Ylides, with thioketones

The 1,3-dipolar cycloaddition reaction of azomethine ylides with thioketones has been used to prepare 1,3-thiazoIidines. The metallated azomethine ylides 67 were generated in situ by treating a-amino acid ester imines 66 with lithium bromide and DBU. The ylides were then treated with highly reactive thioketones such as thiobenzophenone or fluorene-9-thione, to afford 1,3-thiazolidine derivatives 68 (main isomer) and 69 (minor isomer) in good yield and in diastereoisomeric ratios of between 2 1 and 4 1 <01H(55)691>. 

Based on a series of kinetic studies, Huisgen et al. (91-93) established that thiocarbonyl compounds, especially aromatic thioketones, function as very active dipolarophiles (superdipolarophiles) toward thiocarbonyl ylides. In fact, the trapping reaction of thiocarbonyl ylides with thiocarbonyl compounds represents an excellent method for the preparation of 1,3-dithiolanes. 

For preparative purposes, the reaction of thiocarbonyl ylides with carbonyl compounds can be considered as an alternative method for the synthesis of 1,3-oxathiolanes. Aromatic aldehydes, chloral, glyoxalates, mesoxalates, pyruvates as well as their 3,3,3-trifluoro analogues are good intercepting reagents for thioketone (5)-methylides (36,111,130,163). All of these [3 + 2] cycloadditions occur in a regioselective manner to produce products of type 123 and 124. 

Other new oxathiolane syntheses include reaction of an epoxide with a stable thioketone <01HCA3319>. Rhodium catalysed reaction of dimethyl diazomalonate with a thioketone has been used to prepare oxathiole 92 <02PJC551> and the iodonium ylide 8 reacts with thioketones or carbon disulfide to form oxathioles <02TL5997>. 

Semi-stabilized arsonium ylides react with thioketones with cyclic thioketones tri-phenylarsonium benzylides gave only exocyclic alkenes and no thiirans . Benzo-thiopyrones (and, better, benzopyrones) also react to give exocyclic alkenes, in these cases arylidenebenzopy rans ... 

NHCbz (36) Alkenylation. Rtf -catalyzed reaction of dimethyl diazomalonate with thioketones and dithiolactones leads to the formation of sulfur ylides, which rearrange into thiiranes followed by spontaneous desulfurization to alkenes (eqs 39 and 40). ... 

Some thioketones are reported to give 1,3,2-dithiastannolanes in moderate to high yields in reactions with a stannylene Dis2Sn [Dis = CH(SiMc3)2] <930M4>. The key difference with the process discussed above is inversed polarization of intermediate ylide (380) which can exist in an equilibrium with a thiastannirane (381). 

Finally, ylides 52 and 69 were found to react regioselectively with aliphatic thioketones to give the sterically less crowded products of type 117 (36,162,163). 

The following types of dipolarophiles have been used successfully to synthesize five-membered heterocycles containing three heteroatoms by [3 + 2]-cycloaddition of thiocarbonyl ylides azo compounds, nitroso compounds, sulfur dioxide, and Al-sulfiny-lamines. As was reported by Huisgen and co-workers (91), azodicarboxylates were noted to be superior dipolarophiles in reactions with thiocarbonyl ylides. Differently substituted l,3,4-thiadiazolidine-3,4-dicarboxylates of type 132 have been prepared using aromatic and aliphatic thioketone (5)-methylides (172). Bicyclic products (133) were also obtained using A-phenyl l,2,4-triazoline-3,5-dione (173,174). 

Saito et al. <1995S87> described a new method for the synthesis of heterocycle-fused[c]thiophenes via reaction of aryl heteroaryl thioketones with the carbene precursors. Heteroaromatic thioketones A react with carbenoids generated from bis(arylsulfonyl)diazomethanes or phenyliodonium bis(phenylsulfonyl)methylides to give heterocycle-fused[f]thiophenes B. The reaction involves the ring closure of the intermediary thiocarbonyl ylides, followed by restorative aromatization via the elimination of a sulfenic acid (Equation 11). 

Diazoalkanes, treated with sulfur, give episulfides.772 It is likely that R2C=S is an intermediate, which is attacked by another molecule of diazoalkane, in a process similar to that shown in 6-61. Thioketones do react with diazoalkanes to give episulfides.773 Thioketones have also been converted to episulfides with sulfur ylides.758... 

We have already mentioned the synthetic versatility of silyl thioketones249 which is confirmed because they react with 1,3-dipoles (nitrile oxides, nitrile imines and nitrile ylides) to give regiospecifically silyl thiaheterocycles462. Equation 135 illustrates the reaction between phenyl trimethylsilyl thioketone and diphenyl nitrihmine. 

Reaction of heteroaromatic thioketones 638 with the carbenoids, generated from phenyliodonium bis(phenylsul-fonyl)methane or bis(arylsulfonyl)diazomethanes in the presence of a copper acetylacetonate catalyst, affords heterocycle-fused [c]thiophenes 639. The reaction involves ring closure of the intermediary thiocarbonyl ylides and elimination of a sulfenic acid (Equation 33) <1995S87>. 

The reaction of 1,2,3-triphenylcyclopropenylium bromide (3) with a sulfur ylide, dimethylsul-fonium methylide, afforded the dicyclopropenyl thioketone 9, together with a ring-enlarged product, 2,3,4-triphenylthiophene (10). ... 

The reaction of dimethylsulphonium-methylide with triphenylcyclo-propylium bromide produced a 1 1.7 ratio of the thiophen (79) and the thioketone (80). Formation of a new ylide (81) as an intermediate was proposed, with ring expansion to an SS-dimethylthiophen and loss of ethane... 

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