 (14)	0.0694 (12)	0.0762 (12)	−0.0057 (11)	0.0183 (11)	0.0398 (10)
C15	0.1142 (16)	0.0515 (10)	0.0715 (12)	0.0048 (10)	0.0004 (11)	0.0296 (9)
C16	0.0980 (14)	0.0596 (11)	0.0763 (12)	0.0247 (10)	0.0106 (10)	0.0259 (9)
C17	0.0755 (11)	0.0612 (10)	0.0625 (10)	0.0149 (8)	0.0196 (8)	0.0256 (8)

Geometric parameters (Å, º)

C1—C2	1.481 (2)	C8—C9	1.365 (3)
C1—C3	1.508 (2)	C8—H81	0.9300
C2—C3	1.540 (2)	C9—C10	1.367 (3)
C2—C12	1.491 (2)	C9—H91	0.9300
C3—C4	1.4779 (19)	C10—C11	1.382 (2)
O2—C4	1.2362 (17)	C10—H101	0.9300
C3—C5	1.5152 (19)	C11—H111	0.9300
O1—C4	1.2901 (17)	C12—C13	1.378 (2)
O1—H1	1.02 (3)	C12—C17	1.382 (2)
C1—H11	0.9700	C13—C14	1.383 (3)
C1—H12	0.9700	C13—H131	0.9300
C2—H3	0.9800	C14—C15	1.362 (3)
C5—C6	1.508 (2)	C14—H141	0.9300
C5—H51	0.9700	C15—C16	1.363 (3)
C5—H52	0.9700	C15—H151	0.9300
C6—C11	1.378 (2)	C16—C17	1.378 (2)
C6—C7	1.381 (2)	C16—H161	0.9300
C7—C8	1.378 (2)	C17—H171	0.9300
C7—H71	0.9300
C2—C1—C3	62.02 (10)	C8—C7—H71	119.3
C1—C2—C3	59.88 (10)	C6—C7—H71	119.3
C1—C3—C2	58.10 (10)	C9—C8—C7	120.21 (17)
C4—O1—H1	112.8 (14)	C9—C8—H81	119.9
C2—C1—H11	117.6	C7—C8—H81	119.9
C3—C1—H11	117.6	C8—C9—C10	119.25 (17)
C2—C1—H12	117.6	C8—C9—H91	120.4
C3—C1—H12	117.6	C10—C9—H91	120.4
H11—C1—H12	114.7	C9—C10—C11	120.65 (17)
C1—C2—C12	122.77 (13)	C9—C10—H101	119.7
C12—C2—C3	121.19 (12)	C11—C10—H101	119.7
C1—C2—H3	114.1	C6—C11—C10	120.85 (16)
C12—C2—H3	114.1	C6—C11—H111	119.6
C3—C2—H3	114.1	C10—C11—H111	119.6
C4—C3—C1	117.41 (12)	C13—C12—C17	117.62 (15)
C4—C3—C5	116.29 (12)	C13—C12—C2	122.14 (15)
C1—C3—C5	119.54 (12)	C17—C12—C2	120.19 (14)
C4—C3—C2	113.93 (12)	C12—C13—C14	120.67 (18)
C5—C3—C2	118.79 (11)	C12—C13—H131	119.7
O2—C4—O1	123.11 (13)	C14—C13—H131	119.7
O2—C4—C3	120.76 (12)	C15—C14—C13	120.83 (18)
O1—C4—C3	116.12 (13)	C15—C14—H141	119.6
C6—C5—C3	114.71 (11)	C13—C14—H141	119.6
C6—C5—H51	108.6	C14—C15—C16	119.27 (17)
C3—C5—H51	108.6	C14—C15—H151	120.4
C6—C5—H52	108.6	C16—C15—H151	120.4
C3—C5—H52	108.6	C15—C16—C17	120.34 (19)
H51—C5—H52	107.6	C15—C16—H161	119.8
C11—C6—C7	117.59 (14)	C17—C16—H161	119.8
C11—C6—C5	121.85 (13)	C16—C17—C12	121.27 (17)
C7—C6—C5	120.53 (13)	C16—C17—H171	119.4
C8—C7—C6	121.44 (16)	C12—C17—H171	119.4
C1—C3—C4—O2	161.92 (14)	C3—C5—C6—C7	75.75 (17)
C2—C3—C4—O2	−132.99 (14)	C11—C6—C7—C8	0.0 (2)
C1—C2—C12—C13	27.5 (2)	C5—C6—C7—C8	178.11 (14)
C1—C2—C12—C17	−155.23 (15)	C6—C7—C8—C9	−0.7 (3)
C3—C1—C2—C12	109.79 (15)	C7—C8—C9—C10	0.7 (3)
C2—C1—C3—C4	102.45 (14)	C8—C9—C10—C11	0.0 (3)
C2—C1—C3—C5	−107.42 (14)	C7—C6—C11—C10	0.6 (2)
C1—C2—C3—C4	−108.48 (14)	C5—C6—C11—C10	−177.43 (13)
C12—C2—C3—C4	139.17 (14)	C9—C10—C11—C6	−0.6 (2)
C1—C2—C3—C5	108.69 (14)	C3—C2—C12—C13	99.54 (18)
C12—C2—C3—C5	−3.7 (2)	C3—C2—C12—C17	−83.17 (19)
C5—C3—C4—O2	10.82 (19)	C17—C12—C13—C14	−0.1 (2)
C1—C3—C4—O1	−19.14 (19)	C2—C12—C13—C14	177.30 (16)
C5—C3—C4—O1	−170.24 (12)	C12—C13—C14—C15	−0.2 (3)
C2—C3—C4—O1	45.96 (17)	C13—C14—C15—C16	0.1 (3)
C4—C3—C5—C6	69.96 (16)	C14—C15—C16—C17	0.2 (3)
C1—C3—C5—C6	−80.49 (16)	C15—C16—C17—C12	−0.5 (3)
C2—C3—C5—C6	−148.06 (13)	C13—C12—C17—C16	0.4 (3)
C3—C5—C6—C11	−106.23 (16)	C2—C12—C17—C16	−176.98 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2^i	1.02 (3)	1.61 (3)	2.629 (2)	175 (2)

Symmetry code: (i) −x+2, −y+2, −z.