4- -quinolyl sulfides

Note that fluorination of these heteroeyelie eompounds by A -fluoropyridinium and A -fluoro-3,5-diehloropyridinium triflates is unsueeessful (01TL4861). Electrochemi-eal anodie fluorination was carried out for 4-(7-trifluoromethyl)-quinolyl sulfides 31 in Et4NF nHF ( = 3,4) and EtsN 3HF in DME. The eorresponding a monofluoro derivatives 32 of these sulfides are formed in good yields (Table 17) (98JFC(91)153). When X = COMe, compound 33 is also formed (yield 7%) (Scheme 46). 

For 2-quinolyl sulfides 34, the reaction gives three products 35-37 (Table 18) (Scheme 47). 

Table 17. Anodic fluorination of 4(7-trifluoromethyl)quinolyl sulfides (DME) (98JFC(91)153)...

The Sg2 reaction on the 5p -like hybridized carbanion tends to proceed with inversion of the stereochemistry [45]. It is reasonable that a-thio carbanions, having higher s character than a-oxy carbanions, more frequently invert the stereochemistry on the anionic carbon in the reaction with electrophiles. As in the case of a-lithiated benzyl 2-pyridyl sulfide, the reaction of a-lithiated benzyl 2-quinolyl sulfide also proceeds through a dynamic thermodynamic resolution pathway. The quinolyl group is an excellent protecting group of thiols [46] and can be removed to yield the corresponding chiral thiols without racemization (Tables) [47]. 

Tables. Enantioselective reaction of a-lithiated benzyl 2-quinolyl sulfide and subsequent...

Methylation by MeOTf can also be carried out asymmetrically. Treatment of a-lithio benzyl 2-quinolyl sulfide with MeOTf in the presence of a bis(oxazoline) as an external chiral ligand yielded chiral 1-phenylethanethio quinolyl sulfide (eq 17). Lithiation adjacent to nitrogen of chiral 3,4-substituted piperidines and pyrrolidines followed by diastereoselective substitution with MeOTf offered general routes to 2,4,5- and 2,4,5,6-substituted piperidines as well as 2,3,4- and 2,3,4,5-substituted pyrrolidines. ... 

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