X-ray crystallographic determination of the structure and conformation of 1,4,4-trimethyltricyclo[5.4.0.03,5]-undec-7-en-9-one and 1,4,4,8-tetramethyltricyclo[5.4.0.03,5]-undec-T-en-9-one

The crystal structure and conformation of 1,4,4-trimethyltricyclo[5.4.0.0^3,5]undec-7-en-9-one (I) and 1,4,4,8-tetramethyltricyclo[5.4.0.0^3,5]undec-7-en-9-one (II) have been determined by X-ray diffraction. In both cases the crystals are orthorhombic, P2₁2₁2₁,a=6.194 (2) (I); 7.499 (2) (II),b=7.486 (3) (I); 12.855 (3) (II),c=26.283 (7) (I); 13.928 (4) (II) Å,Z=4. The structure was solved by direct methods, and refined to anR value of 0.048 for 1534 (I) and 0.054 for 1357 (II) withI>3.0 (I). In both compounds substituted by carbonyl group ring has the distorted³E sofa conformation whereas the second one possesses the slightly deformed^7.10B boat conformation.The nomenclature of IUPAC for the name of compounds in the title is applied. However, for simplicity the numbering of the atoms in the paper follow Fig. 1a and 1b.