Crystal structure of 1r,2c,3c,4t,5t,6t-1,2,3,4,5,6-hexakistrimethylsilanyloxy- cyclohexane, C24H60O6Si6

Abstract

Source of materialThe title compound was synthesized by treating neo-inositol with trimethylsilyl chloride in triethylamine. Colorless crystals where obtained by slow volatilizing CDCl 3 from an NMR sample. Experimental detailsThe hydrogen atoms were calculated in their expected positions and included in the refinement as riding atoms. The U iso (H) values were constrained to be 1.2 U eq (CH) and 1.5 U eq (CH 3 ), respectively. In one of both molecules two methyl groups of one silanyloxy substituent are disordered over two sides with an occupation ratio of 0.5/0.5. The terminal methyl groups display enhanced librational motions, which is caused by rotation around the silicon-oxygen bond. DiscussionIn connection with our investigations concerning new molecular rods with ketal moeties as key structural element [1-3] we were interested in six-membered saturated rings bearing four hydroxyl groups with the stereochemical pattern 1r,2c,4t,5t and two additional substituents in 3-and 6-position. Two of the eight naturally occurring stereoisomeric inositols (1,2,3,4,5,6-hexahydroxycyclohexanes) meet these demands, namely allo- (1,2,3,4/5,6) and neo- (1,2,3/4,5,6) inositol. If the mentioned two substituents in 3-and 6-position should not break the symmetry of the building block, only the neo-isomer comes into consideration. Whereas myo- (1,2,3,5/4,6) inositol, which differs from neo-inositol only by the configuration of one stereocentre, is cheaply available, the required neo-inositol cannot be purchased in larger amounts. Some methods for the preparation of neo-inositol or its derivatives were reported but none of them were feasible [4]. We therefore developed anew efficient method for the preparation of neo-The crystal structure of the title compound unequivocally proves the correct stereochemistry of the product. The asymmetric unit contains two halfs of two symmetry independent molecules. The other two halfs were generated by inversion centres in both molecules, giving the (1,2,3/4,5,6) arrangement in an ideal chair conformation. The puckering parameters are Q =0 .611(2) Å, q = 3.27(1)°, j =0°.The conformation is closely related to the structure of neo-inositol [6]. However, the compactness of the structure reported here is very small, characterized by alow density (1.049 g·cm -3 ), in contrast to that in neo-inositol with an unusually high density (1.69 g·cm -3 ). Beside above-mentioned disordered methyl groups at one position of one molecule, there are only marginal differences in the conformations of the two molecules. Hence only one molecule is presented in the figure. Since the compound is centrosymmetric, the atoms C1 to C6 of the carbon skeletons are designated as C1, C2 i ,C 3 i ,C 1 i ,C 2a nd C3 (symmetry code i: 2-x,2-y,2-z).