Thioketones, 4-alkyl

Another indole/oxindole synthesis achieves the critical ortho-substitution by Sommelet-Hauser rearrangement of an anilinosiilfonium ion intermediate. Use of P-thioketones (G = R, an alkyl group) generates 2-substituted indoles, whereas P-thioesters (G = OR) lead to oxindoles. In each case, a 3-thio substituent must be removed by desulfuri2ation. 

Selenoketones are less stable than thioketones and cannot be obtained as monomers unless sterically hindered by alkyl groups or stabilized by electronic delocalization of electron rich substituents. Some stable selenoketones are reported in Table 1. 

The preparation of thiiranes is most conveniently performed in solution. However, there are also protocols reported for reaction in the gas and solid phase. By using diazo and thiocarbonyl compounds in ether as solvent, both alkyl and aryl substituted thiiranes are accessible. As indicated earlier, aryl substituents destabilize the initially formed 2,5-dihydro-1,3,4-thiadiazole ring and, in general, thiiranes are readily obtained at low temperature (13,15,35). On the other hand, alkyl substituents, especially bulky ones, enhance the stability of the initial cycloadduct, and the formation of thiiranes requires elevated temperatures (36 1,88). Some examples of sterically crowded thiiranes prepared from thioketones and a macro-cyclic diazo compound have been published by Atzmiiller and Vbgtle (106). Diphenyldiazomethane reacts with (arylsulfonyl)isothiocyanates and this is followed by spontaneous N2 elimination to give thiirane-2-imines (60) (107,108). Under similar conditions, acyl-substituted isothiocyanates afforded 2 1-adducts 61 (109) (Scheme 5.23). It seems likely that the formation of 61 involves a thiirane intermediate analogous to 60, which subsequently reacts with a second equivalent... 

Related investigations of the reaction of diazo compounds with alkyl-substituted thioketones [R2C=S, R = Et, Pr, i-Pi, f-Bu (203) 2,2,4,4-tetramethylcyclobutan-l-one-3-thione (204), and adamantanethione (205,206)] showed that the 3,3-dialkyl-... 

The synthesis of 4-alkyl thioketones is possible by exploiting the stabilizing effect of a sulfur atom upon an adjacent carbanionic center. Ambident allylic anions react so that conjugate addition proceeds exclusively with the a-carbon of the nucleophile,129 243 244 as illustrated in equation (S3) 245 arylsulfinyl and arylsulfonyl groups normally246 behave similarly.247-249 Sulfur-stabilized vinylic carbanions can be prepared and function as Michael donors in difunctionalization sequences.250... 

From 5-[(l,2-dithiol-3-ylidene)alkyl]-l,2-dithiole-3 thiones (74) other extended structures can be obtained,89 90 e.g., (a) a-( 1,2-dithiol-3-ylidene)-a -(l,3-dithiol-2-ylidene)thioketones (77), by reaction... 

N,N-Methyltosylhydrazones. Ketones react only slowly with N,N-methyl-tosylhydrazine (1) but hydrazones of this type can be prepared by N-alkylation of tosylhydrazones with phase-transfer catalysis. The more reactive thioketones also react sluggishly with 1, but in this case, the reaction can be catalyzed by soft Lewis acids. Thus the reaction of 2 with 1 proceeds in high yield at room temperature in the presence of 1 equiv. of silver nitrate. Mercuric acetate also promotes this reaction, but the yield of 3 is only 50% because of formation also of 4 in 44% yield. 

Reactions of alkyl halides with diethyl phosphite in the presence of ammonium acetate/sulfur and acidic aluminia using microwave irradiation provide a simple and general route to thiophosphates. Two diastereoisomers of 1,3,2-dithiadiphosphetane 2-sulfide (19) have been isolated for the first time via the reaction of thioketones (20) with Lawesson s reagent (Figure 5). ... 

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