Crystal structure of 7,8,9,10-tetra­hydro­benzo[b]naphtho­[2,1-d]furan

The reaction of 1-naphthol with cyclo­hexa­diene in the presence of catalytic amounts of Lewis acid, which inter­acts with 1-naphthol with release of protons, does not afford the Diels–Alder adduct but the Friedel–Crafts products followed by aromatization. The crystal structure of the final tetra­hydro­benzo­naphtho­furan product is described.

Abstract

In the title compound, C₁₆H₁₄O, the cyclo­hexene ring has a half-chair conformation. The mean plane, calculated through all non-H atoms of the mol­ecule, except for the central CH₂ atoms of the cyclo­hexene ring, which deviate by 0.340 (3) and −0.369 (3) Å from this mean plane, has an r.m.s. deviation of 0.012 Å. In the crystal, there are C—H⋯π contacts present, resulting in the formation of zigzag chains propagating along the [010] direction.

Chemical context  

The inter­action of Lewis acids with 1-naphthol 1 can be expected to induce metal coordination at the hy­droxy function with concomitant increase in Brønsted-acidity (2) (Yamamoto & Futatsugi, 2005 ▸; Goering, 1995 ▸). It is conceivable that the proton, once released from this inter­mediate 2, adds reversibly to the 4-position with formation of adduct 3, which is the Lewis acid coordinated form of the keto-tautomer of 1. Even if only minute amounts of 3 were to be formed, this inter­mediate should be a highly reactive dienophile in Diels–Alder reactions with such dienes as cyclo­hexa­diene 4 leading to adduct 5 (see Scheme). Such a transformation implies de-aromatization of 1-naphthol 1.

Alternatively, protonation of diene 4 leading to carbocation 6 would set the stage for Friedel–Crafts reaction with formation of the alkyl­ation product 7, which could continue to react acid catalyzed, leading to adduct 8 and possibly to the aromatized furan product 9. In a previous study, Novák and coworkers reported the reaction of 1 with 4 in the presence of TsOH·H₂O in boiling toluene (26 h) or at room temperature (7 d), furan derivative 9 being formed in 58% yield, presumably via the inter­mediacy of 7 and 8 (Orovecz et al., 2003 ▸; Novák et al., 2000 ▸).

In exploratory experiments, we tested Et₂O·BF₃, FeCl₃, TiCl₄ and ZrCl₄ as Lewis acids in the reaction of 1 and 4 at room temperature in CH₂Cl₂. Essentially only products derived from formal Friedel–Crafts alkyl­ation were identified following column chromatographic separation. Small amounts of unidentified compounds which could not be separated were also formed. A general protocol is provided. If a 2.5-fold excess of cyclo­hexa­diene 4 is used in these reactions, only small amounts of Friedel–Crafts products are formed (3–4%). Rather, acid-mediated oligomerization of diene 4 occurs.

In contrast to the acidic conditions employed by Novák and coworkers, using the present protocol we isolated compound 8 and characterized it for the first time. We report herein on the crystal structure of the final product, furan 9.

Structural commentary  

In the title compound 9, illustrated in Fig. 1 ▸, the cyclo­hexene ring (C1–C6) has a half-chair conformation. The mean plane, calculated through all non-hydrogen atoms of the mol­ecule (O1/C1/C2/C5–C16), except atoms C3 and C4 of the cyclo­hexene ring that deviate by 0.340 (3) and −0.369 (3) Å from this mean plane, has an r.m.s. deviation of 0.012 Å. The other C and O atoms lie in this mean plane with a maximum deviation of −0.051 (3) Å for atom C2.

Figure 1.

The mol­ecular structure of compound 9, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Supra­molecular features  

In the crystal of 9, there are C—H⋯π contacts present (Table 1 ▸ and Fig. 2 ▸), but no classical hydrogen bonds and no π–π inter­actions present. Inter­molecular contacts thus appear to be limited to van der Waals inter­actions. The two rather short inter­molecular C—H⋯ring centroid distances are: H5B⋯centroid of ring (C10–C15) = 2.69 Å, H8⋯centroid of ring (C7–C10/C15/C16) = 2.93 Å. These inter­actions result in the formation of zigzag chains propagating along the b-axis direction.

Table 1. Hydrogen-bond geometry (Å, °).

Cg3 and Cg4 are the centroids of rings C7–C10/C15/C16 and C10–C15, respectively.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C5—H5B⋯Cg4i	0.99	2.69	3.664 (3)	167
C8—H8⋯Cg3i	0.95	2.93	3.650 (3)	134

Symmetry code: (i) .

Figure 2.

A view of the nearest C—H⋯ring centroid distances, shown as dashed lines [see Table 1 ▸; symmetry code: (i) −x, −y + 2, z − ].

Database survey  

Only one structure of a tetra­hydro­benzo­naphtho­furan (Refcode PEBDAD; Scully & Porco, 2012 ▸) is present in the current version 5.36 of the CSD (Groom & Allen, 2014 ▸), and the cyclo­hexene ring also has a half-chair conformation.

Synthesis and crystallization  

General Procedure: To a mixture of 1-naphthol (6.48 g, 45 mmol), catalyst (2.25 mmol) in CH₂Cl₂ (10 ml), 1,3-cyclo­hexa­diene (0.7 ml, 22.5 mmol) in CH₂Cl₂ (30 ml) was added drop wise, and the resulting solution was stirred at 273 K for 5 h. After completion of the reaction (TLC) at room temperature, a cold aqueous solution of NaHCO₃ (5%, 20 ml) was added and the mixture was extracted with CH₂Cl₂ (3 × 10 ml). The organic extracts were washed with water (2 ×10 mL) and dried over anhydrous Na₂SO₄, and concentrated in vacuum. The crude product was purified by silica column chromatography (petroleum ether) to give the desired product, which was identified by NMR spectroscopic comparison with authentic samples of 1, 2 and by X-ray diffraction analysis (Fig. 1 ▸).

Compound 8: ¹H NMR (300 MHz, CDCl₃, p.p.m.): δ 1.19–1.27 (m, 1H), 1.34–1.48 (m, 4H), 1.69–1.84 (m, 2H), 1.92–2.02 (m, 1H), 3.17–3.24 (m, 1H), 4.71--4.77 (m, 1H), 7.16–7.18 (m, 1H), 7.24–7.32 (m, 3H), 7.66–7.69 (m, 1H), 7.87–7.90 (m, 1H); ¹³C NMR (300 MHz, CDCl₃, p.p.m.): δ 20.50, 21.86, 27.64, 28.38, 41.41, 83.44, 120.16, 121.16, 121.60, 121.92, 125.13, 125.48, 126.55, 128.01, 134.11, 155.07.

High Resolution Mass Spectrum: (M + H⁺) calculated for C₁₆H₁₆O 225.1274; found (M + H⁺) 225.1275.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. H atoms were located in difference Fourier maps, but subsequently included in the refinement using a riding model: C–H = 0.95-0.99 Å with U _iso(H) = 1.2U _eq(C).

Table 2. Experimental details.

Crystal data
Chemical formula	C16H14O
M r	222.27
Crystal system, space group	Orthorhombic, P n a21
Temperature (K)	100
a, b, c (Å)	13.8369 (9), 12.2202 (8), 6.8468 (4)
V (Å3)	1157.72 (13)
Z	4
Radiation type	Mo Kα
μ (mm−1)	0.08
Crystal size (mm)	0.16 × 0.05 × 0.04
Data collection
Diffractometer	Bruker D8 QUEST area detector
Absorption correction	Multi-scan (SADABS; Bruker, 2014 ▸)
T min, T max	0.94, 1.00
No. of measured, independent and observed [I > 2σ(I)] reflections	5983, 2024, 1808
R int	0.038
(sin θ/λ)max (Å−1)	0.601
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.038, 0.081, 1.09
No. of reflections	2024
No. of parameters	154
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.16, −0.24

Computer programs: APEX2 and SAINT (Bruker, 2014 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL (Sheldrick, 2015b ▸), DIAMOND (Brandenburg, 2006 ▸), publCIF (Westrip, 2010 ▸) and PLATON (Spek, 2009 ▸).

Supplementary Material

CCDC reference: 1429774

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

C16H14O	Dx = 1.275 Mg m−3
Mr = 222.27	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pna21	Cell parameters from 2867 reflections
a = 13.8369 (9) Å	θ = 2.2–25.2°
b = 12.2202 (8) Å	µ = 0.08 mm−1
c = 6.8468 (4) Å	T = 100 K
V = 1157.72 (13) Å3	Prism, colourless
Z = 4	0.16 × 0.05 × 0.04 mm
F(000) = 472

Data collection

Bruker D8 QUEST area-detector diffractometer	2024 independent reflections
Radiation source: microfocus sealed X-ray tube	1808 reflections with I > 2σ(I)
Detector resolution: 7.9 pixels mm-1	Rint = 0.038
ω and φ scans	θmax = 25.3°, θmin = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 2014)	h = −16→16
Tmin = 0.94, Tmax = 1.00	k = −14→14
5983 measured reflections	l = −8→8

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.081	H-atom parameters constrained
S = 1.09	w = 1/[σ2(Fo2) + (0.0435P)2 + 0.0066P] where P = (Fo2 + 2Fc2)/3
2024 reflections	(Δ/σ)max < 0.001
154 parameters	Δρmax = 0.16 e Å−3
1 restraint	Δρmin = −0.24 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.

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

	x	y	z	Uiso*/Ueq
C1	0.03747 (16)	0.7566 (2)	0.3738 (4)	0.0159 (5)
O1	0.09729 (11)	0.83253 (13)	0.4640 (2)	0.0165 (4)
C2	0.00207 (19)	0.6599 (2)	0.4844 (4)	0.0207 (6)
H2A	−0.0492	0.6822	0.5770	0.025*
H2B	0.0557	0.6267	0.5596	0.025*
C3	−0.03802 (19)	0.5773 (2)	0.3369 (4)	0.0237 (6)
H3A	−0.0767	0.5215	0.4070	0.028*
H3B	0.0164	0.5395	0.2716	0.028*
C4	−0.10145 (19)	0.6329 (2)	0.1823 (4)	0.0232 (6)
H4A	−0.1300	0.5763	0.0964	0.028*
H4B	−0.1551	0.6719	0.2480	0.028*
C5	−0.04412 (18)	0.7140 (2)	0.0581 (4)	0.0179 (6)
H5A	−0.0036	0.6738	−0.0369	0.021*
H5B	−0.0891	0.7616	−0.0156	0.021*
C6	0.01857 (16)	0.78260 (19)	0.1870 (4)	0.0138 (5)
C7	0.06900 (16)	0.8841 (2)	0.1498 (3)	0.0137 (5)
C8	0.07806 (17)	0.9549 (2)	−0.0120 (4)	0.0165 (6)
H8	0.0475	0.9381	−0.1326	0.020*
C9	0.13190 (18)	1.0484 (2)	0.0084 (4)	0.0187 (6)
H9	0.1371	1.0973	−0.0991	0.022*
C10	0.18051 (17)	1.07448 (19)	0.1866 (4)	0.0171 (6)
C11	0.23745 (18)	1.1700 (2)	0.2054 (4)	0.0215 (6)
H11	0.2441	1.2179	0.0969	0.026*
C12	0.28309 (18)	1.1947 (2)	0.3768 (4)	0.0243 (7)
H12	0.3209	1.2593	0.3862	0.029*
C13	0.27444 (18)	1.1254 (2)	0.5383 (4)	0.0234 (6)
H13	0.3060	1.1438	0.6571	0.028*
C14	0.22067 (17)	1.0308 (2)	0.5271 (4)	0.0191 (6)
H14	0.2157	0.9837	0.6371	0.023*
C15	0.17295 (17)	1.0040 (2)	0.3507 (4)	0.0151 (5)
C16	0.11541 (17)	0.9100 (2)	0.3225 (3)	0.0141 (5)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
C1	0.0135 (11)	0.0131 (13)	0.0211 (13)	−0.0013 (10)	0.0009 (11)	−0.0021 (11)
O1	0.0202 (8)	0.0147 (9)	0.0144 (8)	−0.0019 (8)	−0.0021 (7)	0.0019 (7)
C2	0.0232 (13)	0.0180 (14)	0.0210 (14)	−0.0019 (11)	0.0019 (12)	0.0042 (12)
C3	0.0263 (14)	0.0171 (14)	0.0277 (14)	−0.0048 (12)	0.0018 (13)	0.0035 (12)
C4	0.0197 (13)	0.0213 (15)	0.0286 (15)	−0.0056 (12)	−0.0006 (12)	−0.0007 (13)
C5	0.0164 (12)	0.0169 (14)	0.0203 (13)	−0.0010 (11)	−0.0023 (11)	−0.0023 (12)
C6	0.0126 (11)	0.0128 (13)	0.0159 (12)	0.0037 (10)	0.0024 (10)	−0.0007 (11)
C7	0.0119 (12)	0.0132 (13)	0.0158 (12)	0.0041 (10)	0.0022 (11)	−0.0027 (11)
C8	0.0185 (12)	0.0172 (14)	0.0140 (12)	0.0036 (11)	−0.0010 (11)	−0.0012 (11)
C9	0.0200 (12)	0.0174 (13)	0.0186 (13)	0.0036 (11)	0.0040 (11)	0.0030 (12)
C10	0.0127 (11)	0.0153 (13)	0.0233 (14)	0.0024 (10)	0.0046 (11)	−0.0019 (12)
C11	0.0168 (13)	0.0174 (15)	0.0303 (15)	0.0005 (11)	0.0056 (13)	0.0015 (13)
C12	0.0140 (12)	0.0199 (15)	0.0391 (17)	−0.0041 (11)	0.0037 (13)	−0.0069 (14)
C13	0.0167 (12)	0.0257 (16)	0.0278 (15)	−0.0006 (12)	−0.0023 (12)	−0.0106 (14)
C14	0.0149 (12)	0.0209 (14)	0.0216 (13)	0.0012 (11)	0.0002 (11)	−0.0020 (13)
C15	0.0115 (11)	0.0159 (13)	0.0180 (12)	0.0020 (10)	0.0021 (10)	−0.0026 (11)
C16	0.0155 (12)	0.0117 (13)	0.0152 (13)	0.0035 (10)	0.0039 (11)	0.0003 (11)

Geometric parameters (Å, º)

C1—C6	1.343 (3)	C7—C16	1.383 (3)
C1—O1	1.388 (3)	C7—C8	1.411 (3)
C1—C2	1.486 (3)	C8—C9	1.371 (3)
O1—C16	1.377 (3)	C8—H8	0.9500
C2—C3	1.532 (4)	C9—C10	1.429 (4)
C2—H2A	0.9900	C9—H9	0.9500
C2—H2B	0.9900	C10—C11	1.414 (4)
C3—C4	1.534 (4)	C10—C15	1.419 (3)
C3—H3A	0.9900	C11—C12	1.366 (4)
C3—H3B	0.9900	C11—H11	0.9500
C4—C5	1.528 (4)	C12—C13	1.398 (4)
C4—H4A	0.9900	C12—H12	0.9500
C4—H4B	0.9900	C13—C14	1.377 (3)
C5—C6	1.494 (3)	C13—H13	0.9500
C5—H5A	0.9900	C14—C15	1.415 (4)
C5—H5B	0.9900	C14—H14	0.9500
C6—C7	1.446 (3)	C15—C16	1.411 (3)
C6—C1—O1	112.4 (2)	C16—C7—C8	119.4 (2)
C6—C1—C2	127.5 (2)	C16—C7—C6	105.6 (2)
O1—C1—C2	120.1 (2)	C8—C7—C6	135.0 (2)
C16—O1—C1	104.80 (18)	C9—C8—C7	118.6 (2)
C1—C2—C3	107.9 (2)	C9—C8—H8	120.7
C1—C2—H2A	110.1	C7—C8—H8	120.7
C3—C2—H2A	110.1	C8—C9—C10	121.9 (2)
C1—C2—H2B	110.1	C8—C9—H9	119.1
C3—C2—H2B	110.1	C10—C9—H9	119.1
H2A—C2—H2B	108.4	C11—C10—C15	118.0 (2)
C2—C3—C4	111.7 (2)	C11—C10—C9	121.6 (2)
C2—C3—H3A	109.3	C15—C10—C9	120.4 (2)
C4—C3—H3A	109.3	C12—C11—C10	121.2 (3)
C2—C3—H3B	109.3	C12—C11—H11	119.4
C4—C3—H3B	109.3	C10—C11—H11	119.4
H3A—C3—H3B	107.9	C11—C12—C13	120.4 (2)
C5—C4—C3	112.0 (2)	C11—C12—H12	119.8
C5—C4—H4A	109.2	C13—C12—H12	119.8
C3—C4—H4A	109.2	C14—C13—C12	120.7 (3)
C5—C4—H4B	109.2	C14—C13—H13	119.6
C3—C4—H4B	109.2	C12—C13—H13	119.6
H4A—C4—H4B	107.9	C13—C14—C15	119.6 (2)
C6—C5—C4	109.7 (2)	C13—C14—H14	120.2
C6—C5—H5A	109.7	C15—C14—H14	120.2
C4—C5—H5A	109.7	C16—C15—C14	124.6 (2)
C6—C5—H5B	109.7	C16—C15—C10	115.3 (2)
C4—C5—H5B	109.7	C14—C15—C10	120.1 (2)
H5A—C5—H5B	108.2	O1—C16—C7	111.1 (2)
C1—C6—C7	106.1 (2)	O1—C16—C15	124.5 (2)
C1—C6—C5	122.8 (2)	C7—C16—C15	124.4 (2)
C7—C6—C5	131.1 (2)
C6—C1—O1—C16	0.3 (2)	C15—C10—C11—C12	−0.7 (4)
C2—C1—O1—C16	−179.7 (2)	C9—C10—C11—C12	179.5 (2)
C6—C1—C2—C3	15.0 (3)	C10—C11—C12—C13	0.1 (4)
O1—C1—C2—C3	−165.0 (2)	C11—C12—C13—C14	0.6 (4)
C1—C2—C3—C4	−44.6 (3)	C12—C13—C14—C15	−0.6 (4)
C2—C3—C4—C5	63.3 (3)	C13—C14—C15—C16	−179.5 (2)
C3—C4—C5—C6	−45.0 (3)	C13—C14—C15—C10	−0.1 (4)
O1—C1—C6—C7	−0.5 (3)	C11—C10—C15—C16	−179.8 (2)
C2—C1—C6—C7	179.5 (2)	C9—C10—C15—C16	0.0 (3)
O1—C1—C6—C5	−179.9 (2)	C11—C10—C15—C14	0.7 (3)
C2—C1—C6—C5	0.0 (4)	C9—C10—C15—C14	−179.5 (2)
C4—C5—C6—C1	14.8 (3)	C1—O1—C16—C7	0.0 (2)
C4—C5—C6—C7	−164.5 (2)	C1—O1—C16—C15	179.4 (2)
C1—C6—C7—C16	0.4 (2)	C8—C7—C16—O1	179.21 (19)
C5—C6—C7—C16	179.8 (2)	C6—C7—C16—O1	−0.2 (3)
C1—C6—C7—C8	−178.9 (3)	C8—C7—C16—C15	−0.2 (3)
C5—C6—C7—C8	0.5 (4)	C6—C7—C16—C15	−179.6 (2)
C16—C7—C8—C9	−0.9 (3)	C14—C15—C16—O1	0.8 (4)
C6—C7—C8—C9	178.4 (2)	C10—C15—C16—O1	−178.7 (2)
C7—C8—C9—C10	1.4 (3)	C14—C15—C16—C7	−179.9 (2)
C8—C9—C10—C11	178.8 (2)	C10—C15—C16—C7	0.6 (3)
C8—C9—C10—C15	−1.0 (4)

Hydrogen-bond geometry (Å, º)

Cg3 and Cg4 are the centroids of rings C7–C10/C15/C16 and C10–C15, respectively.

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5B···Cg4i	0.99	2.69	3.664 (3)	167
C8—H8···Cg3i	0.95	2.93	3.650 (3)	134

Symmetry code: (i) −x, −y+2, z−1/2.