Heterocyclics thietanes

Only a few papers on the formation of compounds with small rings have been published. One example is the [2 + 2]-cycloaddition of electron-rich enamines to Schiff bases under high pressure (1.4 GPa) (87JOC365). The reaction leads to substituted azetidines (1). Four-membered ring heterocycles, thietane derivatives (4), are formed by interaction of sulfene (2) with enamines (3) (86CB257 93JOC3429). 

The analogous sulfur nickelacycles are prepared by an entirely different method. Thus, the oxidative addition of ethylene sulfide to a nickel(O) complex, formed in situ from 41 by reductive elimination of butane, gives thianickelacycle 42 (Scheme 11). Similarly, the oxidative addition of the four-membered heterocycle thietane with Ni(COD)bpy leads to five-membered ring complex 43. ... 

A few special syntheses of thiirane derivatives from four-membered sulfur heterocycles are known. Methylenethiiranes are derived by thermolysis of the tosylhydrazones of thietan-3-ones (Scheme 143) (81TL4815), and 2,2,3,3-tetrakis(trifluoromethyl)thiirane is obtained by thermolysis of 2,2,4,4-tetrakis(trifluoromethyl)-l,3-dithietane 1,1-dioxide with loss of sulfur dioxide. 2,2,3,3-Tetrakis(trifluoromethyl)thiirane 1,1-dioxide is obtained in low yield by heating a mixture of 3,3-bis(trifluoromethyl)-l,2,4-oxadithietane 2,2,4,4-tetroxide and bis(trifluoromethyl)ketene. The mono-episulfide of norbornadiene is obtained from thietane derivative (65 Scheme 144) (73JOC649). 

Similarly, only selected cyclic systems containing more than one sulfoxide or sulfone groups have been included and discussed here, primarily in the thietane (i.e. 1,2- and 1,3-dithietanes) and thiane (i.e. 1,2-, 1,3- and 1,4-dithianes) series. The criterion for the inclusion of these multifunctional heterocycles was their contribution to the understanding of the physical properties and chemical reactivity of cyclic sulfones and sulfoxides, and the effects of these groups on either their immediate vicinity or on the behavior of the whole molecule. 

Other thietane derivatives have been obtained by isomerization of nitrogen-containing heterocycles. The reaction of an acyl isothiocyanate (RCONCS) with diphenyldiazomethane gave 20 and this isomerized in solution to the tetraphenyl-3-thietanone 21 <96BSB253>. Additionally, the isoxazolidine 22 was converted into 23 by the action of trimethylsilyl iodide and zinc iodide <96H1211>. 

The classification adopted in this review is by type of sulfur reagent it is useful to list by section the more important heterocycles that can be made thiiranes, II,C, IV,B, VIII,D thietanes and thietanones, V,B,2, VI,B,... 

In its mirror image form, for unpaired and paired anions, this equation has been used to good effect to determine the kp and in a large number of anionic polymerisations. In the field of cationic polymerisation, analogous studies have so far only been reported for thietans [2b] for which the kp and do not differ very much this seems to be a characteristic feature of heterocyclic systems which will be discussed below.b... 

The present review is concerned with four-membered heterocycles that contain one sulfur atom either alone or associated with another heteroatom. The classes of compounds that will be discussed are the thietanes (1) and thietes (2), the 1,2-oxathietanes (3), the / -sultines and -sultones (4 and 5), the 1,2- and 1,3-thiazetidines (6 and 7) and thiazetes (8), the 1,2- and 1,3-thia-phosphetanes (9 and 10), and the 1,3-silathietanes and 1,3-selenathietanes (11 and 12). 

Thietanes and 3-thietanones represent the only four-membered sulfur-containing heterocycles of the title group that have been isolated from natural sources. Even in petroleum deposits, where 5- and 6-membered cyclic sulfur compounds are common, thietanes occur only in small amounts. However, thiacyclobutane (1) and thiacyclopentane are both commonly found in shale oil and could be utilized as a possible source of fuel. ... 

Thietane and thiophene deposits in shale oil may be used as a future fuel source. Laser-induced fragmentation of these heterocycles in the presence of oxygen could produce a variety of useful gaseous molecules. Unfortunately, these could create a severe pollution problem. ... 

The mass spectrometry of four-membered heterocycles has been considerably investigated by Scala and Colon. Holmes et have provided structures associated with metastabile ion peaks. The effect of ring size on the fragmentation process of cyclic sulfoxides was studied by Tamagaki and Oae. Thietane 1-oxide appears as a strong radical ion at mje 90. At 80 eV no appreciable deoxygenation takes place. Instead, the loss of OH and/or SOH is observed, giving the peak at mje a value of 73 for CaHjS" and the base peak at mje 41 for CaH ". ... 

Gotthard, however, showed that by lowering the thione concentration the thietane-dithiolane yield ratio could be systematically directed to favor the four-membered heterocycle. A low thione concentration inhibits addition of the intermediate diradical to another thiophenone molecule to produce the dithiane (Scheme 5). 

Thietanes can also be prepared by ring contraction of higher-membered heterocyclic rings. Thermolysis of the dithiolane dioxide 129 in benzene leads to trans-2-phenyl-3-benzoylthietane (130) and benzalacetophenone (Eq. 20). 

Reviews of thietanes <99MI138> and saturated oxygen heterocycles including oxetanes are available <98JCS(P1)4175>. 

Simple heterocyclic compounds Three-membered heterocycles containing one heteroatom Oxiranes (epoxides), thiiranes (episulfides), aziridines Three-membered heterocycles containing more than one heteroatom Oxaziridines, dioxiranes, diazirines Four-membered heterocycles containing one heteroatom Oxetanes, thietanes, azetidines... 

One instance of the formation of a thietane derivative from a seven-membered heterocyclic precursor is seen in the photochemical fragmentation of dione (180) (73T2135). 

There are a few reports in the literature in which the carbonyl group has been formally replaced by another unsaturated function. Thio-benzophenone (268) undergoes photochemical 1,2-cycloaddition to a-phellandrene (269) to give the thietane (270), together with the sulfur heterocycles (271 and 272) formed by 1,4-cycloaddition.298 Isoprene, cyclopentadiene, and 1,4-diphenylbutadiene also undergo 1,4-cycloaddition with thiobenzophenone, but 1,3-cyclooctadiene... 

A variety of examples of photochemically induced elimination of sulfur dioxide from sulfur heterocycles have been reported, with particular attention to cyclic sulfones. Thietan-3-one 1,1-dioxide (525), however, undergoes fragmentation on irradiation in acetonitrile to ketene (526) and to the sulfene (527), the latter identified by infrared spectroscopy and as the methanol... 

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