(5R)-5-[(1R)-2,2-Dichloro-1-methylcyclopropyl]-2-methylcyclohex-2-en-1-one

The title compound, C11H14Cl2O, was synthesized by the reaction of a dichloromethane solution of (R)-carvone and potassium tert-butanolate in the presence of a catalytic amount of benzyltriethylammonium chloride in chloroform. The cyclohexene ring adopts a half-boat conformation. The cyclopropyl ring is unsymmetrical, the shortest C—C bond being distal to the alkyl-substituted C atom. The crystal packing is stabilized only by van der Waals interactions.

The title compound, C 11 H 14 Cl 2 O, was synthesized by the reaction of a dichloromethane solution of (R)-carvone and potassium tert-butanolate in the presence of a catalytic amount of benzyltriethylammonium chloride in chloroform. The cyclohexene ring adopts a half-boat conformation. The cyclopropyl ring is unsymmetrical, the shortest C-C bond being distal to the alkyl-substituted C atom. The crystal packing is stabilized only by van der Waals interactions.
Financial support from the Universitá degli Studi di Parma is gratefully acknowledged.

Comment
Dichlorocyclopropanes play an important role in organic synthesis, due to the widespread occurrence of these structures in biologically active compounds (Hirota et al., 1996;Künzer et al., 1996). These compounds have found wide applications as substrates for the synthesis of many class of compounds such as pyrethroides (Ziyat et al., 2004), benzocyclopropenes or cyclopentadiene derivatives (Fedorynski, 2003), which are not easily obtained using other starting materials. As a part of our ongoing research aimed at the synthesis of optically active dihalogenocylopropanes from terpenes (Ziyat et al., 2002;Ziyat et al., 2004;Boualy et al., 2009;Ziyat et al., 2006), the title compound has been prepared and its crystal structure is reported herein.

Experimental
Potassium tert-butanolate (4.00 g, 19.8 mmol) was added to (R)-carvone (1.47 g, 9.8 mmol) and benzyltriethylammonium chloride (0.02 g, 0.1 mmol) in dichloromethane (60 ml). The mixture was stirred for 10 min, then chloroform (0.8 ml, 9.8 mmol) was added dropwise over a period of 30 min. The mixture was stirred for 8 h at 25°C, and then hydrolyzed by addition of water (20 ml). The organic layer was separated and the aqueous layer was extracted with dichloromethane (3 × 10 ml). The combined organic extracts were dried over Na 2 SO 4 and the solvent was removed under reduced pressure. supplementary materials sup-2

Refinement
All H atoms were fixed geometrically and treated as riding, with C-H = 0.93-0.98 Å, and with U iso (H) = 1.2 U eq (C) or 1.5 U eq (C) for methyl H atoms. The absolute configuration of the molecule was established by the known chirality of the (R)-carvone starting material and, in spite of the low Friedel pair coverage (40%), the value of the resulting Flack (1983) parameter was in accordance with this configuration. For the inverted structure, the Flack parameter refined to 0.71 (3), and the values of R[F 2 >2σ(F 2 )] and wR(F 2 ) increased to 0.0583 and 0.1695, respectively. Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 40% probability level.

Special details
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 )
x y z U iso */U eq Cl1