Dithiiranes oxidation

Tlie reaction of 5,6-dithiabicyclo[2.1.1]hexaiie 11a with OXONE led to the corresponding dithiirane 12a, which was, however, stable only in solution (Amax at 442 nm in CH2CI2). Treatment of the reaction mixture containing 12a with MCPBA gave the dithiirane 1-oxide 13a (8%) (95TL1867). Tire introduction of electron-withdrawing substituents on the benzene rings provided the dithiirane oxide 13b in a better yield (21%). 

All the isolable dithiiraiies described previously contain a carbonyl group in their structures. Tire oxidation of tetrathiolanes 16 enabled the preparation of dithiirane oxides 17 that possess no other functional groups (98TL3525). 

The previous chapter in CHEC-II(1996) reported on the stability and derived thermochemical data for the isomerization of /3-sultones, the cycloreversion of 1,2-oxathietanes, the relative stability of 1,2- and 1,3-oxathietanes, the isomerization of 1,2-oxathietes, as well as aspects related to stereoisomerization <1996CHEC-II(1B)1083>. Unfortunately, no new studies or information has been presented over the last decade. The only experimental observation worthy of mention is that an equilibrium mixture of the thioketone 27 along with the 6-oxa-7-thiabicy-clo[3.1.1]heptane 28 was isolated in 48% yield from the thermal decomposition of a precursor dithiirane oxide <1997BCJ509>. This indicated that the activation barrier for cycloaddition-cycloreversion is low at ambient temperature. 

The reaction of the eeo-sulfoxide 42 with Oxone gave the dithiirane oxide 43 (57%) and other products (Equation 6), while endo-sulfoxide 44 gave both 43 (16%) and its isomer 45 (2%), with no other products (Equation 7) < 1997BCJ509>. 

The reaction sequence leading to the formation of the dithiirane oxides 43 and 45 is shown in Scheme 3 <1997BCJ509>. 

Tire reaction of 1,3-dithietanes 14 with OXONE produced dithiirane 1-oxides 15 directly (95TL1867). Dithiirane 1-oxides 15 would be formed through the initially formed 1,3-dithietane oxides. 

A ring opening of the dithiirane 39 to the thioketone 5-sulfide 35 was proposed for the reaction of thiobenzophenone 5-oxide (40) with the thioketone 41 (81LA187). Tlie conjugation with the phenyl group would stabilize 35 relative to the dithiirane form. 

Relevant Bond Lengths (A) and Angles (deg) of Dithiirane AND Dithiirane 1-Oxides... 

Tire presence of two different substituents on the ring carbon atom of dithiirane 1-oxides provides two asymmetric centers, i.e., four stereoisomers. 

Optical resolution of the dithiirane 1-oxides 2 and 3 was accomplished by HPLC equipped with a chiral column (97T12203). Absolute configurations of 2a and 2b were determined by X-ray crystallography. Tire stereospecific isomerization (epimerrzation) of 2a to 3b and 2b to 3a was observed during the resolution study. 

Tlie isolable dithiiranes (4 and 7) are fairly stable under acidic conditions but quickly lose a sulfur atom to give the corresponding thioketones under basic conditions (97BCJ509). Tliey are quite sensitive toward amines and phosphines. Oxidation with MCPBA gave the corresponding dithiirane 1-oxides in high yields. 

Oxidation of tetrathioianes (8) with DMDO gave mixtures of dithiirane 1-oxides (10) and thioketones (11) (Scheme 5). The existence of the intermediate tetrathioiane 1-oxides (9) was verified by NMR of the cooled and evaporated reaction mixture. ... 

A stable dithiirane 223 was obtained from the oxidation of 6,7-dithiabicyclo[3.1.1]heptane 222 with oxone (2KHS0s KHS04 K2S04). Heating in solution afforded a thioketone 224 and 8-oxa-6,7-dithiabicyclo[3.2.1]octane 225 (resulted from an intramolecular [3+2] cycloaddition of the 5-thioketone J-sulfide indermediate) (Scheme 74) C1997TL1431, 1997BCJ509>. 

The same product but in higher yield (50%) was obtained by oxidation of 38 with NaOCl with LiClC>4 or NaCKT as additive. In a similar manner, dithiiranes 41a and 41b were synthesized from the corresponding bicyclic 1,3-dithietanes 40a and 40b in 39% and 37% yields, respectively (Equation 5) <1997BCJ509>. 

Fascinating chemistry has been developed by Nakayama and Ishii on the first dithiiranes, which were prepared by oxidation of dithietanes and subsequent rearrangement. It was recently reviewed [82, 83]. Monodesulfurisa-tion of dithiiranes was achieved with triphenylphosphine or triethylamine to yield the corresponding thioketones [84-86]. 

Ishii A, Saito M, Murata M, Nakayama J (2002) Reaction between dithiirane 1-oxides and a platinum(O) complex. Eur J Org Chem 979-982... 

The reaction of the 6,7-dithiabicyclo[3.1.1]heptane exo- and endo-6-oxides 1 with 2KHS05KHS04K2S04 (OXONE) in CH2C12-H20 gave the first isolable dithiirane 1-oxides 2 and 3 (93JA4914).The two isomeric dithi-irane 1-oxides are colorless, crystalline compounds and stable up to 124° and 110°C, respectively. X-Ray crystallography confirmed their structure unambiguously. 

After CHEC-II(1996), more new stable dithiiranes 3 and dithiirane A-oxides have been characterized using X-ray single crystal structure analysis. This method has also been used to determine the absolute configuration of resolved enantiomers of 16, previously known and characterized by X-ray only as a racemic mixture <1997T12203>. (The assignment of the absolute configuration of enantiomers of 17 is discussed in Section 1.14.4.1.). 

H and nuclear magnetic resonance (NMR) spectroscopic data for all indicated dithiiranes have been reported and important chemical shifts are collected in Table 1. The configurations of the sulfmyl sulfur of 18 and 19 have been assigned by comparison of the chemical shifts of the geminal methyl groups with those of known cis- and trans-dithiirane A-oxides <1995TL1867>. 

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