Structures of Two Diastereomeric Aldol Products from a New Silicon-Directed Condensation

Abstract

Hexahydro-3,3,6-trimethyl-5-phenyl- 1 H,7H-pyrrolo[2,1-e][1,3,6,2]dioxazasilonin-7-one, C17H25NO3Si, Mr=319.48. (2S,3R)-anti-Diastereomer (I), orthorhombic, P212121, a= 8-716(4), b=11-677(3), c=17.161(6)A, V=1746(1)A3, Z=4, Dx=1.22 g cm-3, wavelength(Mo Kce) = 0.71073 A, u=1.50 cm-1 F(000)=688, room temperature, final R=0.040 for 1683 reflections with Fo2 greater than 0. (2S,3S)-syn- Diastereomer (II), monoclinic, P21, a=6.633(2), b=14.645(3), c=9.630(2) A, Beta=109.96(2)o, V=879.3(4) A3, Z=2, Dx=1.21 g cm-3, wavelength(Mo Ka)=0.71073 A,u = 1-49 cm-1, F(000)=344, room temperature, final R = 0.042 for 2537 reflections with F2o greater than 0. The compounds have a nine-membered hetero-cyclic ring containing the Si atom, the N atom of the pyrrolidine ring, two O atoms bonded to silicon and a carbonyl C atom. Bond distances in the molecules are normal and equivalent bonds are equal within three times their e.s.d.'s. Isomer (I) shows a disorder in the pyrrolidine ring that is absent in isomer (II).