Dithiins, review

Other heterocyclic systems prepared by a thionyl chloride reaction include fused thiazoles,71 thiatriazoles,72 oxathiins,73 and dithiins 74 some further examples are given in reviews.53... 

As in the case of the 1,2-dioxins, the 1,2-dithiins exist in various states of saturation, oxidation, and benzoannelation (cf. Scheme 1, 17-27) and they have been studied in detail both theoretically and experimentally. Not only were the conformations of the ring and attached substituents investigated, but the valence isomerism of 1,2-dithiin by both NMR and high-level ab initio molecular orbital (MO) calculations and the dithiol/disulfide equilibrium by MP2 calculations were also examined. The latter equilibrium has been applied successfully as a luminescent molecular switch (cf. Section 8.10.2.1). Finally, as a very interesting 1,2-dithiin derivative, the synthesis, structure, and reactivity of the (-l-)-camphor-derived analog 25 and its sulfoxide 26 and sulfone 27 have been reported. Both the synthesis and the antimalarial activity of the 2,3-dioxabicyclo[3.3.1]nonane pharmacophore 28, which contains the 1,2-dioxane moiety, have been reviewed recently <2006BML2991>. 

Recently, synthetic methods for preparing 1,2-dioxins and their benzo- and dibenzofused derivatives <2004SOS(16)13> and 1,2-dithiins <2004SOS(16)39> have been reviewed. 

Dioxins, 1,4-oxathiins, 1,4-dithiins, and annulated derivatives have been reviewed in 1997 <1997HOU(9a)l> More recently, synthetic methods for preparing 1,4-dioxins and their benzo- and dibenzofused derivatives <2004808(16)15, 20048L2449>, 1,4-dithiins <2004SOS(16)57> and 1,4-oxathiins, and their annulated analogs... 

An authoritative review covering application of UV photoelectron spectroscopy to heterocycles appeared in 1974 <74PMH(6)l) and important work on saturated multi oxygen and sulfur compounds is discussed therein. However, the studies of 1,4-dioxin, its dibenzo analogue, 1,4-dithiin and phenoxathiin, which are referred to in the first part of this section, appeared after the publication of that review. 

The chemistry of the l,3-dithiole-2,4,5-trithione oligomer system 374 derived from monomers 375 and 376 (Scheme 49) has been the subject of a review <2006CHE423>. This system easily depolymerized (heat or UV irradiation at 253 nm) and was effective in Diels-Alder-type cycloadditions. Reactions with unsaturated compounds constituted an efficient method for synthesis of functionalized l,3-dithiole-2-thiones containing substituted 1,4-dithiin rings and are examples of reactivity of thione or sulfenyl substituents (stmctures 374-376) attached to the 1,3-dithiole ring carbon atom. 

Similarly to tetrathioethylenes and tetrathiafulvalenes, 1,4-dithiin (LV) and its benzoder-ivatives (LVI and LVII) are electron-rich compounds that can be easily oxidized to their corresponding cation radicals and dications. There are several reviews [2, 3, 186, 187] on the chemistry of the radical cations of dibenzo-1,4-dithiin (LVH) and related compounds. 

The general reactivity of the 1,3-dithiins and related species has been reviewed <66CHE(21)1028, 72IJS(B)101>. 

As in the case of the corresponding anhydride (23) (Section III.1.C), didehydromaleimide (30) probably does not qualify as a true aryne, but is expected to be sufficiently similar in properties to be covered in this review (Section I.2.C). This species (30) was first suggested as an intermediate along with the 1,2-dithiete (274) in the decomposition of the dithiin (275) in pyridine at 120°C to explain the formation of the aryne trimer (276). When this reaction was carried out in the presence of cyclopentadiene (146b), however, the failure to obtain the appropriate aryne adduct (277) was rationalized as being due to its presumed instability. The only products obtained from this reaction, as well as from butadiene (146c) and anthracene (147), were Diels-Alder adducts such as 278 and 279 of the dithiin (275) and the dithiete (274), respectively. 

In contrast to a statement in a recent review, therefore, the didehydromaleimide (30) has not been trapped and only a product 276 which could arise by an alternate addition-elimination process is obtained. Both the ability of the alleged aryne precursor 275 to form Diels-Alder adducts (278) and its stability in inert solvents or upon sublimation to 300 C support this suggestion. Furthermore, several properties of 275 compared to other dithiins have led to the... 

Methyl propiolate in benzene treated with p-chlorobenzaldehyde and BFg-etherate in the same solvent, HgS passed into the soln. for 5 min., stirred and refluxed 0.5 hr. methyl 2,4-di-p-chlorophenyl-m-dithiin-5-carboxylate. Y ca. 100%. F. e. and limitations s. U. Eisner and T. Krishnamurthy, Tetrahedron 27, 5753 (1971) review of dithiins s. Intern. J. Sulfur Chem. B 7, 101 (1972). 

High-level quantum-chemical calculations on the 3 + 2-cycloadditions of thioformaldehyde 5 -imides, S -methylide, S-oxide, and 5-sulfide have been reviewed. Theoretical studies on the 1,3-dipolar cycloaddition between thioketene 5-oxide and methyleneimine show that this reaction is concerted but non-synchronous. Adamantanethione 5-methylide reacts with thiocarbonyl compounds to produce 1,3-dithiolanes. A density-functional-theory study of the cycloaddition of the sulfine H2CSO predicts the 2 + 3-mechanism having the lowest pathway, with an activation barrier of 12.3kcalmoP. R The thermal and photochemical reactions of fluorenethione 5-oxide (69) with cyclooctyne (70) involves an initial 1,3-dipolar cycloaddition to produce the adduct (71), followed by an efficient sulfur transfer to cyclooctyne to produce the enone (72) and the dithiin (73) (Scheme 26). ° ... 

In general, these Reports cover the period from April 1974 to March 1976 unless otherwise stated. Due to necessary limitations of space, the topics have, in parts, been treated more summarily than in previous Reports. A review of the chemistry of thiepins and dithiins, omitted from Volume 3, has been included in this volume, but accounts of the chemistry of thiazepines and of heterocyclic compounds of quadricovalent sulphur have been held over to Volume 5. 

A companion volume has been published which brings up to date an important treatise on flavonoids. The final part of a comprehensive review of pyrylium salts provides full documentation of this field which has also been reviewed in Russian. The synthesis and reactions of kojic acid have been reviewed as also (in Japanese) have those of 1,4-dithiins. The proceedings of the 6th International Symposium on Flavonoids and Bioflavonoids (1981) have been published and contain both reviews and shorter original contributions. Amongst the former are reviews on such topics as the reactions of chromones with hydroxylamine, the synthesis and reactions of 3-acylchromones, chemical and biomimetic studies on condensed... 

Theoretical Aspects of Organosulphur and Organoselenium Compounds is a review for the period April 1970 to March 1974, with emphasis in this volume on conjugated systems. A review of the chemistry of Thiepins, Dithiins, and Thiazepines has been omitted. A review of these subjects, covering the four-year period April 1972 to March 1976, will appear in Volume 4. Reviewing of all other material covered in this Volume is for the two-year period April 1972 to March 1974. 

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