4//-Thiopyran, 2,6-diphenyl-4

The relative stability of lithiated thiopyrans seems to depend upon the heterocyclic ring substitution. Thus, a-lithiated 2,6-diphenyl-2//-thiopyran 16 rearranges into the y-lithiated derivative 17 (Scheme 5) (82JOC680), while the reverse transformation occurs on lithiation of 2,6-diphenyl-4-diethylphosphonylthiopyran (80JOC2453). 

Diphenyl-4/7-thiopyran (9) was prepared by application of the known two-step procedure involving the 2,6-dichloro intermediate from the corresponding bis-dimethylacetal (82CJC574). 

Diphenyl-4//-thiopyran (9) was oxidized to its S,S-dioxide 141g with Ru04 (82CJC574). 2,4,4,6-Tetraphenyl-4//-thiopyran-S-oxide (143) was obtained from 56 (R = Ph) with H202-Ac0H under mild conditions [92JCS(P2) 1301 ]. 

Two examples involving as key intermediates the corresponding thio- or selenopyran anions are mentioned in Section IV,A,2, e.g., 48e — 60 + 56 (R = /-Bu) and 54d + 55d -> 59 (85CL1119 90ACS524). A deuteriode-protonation of 2,6-diphenyl-2//-thiopyran (87) to 4-deuterio-2,6-diphenyl-4//-thiopyran (51) took place after the initial reaction with BuLi-THF at... 

Ried and Bopp76 have shown that the photolysis of 3,5-diphenyl-4H-thiopyran-4-one 1,1-dioxide (58) in chloroform very rapidly leads to a trimer, or to photoadducts with... 

Analogous cyclizations with 1,5-diketones show that ring closure readily occurs in protic solvents such as acetic acid92"94 or alcohols.94"96 Typical examples include the preparations of 4//-thiopyran derivatives 43, 45, and 47a from the corresponding l,5-diphenyl-l,5-diones 44 and 46, respectively.92,93... 

Diphenyl-2//-thiopyran 233 is one of the products (12 to 72%) formed by ethanolic methylamine, ethylamine, benzylamine or triethylamine with 2,4-diphenylthiopyrylium perchlorate.273 Trichlorosilane was found to demethylate thiabenzene sulfoxide 234 reductively to mixtures of isomeric thiopyrans 222 and 223.267,274... 

Self-condensation of some dithiolyl perchlorates in the presence of base proceeds via spirothiopyrans.3453 Similarly, the reaction of 2,3-dimethyl-benzothiazolium and 3,5-diphenyl-l,2-dithiolyium perchlorates led to 90% of a 2//-thiopyran product, as shown in Eq. (17a). 

Methyl-2,4,6-triphenyl-4//-thiopyran (47) and 2,4-diphenyl-3-methyl-6-fe/7-butyl-4//-thiopyran (58) reacted with perchloric acid in acetic acid or with oxygen to give perchlorates 405a105,362,364 and 405b.98,363 Analogously,... 

The aromatization of 3,4,5-trisubstituted 2,6-diphenyl-4//-thiopyrans, e.g., 55 - 405c,40,362,364 226b,c - 406b,c,40 and 409b - 410b362 occurred with perchloric acid alone or in conjunction with molecular oxygen.364... 

Diphenyl-3,5-dimethyl-4//-thiopyran (435) was found to isomerize to its 2H isomer 481 under the influence of a HCl-AcOH or HCl-Et20 mixture92 or hydrogen bromide and iodide.93... 

The cycloaddition of a variety of sulfur heterocycles to alkenes has also been reported. Dibromomaleic anhydride undergoes [ 2 + 2] cycloaddition to thiophen295 and to benzo[b]thiophen.296 The photoaddition of benzo-[(>]thiophen 1,1-dioxides to alkenes also affords cyclobutane derivatives.297 Of particular interest is the addition of 3-acetoxybenzo[6]thiophen (350) to cyclohexene to give the adduct (351), which on treatment with base, undergoes a retro-aldol ring opening to benzo[6]thiepinone (352).298 A mixture of stereoisomeric cyclobutane derivatives were obtained on irradiation of 2,6-diphenyl-4//-thiopyran-4-one 1,1-dioxide in cyclohexene.299 The [ 2 + 2] cycloaddition of sulfolen to maleic anhydride and to maleimide has been reported.300... 

Both 3,5-dibromo-2,4,4,6-tetraphenyl-47/-thiopyran and 2,6-bis(4-bromophenyl)-4,4-diphenyl-4/7-thiopyran are good substrates for the synthesis of highly substituted 477-thiopyrans through reaction with various electrophilic and nucleophilic species (Scheme 76) <1998CCC662>. 

The anodic oxidation of spiro[4,9 -fluorenyl]-2,6-diphenyl-4//-thiopyran at high potential leads to deposition on the anode of polymeric material which consists of a polyphenylene framework bearing thiopyran or thiopyrylium substituents depending on the oxidation state. This conducting material is electrochromic, appearing blue, red, or yellow according to its oxidation state. It is proposed that the reaction proceeds via a radical thiopyran cation. 

The anions derived from 277-thiopyran 1,1-dioxides behave as ligands for various transition metal single site catalysts 591 that are employed for the polymerization of olefins <2002USP2002156211>. A nickel(ll) ion selective PVC-membrane electrode based on the 2,6-diphenyl-277-thiopyran 592 has been described. The electrode exhibits a Nernstian response over a wide concentration range of Niz+ with a lower detection limit of 9 X 10-6M and a response time of ca. 10 s <2000ELA1138>. 

H NMR data have been reported for 2,6-dimethyl- and 2,6-diphenyl-4ff-pyran-4-one and -thiopyran-4-one and -selenopyran-4-one, in their neutral and protonated forms (75MI2). 

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