(±)-2,3,3a,4,5,6-Hexahydro-7-methyl-1,12-dioxo-2,3a-propanophenalene: a new four-ring carbocyclic system

The title racemate, C₁₇H₁₈O₂, is a tetra­cylic diketone isolated from the base-catalysed Robinson annulation of 2-(2-carbethoxy­ethyl)cyclo­hexa­none. It represents a previously unreported four-ring carbocyclic system. In the crystal structure, the packing includes three close inter­molecular C—H...O dipolar contacts, involving both ketones.

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.051
• wR factor = 0.132
• Data-to-parameter ratio = 14.9

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT230_ALERT_2_C Hirshfeld Test Diff for    C1     -   C9A     ..       5.13 su
PLAT380_ALERT_4_C Check Incorrectly? Oriented X(sp2)-Methyl Moiety        C13
PLAT480_ALERT_4_C Long H...A H-Bond Reported H8     ..  O1      ..       2.61 Ang.
PLAT480_ALERT_4_C Long H...A H-Bond Reported H11A   ..  O2      ..       2.61 Ang.

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

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

---

S1. Comment

An interest in keto acids containing the naphthalene skeleton led us to study the Robinson annulation of several 2-substituted cyclohexanones, utilizing a variety of base and acid catalysts (Zewge et al., 1998; Davison et al., 2004). One such reaction, employing 2-(2-carbethoxyethyl)cyclohexanone, methyl vinyl ketone (MVK) and sodium methoxide, provided a low yield of an unknown crystalline material (I) that was neutral and resisted saponification. X-ray crystallography established the structure of (I).

Compound (I) evidently arises from a normal Robinson annulation of our starting material at the more highly substituted carbon (House, 1972), followed by Michael condensation with a second molecule of MVK at the newly created enone's αposition and a subsequent ring closure originating from the same enone's γ position. This substituted phenalene system then requires an oxidation from some source, possibly air, to aromatize the methylated ring. Attachment of the second molecule of MVK in the reverse sense, leading to a 9-methylated product, is an imaginable but unobserved outcome. This double condensation occurs despite a significant insufficiency of MVK; however, the recovered yield of (I) was extremely low (see Experimental). At some point, necessarily after the enone formation, an internal Claisen condensation also creates the oxopropane bridge. The only diastereomers possible are the two enantiomers present.

Within the 2.7 Å range we surveyed for non-bonded C—H···O packing interactions (Steiner, 1997); three close intermolecular contacts were found, involving both ketones (Table 1, Fig. 2).

S2. Experimental

Compound (I) was isolated from a reaction in which 41 mmol of ethereal MVK was added slowly to a cold methanolic solution of 50 mmol of keto ester and 67 mmol of sodium methoxide. Overnight stirring, heating with water and the usual workup led to a 1.1% yield of (I), isolated from the highest boiling of three distillation fractions. The reactions, but not the isolative manipulations, were carried out under N₂. Crystals suitable for X-ray were produced from acetone–hexane, m.p. 462 K.

S3. Refinement

All H atoms were located in electron density difference maps but were placed in calculated positions with C—H = 0.96–0.98 Å and allowed to refine in a riding-model approximation with U_iso(H) = 1.2U_eq(C) or 1.5U_eq(C) for methyl H atoms.

Computing details

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of the asymmetric unit of (I), with displacement ellipsoids drawn at the 20% probability level.
	Fig. 2. Packing diagram for (I), with displacement ellipsoids drawn at the 20% probability level. Hydrogen bonds are shown as dashed lines

(±)-2,3,3a,4,5,6-Hexahydro-7-methyl-1,12-dioxo-2,3a-propanophenalene

Crystal data

C17H18O2	F(000) = 544
Mr = 254.31	Dx = 1.298 Mg m^−3
Monoclinic, P21/n	Melting point: 462 K
Hall symbol: -P 2yn	Mo Kα radiation, λ = 0.71073 Å
a = 7.963 (1) Å	Cell parameters from 24 reflections
b = 13.526 (2) Å	θ = 3.1–8.2°
c = 12.159 (2) Å	µ = 0.08 mm^−1
β = 96.24 (1)°	T = 296 K
V = 1301.9 (3) Å^3	Parallelepiped, colourless
Z = 4	0.50 × 0.34 × 0.20 mm

Data collection

Siemens P4 diffractometer	1501 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.034
Graphite monochromator	θmax = 26.0°, θmin = 2.3°
2θ/θ scans	h = −1→9
Absorption correction: numerical (SHELXTL; Sheldrick, 1997)	k = −16→1
Tmin = 0.964, Tmax = 0.985	l = −14→14
3394 measured reflections	3 standard reflections every 97 reflections
2555 independent reflections	intensity decay: variation <2.3%

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)] = 0.051	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.132	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0531P)^2 + 0.1948P] where P = (Fo^2 + 2Fc^2)/3
2555 reflections	(Δ/σ)max < 0.001
172 parameters	Δρmax = 0.20 e Å^−3
0 restraints	Δρmin = −0.17 e Å^−3

Special details

Experimental. crystal mounted on glass fiber using cyanoacrylate cement

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	0.1215 (2)	0.71264 (14)	0.72359 (13)	0.0660 (5)
O2	0.2668 (3)	0.50624 (14)	0.56308 (18)	0.0837 (7)
C1	0.1278 (3)	0.72906 (18)	0.62508 (17)	0.0467 (6)
C2	0.0875 (3)	0.64692 (17)	0.54109 (18)	0.0489 (6)
H2	0.0031	0.6024	0.5672	0.059*
C3	0.0185 (3)	0.69052 (18)	0.42855 (18)	0.0495 (6)
H3A	−0.0047	0.6376	0.3753	0.059*
H3B	−0.0865	0.7251	0.4355	0.059*
C3A	0.1464 (3)	0.76193 (16)	0.38771 (15)	0.0395 (5)
C4	0.0738 (3)	0.80593 (19)	0.27613 (17)	0.0572 (7)
H4A	0.0544	0.7533	0.2221	0.069*
H4B	−0.0340	0.8370	0.2842	0.069*
C5	0.1919 (4)	0.8813 (2)	0.23514 (18)	0.0627 (7)
H5A	0.1429	0.9071	0.1644	0.075*
H5B	0.2981	0.8496	0.2241	0.075*
C6A	0.2277 (3)	0.93936 (16)	0.43736 (17)	0.0416 (5)
C6	0.2250 (3)	0.96571 (19)	0.31601 (19)	0.0588 (7)
H6A	0.1389	1.0157	0.2984	0.071*
H6B	0.3330	0.9951	0.3048	0.071*
C7	0.2683 (3)	1.01416 (17)	0.5164 (2)	0.0493 (6)
C8	0.2631 (3)	0.99329 (19)	0.6277 (2)	0.0565 (7)
H8	0.2919	1.0440	0.6817	0.068*
C9A	0.1774 (3)	0.82684 (16)	0.58516 (16)	0.0399 (5)
C9B	0.1848 (2)	0.84503 (16)	0.47107 (15)	0.0371 (5)
C9	0.2175 (3)	0.90164 (19)	0.66194 (18)	0.0503 (6)
H9	0.2131	0.8890	0.7393	0.060*
C10	0.3081 (3)	0.70290 (17)	0.37328 (16)	0.0465 (6)
H10A	0.2837	0.6565	0.3128	0.056*
H10B	0.3937	0.7483	0.3527	0.056*
C11	0.3801 (3)	0.64574 (17)	0.47641 (17)	0.0473 (6)
H11A	0.4644	0.5994	0.4561	0.057*
H11B	0.4359	0.6918	0.5296	0.057*
C12	0.2475 (3)	0.59020 (18)	0.52978 (19)	0.0508 (6)
C13	0.3159 (3)	1.11664 (19)	0.4820 (2)	0.0684 (8)
H13A	0.3394	1.1573	0.5466	0.103*
H13B	0.2240	1.1448	0.4345	0.103*
H13C	0.4144	1.1131	0.4432	0.103*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0744 (12)	0.0809 (13)	0.0458 (9)	0.0082 (11)	0.0205 (8)	0.0116 (9)
O2	0.0948 (16)	0.0510 (12)	0.1088 (16)	0.0161 (11)	0.0267 (13)	0.0231 (11)
C1	0.0385 (12)	0.0593 (15)	0.0438 (12)	0.0067 (12)	0.0111 (10)	0.0037 (11)
C2	0.0462 (13)	0.0453 (13)	0.0568 (13)	−0.0084 (12)	0.0124 (11)	0.0031 (11)
C3	0.0411 (13)	0.0519 (14)	0.0540 (13)	−0.0044 (12)	−0.0008 (10)	−0.0085 (11)
C3A	0.0388 (11)	0.0452 (13)	0.0333 (10)	−0.0012 (11)	−0.0015 (9)	−0.0045 (9)
C4	0.0604 (15)	0.0668 (17)	0.0408 (12)	0.0023 (14)	−0.0106 (11)	0.0001 (12)
C5	0.0744 (18)	0.0757 (19)	0.0360 (12)	0.0055 (16)	−0.0032 (11)	0.0105 (13)
C6A	0.0339 (12)	0.0420 (13)	0.0479 (12)	0.0042 (10)	−0.0001 (9)	0.0020 (10)
C6	0.0552 (15)	0.0617 (17)	0.0583 (15)	−0.0003 (14)	0.0002 (12)	0.0184 (13)
C7	0.0381 (12)	0.0422 (13)	0.0664 (15)	0.0045 (11)	0.0006 (11)	−0.0058 (12)
C8	0.0544 (15)	0.0528 (16)	0.0609 (15)	0.0073 (13)	−0.0006 (12)	−0.0234 (13)
C9A	0.0386 (12)	0.0416 (13)	0.0392 (11)	0.0070 (10)	0.0036 (9)	−0.0021 (10)
C9B	0.0312 (11)	0.0412 (13)	0.0384 (11)	0.0037 (10)	0.0014 (9)	−0.0019 (10)
C9	0.0513 (14)	0.0613 (16)	0.0375 (11)	0.0113 (13)	0.0008 (10)	−0.0085 (12)
C10	0.0515 (13)	0.0487 (13)	0.0394 (11)	0.0031 (12)	0.0052 (10)	−0.0086 (10)
C11	0.0460 (13)	0.0455 (13)	0.0506 (12)	0.0075 (12)	0.0058 (10)	−0.0035 (11)
C12	0.0593 (15)	0.0390 (13)	0.0535 (13)	0.0049 (12)	0.0036 (11)	0.0020 (11)
C13	0.0594 (16)	0.0429 (14)	0.102 (2)	0.0016 (13)	0.0057 (15)	−0.0061 (14)

Geometric parameters (Å, º)

O1—C1	1.225 (2)	C6A—C7	1.409 (3)
O2—C12	1.210 (3)	C6A—C6	1.516 (3)
C1—C9A	1.477 (3)	C6—H6A	0.9700
C1—C2	1.520 (3)	C6—H6B	0.9700
C2—C12	1.506 (3)	C7—C8	1.388 (3)
C2—C3	1.536 (3)	C7—C13	1.508 (3)
C2—H2	0.9800	C8—C9	1.369 (3)
C3—C3A	1.525 (3)	C8—H8	0.9600
C3—H3A	0.9700	C9A—C9	1.390 (3)
C3—H3B	0.9700	C9A—C9B	1.416 (3)
C3A—C9B	1.522 (3)	C9—H9	0.9600
C3A—C4	1.536 (3)	C10—C11	1.531 (3)
C3A—C10	1.541 (3)	C10—H10A	0.9700
C4—C5	1.509 (4)	C10—H10B	0.9700
C4—H4A	0.9700	C11—C12	1.500 (3)
C4—H4B	0.9700	C11—H11A	0.9700
C5—C6	1.511 (3)	C11—H11B	0.9700
C5—H5A	0.9700	C13—H13A	0.9600
C5—H5B	0.9700	C13—H13B	0.9600
C6A—C9B	1.394 (3)	C13—H13C	0.9600
O1—C1—C9A	121.6 (2)	C5—C6—H6B	108.3
O1—C1—C2	119.8 (2)	C6A—C6—H6B	108.3
C9A—C1—C2	118.57 (18)	H6A—C6—H6B	107.4
C12—C2—C1	108.34 (19)	C8—C7—C6A	119.4 (2)
C12—C2—C3	109.78 (18)	C8—C7—C13	119.5 (2)
C1—C2—C3	110.31 (19)	C6A—C7—C13	121.1 (2)
C12—C2—H2	109.5	C9—C8—C7	121.2 (2)
C1—C2—H2	109.5	C9—C8—H8	119.4
C3—C2—H2	109.5	C7—C8—H8	119.4
C3A—C3—C2	110.27 (17)	C9—C9A—C9B	120.0 (2)
C3A—C3—H3A	109.6	C9—C9A—C1	118.75 (19)
C2—C3—H3A	109.6	C9B—C9A—C1	121.22 (18)
C3A—C3—H3B	109.6	C6A—C9B—C9A	118.98 (19)
C2—C3—H3B	109.6	C6A—C9B—C3A	121.19 (18)
H3A—C3—H3B	108.1	C9A—C9B—C3A	119.82 (19)
C9B—C3A—C3	110.09 (17)	C8—C9—C9A	120.3 (2)
C9B—C3A—C4	109.34 (18)	C8—C9—H9	119.9
C3—C3A—C4	109.39 (17)	C9A—C9—H9	119.9
C9B—C3A—C10	110.41 (16)	C11—C10—C3A	114.31 (17)
C3—C3A—C10	107.74 (19)	C11—C10—H10A	108.7
C4—C3A—C10	109.84 (18)	C3A—C10—H10A	108.7
C5—C4—C3A	111.42 (19)	C11—C10—H10B	108.7
C5—C4—H4A	109.3	C3A—C10—H10B	108.7
C3A—C4—H4A	109.3	H10A—C10—H10B	107.6
C5—C4—H4B	109.3	C12—C11—C10	112.87 (19)
C3A—C4—H4B	109.3	C12—C11—H11A	109.0
H4A—C4—H4B	108.0	C10—C11—H11A	109.0
C4—C5—C6	111.5 (2)	C12—C11—H11B	109.0
C4—C5—H5A	109.3	C10—C11—H11B	109.0
C6—C5—H5A	109.3	H11A—C11—H11B	107.8
C4—C5—H5B	109.3	O2—C12—C11	123.0 (2)
C6—C5—H5B	109.3	O2—C12—C2	121.7 (2)
H5A—C5—H5B	108.0	C11—C12—C2	115.27 (19)
C9B—C6A—C7	120.1 (2)	C7—C13—H13A	109.5
C9B—C6A—C6	121.6 (2)	C7—C13—H13B	109.5
C7—C6A—C6	118.3 (2)	H13A—C13—H13B	109.5
C5—C6—C6A	116.0 (2)	C7—C13—H13C	109.5
C5—C6—H6A	108.3	H13A—C13—H13C	109.5
C6A—C6—H6A	108.3	H13B—C13—H13C	109.5
O1—C1—C2—C12	−87.6 (3)	C6—C6A—C9B—C9A	−175.34 (19)
C9A—C1—C2—C12	91.1 (2)	C7—C6A—C9B—C3A	−177.82 (19)
O1—C1—C2—C3	152.2 (2)	C6—C6A—C9B—C3A	4.8 (3)
C9A—C1—C2—C3	−29.1 (3)	C9—C9A—C9B—C6A	−1.8 (3)
C12—C2—C3—C3A	−61.2 (2)	C1—C9A—C9B—C6A	178.2 (2)
C1—C2—C3—C3A	58.2 (2)	C9—C9A—C9B—C3A	178.00 (19)
C2—C3—C3A—C9B	−58.9 (2)	C1—C9A—C9B—C3A	−1.9 (3)
C2—C3—C3A—C4	−179.06 (19)	C3—C3A—C9B—C6A	−149.4 (2)
C2—C3—C3A—C10	61.6 (2)	C4—C3A—C9B—C6A	−29.1 (3)
C9B—C3A—C4—C5	56.3 (3)	C10—C3A—C9B—C6A	91.8 (2)
C3—C3A—C4—C5	176.9 (2)	C3—C3A—C9B—C9A	30.8 (2)
C10—C3A—C4—C5	−65.0 (3)	C4—C3A—C9B—C9A	151.02 (19)
C3A—C4—C5—C6	−59.6 (3)	C10—C3A—C9B—C9A	−88.0 (2)
C4—C5—C6—C6A	33.4 (3)	C7—C8—C9—C9A	0.9 (4)
C9B—C6A—C6—C5	−6.4 (3)	C9B—C9A—C9—C8	0.4 (3)
C7—C6A—C6—C5	176.2 (2)	C1—C9A—C9—C8	−179.7 (2)
C9B—C6A—C7—C8	−0.8 (3)	C9B—C3A—C10—C11	66.1 (2)
C6—C6A—C7—C8	176.7 (2)	C3—C3A—C10—C11	−54.2 (2)
C9B—C6A—C7—C13	179.7 (2)	C4—C3A—C10—C11	−173.26 (19)
C6—C6A—C7—C13	−2.8 (3)	C3A—C10—C11—C12	45.7 (3)
C6A—C7—C8—C9	−0.7 (4)	C10—C11—C12—O2	136.4 (2)
C13—C7—C8—C9	178.8 (2)	C10—C11—C12—C2	−44.6 (3)
O1—C1—C9A—C9	−0.1 (3)	C1—C2—C12—O2	110.7 (3)
C2—C1—C9A—C9	−178.8 (2)	C3—C2—C12—O2	−128.7 (2)
O1—C1—C9A—C9B	179.8 (2)	C1—C2—C12—C11	−68.3 (2)
C2—C1—C9A—C9B	1.1 (3)	C3—C2—C12—C11	52.2 (3)
C7—C6A—C9B—C9A	2.0 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C8—H8···O1^i	0.96	2.61	3.543 (3)	163
C10—H10B···O1^ii	0.97	2.58	3.440 (3)	148
C11—H11A···O2^iii	0.97	2.61	3.557 (3)	167

Symmetry codes: (i) −x+1/2, y+1/2, −z+3/2; (ii) x+1/2, −y+3/2, z−1/2; (iii) −x+1, −y+1, −z+1.