Crystal structure of 1,3-diallyl-1,3,3a,4,7,7a-hexahydro-4,7-methano-2-benzothiophene 2,2-dioxide

The title compound C15H20O2S, was identified as a product of diallylation of the meso-isomer of the corresponding norbornene sulfone, and it is an achiral compound. The five-membered heterocycle adopts an envelope conformation with the S atom deviating by 0.795 (3) Å from the other atoms of the ring (r.m.s. deviation = 0.0131). Both allyl groups are anti-oriented relative to the S atom but their double bonds are directed in opposite directions relative to the plane of the heterocycle.

The corresponding mono-allylated sulfone has been reported previously (Bloch et al., 1984). The starting sulfone was allylated with allyl bromide using n-BuLi as a base at -75 °C to room temperature for 25 h to furnish the desired di-allylated sulfone 1 in 80% yield along with the mono-allylated sulfone in 10% yield. After recrystallization from a mixture of hexane-dichloromethane (3:1), we obtained monoclinic crystals of the compound 1. The single-crystal X-ray study of the compound 1 clearly indicates that the di-allylation has been occurred at α,α ′ -positions of the sulfone functionality with the allyl groups cis-positioned relatively to each other (see Figure 1). This stereoselectivity can be explained by stronger  , 1992). The bond angle C3-C7-C6 of 94.14 (17) Å is contracted the most relative to the standard tetrahedral value of 109.5°. The angle C13-C14-C15 is found to be the most expanded one at 125.1 (2)°. The five-membered heterocycle has an envelope conformation, in which four C atoms are in the same plane (C8-C5-C4-C12) and SO 2 group deviates from it. Two allylic double bonds are oriented in opposite direction to each other. Previously, Pool and White (2000) have also reported that the average lengths of C-C bonds corresponding to C3 -C4 and C5-C6 in our structure in the similar bicyclic cyclohexene derivatives are also significantly longer (by 0.02 Å) than the corresponding C-C bond distances for the saturated bicyclic cyclohexane derivatives. Later, Birney and coworkers (Birney et al., 2002) have studied the X-ray crystal data of bicyclo[2.2.1]moiety containing compounds in order to estimate their retro-Diels-Alder reactivity.

S2. Experimental Section
Melting points were recorded on Veego melting point apparatus and are uncorrected. Nuclear Magnetic Resonance (NMR) spectra were recorded on a Bruker (Avance III TM 500) spectrometer operated at 500 MHz for 1 H and 125.7 MHz for 13 C nuclei. The high-resolution mass spectrometric (HRMS) measurements were carried out using Bruker (Maxis Impact) instrument. Infrared (IR) spectrum of solid sample was recorded as KBr pellets on Nicolet Impact-400 FT IR spectrometer.
supporting information

S2.1. Synthesis and Crystallization of Compound_1
The solution of the precursor sulfone (600 mg, 3.26 mmol) in anhydrous THF (15 mL) was cooled to -75 °C under nitrogen (N 2 ). To this solution, n-BuLi (4.90 mL, 2.4 equiv, 1.6 M solution in hexanes) was added in dropwise manner and the reaction mixture was stirred for 30 min. Later, allyl bromide (0.83 mL, 9.77 mmol) was added slowly and the stirring continued at the same temperature for 2 h. Then, the reaction mixture was allowed to raise to the room temperature and the stirring continued for 22 h more. At the conclusion of the reaction (TLC monitoring), the reaction mixture was quenched with water (5 mL) and the solvent was removed under reduced pressure. Then, the resulting residue was extracted with diethyl ether (3 × 30 mL). The combined organic layers were washed with brine (2 × 20 mL) and dried over anhydrous Na 2 SO 4 . The solvent was removed under reduced pressure and the crude product was purified by silica gel column chromatography using ethyl acetate-petroleum ether (1:9) as an eluent to afford the di-allylated sulfone 1 (690 mg, 80%) as a white crystalline solid. A further elution with ethyl acetate-petroleum ether (2:8) delivered the previously known mono-allylated sulfone (75.40 mg, 10%) as a pale yellow liquid. 1 H and 13 C NMR spectroscopic data of the monoallylated sulfone was compared with the literature report (Bloch et al., 1984) and found to be identical. After purification the title compound was recrystallized from a mixture of hexane-dichloromethane

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 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 R-factors(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. All nonhydrogen atoms are refined anisotropically and all hydrogen atoms are refined using riding model.