Syntheses and structures of 3-stannylcholest-5-ene species

The compounds, 3α- and 3β-triphenylstannylcholest-5-ene, 1 and 2 respectively, have been prepared stereospecifically in reactions of Ph₃SnLi with cholesteryl methane- or toluene-p-sulfonates, and of Ph₃SnCl with the Grignard reagent from cholesteryl chloride, respectively. Complete ¹H and ¹³C NMR spectral assignments for 1 have been obtained using HMBC and HMQC techniques: these have been used to aid the ¹³C NMR spectral assignments for 2 and 3α- and 3β-(I_nPh_3-nSn)cholest-5-enes (n = 1-2) (9-12). Crystal structure determinations of 3α-(IPh₂Sn)cholest-5-ene 9 and 3α-(I₂PhSn)cholest-5-ene 10 indicate distorted tetrahedral geometries about the tin centres in both compounds. The Sn-I bond lengths are 2.731(5) Ȧ in 9 and between 2.6979(12) and 2.7173(12) Ȧ in 10. Despite the similarity in the values (ca. 60°) of the dihedral angles, Sn-C(3)-C(2)-C(1) [C(1) aliphatic carbon] and Sn-C(3)-C(4)-C(5) [C(5) olefinic carbon], the values of ³J[¹¹⁹Sn^-13C(1)] are about twice the ³J[¹¹⁹Sn^-13C(5)] values in each of 1, 9 and 10; in contrast, ³J[¹¹⁹Sn^-13C(1)] and ³J[¹¹⁹Sn^-13C(5)] values are essentially the same in each of 2, 11 and 12 [Sn-C(3)-C(2)-C(1) and Sn-C(3)-C(4)-C(5) ca. 180°].