6-Hydroxy-2,2-di­methyl-3,4-di­hydro-2H-benzo[b]pyran

The title compound, 2,2-di­methyl­chroman-6-ol, C₁₁H₁₄O₂, has been identified as a side product from the condensation of hydro­quinone with 2-methyl­but-3-en-2-ol. The pyran ring has a half-chair conformation. The hydroxyl groups are involved in intermolecular hydrogen bonding which generates infinite spiral chains around the fourfold screw axes; the O...O hydrogen-bonded distances are 2.661 (1) Å.

S1. Comment

Chromans are known to possess pronounced antioxidant activity (Cotelle et al., 1991, 1992; Pearce et al., 1994). This basic unit is also present in α-tocopherol which is a commercial, naturally occurring antioxidant. Such compounds are also used as colour photographic recording materials (Fujiwhara et al., 1978) and in pharmaceutical compositions (Evans et al., 1981). We have prepared several chromanols for biotransformation studies for structure-activity relationship studies as antitumour agents (Parmar et al., 1994, 1997). In one such reaction, the title compound, (I), was obtained as a side product during the condensation of hydroquinone with 2-methylbut-3-ene-2-ol in the form of colourless crystals; its structure was determined in order to assign its constitution unambiguously. \sch

The molecular structure is illustrated in Fig. 1 and selected geometric parameters are given in Table 1. Bond lengths and angles are largely unexceptional. An analysis (Cremer & Pople, 1975; Farrugia, 1998) of the puckering in the six-membered pyran ring gives a puckering amplitude of 0.485 Å, with θ = 49.9 and ϕ = 85.95°; this corresponds to a half-chair conformation. The C12 methyl group occupies an axial position, whilst the hydrogen atoms are attached to C4 in axial and bisectional orientations.

The title compound has been briefly reported in an earlier study (Mukai et al., 1993) concerned with the extent of orbital overlap between the 2p lone pair on the ring oxygen with the aromatic π-electron system in a series of related compounds. It was argued that the larger this overlap, the smaller the torsion angle C2—O1—C9—C10. This torsion angle was given as 18.0° based upon an X-ray investigation and as 20.1° from ab initio calculations; the value of −19.7 (2)° obtained in the present study is in excellent agreement with that obtained from the theoretical study.

The hydroxyl oxygen atoms form inter-molecular hydrogen bonds with two other molecules (Table 2 and Fig. 2) thus producing infinite polymeric spiral chains around the fourfold screw axes.

S2. Experimental

To a stirred solution of hydroquinone (2.2 g, 20 mmol) and boron trifluoride etherate (0.3 ml) in dioxane (15 ml) at 300 K, a solution of 2-methylbut-3-ene-2-ol (2.6 g, 20 mmol) was added dropwise over 30 min. The reaction mixture was stirred for a further hour at 300 K and then quenched using moist ether; the mixture was diluted with water (100 ml) and extracted with ether (3 x 50 ml). The ether layer was dried over anhydrous Na₂SO₄, the solvent was removed and the residue chromatographed over silica gel to afford (I). It was recrystallized from chloroform as colourless crystals, m.p. 348 K (literature m.p. 348–49 K; Nilsson et al., 1968).

S3. Refinement

The hydroxyl hydrogen atom was added from an electron density map and freely refined. Other hydrogen atoms were added at calculated positions and refined using a riding model with C—H distances 0.95–0.99 Å. H atoms were given isotropic displacement parameters equal to 1.2 (or 1.5 for methyl H atoms) times the equivalent isotropic displacement parameter of their parent atoms.

Computing details

Data collection: SMART (Siemens, 1994a); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT; program(s) used to solve structure: SHELXTL/PC (Siemens, 1994b); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL/PC; software used to prepare material for publication: SHELXTL/PC.

Figures

	Fig. 1. Atomic numbering with displacement ellipsoids at the 50% level.
	Fig. 2. Packing diagram viewed down the c axis.

2,2-Dimethyl-3,4-dihydro-6-hydroxy-(2H)-benzo-(1,2 − b)-pyran

Crystal data

C11H14O2	Dx = 1.206 Mg m^−3
Mr = 178.22	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I41/a	Cell parameters from 4204 reflections
Hall symbol: -I 4ad	θ = 2.3–27.5°
a = 25.1353 (12) Å	µ = 0.08 mm^−1
c = 6.2139 (4) Å	T = 180 K
V = 3925.8 (4) Å^3	Block, colourless
Z = 16	0.30 × 0.22 × 0.20 mm
F(000) = 1536

Data collection

Siemens SMART CCD area-detector diffractometer	2237 independent reflections
Radiation source: normal-focus sealed tube	1510 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.047
Detector resolution: 8.192 pixels mm^-1	θmax = 27.5°, θmin = 2.3°
ω scans	h = −31→32
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	k = −21→32
Tmin = 0.976, Tmax = 0.984	l = −8→6
11034 measured reflections

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)] = 0.047	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.115	H atoms treated by a mixture of independent and constrained refinement
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0488P)^2 + 1.8457P] where P = (Fo^2 + 2Fc^2)/3
2237 reflections	(Δ/σ)max < 0.001
124 parameters	Δρmax = 0.14 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3

Special details

Experimental. UV(MeOH) λ_max(nm): 297 and 268; IR(KBr) ν_max/cm⁻¹: 3202, 1594, 1380, 1367, 1353, 1322, 1289, 1249, 1201, 1160, 1149, 1122, 948, 923, 894, 864, 819, 793, 620, 579, 501, 470; ¹H NMR (δ, CDCl₃, 300 MHz): 1.30 (6H, s, 2xCH₃), 1.75 (2H, t, J = 6.5 Hz, H-3), 2.69 (2H, t, J = 6.5 Hz, H-4), 5.36 (1H, s, C-6 OH) & 6.55–6.65 (3H, m, H-5, H-7 & H-8); ¹³C NMR (δ, CDCl₃, 75 MHz): 22.60 (C-3), 26.70 (2xCH₃), 32.77 (C-4) 74.01 (C-2), 114.59, 115.55, 117.78 (C-5, C-7 & C-8), 121.83 (C-4a), 147.73 & 148.57 (C-6 & C-8a); EIMS, m/z (% rel. int.): [M⁺] 178 (53), 163 (18), 123 (95), 107 (43), 94 (100), 77 (40), 65 (58).

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.

The temperature of the crystal was controlled using the Oxford Cryosystem Cryostream Cooler (Cosier & Glazer, 1986). Data were collected over a hemisphere of reciprocal space, by a combination of three sets of exposures. Each set had a different ϕ angle for the crystal and each exposure of 10 s covered 0.3° in ω. The crystal to detector distance was 5.01 cm. Coverage of the unique set was over 99% complete to at least 27° in θ. Crystal decay was monitored by repeating the initial frames at the end of the data collection and analyzing the duplicate reflections.

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

	x	y	z	Uiso*/Ueq
O1	0.50790 (4)	0.43699 (4)	0.80152 (18)	0.0355 (3)
O2	0.31070 (4)	0.49708 (5)	0.49208 (19)	0.0354 (3)
H2	0.2935 (9)	0.5180 (9)	0.587 (4)	0.070 (7)*
C2	0.53615 (6)	0.39350 (6)	0.6972 (3)	0.0325 (4)
C3	0.53548 (6)	0.40296 (7)	0.4561 (3)	0.0362 (4)
H3A	0.5559	0.3745	0.3836	0.043*
H3B	0.5530	0.4373	0.4241	0.043*
C4	0.47889 (7)	0.40384 (7)	0.3671 (3)	0.0381 (4)
H4A	0.4790	0.4199	0.2216	0.046*
H4B	0.4655	0.3669	0.3545	0.046*
C5	0.39220 (6)	0.45176 (6)	0.4434 (3)	0.0310 (4)
H5A	0.3803	0.4423	0.3033	0.037*
C6	0.35948 (6)	0.48131 (6)	0.5748 (3)	0.0282 (4)
C7	0.37583 (6)	0.49519 (6)	0.7802 (3)	0.0311 (4)
H7A	0.3531	0.5152	0.8716	0.037*
C8	0.42549 (6)	0.47954 (6)	0.8503 (3)	0.0323 (4)
H8A	0.4371	0.4892	0.9903	0.039*
C9	0.45861 (6)	0.44976 (6)	0.7182 (2)	0.0287 (4)
C10	0.44249 (6)	0.43542 (6)	0.5120 (3)	0.0291 (4)
C11	0.59202 (6)	0.39632 (7)	0.7880 (3)	0.0422 (4)
H11A	0.6087	0.4299	0.7445	0.063*
H11B	0.6130	0.3664	0.7328	0.063*
H11C	0.5905	0.3944	0.9454	0.063*
C12	0.50900 (7)	0.34199 (7)	0.7608 (3)	0.0450 (5)
H12A	0.5120	0.3370	0.9167	0.067*
H12B	0.5261	0.3122	0.6865	0.067*
H12C	0.4714	0.3436	0.7203	0.067*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0316 (6)	0.0410 (7)	0.0338 (7)	0.0081 (5)	−0.0037 (5)	−0.0027 (5)
O2	0.0270 (6)	0.0378 (7)	0.0415 (7)	0.0041 (5)	−0.0054 (5)	−0.0121 (6)
C2	0.0287 (8)	0.0320 (8)	0.0368 (9)	0.0045 (7)	0.0044 (7)	0.0043 (7)
C3	0.0329 (9)	0.0394 (9)	0.0364 (10)	0.0060 (7)	0.0073 (7)	0.0039 (8)
C4	0.0400 (10)	0.0414 (10)	0.0329 (9)	0.0112 (8)	0.0019 (8)	−0.0042 (8)
C5	0.0322 (8)	0.0324 (8)	0.0284 (9)	0.0008 (6)	−0.0020 (7)	−0.0040 (7)
C6	0.0250 (8)	0.0256 (8)	0.0340 (9)	−0.0016 (6)	−0.0013 (7)	−0.0010 (7)
C7	0.0315 (8)	0.0309 (8)	0.0310 (9)	0.0011 (6)	0.0034 (7)	−0.0037 (7)
C8	0.0349 (9)	0.0366 (9)	0.0252 (8)	0.0004 (7)	−0.0005 (7)	−0.0027 (7)
C9	0.0277 (8)	0.0292 (8)	0.0291 (8)	0.0000 (6)	0.0007 (7)	0.0028 (7)
C10	0.0307 (8)	0.0270 (8)	0.0297 (9)	0.0013 (6)	0.0033 (7)	0.0008 (7)
C11	0.0323 (9)	0.0470 (11)	0.0474 (11)	0.0050 (8)	−0.0009 (8)	0.0041 (9)
C12	0.0372 (10)	0.0400 (10)	0.0577 (12)	0.0032 (8)	0.0029 (9)	0.0157 (9)

Geometric parameters (Å, º)

O1—C9	1.3805 (19)	C5—C10	1.396 (2)
O1—C2	1.4560 (19)	C5—H5A	0.9500
O2—C6	1.3873 (18)	C6—C7	1.386 (2)
O2—H2	0.90 (2)	C7—C8	1.379 (2)
C2—C11	1.515 (2)	C7—H7A	0.9500
C2—C12	1.516 (2)	C8—C9	1.388 (2)
C2—C3	1.517 (2)	C8—H8A	0.9500
C3—C4	1.526 (2)	C9—C10	1.391 (2)
C3—H3A	0.9900	C11—H11A	0.9800
C3—H3B	0.9900	C11—H11B	0.9800
C4—C10	1.509 (2)	C11—H11C	0.9800
C4—H4A	0.9900	C12—H12A	0.9800
C4—H4B	0.9900	C12—H12B	0.9800
C5—C6	1.376 (2)	C12—H12C	0.9800
C9—O1—C2	116.44 (12)	C7—C6—O2	122.10 (14)
C6—O2—H2	110.4 (14)	C8—C7—C6	119.17 (15)
O1—C2—C11	104.54 (13)	C8—C7—H7A	120.4
O1—C2—C12	107.80 (13)	C6—C7—H7A	120.4
C11—C2—C12	111.11 (14)	C7—C8—C9	120.66 (15)
O1—C2—C3	108.45 (13)	C7—C8—H8A	119.7
C11—C2—C3	111.76 (14)	C9—C8—H8A	119.7
C12—C2—C3	112.72 (15)	O1—C9—C8	116.22 (14)
C2—C3—C4	111.74 (14)	O1—C9—C10	123.13 (14)
C2—C3—H3A	109.3	C8—C9—C10	120.63 (14)
C4—C3—H3A	109.3	C9—C10—C5	117.96 (14)
C2—C3—H3B	109.3	C9—C10—C4	120.59 (14)
C4—C3—H3B	109.3	C5—C10—C4	121.44 (15)
H3A—C3—H3B	107.9	C2—C11—H11A	109.5
C10—C4—C3	110.89 (14)	C2—C11—H11B	109.5
C10—C4—H4A	109.5	H11A—C11—H11B	109.5
C3—C4—H4A	109.5	C2—C11—H11C	109.5
C10—C4—H4B	109.5	H11A—C11—H11C	109.5
C3—C4—H4B	109.5	H11B—C11—H11C	109.5
H4A—C4—H4B	108.0	C2—C12—H12A	109.5
C6—C5—C10	121.24 (15)	C2—C12—H12B	109.5
C6—C5—H5A	119.4	H12A—C12—H12B	109.5
C10—C5—H5A	119.4	C2—C12—H12C	109.5
C5—C6—C7	120.34 (14)	H12A—C12—H12C	109.5
C5—C6—O2	117.55 (14)	H12B—C12—H12C	109.5
C9—O1—C2—C11	168.31 (13)	C2—O1—C9—C8	162.00 (13)
C9—O1—C2—C12	−73.38 (17)	C2—O1—C9—C10	−19.7 (2)
C9—O1—C2—C3	48.95 (17)	C7—C8—C9—O1	178.76 (13)
O1—C2—C3—C4	−61.43 (18)	C7—C8—C9—C10	0.4 (2)
C11—C2—C3—C4	−176.15 (14)	O1—C9—C10—C5	−178.38 (14)
C12—C2—C3—C4	57.86 (19)	C8—C9—C10—C5	−0.2 (2)
C2—C3—C4—C10	43.3 (2)	O1—C9—C10—C4	0.7 (2)
C10—C5—C6—C7	−0.5 (2)	C8—C9—C10—C4	178.96 (15)
C10—C5—C6—O2	178.37 (14)	C6—C5—C10—C9	0.2 (2)
C5—C6—C7—C8	0.7 (2)	C6—C5—C10—C4	−178.92 (15)
O2—C6—C7—C8	−178.08 (14)	C3—C4—C10—C9	−13.3 (2)
C6—C7—C8—C9	−0.7 (2)	C3—C4—C10—C5	165.84 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O2^i	0.90 (2)	1.77 (2)	2.6608 (12)	172 (2)

Symmetry code: (i) −y+3/4, x+1/4, z+1/4.