Thiapyran

Besides being useful precursors to pyrroles pyridine-2-ones -4-ones, -4-thiones. and -4-imines 4-alkylidene-dihydropyridines thiophenes 1,2,4-triazoles thiapyrane-2-thiones, isoquinoline-3-ones isoben-zothiophenes and 4-mercaptoimidazolium hydroxide inner salts, mesoionic thiazoles are potentially useful in the construction of molecules with herbicidic (39). central nerve stimulating, and antiinflammatory properties (40,41). Application in dye synthesis has likewise been reported (42). 

UV spectra, 3, 955 X-ray crystallography, 3, 948 Thianthrenium salts, 5-phenyl-chloroplatinate salts, 3, 967 Thianylium salts chlorination, 3, 901 1,2A -Thiaphosphiranes synthesis, 7, 196 Thiapyrans — see Thiins l,3A -Thiarsoles nomenclature, 1, 32 Thiaselenafulvenes synthesis, 6, 965 Thiaselenins synthesis, 3, 914... 

Traynelis et al. described the preparation of 4-chlorobenzo[6]thiepin (24) via the key intermediate, 7a-chlorocyclopropa[6]benzo[6]thiapyran-7-one (25fK The ketone 25 underwent reduction with sodium borohydride to give the corresponding alcohol, which was ring opened with hydrochloric acid to yield the precursor 26 of... 

Obviously, the advantages of this new synthetic method are i) valence isomerization can be performed under very mild conditions and ii) due to the fairly strong acidity of the bridgehead hydrogens of a bicyclobutane moiety, some substituents can be introduced regioselectively. Nevertheless, one serious disadvantage of this synthesis is the limitation of its applicability Thus, the formation of the precursor bicyclobutane derivatives is limited only to 46 and 56, and many attempts to prepare bicyclobutane precursors from other thiapyran derivatives have been unsuccessful so far. 

Thiapyran derivatives can be prepared from preformed organoiron and -cobalt complexes as in Scheme 160 the organocobalt complex (136) can be used as an intermediate in the synthesis of 1,2-dithia cyclopent-4-en-3-thione (See Scheme 122 in Section IV,H.)... 

Analogously, the mesoionic jV-methyl thiazol-5-ones and l,3-dithiol-4-ones afforded A-methyl-4-pyridones and thiapyran-4-ones when reacting with diphenyl cyclopropenone and its thione261. Benzonitrile oxide apparently gives a 1,3-dipolar cycloaddition to the C=0 group of diphenyl cyclopropenone rationalizing the formation of triphenyl-l,3-oxazin-6-one 41626i ... 

In cyclopenta[c]thiapyran [238] there are also two possible protonation sites, C-5 and C-7 (Anderson and Harrison, 1964). A firm assignment of the position of protonation on the basis of the... 

The thiapyran ring does, like thiophene, provide a heterocyclic system on which one can perform standard sorts of reactions and then through a reductive desulfurization step expose a functionalized carbon chain. Such chemistry was first employed in a very elegant synthesis of the Cecropia juvenile hormones (Scheme 166) (73JA4444). 

A nitrile ylide intermediate has also been postulated for the thermolysis of the thiapyrans 32 (X = S) [75CR(C)37], The intermediacy of a nitrile ylide 37 and its 1,7-electrocyclization onto a nitro group to give intermediate 38 have been proposed as key steps in the thermolysis of 3-oxazolin-5-ones 36 to 1-acyloxyindazoles 39 (Scheme 14) (73CB2870). 

A different route to pyrones is the preparative electrochemical oxidation of enamines in acetonitrile in the presence of tetraethylammonium perchlorate (88MI2) (Scheme 46). The synthesis of 2-pyrone derivatives has been carried out by reaction of /3-dicarbonyl compounds with methyl-a-benzoylamino-/3-dimethylaminoacrylate (96JHC751). Thiapyran derivatives can be obtained by interaction of enamines based on (/3-amino-a-cyanoacryloylmethyl)pyridinium chloride derivatives with carbon disulfide (95M711).The synthesis of pyridine derivatives based on analogous enamines has been described as well (95M711). 

The nomenclature of the family of compounds to be discussed below has for long been the cause of much confusion. The systematic name for a six-membered ring containing one sulfur atom is thiin, but Chemical Abstracts uses the name thiopyran, while many earlier publications have used the replacement nomenclature thiapyran (which is strictly inaccurate as thia implies replacement of carbon, rather than oxygen, by sulfur). Throughout this chapter the terms thiopyran and thiin will be used interchangeably, while thiadecalin nomenclature will be found convenient for the perhydrobenzothiopyran systems. 

The treatment of cyclopenta[c]thiapyrane (31a) with potassium t-butoxide in 95° O-deuterated /-butyl alcohol at room temperature resulted in more than 90"o deuteration at the 1- and 3-positions and less than 5" , at the 4-, 5-, 6-, and 7-positions.86 Thus, the hydrogen-deuterium exchange takes place at the positions calculated by quantum chemistry (see Section IV,B). Completely analogous is the same reaction in the indeno[2,l-fi]-1-benzopyrane system (44).126... 

Azulene can be thermally transformed to naphthalene. An analogous isomerization is known for cyclopenta[c]thiapyrane (31a).85 If 31a was kept... 

If the position ortho to the sulfur atom is blocked by a substituent, then only attack on the peri-position takes place. For instance, 2-chloro-l-naphthothioacetic aldehyde acetal gives rise to 9-chloronaphtho[fcc]-thiapyran 304 [51P1A(A)78]. By analogy, the heterocyclization of a-naph-thothioacetic acid chloride 305 (R = H) leads to a mixture of peri- and... 

JOC2372). The interaction of 1,8-dehydronaphthalene 240, generated from N-aminonaphtho[[Pg.53]

Naphtho[o/]pyran derivatives with various oxidation states of the a,a -carbon atoms in the heteroring have been described. 2,9-Dihydronaphtho[crf]pyran derivatives 349 are formed on treating peri-bromomethylperoxide 347 with silver nitrate (84TL3769 86JOC2612) or on photolysis of naphtho[o/]thiapyran 5-oxide 348 (73TL3605). 

One of the pathways to synthesis of a,a -dehydronaphtho[c f)-thiapyrans 383a-d includes step-by-step heterocyclization of peri-bis-bromomethyl, peri-bis-hydroxymethyl, or peri-bis-hydroxybenzyl-... 

The stable tetra-phenyl-substituted at,a -dehydroacenaphthylene [4,5-crf)thiapyran 390 is formed in high yield on heating I,4,5,8-tetrabenzoylnaphthalene 387 or l,2-diphenyl-5,6-dibenzoyl-acenaph-... 

Diketone 388 and monoketone 389, which are depicted in the scheme as intermediates, have been obtained independently and have also been converted into compounds 390 by all the previously listed methods. Two more examples of naphtho[crf]thiapyrans are thionaphthalic anhydride 391, which is formed on interaction between naphthaloyl dichloride 367 and hydrogen sulfide (30RC657), and 2-oxo-9-thiononaphtho[cd]thiapyran 399, obtained on base-catalyzed recyclization of dithione 392 (84JA6084). 

Compounds 405, which are nitrogen analogs of a,a -dehydro-naphtho[a/]thiapyrans 383, are unknown. However, their valence isomers 404, obtained on interaction of acenaphthylene with N,N-dichlorosulfa-mides, have been described (80MI3). 

The thermal chemistry of pyran-2-thione in the vapour phase has been shown to give thiapyran-2-one, which was trapped into an argon matrix at 10 K (Scheme 110). The reaction pathways have been investigated by computational methods.161... 

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