Fabio Urso

Steric consequence of the diastereoselective addition of chiral lithium 2-(1-dimethylaminoethyl)phenyl cuprates to some enones

Abstract Conjugate addition of the mixed chiral species lithium [(S)-2-(1-dimethylaminoethyl)phenyl](2-thienyl)cuprate to (E)-4-phenyl-3-buten-2-one, 2-cyclohexenone or to 2-cyclopentenone proceeds with high diastereoselectivity. The first two enones gave crystalline adducts directly, while the non-crystalline cyclopentenone adduct was converted into a crystalline methiodide. The crystal structures of the compounds have been determined from single-crystal X-ray diffractometer data in order to reveal the configurations at the new chiral centres. In all three cases the configuration at the new asymmetric centre is S. (S,S)-4-[2-(1-Dimethylaminoethyl)phenyl]-4-phenyl-2-butenone, C20H25NO, crystallizes in space group P21 with a 7.604(2), b 9.398(5), c 12.290(6) A, β 92.30(3)° and Z = 2. Full-matrix least-squares refinement of 273 structural parameters gave R = 0.066 for 1015 observed independent reflections. (S,S)-3-[2-(1-Dimethylaminoethyl)phenyl]-2-cyclohexanone, C16H23NO crystallizes in space group P212121 with a 12.499(4), b 6.645(3), c 17.568(7) A and Z = 4. Full-matrix least-squares refinement of 142 structural parameters gave R = 0.068 for 1507 observed independent reflections. (S,S)-1-[2-(3-Oxocyclopentyl)phenyl]ethyltrimethylammonium iodide, C16H24NOI, crystallizes in space group P41, with a 10.569(3), c 30.895(7) A and Z = 8; there are thus two crystallographically independent cations in the asymmetric unit. Full-matrix least-squares refinement of 342 structural parameters gave R = 0.054 for 2119 observed independent reflections. The (S,S)-configuration observed in these adducts indicates that the conjugate addition gives the least crowded lithium enolate as the major product.