6-Bromo-5,8-dimethyl-2,2-diphenyl-2H-1-benzopyran

2H-Benzopyrans (chromenes) and their analogues are the subject of considerable current inter­est due to their highly desirable photochromic properties. In the title compound, C₂₃H₁₉BrO, the pyran ring displays a half-chair conformation. Crystal stability is governed only by van der Waals inter­actions.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.046
• wR factor = 0.115
• Data-to-parameter ratio = 20.3

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......       0.98
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       1.08
PLAT128_ALERT_4_C Non-standard setting of Space group P21/c   ....    P21/a

Alert level G
ABSTM02_ALERT_3_G  When printed, the submitted absorption T values will be
            replaced by the scaled T values. Since the ratio of scaled T's
            is identical to the ratio of reported T values, the scaling
            does not imply a change to the absorption corrections used in
            the study.
            Ratio of Tmax expected/reported      1.076
            Tmax scaled      0.570 Tmin scaled      0.516
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   3 ALERT level C = Check and explain
   3 ALERT level G = General alerts; check

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

This type of compounds (Gemert et al., 1999; Vol. 1, Chapter 3.) has many useful applications in the marketplace (Pozzo et al., 1996; Pozzo et al., 1997; Crano et al., 1996), for example they are used to construct ophthalmic glasses (Crano et al., 1996). Functionalization of chromenes with halogen units greatly enlarges their field of applications. Bromine-substituted 2H-benzopyrans are very convenient starting material for the synthesis of a wide range of modified chromenes (Shilova, Perevalov et al., 2007). The structure of this class of compounds has been well documented by UV and NMR spectroscopy (Kodaman et al., 2000; Bougdid et al., 2007). However no X-ray crystallographic analysis for halogen-substituted 2H-benzopyrans were presented to date. The aim of the current study is to identify more exactly the structure of these key chromenes.

As observed in compound (I) (Shilova, Bougdid et al., 2007) the pyran ring displays half-chair conformation with puckering amplitude (Q) = 0.446 (2) Å, θ = 112.1 (4)°, φ = 214.7 (4)° (Cremer & Pople, 1975) (Fig. 1). Except for the C7 atom which is out of the mean plane defined by the benzopyran ring, by 0.492 Å, this fragment is roughly planar. The crystal stability is only assumed by van der Waals interactions.

Figure 2, where the pyran rings have been superimposed, shows light geometry differences at the benzene rings level. They correspond to rotations around the bonds linking these rings to the pyran one, as it appears in the values of the torsion angles O14—C7—C8—C9; O14—C7—C6—C5, respectively 142.9 (2); 161.2 (2) for compound (I) and 134.5 (2); 171.6 (2) for compound (II). These rotations around σ bonds are not significative in terms of strain energy.

Related literature

For related literature, see: Bougdid et al. (2007); Crano et al. (1996); Cremer & Pople (1975); Gemert (1999); Kodaman et al. (2000); Pozzo et al. (1996, 1997); Shilova, Bougdid et al. (2007); Shilova, Perevalov et al. (2007).

S2. Experimental

6-Bromo-5,8-dimethyl-2,2-diphenyl-2H-1-benzopyran. 3,3-diphenylprop-1-yn-3-ol (11 mmol), 4-bromo-2,5-dimethylphenol (Bougdid et al., 2007) (10 mmol), a catalytic amount of p-toluene sulfonic acid (PTSA) and dry dichloromethane (20 ml) purged with argon and stirred at room temperature for 6–10 h. The progress of the reaction was monitored by TLC (pentane/Et₂O, 1:1). After complete disappearance of the bromophenol, the reaction mixture was washed with brine (3x20 ml). The organic layer was dried with MgSO₄, filtered and concentrated to dryness under reduced pressure. Purification by column chromatography (SiO₂; cyclohexane/dichloromethane gradient 100:0 to 50:50) afforded pure compound as a white solid (yield 85%). Light yellow crystals appropriate for data collection were obtained by slow evaporation from acetonitrile solution at 277 K. M.p. 153–154 ^oC. FT—IR (KBr): ν = 3060, 3024, 2952, 2921, 2853, 1625, 1593, 1493, 1450, 1380, 1364, 1236, 1230, 1203, 1168, 1095, 1062, 1031, 970, 907, 864, 770, 754, 700, 573 cm^-1 _. ¹H NMR (250 MHz, CDCl₃): δ = 2.25 (s, 3 H), 2.35 (s, 3 H), 6.21 (d, J = 10.0 Hz, 1 H), 6.84 (d, J = 10.0 Hz, 1 H), 7.18 (br s, 1 H), 7.21–7.46 (m, 10 H). ¹³C NMR (62.5 MHz, CDCl3): δ = 15.5 (CH₃), 18.1 (CH₃), 81.6 (OC), 116.2 (C), 120.9 (C), 121.4 (CH=), 125.2 (C), 126.7 (4 x CH=), 127.5 (2 x CH=), 128.1 (4 x CH=), 129.3 (CH=), 130.8 (C), 133.7 (CH=), 144.9 (2 x C), 149.8 (C). Anal. Calcd. for C₂₃H₁₉BrO: C, 70.59; H, 4.89; Br, 20.42. Found: C, 70.56; H, 4.79; Br, 20.48.

S3. Refinement

All H atoms were fixed geometrically and treated as riding with C—H = 0.93 Å (aromatic) or 0.96 Å (methyl) with U_iso(H) = xU_eq(C) where x = 1.2 for H aromatic and 1.5 for H methyl.

Computing details

Data collection: KappaCCD Reference Manual (Nonius, 1998); cell refinement: DENZO and SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: PLATON (Spek, 2003).

Figures

	Fig. 1. Molecular view of compound (I) with the atom-labelling scheme. Ellipsoids are drawn at the 50% propability level. H atoms are represented as small sphers of arbitrary radii.
	Fig. 2. Compounds (I) and compound (II) with the pyran rings superimposed.

6-Bromo-5,8-dimethyl-2,2-diphenyl-2H-1-benzopyran

Crystal data

C23H19BrO	Dx = 1.417 Mg m^−3
Mr = 391.29	Melting point: 427(1) K
Monoclinic, P21/a	Mo Kα radiation, λ = 0.71073 Å
a = 8.8953 (2) Å	Cell parameters from 17209 reflections
b = 22.4365 (5) Å	θ = 0.9–28.7°
c = 9.2114 (1) Å	µ = 2.25 mm^−1
β = 93.921 (2)°	T = 293 K
V = 1834.10 (6) Å^3	Cube, light yellow
Z = 4	0.30 × 0.25 × 0.25 mm
F(000) = 800

Data collection

Nonius KappaCCD area-detector diffractometer	4630 independent reflections
Radiation source: fine-focus sealed tube	3552 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.038
φ scans	θmax = 28.7°, θmin = 3.2°
Absorption correction: multi-scan (Blessing & Langs, 1987)	h = −11→9
Tmin = 0.48, Tmax = 0.53	k = −30→27
17209 measured reflections	l = −10→12

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)] = 0.046	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.115	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0381P)^2 + 1.5124P] where P = (Fo^2 + 2Fc^2)/3
4630 reflections	(Δ/σ)max = 0.014
228 parameters	Δρmax = 0.75 e Å^−3
0 restraints	Δρmin = −0.89 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
C1	0.1988 (3)	0.46171 (12)	0.1181 (3)	0.0500 (6)
H1	0.1956	0.4588	0.0172	0.060*
C2	0.1233 (3)	0.50778 (13)	0.1826 (4)	0.0607 (7)
H2	0.0706	0.5357	0.1244	0.073*
C3	0.1255 (3)	0.51266 (14)	0.3307 (4)	0.0655 (8)
H3	0.0749	0.5437	0.3731	0.079*
C4	0.2032 (4)	0.47115 (16)	0.4163 (4)	0.0692 (8)
H4	0.2048	0.4741	0.5171	0.083*
C5	0.2789 (3)	0.42512 (14)	0.3535 (3)	0.0578 (7)
H5	0.3306	0.3972	0.4124	0.069*
C6	0.2786 (3)	0.42021 (11)	0.2033 (3)	0.0421 (5)
C7	0.3662 (3)	0.36977 (10)	0.1367 (2)	0.0384 (5)
C8	0.5311 (3)	0.37212 (10)	0.1974 (2)	0.0385 (5)
C9	0.5947 (3)	0.32934 (11)	0.2914 (3)	0.0456 (5)
H9	0.5374	0.2969	0.3177	0.055*
C10	0.7431 (3)	0.33457 (14)	0.3465 (3)	0.0551 (7)
H10	0.7845	0.3059	0.4103	0.066*
C11	0.8296 (3)	0.38209 (15)	0.3073 (3)	0.0605 (7)
H11	0.9292	0.3855	0.3440	0.073*
C12	0.7673 (3)	0.42461 (15)	0.2131 (3)	0.0636 (8)
H12	0.8256	0.4565	0.1855	0.076*
C13	0.6186 (3)	0.42003 (12)	0.1595 (3)	0.0530 (6)
H13	0.5771	0.4493	0.0975	0.064*
O14	0.36250 (18)	0.38213 (7)	−0.01785 (16)	0.0401 (4)
C15	0.4191 (2)	0.33737 (10)	−0.1008 (2)	0.0383 (5)
C16	0.3976 (3)	0.27765 (11)	−0.0641 (3)	0.0416 (5)
C17	0.3108 (3)	0.26690 (11)	0.0623 (3)	0.0469 (6)
H17	0.2682	0.2296	0.0759	0.056*
C18	0.2926 (3)	0.30986 (11)	0.1574 (3)	0.0460 (5)
H18	0.2349	0.3034	0.2365	0.055*
C19	0.4881 (3)	0.35455 (11)	−0.2249 (3)	0.0439 (5)
C20	0.5425 (3)	0.30952 (12)	−0.3095 (3)	0.0503 (6)
H20	0.5911	0.3192	−0.3926	0.060*
C21	0.5256 (3)	0.25056 (12)	−0.2724 (3)	0.0499 (6)
C22	0.4524 (3)	0.23218 (11)	−0.1512 (3)	0.0472 (6)
C23	0.5019 (4)	0.41928 (13)	−0.2651 (3)	0.0616 (7)
H23A	0.5482	0.4225	−0.3560	0.092*
H23B	0.5627	0.4396	−0.1906	0.092*
H23C	0.4035	0.4370	−0.2745	0.092*
Br24	0.60679 (4)	0.192806 (16)	−0.39843 (4)	0.07243 (14)
C25	0.4343 (4)	0.16768 (13)	−0.1121 (4)	0.0683 (8)
H25A	0.3649	0.1490	−0.1824	0.102*
H25B	0.3963	0.1648	−0.0173	0.102*
H25C	0.5303	0.1481	−0.1116	0.102*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0454 (14)	0.0468 (14)	0.0574 (15)	0.0011 (11)	0.0006 (11)	−0.0021 (11)
C2	0.0478 (15)	0.0481 (15)	0.086 (2)	0.0045 (12)	0.0019 (14)	−0.0048 (14)
C3	0.0476 (16)	0.0611 (18)	0.089 (2)	0.0034 (13)	0.0184 (15)	−0.0213 (16)
C4	0.0638 (19)	0.085 (2)	0.0607 (18)	0.0075 (17)	0.0183 (14)	−0.0171 (16)
C5	0.0547 (16)	0.0704 (18)	0.0491 (15)	0.0091 (14)	0.0096 (12)	−0.0023 (13)
C6	0.0344 (11)	0.0439 (12)	0.0484 (13)	−0.0035 (10)	0.0049 (9)	−0.0023 (10)
C7	0.0397 (11)	0.0400 (12)	0.0357 (11)	−0.0021 (9)	0.0033 (8)	0.0023 (8)
C8	0.0408 (12)	0.0410 (12)	0.0340 (11)	0.0014 (9)	0.0049 (8)	−0.0027 (8)
C9	0.0468 (13)	0.0483 (13)	0.0419 (13)	0.0031 (11)	0.0039 (10)	0.0013 (10)
C10	0.0487 (15)	0.0694 (18)	0.0464 (14)	0.0136 (13)	−0.0024 (11)	0.0011 (12)
C11	0.0398 (14)	0.083 (2)	0.0573 (16)	0.0015 (14)	−0.0031 (11)	−0.0092 (14)
C12	0.0490 (16)	0.0716 (19)	0.0696 (19)	−0.0171 (14)	−0.0012 (13)	0.0048 (15)
C13	0.0495 (15)	0.0527 (15)	0.0562 (15)	−0.0075 (12)	−0.0019 (11)	0.0081 (12)
O14	0.0463 (9)	0.0382 (8)	0.0359 (8)	0.0003 (7)	0.0021 (6)	0.0026 (6)
C15	0.0357 (11)	0.0401 (12)	0.0382 (11)	−0.0025 (9)	−0.0038 (8)	−0.0027 (9)
C16	0.0406 (12)	0.0404 (12)	0.0430 (12)	−0.0065 (10)	−0.0027 (9)	0.0005 (9)
C17	0.0483 (14)	0.0391 (13)	0.0531 (14)	−0.0122 (11)	0.0013 (10)	0.0057 (10)
C18	0.0457 (13)	0.0470 (14)	0.0458 (13)	−0.0086 (11)	0.0071 (10)	0.0070 (10)
C19	0.0420 (12)	0.0495 (13)	0.0396 (12)	−0.0082 (10)	−0.0013 (9)	0.0006 (10)
C20	0.0472 (14)	0.0657 (17)	0.0379 (12)	−0.0065 (12)	0.0017 (10)	−0.0054 (11)
C21	0.0426 (13)	0.0581 (15)	0.0478 (14)	0.0030 (11)	−0.0063 (10)	−0.0148 (11)
C22	0.0450 (13)	0.0417 (13)	0.0531 (14)	−0.0021 (10)	−0.0092 (10)	−0.0059 (10)
C23	0.079 (2)	0.0568 (17)	0.0496 (15)	−0.0152 (15)	0.0081 (13)	0.0084 (12)
Br24	0.0667 (2)	0.0817 (3)	0.0678 (2)	0.01434 (16)	−0.00321 (14)	−0.03119 (16)
C25	0.081 (2)	0.0399 (15)	0.083 (2)	−0.0024 (14)	−0.0017 (17)	−0.0063 (14)

Geometric parameters (Å, º)

C1—C6	1.383 (4)	C12—H12	0.9300
C1—C2	1.388 (4)	C13—H13	0.9300
C1—H1	0.9300	O14—C15	1.378 (3)
C2—C3	1.367 (5)	C15—C19	1.389 (3)
C2—H2	0.9300	C15—C16	1.398 (3)
C3—C4	1.376 (5)	C16—C22	1.406 (3)
C3—H3	0.9300	C16—C17	1.460 (3)
C4—C5	1.381 (4)	C17—C18	1.320 (4)
C4—H4	0.9300	C17—H17	0.9300
C5—C6	1.388 (4)	C18—H18	0.9300
C5—H5	0.9300	C19—C20	1.383 (4)
C6—C7	1.526 (3)	C19—C23	1.506 (4)
C7—O14	1.449 (3)	C20—C21	1.377 (4)
C7—C18	1.513 (3)	C20—H20	0.9300
C7—C8	1.534 (3)	C21—C22	1.393 (4)
C8—C13	1.386 (3)	C21—Br24	1.914 (3)
C8—C9	1.388 (3)	C22—C25	1.503 (4)
C9—C10	1.387 (4)	C23—H23A	0.9600
C9—H9	0.9300	C23—H23B	0.9600
C10—C11	1.377 (4)	C23—H23C	0.9600
C10—H10	0.9300	C25—H25A	0.9600
C11—C12	1.380 (4)	C25—H25B	0.9600
C11—H11	0.9300	C25—H25C	0.9600
C12—C13	1.384 (4)
C6—C1—C2	120.2 (3)	C12—C13—H13	119.7
C6—C1—H1	119.9	C8—C13—H13	119.7
C2—C1—H1	119.9	C15—O14—C7	114.90 (17)
C3—C2—C1	120.8 (3)	O14—C15—C19	117.0 (2)
C3—C2—H2	119.6	O14—C15—C16	120.2 (2)
C1—C2—H2	119.6	C19—C15—C16	122.7 (2)
C2—C3—C4	119.3 (3)	C15—C16—C22	119.9 (2)
C2—C3—H3	120.3	C15—C16—C17	116.1 (2)
C4—C3—H3	120.3	C22—C16—C17	123.9 (2)
C3—C4—C5	120.4 (3)	C18—C17—C16	120.3 (2)
C3—C4—H4	119.8	C18—C17—H17	119.9
C5—C4—H4	119.8	C16—C17—H17	119.9
C4—C5—C6	120.6 (3)	C17—C18—C7	119.4 (2)
C4—C5—H5	119.7	C17—C18—H18	120.3
C6—C5—H5	119.7	C7—C18—H18	120.3
C1—C6—C5	118.6 (2)	C20—C19—C15	116.9 (2)
C1—C6—C7	121.9 (2)	C20—C19—C23	121.9 (2)
C5—C6—C7	119.6 (2)	C15—C19—C23	121.2 (2)
O14—C7—C18	108.25 (18)	C21—C20—C19	120.9 (2)
O14—C7—C6	105.95 (18)	C21—C20—H20	119.6
C18—C7—C6	111.76 (19)	C19—C20—H20	119.6
O14—C7—C8	107.96 (17)	C20—C21—C22	123.3 (2)
C18—C7—C8	113.33 (19)	C20—C21—Br24	116.6 (2)
C6—C7—C8	109.25 (18)	C22—C21—Br24	120.2 (2)
C13—C8—C9	118.8 (2)	C21—C22—C16	116.3 (2)
C13—C8—C7	118.3 (2)	C21—C22—C25	122.7 (3)
C9—C8—C7	122.9 (2)	C16—C22—C25	121.0 (3)
C10—C9—C8	120.5 (2)	C19—C23—H23A	109.5
C10—C9—H9	119.7	C19—C23—H23B	109.5
C8—C9—H9	119.7	H23A—C23—H23B	109.5
C11—C10—C9	120.3 (3)	C19—C23—H23C	109.5
C11—C10—H10	119.9	H23A—C23—H23C	109.5
C9—C10—H10	119.9	H23B—C23—H23C	109.5
C10—C11—C12	119.5 (3)	C22—C25—H25A	109.5
C10—C11—H11	120.2	C22—C25—H25B	109.5
C12—C11—H11	120.2	H25A—C25—H25B	109.5
C11—C12—C13	120.4 (3)	C22—C25—H25C	109.5
C11—C12—H12	119.8	H25A—C25—H25C	109.5
C13—C12—H12	119.8	H25B—C25—H25C	109.5
C12—C13—C8	120.5 (3)
O14—C7—C8—C9	−134.5 (2)	O14—C7—C6—C5	−171.6 (2)