α-hydroperoxy sulfide in sulfide photooxidation. Formation and isolation in the photooxidation of thiazolidine derivatives in aprotic media

Regioselective air oxidation of sulfides to O,S-acetals in a bubble column

In this paper the use of a bubble column for a metal-free, selective oxidation of α-alkylthio-imines to O,S-acetals is presented. During the synthesis, which is straightforward to perform, the sulfides are oxidized to α-alkoxy- or, respectively, α-hydroxysulfide by adding activated carbon in the presence of atmospheric oxygen only. We show that the use of the bubble column, which is unusual on laboratory scale, improves the efficiency of the reaction in comparison to common laboratory techniques. As atmospheric oxygen alone is used for oxidation, this method is cost saving, environmentally friendly, and safe.

Isotope effects as mechanistic probes in solution and in intrazeolite photooxygenations. The formation of a hydroperoxysulfonium ylide

The reactions of singlet oxygen with 2,2,6,6-tetradeuterio-1,4-dithiane have been examined in acetone and methanol, and in the interior of the zeolite NaY. The product isotope effects k(H)/k(D) have been measured for sulfoxide and, when possible, for sulfone formation. The results provide evidence for a hydroperoxysulfonium ylide intermediate in acetone, a hydrogen bonded or sulfurane intermediate in methanol, and an interesting equilibrium between two complexed forms of the substrate in NaY.

Mechanistic organic chemistry in a microreactor. Zeolite-controlled photooxidations of organic sulfides

The intrazeolite and solution photooxygenations of a series of sulfides have been compared. The unusual zeolite environment enhances the rates of reaction, it suppresses the Pummerer rearrangements, and it has a dramatic effect on the sulfoxide/sulfone ratio. A detailed kinetic study utilizing trapping experiments and intramolecular competition provides evidence for cation complexation to a persulfoxide intermediate as the underlying phenomenon for the unique intrazeolite behavior. For example, the enhanced rate of reaction is traced to the cation stabilization of the persulfoxide toward unproductive decomposition to substrate and triplet oxygen.

Substituent-dictated partitioning of intermediates on the sulfide singlet oxygen reaction surface. A new mechanism for oxidative C--S bond cleavage in alpha-hydroperoxy sulfides

The reactions of singlet oxygen with 17 sulfides bearing either anion or radical stabilizing substituents are reported. The abilities of substituents to modify product compositions in both the oxidative cleavage and sulfide oxidation pathways are analyzed in terms of partitioning of the hydroperoxy sulfonium ylide intermediate. Evidence is presented that suggests that the hydroperoxy sulfonium ylide exists in both diradical and zwitterionic forms. In addition, both inter- and intramolecular pathways for decomposition of alpha-hydroperoxy sulfides are suggested to rationalize the substituent-dependent formation of oxidative C--S bond cleavage products.

Effect of protic cosolvents on the photooxygenation of diethyl sulfide

The sluggish (kr < 10kq) photooxygenation of diethyl sulfide in both benzene and other aprotic solvents such as acetone and acetonitrile is made efficient by addition of small amounts of alcohols and, with a much more conspicuous increase, of phenols and carboxylic acids (<<0.1% additive is sufficient in this case). A kinetic analysis shows that the effect is accounted for by interaction of the protic additives with the first formed intermediate, the persulfoxide, in competition with cleavage to the components. The thus obtained rate constants kH linearly correlate with the acid strength of the additives, and the effect is rationalized as a general acid catalysis. Hydrogen bonding of the persulfoxide under this condition accounts in an economic way for the observed data, including co-oxygenation of Ph2SO in mixed solvents.

The Reactions of O(2) ((1)Delta(g)) with Anancomeric 1,3-Dithianes. The First Experimental Evidence in Support of a Hydroperoxy Sulfonium Ylide as a Precursor to Sulfoxide on the Sulfide Singlet Oxygen Reaction Surface

The kinetic isotope effects for the formation of anancomeric 1,3-dithiane-1-oxides in the reactions of singlet oxygen with the parent 1,3-dithianes have been determined for a series of 2-protio and 2-deuterio analogues. The substantial isotope effects are used to argue for formation of a hydroperoxysulfonium ylide as a key intermediate in sulfoxide formation. These results confirm an earlier theoretical prediction and force a change in the currently accepted mechanism for this important reaction. The first experimental demonstration of a novel singlet oxygen-induced epimerization of a 1,3-dithiane and a novel intramolecular electron transfer within a hydroperoxysulfonium ylide are also reported.

Photooxidation of troglitazone, a new antidiabetic drug

Troglitazone (CS-045) is a new oral antidiabetic drug reported to be effective in insulin-resistant diabetes and to show antihypertensive effects. Photooxidation of troglitazone gave the quinone and quinone epoxide as the major final stable products. An intermediate observed by NMR spectroscopy was shown to be the hydroperoxydienone, which is moderately stable at room temperature. The rate constant of singlet oxygen quenching by troglitazone is 2.14 x 10(8) M(-1) s(-1) and the reaction rate constant in acetone-d6 is 8.64 X 10(6) M(-1) s(-1). Only the chroman ring of troglitazone reacts with and quenches singlet oxygen significantly, and its reactivity and products are analogous to those of alpha-tocopherol. The reactivity of CS-45 toward singlet oxygen is much larger than that of the related compounds lacking the chroman ring.