Synthesis and Stereochemistry of Thiaspiro-α-methylene-γ-butyrolactones. Single-Crystal X-ray Diffraction Analysis of 2,2,6,6-Tetramethyl-9-methylene-7-oxa-1-thiaspirodecan-8-one

Article abstract of DOI:10.1021/jo00334a037

α-Methylene-γ-butyrolactone systems attached to the heterocycles are rare.We reported the synthesis of a few 9-methylene-7-oxa-1-thiaspiro<4.5>decan-8-ones via a Reformatsky-type reaction on substituted 4-thianones.All products were characterized by 1H and 13C NMR analysis as well as by mass and infrared spectra and elemental analyses.Downfield shifts for C(2,6) in 2,2,6,6-tetramethyl-9-methylene-7-oxa-1-thiaspiro<4.5>decan-8-one in the 13C NMR spectrum were of such magnitude, compared to model cyclohexyl systems, that the thianone ring was suggested to be flattened near the sulfur end of the molecule.The structure of solid 2,2,6,6-tetramethyl-9-methylene-7-oxa-1-thiaspiro<4.5>decan-8-one was etablished by means of an X-ray diffraction analysis of a single crystal and confirmed such a flattening.The molecule crystallized in the space group P2₁/c with unit cell parameters of a= 6.189 (3) Angstroem, b= 11.244 (4) Angstroem, c= 18.960 (9) Angstroem, and β= 92.39 (4) deg.The structure was solved by direct methods and refined by least-squares methods to an R value of 0.057 for 2515 reflections.The five-membered lactone ring is flattened twist (C₂) conformation, and the C-O bond has an axial orientation at the 4-position of the thiane ring system.