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Thianthrene 5‐Oxide as a Mechanistic Probe in Oxygen Transfer Reactions: The Case of Carbonyl Oxides versus Dioxiranes Revisited
Author(s) -
Adam Waldemar,
Golsch Dieter,
Görth Felix Christian
Publication year - 1996
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19960020304
Subject(s) - oxide , thianthrene , chemistry , oxygen , photochemistry , organic chemistry
Thianthrene 5‐oxide (SSO) constitutes a useful mechanistic tool for the assessment of the electronic character of oxygen transfer agents by means of their X so values, which reflect the extent of nucleophilic oxidation at the SO site in SSO. Treatment of dioxiranes 1 a–d with the SSO probe confirms that these are electrophilic oxidants ( X so < 0.15). Dioxirane sulfoxidation is sensitive to protic solvents and acids, which implies a polar mechanism (S N 2) with nucleophilic attack of the sulfide electron pair on the dioxirane peroxide bond. In contrast, the carbonyl oxides 2 a and b , diethyl persulfoxide ( 3 ), and adamantylideneadamantane perepoxide ( 4 ) are nucleophilic oxidants ( X so > 0.85). However, the cyclopentadienone carbonyl oxides 2 c and d show low X so values typical for electrophilic oxygen transfer agents. For these carbonyl oxides, photoisomerization to the respective dioxiranes is proposed under the photooxidation conditions of the diazoalkanes. Additionally, the trans / cis ratio of bissulfoxides (SOSO) formed provides valuable information on the stereochemical course of the oxygen‐transfer process due to the steric requirements of the oxidant. Thus, the electrophilic dioxiranes preferentially attack the axial lone pair of SSO because of repulsion by the peri hydrogen atoms to afford trans ‐SO‐SO.