2-Thiabicyclohept-5-ene and Its S-Oxides and 3-Alkyl Derivatives: Sulfine and Sulfene Cyclopentadiene Diels-Alder Adducts. Conversion of the Cyclopentadiene-Sulfine Adducts into 2-Oxa-3-thiabicyclooct-7-enes, Novel Bicyclic Sultenes

Article abstract of DOI:10.1021/jo00381a020

Reaction of (trimethylsilyl)methanesulfonyl chloride (6a) or -sulfonic anhydride (6b) with cesium fluoride in the presence of cyclopentadiene affords 2-thiabicyclo<2.2.1>hept-5-ene 2,2-dioxide (4) by way of sulfene CH2=SO2.Similar reaction of (trimethylsilyl)methanesulfinyl chloride (7) gave unstable 2-thiabicyclo<2.2.1>hept-5-ene endo-2-oxide (3) via the intermediacy of sulfine CH2=SO.Compound 3 can be oxidized to 4 and reduced to 2-thiabicyclo<2.2.1>hept-5-ene (1) and the latter oxidized to the stable 2-thiabicyclo<2.2.1>hept-5-ene exo-2-oxide (2).Fluorodesilylation of 1-(trimethylsilyl)propanesulfonic anhydride (8) in the presence of cyclopentadiene gave a 77/23 ratio of endo/exo-3-ethyl-2-thiabicyclo<2.2.1>hept-5-ene 2,2-dioxide (9a/b) by way of propanethial S,S-dioxide.The structure of the major isomer 9a was established by an X-ray structure of the corresponding exo-epoxide 11a, formed from 9a by oxidation.Reaction of 4 with n-butyllithium followed by ethyl iodide gave a compound identical with minor isomer 9b.Reaction of propanethial S-oxide with cyclopentadiene gave unstable endo-3-ethyl-2-thiabicyclo<2.2.1>hept-5-ene endo-5-oxide (10a).The structure of 10a was established by oxidation to sulfone 9a, by reduction and reoxidation to a stable exo-5-oxide 10b, by its facile <2,3> sigmatropic rearrangement to exo-4-ethyl-2-oxa-3-thiabicyclo<3.3.0>oct-7-ene (14c), and by NMR spectroscopic methods.Compound 14c was characterized by NMR spectroscopy and by its reactions.Oxidation of 14c gave the endo/exo-3-oxides 15c/15c' and the 3,3-dioxide 16c.Reaction of 14c with phenyllithium gave alcohol 17c, which was desulfurized and oxidized to 5-propyl-2-cyclopentenone or was oxidized at both carbon and sulfur to give (E)-5-propylidene-2-cyclopentenone 21c on gentle warming.Reaction of 14c with tert-butyl alcohol gave exo-6-tert-butoxy-exo-3-ethyl-syn-7-hydroxy-2-thiabicyclo<2.2.1>heptane (24), characterized by further oxidation to crystalline hydroxy sulfone 25 and keto sulfone 26.Mechanisms are proposed for the above series of reactions.