Thietane

Abstract: The reaction mechanism of oxygen and sulfur ylide mediated rearrangements is even today a matter of debate. In this report, we describe ring expansion reactions of oxetane and thietane heterocycles that allow probing the underlying reaction mechanism under metal-free, photochemical conditions. This ring expansion proves highly efficient and allows the synthesis of tetrahydrofuran and thiolane heterocycles under mild and operationally simple reaction conditions. These studies reveal marked differences in the stereoselectivity of the ring expansion of oxygen or sulfur ylides, which were further investigated computationally. DFT calculations show that carbenes react under ylide formation and that the corresponding ring expansion reactions proceed via a diradical pathway. The different bond lengths in free oxygen or sulfur ylide intermediates cause the distinctive stereochemical outcome.

Abstract: Thiete 1,1-dioxide (1) rearranges to 5H-1,2-oxathiole-2-oxide (3) on heating in solution or in the vapor phase. The presence of phenol in the solution leads to formation of phenyl 2-propene-1-sulfonate (CH2=CHCH2SO2OPh) in 15% yield. The results are rationalized in terms of a mechanism involving vinylsulfene (2). Flash thermolysis of some thietane 1,1-dioxides (16) and 3-thietanone 1,1-dioxides (15) gave products derived from extrusion processes, but 3-thietanol 1,1-dioxide (17) yielded, among other products, acetaldehyde and formaldehyde. The latter is believed to arise by "desulfinylation" of sulfene (CH2=SO2) formed along with the enol form of acetaldehyde by cycloreversion from 17.

Abstract: Free-standing ultrathin films of a porphyrin homopolymer have been synthesized by interfacial polymerization of a mercaptoporphyrin. Coupling of 5,10,15,20-tetrakis(α-mercapto-p-tolyl)porphyrin at the water/chloroform interface by copper acetate yields continuous, flexible films after drying with supercritical CO2. These films are amorphous and retain many characteristics of the monomeric porphyrin, such as the property that they may be metalated. Spectroscopic evidence suggests efficient cross-linking of thiols through disulfide coupling occurs in these polyporphyrins to form a network. Polymerization is accompanied by the introduction of carbonyl functionality, probably the transformation of residual thiols to thioacetate by metal-mediated reaction with excess acetate ion. As an example of the catalytic properties of these polymers, they are shown to promote photooxidation of thietane to the corresponding sulfoxide by sensitizing singlet oxygen production.