Kurt Schank

Reactions of 2,3-dihydro-2-phenyliodonium-3-oxo-benzo[b] thiolenide-1,1-dioxide

Abstract 2,3-Dihydro-2-phenyliodonium-3-oxo-benzo[b]thiolenide-1,1-dioxide was found to react with various substrates like alkenes, alkynes, thiobenzophenones etc.

Chemiluminescent and Non-Chemiluminescent Ozonations of Selected Electron-Rich Alkynes in Halomethanes

Alkynes of sufficiently high nucleophilicity react with electrophilic O3 under conversion of the alkyne function to a vicinal dicarbonyl function. Contrary to earlier investigations with alkylated or arylated acetylene, products of complete C−C cleavage were not found as primary products, and, beyond that, peroxidic reaction products were absent. Trimethylsilylated alkynes reacted with O3 either by uptake of two or three O-atoms, but again without C−C cleavage or formation of peroxides. Two particularly electron-rich, symmetrically substituted alkynes revealed strong chemiluminescence during ozonation at low temperature, whereas this behavior was not observed with unsymmetrically substituted alkynes. The results are summarized in terms of a mechanistic discussion.

2,3-Dihydro-3-oxo-2-phenyliodonium-benzo[b]thiolenide-1,1-dioxide: Synthesis, decomposition and Cu-catalyzed thermal reactions

Abstract Iodonium ylide 4 was prepared in 93% yield from the reaction of β-ketosulfone 3 with phenyl iodosyl bis(trifluoroacetate). Although insoluble in most solvents, ylide 4 was readily soluble in a mixture of CH2Cl2/ethanol (1:1), yielding trimer 5 quantitatively. Upon reaction with various heteroatom nucleophiles the new ylides 7 were isolated, while reaction with CS2 and thiobenzophenones yields thione 10 and alkenes 14 respectively. Furthermore 4 reacts with various alkenes 15 affording cyclopropanes 16 in moderate yields as well as with alkyne 17 affording furan 18.

Ozonolysis of Allenes and Alkylidenecyclopropanes (Homoallenes)

Allenyl methyl ether (1) and (diphenylmethylene)cyclopropane (5) were ozonized with an ozone/oxygen mixture. Formation of the observed products cannot be satisfactorily rationalized via the familiar modified Criegee mechanism. However, a single-electron transfer (SET) mechanism provides a simple rationale.

Ozonation of 1,1,2,2-Tetraphenylethene Revisited: Evidence for Electron-Transfer Oxygenations

Ozonolyses of 1,1,2,2-tetraphenylethene (TPE, 1) have been described many times in the literature, but the reports are contradictory. This reaction is particularly important for understanding the mechanism of alkene ozonolysis, in view of possible stabilization of reactive intermediates by aryl groups. Thus, systematic investigations of ozonolysis in both aprotic solvents and in protic solvents are reported here. Attention is directed to the following details that have been underestimated in the past: i) the actual electronic structure of ground-state ozone (O3), ii) differentiation between strained and unstrained alkenes, iii) the significance of both the O3 concentration and the TPE concentration, iv) the influence of various solvents, including pyridine, v) the influence of the reaction temperature, vi) the role of electron-transfer catalysis (ETC) and, vii) the effect of structural modifications. Our results suggest that ozonolysis of TPE (1) does not include a 1,3-dipolar reaction step, but represents a particularly interesting example of electron-donor (TPE)/electron-acceptor (O3) redox chemistry. The present investigations include several crucial results. First, pure 3,3,6,6-tetraphenyltetroxane (3, m.p. 221° (dec.)) and pure tetraphenylethylene ozonide (4, m.p. 153° (dec.)) are prepared for the first time, although 3 and 4 have long been known. Second, the singlet diradical character of O3, lessened by means of hypervalent-electron interaction and predicted by different calculations, is evidenced via reaction with the spin-trap galvinoxyl (2,6-bis(1,1-dimethylethyl)-4-{[3,5-bis(1,1-dimethylethyl)-4-oxocyclohexa-2,5-dien-1-ylidene]methyl}phenoxy; 8), and the zwitterionic reaction behavior of ground-state O3 is ruled out. Third, the electron-acceptor ability of O3 is evidenced by reactions with suitable tetraaryl ethylenes: it is enhanced by addition of catalytic amounts of protons or Lewis acids. Fourth, the observed distribution of the O3 O-atoms to the two different olefinic C-atoms of the unsymmetric alkene 27b is in full agreement with an initial single-electron transfer (SET) step, followed by a radical mono-oxygenation to cause the crucial C,C cleavage. Final dioxygenation should lead to the generally known products (ozonides, tetroxanes, hydroperoxides). The regioselectivity is found to be inconsistent with the expected decay of an intermediate primary ozonide. Finally, the treatment of 1,2-bis(4-methoxyphenyl)acenaphthylene (36) with O3 (simultaneous transfer of three O-atoms) leads to the same experimental result as a stepwise transfer of one O-atom followed by a transfer of two O-atoms.

Redox Activation of Molecular Oxygen by Arenesulfinic Acids

Principally, 3O2 can be easily activated [1] via Single-Electron-Transfer (SET) from a suitable Donor D: and a concomitant proton transfer (PT) from a suitable proton donator H - A [2]:

Donor substituted sulfonyl carbenes, 2: Organothio sulfonyl carbenes

Abstract Organothio sulfonyl carbenes 3 have been generated via ylid thermolysis or via α-elimination starting from α-chloro α-organothio sulfones and their derivatives. They have been captured by suitable nucleophilic tapping reagents (diazomethane, enol ethers, and others). Their nucleophilic carbenoid precursors could be trapped by an electrophilic olefin (ketene dithioacetal S,S-dioxides as Michael acceptors). Stable carbene Z-dimers could be obtained under various conditions. Bromine catalyzed isomerization to E-isomers proved to be reversible.

Sulfones from Mono- and Dithioacetals as Sulfur Chemist'S Tool

Abstract Mainly applied syntheses of sulfones of O,S- and of S,S-acetals are briefly summarized; special types of these compounds represent the corresponding ketene acetals. Characteristic reactions all of these classes of compounds - including α sulfonyl carbanions as nucleophiles, α-substituted vinyl sulfones as Michael-acceptors or as cycloaddition partners, especially with regard to their synthon properties - are discussed.

Überraschende Ergebnisse bei der Nachprüfung der Bildung und Zersetzung von Tripten-ozonid

Surprising Results during the Re-investigation of the Formation and Decomposition of Triptene Ozonide. Revision of the ozonolysis of triptene (=2,3,3-trimethylbut-1-ene; 1) revealed that molecular oxygen of an applied ozone/oxygen gas mixture participates as well in the cleavage of the C=C bond as in the ozonide formation. Ozone-to-olefin stoichiometry varies in the range of 0.64 – 0.95 : 1 in terms of complete olefin consumption, depending on solvents, on reaction temperature, and on reaction conditions. Thermal decomposition of distilled monomeric triptene ozonide (2) does not lead to 3,6-di(tert-butyl)-3,6-dimethyl-1,2,4,5-tetroxane (5), which is formed by formaldehyde extrusion from an unstable oligomeric (probably dimeric) triptene ozonide 2′. Acid-catalyzed decomposition of 2 exclusively yields pinacolone (7) and formic acid (9).

Ozonolysis of 3,4-Dimethylsulfolene Revised Once More - the End of an Old Puzzle

Abstract Reinvestigation of ozonolyses of 3,4-dimethylsulfolene (1) removes ealier errors and uncertainties. A novel mechanistic proposal on the ozonolyses of cyclopentenes is presented.