Complex Thiopyran Derivatives

Synthetic work on thienothiopyran derivatives continues. Amongst the systems reported are compounds (83) and (84), related to benzo[h]thiophen 

Attempts to synthesize thiopyranothiopyrans (91) and (92) from the reduced forms, for example (93), have not been completely successful, although some evidence has been obtained for the existence of compound (92). Systems of this type are included in a theoretical (HMO) treatment of various sulphur heterocycles.  

Systems in which oxygen-containing rings are involved are represented by compounds (94) and related structures, and by more complicated examples (95) and (%).  

Pyridine and pyridazinone rings appear in compounds (97) and (98), the indole ring features in a series of compounds of type (99), and a diazepinone ring in the thiopyran (100).  

Kodomari and K. Itabashi, Yitfci Gosei K diu Kyokat Shi, 1972, 30, 629 (Chem. Abs 

A novel carbene-insertion reaction at the 3-position of the benzothiophen group was postulated for the formation of (47) from the tosylhydrazone of 2-(2 -benzo-thienylthiq)-5-nitrobenzaldehyde under Bamford-Stevens conditions. The new 

When the phthalides (49) or (50) were heated with concentrated sulphuric acid, rearrangement to (52) took place. Mixtures of (49), (51), and (52) were 

Compounds in which other heterocyclic rings (pyrazoles, isoxazoles, imidazoles ) are fused to thiopyrans have been described. The interesting thiazolium salts (56) were prepared by allowing the betaines (55) to react with 4-thioxothiazolidin-2-ones. Application of the Fischer indole synthesis and the Friedlander reaction to tetrahydrothiopyran-3-one led to the exported indolo-and quinolino-derivatives. Ring closure of (57) under acidic conditions afforded the rearranged product (58). Syntheses of benzothiopyrano[4,3,2-flfe]-quinazolines (59) from 1-amino-thioxanthones and of their S- and 7V-oxides have been described.  

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Treatment of 2,7-di-/ert-butylthiepin (1) either directly with bromine at — 78 °C, or with pyridinium bromide perbromide at room temperature, gives the thiophene compound 2. In contrast, bromination with bromine-1,4-dioxane complex or pyridinium bromide perbromide in the presence of acetic acid leads to the thiopyran derivative 3.87 To account for these results a homothiopyrylium ion has been proposed as a common intermediate, formed by electrophilic bromination at C4 in the first step. 

Complex 2//-thiopyran derivatives 291 afforded 25% of isomeric thiophene 581 on heating at 240°C in a nitrogen atmosphere.302... 

The complexes 432 derived from the reaction of cinnamaldehyde with Ru-SH complexes 433 undergo [4+2] cycloaddition reactions with a range of electron-rich, electron-deficient, and strained dienophiles. The products are Ru complexes of di- or tri-substituted 3,4-dihydro-2/7-thiopyrans. Generally, the reaction shows high regioselectivity and good diastereoselectivity with a marked preference for the endo adducts (Scheme 139). Ethyl propynoate affords the 3,4-disubstituted-477-thiopyran <2006CEJ4821>. 

In this context, it is interesting that the first examples of mesomorphic CT complexes of discoid or sheet-like donor compounds and a strong electron acceptor [7,7,8,8-tetracyano-1,4-quinodimethane (TCNQ)] constitute an exception from the usually observed behavior. These complexes of bi-4-H pyran or bi-4-H thiopyran derivatives carrying four alkyl- or alkyloxy-phenyl substituents with TCNQ (see Fig. 2), have been prepared as organic conductors [40]. The neat alkylphenyl derivatives in the bi-4-H pyran series and alkyl- or alkyloxy-phenyl-substituted bi-4-H thiopyran donors are mesomorphic [40], but the structures of their mesophases are still not clear. 

M 02(trop)2-Htrop (M = U, Pu) and U02(trop)2-H20 have been recorded, as well as complexes of composition UO2L2 with ligands related to tropolone, such as 3-hydroxy-2-met%l-4/f-thiopyran-4-one (thiomaltol) and 3-hydroxy-2-methyl-4if-pyran-4-one (maltol trihydrate), and derivatives of more complex 1,2-diketones. 

The photochemical synthesis of a thiepin 1,1-dioxide from a 4/f-thiopyran-4-one 1,1-dioxide has been reported earlier (see Vol. 3, p. 528). The j8-keto-sulphides (13) and (14) underwent photochemical rearrangement, involving a 1,3-sulphur shift, which yielded complex 2,3,4,5-tetrahydrothiepin-3-one derivatives. ... 

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