Sulphides diaryl, synthesis

Chiral alcohols have also been used in an asymmetric synthesis of sulphoxides based on halogenation of sulphides. Johnson and coworkers have found319 that the reaction of benzyl p-tolyl sulphide with JV-chlorobenzotriazole (NCBT) followed by addition of (—) menthol and silver tetrafluoroborate afforded diastereoisomeric menthoxysulphonium salts 267 which, upon recrystallization and hydrolysis, gave benzyl p-tolyl sulphoxide with 87% optical purity (equation 145). More recently, Oae and coworkers reported320 that optically active diaryl sulphoxides (e.e. up to 20%) were formed either by hydrolysis or thermolysis of the corresponding diaryl menthoxysulphonium salts prepared in situ from diaryl sulphides using ( —) menthol and t-butyl hypochlorite. 

The profitable conversion of thiouronium salts into dialkyl thioethers (see Section 4.1) is less successful for synthesis of diaryl thioethers. For example, l-chloro-4-nitrobenzene reacts with bis-thiouronium salts of the type (H2N)2CS(CH2) SC(NH2)2+ under soliddiquid and liquidrliquid conditions to produce the desired bis-thioethers, ArS(CH2) SAr, (20-35%), together with the diaryl sulphide, Ar2S (5-15%). Higher yields of the diaryl sulphide are observed under liquiddiquid conditions whereas, under solidiliquid conditions, the diaryl disulphide, (ArS)2, (20%) is also formed [56], Diaryl disulphides are the sole products (>65%) from the stoichiometric reaction of aryl diazonium salts with benzyltriethylammonium tetrathiomolybdate [57],... 

Details are now available of the synthesis reported last year (4,165) of unsymmetrical sulphides from an alcohol and a thiol in the presence of bis(2,2,2-trifluoroethoxy)triphenylphosphorane (83) (Scheme 45), and the same authors have published a closely analogous sequence involving the sulphuranes (84) (also Scheme 45)/ both procedures are most satisfactory for diaryl or arylalkyl sulphides. 

Geranyl phenyl sulphides or sulphones, Me2C=CHCH2CMe=CHCHXY (33 X = H Y = SPh or SOjPh), cyclized to cyclocitral derivatives under acid conditions, whereas the corresponding dithioacetal (33 X = Y = SPh) gives the thiochroman (34). The novel heterocycles (35) have been prepared by standard methods from the corresponding tellurochromanones. The critical step in the synthesis of the latter consists of reduction of the appropriate diaryl ditelluride with borohydride and subsequent reaction with 3-chloropropionic acid under carefully controlled conditions. 

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