Thiochromone

Thianaphtheneqiiinone - (109) and diazomethane give a different reaction from that found with isatin, A -methylisatin and coumarandione. In as far as crystalline products could be isolated, the ring expansion occurs here between the sulfur and the carbonyl group in the 2-position. Depending on the solvent, there are formed 3-hydroxy-thiochromone (110), its 0-methyl derivative (111), or (presumably by attack on the 3-keto group of the tautomeric 3,4-diketo form of 110), 3,3 -epoxy-3-methylthiochromone (108). 

Unusual reactions occur between diazomethane and heterocyclic thiocarbonyl compounds. For example, pyran-4-thiones give methylene ethers of 1,2-dimercaptans formed by dimerization (cf. 115 —>116). 4-Thioflavones and 4-thiochromones react similarly. 

The photodimerization of thiochromone 1,1-dioxide (67) has also been studied. In... 

Treatment of dibromides 2 with sodium azide in N,N-dimethylformamide (DMF) at room temperature resulted in the formation of two products, 3-(a-azidobenzyOchromones 2a-c,g or -1-thiochromones 2d-f and the 3-arylidenechromanones la-c,g,h or -1-thiochromanones Id-f, respectively (eqn. 2). As shown by yield data given in Table 2, the substituent at position 2 plays decisive role in the product ratio. Dibromides unsubstituted at position 2 tended to give almost exclusively azides 3a-f and only a small amount of 1 was obtained. On the contrary, the reaction of flavanone derivatives 2gjh gave 3-arylideneflavanones... 

Chromones 2a-c,g were found to show separated vC = 0 and vC = C bands at 1640 and 1620 cm l, respectively, whereas 1-thiochromones 3d-f had coalesced... 

A one-pot process to form 1,3,4-substituted pyrazoles 25 by Suzuki coupling of arylboronic acids to chromone 24, followed by condensation with hydrazine has been reported <06JCO286>. The synthesis of 3 or 5-o-hydroxyphenol-4-benzylpyrazoles has been accomplished by treatment of 3-benzylchromones, 3-benzylflavones and their 4-thiochromone analogs with hydrazine hydrate in hot pyridine <06EJO2825>. 

Thiophenols undergo base-catalyzed, Michael addition to acetylenic acids and esters to give trans addition products. These vinyl thioethers have been used in the synthesis of thiochromones. " Recently, Undheim and Lie have shown that thiophenol adds to DMAD with concomitant cyclization to give benzo[6]thiophenes. 

Formation of cinnamoyl esters of thiophenols is readily accomplished. These esters cyclize, with elimination of benzene, by the action of aluminum chloride (Scheme 3). An alternative approach, exemplified in Scheme 4, utilizes the ready thermal isomerization of thiochromones to thiocoumarins (see p. 121), the former being derived from phenylthioacrylic esters. ... 

Ultraviolet and near ultraviolet spectra of a number of thiocoumarins have been recorded and discussed. Infrared spectra, in particular concerned with carbonyl absorptions, have been frequently collected,and comparisons made with those of thiochromones. All the usual spectra of thiocoumarin itself have been recorded and analyzed as well as the C-NMR spectrum and the fluorescent characteristics. ... 

The spectroscopic distinction between thiocoumarins and thiochromones is best made by observing the low-field 5-proton in the NMR spectrum of the latter and also the characteristic retro-Diels-Alder fragmentation always observed in the mass spectrum of thiochromones. Thiochromones also show distinctive, strong ultraviolet absorptions at 250-270 nm. ... 

The focus will be directed to five ring systems thiochromans (1), thiochromones (2), isothiochromans (3), benzothiopyrans (4—6), and, benzothiopyrylium salts (7, 8). It is difficult completely to segregate their chemistry since they are so interrelated cross-references will be employed as often as possible. Thiocoumarins and thioxanthones are excluded since these molecules differ considerably from those reviewed here. 

Two principal routes yield thiochromones. The first involves Michael addition of a thiophenol to a propiolic acid, followed by Friedel-Crafts cyclization of the chloride of the resultant j8-phenylmercaptoacrylic acid169-174 [Eq. (18)]. The preferred cyclization catalyst is stannic... 

Ethoxy-2/7-l-benzothiopyran with dichlorocarbene yields the dichlorocyclopropane (67),279 280 which in the presence of hot quinoline279 produces the thiochromone (68), or with methoxide280 forms the ring-expanded benzo[6]thiepin (69) and 2//-l-benzothiopyran (70), as in Scheme 13. Reaction of dichlorocarbene with the simple 2//-l-benzo-thiopyran (4) produces281 the dichloromethyl derivatives (71) and (72) of Eq. (33). 

These reactions are virtually limited to molecules possessing an ylidene functionality at the 4-carbon, formally derived from thiochromone condensations with active methylene compounds (e.g., see Section... 

The present volume encompasses a wide range of heterocyclic chemistry. Syntheses of heterocycles from thioureas are reviewed by T. S. Criffin, T. S. Woods, and 1). L. Klayman, while S. W. Schneller describes the chemistry of benzothiins and their derivatives (thiochromans, thiochromones, and thio-chromanones). Developments in chrom-3-ene chemistry are reviewed by L. Merlini. F. D. Popp contributes a chapter on the isatins. A discussion of theoretical aspects of the tautomerism of pyrimidines, by J. S. Kwiatkowski and B. Pullman, follows up a corresponding earlier contribution (Vol. 13) on tautomeric purines. In the final chapter P. and D. Cagniant describe the natural occurrence and synthesis of the benzofurans. 

Oxidation of 2H-1 - benzothiopyrans with selenium dioxide leads to the thiaselenin system, together with thiocoumarins, thiochromones and other cleavage products. Careful choice of conditions can lead to 35% yield of the selenium insertion product as shown in equation (49) (75T2099). 

Oxidation of thiochromones does not lead to the sulfoxide or sulfone derivatives these are better prepared from the corresponding thiochromanones by oxidation followed by bromination and dehydrobromination. The 1-oxide is an extremely reactive species and gives a Diels-Alder adduct with butadiene. The 1,1-dioxide is also very reactive. Photolysis in benzene affords a 2 1 adduct in 30% yield (116) (79TL1097) via an initial [2 + 2] addition followed by a Diels-Alder reaction. Simple [2 + 2] addition is found with cyclohexene. 

Ring synthesis by y- closure is a somewhat more versatile entry into this class of compound, though even then it is restricted to suitably activated precursors such as (142) (equation 101) (72T5197). Thiochromones and thioxanthones are probably most frequently prepared by this mode of closure, usually via an intramolecular Friedel-Crafts condensation of a carboxylic acid with an aromatic ring (equation 102) (71GEP2006196). 

In certain cases benzene will undergo photocycloaddition to oxygen and sulfur heterocycles. The two major photoproducts of irradiation of a mixture of furan and benzene are adducts 356 and 357, arising, respectively, by [ 2 + 2] and [ 4 + 4] cycloaddition processes.306 Irradiation of benzene and 2,2-dimethyl-l,3-dioxol (358) similarly affords adducts 359 and 360, together with dimer 361.307 Thiochromone 1,1-dioxide also undergoes photoaddition to benzene.308... 

Silyloxybenzopyrylium salts, readily derived from thiochromones, undergo a diastereoselective annulation on reaction... 

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