Alkylation of sulfides

Another way to prepare fluorinated sulfides is the photochemical alkylation of sulfides or disulfides by perfluoroalkyl iodides [69, 70, 71] (equations 62-64). Reaction of trifluoromethyl bromide with alkyl or aryl disulfides in the presence of a sulfur dioxide radical anion precursor, such as sodium hydroxymethanesulfi-nate, affords trifluoromethyl sulfides [72] (equation 65). 

Sulfonium salts are available by alkylation of sulfides. They have been known for a long time, and their syntheses and general reactivity have been reviewed [194-199]. 

Scheme 10.18 Catalytic asymmetric aziridination via alkylation of sulfide 24 and deprotonation.

Destlylation. Anhydrous cesium fluoride desilylates trimethylsilylmethyl-sulfonium, trimethylsilylmethylammonium, and trimethylsilylmethylphosphonium salts at room temperature to produce ylides, which undergo various useful transformations. Use of potassium fluoride-18-crown-6 or a tetraalkylammonium fluoride gives products in low yield in these reactions. The trimethylsilylmethyl-onium salts are prepared by alkylation of sulfides, amines, imines, and phosphines with (trifluoromethanesulfonylmethyl)trimethylsilane (1). 

A class of compounds which have drawn some interest are the sulfonium salt complexes 416, prepared by alkylation of sulfide derivatives (415) (Table IV). These coordinated ylides have found use as stable, stereospecific cyclopropanating reagents yielding compounds of the class 417. 

These reactions, coupl with the alkylations of sulfides and selenides, allow the homologation of primary alkyl halides - - - and the transformation of allyl halides to homoallyl halides. A related process, employing 2-methylthio- and 2-allylthio-thiazoline, allows the iodomeAylation (ICH2—) and the iodopropenylation (ICH2CH=CH—) of alkyl halides (Scheme 54).i3iii,i32.i7i... 

Rearrangements of ylidic intermediates proceed with allylic transposition. This useful property is the key feature of one of the best preparations of 1, S-dienes (Scheme 9). Trost has used this approach to synthesize yomogi alcohol (165) in a particularly simple way by 5-alkylation of sulfide (31) and solvolysis of the resulting sulfonium ion (Scheme 37). ... 

Alkylation of sulfides. In a study of the possible role of sulfonium ylides in the coupling of allyl units to give squalene and related terpenes, Baldwin el al. examined the alkylation of the sulfide (1). The only product was the symmetrical salt (2). 

The following are substituent modifications without alteration of the heterocyclic system A (Ar = 1,4,2-benzodithiazinyl) alkylations of sulfides to thiols (ArSH-> ArSR) 45 59 carboxylic acid chlorides to carboxamides (ArCOCl - ArCONH2) 65 carboxamides to nitriles (ArCONH2 - ArCN).61... 

Sulfonium and ammonium salts are prepared readily by alkylation of sulfides or amines. For example, allylation of the amine 318 gave the intermediate ammonium salt 319 (3.205). Deprotonation to the ylide with sodium hydride was followed by [2,3]-sigmatropic rearrangement at room temperature to give the peni-cilhn derivative 320. In a synthesis of y-cyclocitral, the sulfonium salt 321 was prepared by alkylation of 1,3-dithiane and was converted to the ylide 322 and hence the rearranged product 323 (3.206). 

---