Sulphur nucleophiles

There are two distinctly different copper catalyzed procedures that allow for the introduction of sulphur nucleophiles onto the thiophene core. 2-... 

When the pentamer (66) reacts with alkoxide anions at low temperatures (-30 to -40°C), then the products of kinetic control (102) are isolated, whereas at higher temperatures, thermodynamic control prevails and the products (103) are obtained [131,132] (Scheme 68). Similar observations have been made with sulphur nucleophiles [132], and complex products are obtained with amines, including the formation of heterocycles [132]. Reaction of (66) with ethyl acetoacetate gave a pyran derivative (104) in a reaction that may be rationalised as shown in Scheme 69 [133]. In an analogous way.furan derivatives are formed from perfluoro-2-butene and -cyclohexene in base-induced reaction with 1,3-dicarbonyl derivatives [133]. 

On the other hand, some evidence for the longer life-time of the intermediate formed with amines may be inferred from the formation of small amounts of (116a) from piperidine and /J-chloroacrylonitrile, in addition to the main substitution product. (116a) is also the sole substitution product with aniline (R1=Ph, R2 = H) but no such products were reported for reactions with oxygen or sulphur nucleophiles. For formation of (116a) the initially-formed carbanion should be long-lived enough as to attack another j8-chloroacrylonitrile molecule (Scotti and Frazza, 1964). 

Vivona, N., Buscemi, S., Asta, S. and Caronna, T. (1997) Photoinduced molecular rearrangements. The photochemistry of 1,2,4-oxadiazoles in the presence of sulphur nucleophiles. Synthesis of 1,2,4-thiadiazoles. Tetrahedron, 53 (37), 12629-12636. 

Another sulphur nucleophile, 2-mercaptobenzimidazole, gave similarly 2-phen-acylthio-benzimidazole [29]. Acetophenones on treatment with methanolic HTI underwent rearrangement affording methyl arylacetates, Ar H2C02Me the same compounds were obtained with iodosylbenzene in acidic methanol (Section 5.2.3). 

Whereas oxygen nucleophiles gave poor yields of alkenylated products with alkenyl iodonium salts, the reactions with sulphur nucleophiles proceeded more efficiently, leading to unsaturated sulphides and sulphones. Thus, 4-t-butylcyclohexenyl phenyliodonium salts afforded with sodium thiophenoxide 4-t-butylcyclohexenyl phenyl sulphide (81%) [3] and with sodium phenylsulphinate the corresponding sulphone (29%) in the presence of 18-crown-6, the yield of the latter rose to 80% [45]. jS-Phenylsulphonylalkenyl iodonium salts with sodium phenylsulphinate at 0°C, without any catalyst, afforded Z-l,2-bis(phenylsulphonyl)alkenes, in high yield with retention of the stereochemistry [45] ... 

An alternative approach to 9-substituted acridinium salts and thence the corresponding acridines involves the conversion of 9-acridones into the 9-trifluoromethanesulphonyloxy acridinium salts (17), which react readily with halides, pseudohalides such as azide and isothiocyanate, and sulphur nucleophiles (B. Singer and G. Maas, Z. Naturforsch., 1984, 39b, 1399). The free base restilts on reaction with diisopropyletlylamine. 9,9 -Bisacridine ethers are also available by this methodology. 

Reactions with Sulphur Nucleophiles. The addition of Et2AlSPh to the vinyl-oxiran (159) in benzene at 25 °C for 1 hour gives the (Z)-vinyl alcohol (160) (91%) with about 2% of the ( )-isomer. A novel route to the phenoxathiins... 

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