Thiapyran Derivatives

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.)... 

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). 

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). 

The 4 -thiapyran-4-thione route to thiathiophthens has been modified so as to yield 6a-selenahthiopthens (35). The intermediate selenoketones (38) are unstable, but react satisfactorily with sodium sulphide in aqueous dimethyl sulphoxide to give dianions which are oxidized, as in the original synthesis, with ferricyanide. N.m.r. data on 6a-selenathiophthen, and on its 3,4-dimethyl and 2,5-diphenyl derivatives, indicate real or time-averaged... 

Two (3,6-dihydro-2-methylsulfanyl-2/f-thiapyran-2-yl)phosphonate derivatives (212a,b) have been chemoselectively oxidized at the thiopyranyl sulfur. The obtained allylic six-membered cyclic sulfoxides (213a) and (213b) reacted under Pummerer reaction conditions with trifluoroacetic anhydride (TFAA) leading to new thiopyran derivatives (214) and (215), respectively. Unexpectedly an additional product (216) has been obtained from the substrate (213b) (Scheme 75). ... 

Electrochemical reduction of the trithiapentalenes (804 R = H, Me, or Ph) yields the corresponding radical anions, which are converted into the thiapyran-thiones (807)/" ° 1-Phenyl-6,6a-dithia-l,2-diazapentalene (808) is nitrated mainly in position 3, but the 3,4-dimethyl derivative undergoes nitro-dediazoniation to the dithiole (809). Treatment of compound (808) with nitrous acid yields the phenylazo-oxadithiazapentalene (810) a similar reaction is the transformation of dioxathiapentalene (805) into the oxathiadiazapentalene (811) by the action of nitrobenzene-p-diazonium fluoroborate. ... 

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