Thiopyrylium reaction with

Addition reactions of thiopyrylium salts with nucleophiles (83AHC145, Section IV,B) have widely been used for the preparation of various thiopyrans in the last decade (92MI3). On the other hand, the application of catalytic processes still seems to be rare. 

Any preparative utilization of the addition reactions of thiopyrylium salts with amines appears to be significantly dependent on the nucleophili-... 

MO calculations were performed rarely for thiopyrans except for an MNDO study of 2 [84ZN(A)267], Charge distribution and orbital interaction concepts were explored in an interpretation of model reactions of thiopyrylium ions with azides giving 68 and the corresponding 3,5-unsub-stituted thiopyrans (84T3549) as well as for the equilibria between 1 and 2 or 167 and 168, respectively (92JOC4431). 

Triphenylpyrylium tetrafluoroborate is a versatile and useful stable starting material. Its reaction with nitromethane under basic conditions has made 2,4,6-triphenylnitrobenzene easily available. In addition, pyrylium salts are readily converted to a variety of pyridine derivatives i i . 20 including alkyl- and arylpyridinium salts, to thiopyrylium salts," and to substituted azulenes. ... 

The reaction of thiopyrylium salts with tetramethylammonium fluoride or AgF yields 2-fluoro-2//-thiopyran together with very minor amounts of 4-fluoro-4//-thiopyran (Equation 111). In like manner, the 2,4,6-tri-/-butyl derivative gives mainly the 2-fluoro compound and bcnzo /( thiopyrylium salts mainly afford 2-fluoro-2//-l-ben-zothiopyran (Equation 112). Both thioxanthylium tetrafluoroborate and the 9-phenyl derivative give the 9-fluoro-thioxanthene. In no reaction was there any evidence of attack of F at sulfur <2003JFC(120)49>. 

A range of 2.4.4.6-tetraary 1-4//-thiopyrans has been obtained by the reaction of 3,5-disubstituted 2,4,6-triphenyl-thiopyrylium salts with aryl Grignard and organolithium reagents (Equation 122) <1996JPH(101)33, 1997PS(120)403>. 

An improved route to both bis- and tris- thiopyrylium salts 552 involves the initial Michael addition of pinacolone to a bis-enone and tris-enone, respectively, promoted by NaNH2 in toluene. The resulting pentandione derivatives are then cyclized by reaction with P4S10 in the presence of LiCKTj (Scheme 233) <2005JOC6422>. 

Provided electron-withdrawing groups are absent from the aryl substituents, pyrylium salts are converted into thiopyrylium salts 553 by reaction with Na2S and HBF4 (Equation 202) <1996J(P2)307, 2002JP0689, 2006EJO2644>. 

Thiopyran, derived from ethyl vinyl sulfide, is converted into thiopyrylium fluoroborate by reaction with triphenylcarbenium fluoroborate in 54% overall yield (Scheme 235) <2001EJ02477>. 3-Benzoylisothiochromene is oxidized to the 2-benzothiopyrylium salt in a similar manner <1994J(P1)3129>. 

Mercapto-2,4-pentadienones undergo cyclization to thiopyrylium perchlorates 91 by reaction with POCI3 followed by treatment with a NaC104 solution (Scheme 2). In structure 91 both R and R are phenyl or substituted-phenyl groups, whereas R can be H, Me, or Ph (86EGP240745 89S515). 

The reaction of thiopyrylium salts with amines can afford different products, depending on the substitution pattern of the heteroaromatic cation, the nature of the amine, and reaction conditions. In most cases... 

The formation of 1,2-diazepine by reaction of thiopyrylium salts with hydrazine hydrate in an organic solvent has also been patented (85EGP218360). 

The reactions of thiopyrylium ions with sulfur ylides have been also investigated. Thus 2,4,6-triphenylthiopyrylium cation (9) reacts with Me2S (0)CH2 or with MeS (R)CH"COPh (R = Me, Ph) to yield compound 358 with X = H or COPh, respectively [72C1(L)498 80NKK604]. The reaction with the latter reagents also occurs with 2,3,4,6-tetraphenyl-thiopyrylium cation (313) (80NKK604). 

The unsubstituted thiopyrylium ion (2) undergoes the Diels-Alder reaction with cyclopentadiene as shown in Scheme 26 (74MI1). 

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