Propargylic sulfonium ylides

Further study by Katsuki, McMillen, Hashimoto, and Wang improved the enantioselectivity up to a moderately high level.Wang and co-workers further extended the asymmetric catalysis to the [2,3]-sigmatropic rearrangement of propargyl sulfonium ylide to give allenic products with up to 81% ee (Equation (18))." ... 

Sigmatropic Rearrangements of Propargylic Sulfonium Ylides and Related Systems... 

Scheme 6 Iron-catalyzed carbene generation/[2,3]sigmatropic rearrangement of propargyl sulfonium ylides...

Scheme 7 [2,3]Sigmatropic rearrangement of propargyl sulfonium ylides as a ring forming reaction...

A more direct access to the unstable and non isolated sulfonium ylides 58a- c is the reaction of diisopropyl diazomethylphosphonate 57 with allylic sulfides, catalyzed by Cu(II), Rh(II) [39], or ruthenium porphyrins.[40] For example, the a-phosphorylated y,d-unsaturated sulfides 59-61 are obtained through the [2,3] -sigmatropic rearrangement of 58a-c. This method allows the use of a greater variety of starting allylic sulfide substrates, such as 2-vinyl tetrahydrothiophene, or propargylic sulfides (Scheme 15). 

The [2,3]sigmatropic rearrangement of sulfonium ylide (24) derived from rhodium-catalyzed decomposition of ethyl 3,3,3-trifluoro-2-diazopropanoate (23) in the presence of propargyl sulfide (22a) affords the corresponding functionalized CF3-containing carboxylic ester sulfide (25a). The latter was... 

Allenic sulfides (37) have been obtained with moderate to good enantio-selectivities (up to 81%) in sigmatropic rearrangements of sulfonium ylides generated from propargyl aryl sulfide (35) and aryldiazoacetates (36) as carbenoid source catalyzed by chiral Rh(ll) (38a,b) and Cu(l) (38c) catalysts [34] (Scheme 8). 

This reaction illustrates the stabilising effect exerted by the sulfonium centre on the adjacent double bonds. Isomeric allenes (32) may be similarly obtained from propargylic sulfonium salts (33) (Scheme 18). The allene (32), by treatment with diethyl sodiomalonate (34), followed by addition and rearrangement of the derived sulfonium ylide (35), affords the methyl sulfide (36) (Scheme 18). 

The Cu(I)-catalyzed cyclization for the formation of ethyl ( )-tetrahydro-4-methylene-2-phenyl-3-(phenylsulfonyl)furan-3-carboxylate 82 has been accomplished starting from propargyl alcohol and ethyl 2-phenylsulfonyl cinnamate. Upon treatment with Pd(0) and phenylvinyl zinc chloride as shown in the following scheme, the methylenetetrahydrofuran 82 can be converted to a 2,3,4-trisubstituted 2,5-dihydrofuran. In this manner, a number of substituents (aryl, vinyl and alkyl) can be introduced to C4 <00EJO1711>. Moderate yields of 2-(a-substituted N-tosyIaminomethyl)-2,5-dihydrofurans can be realized when N-tosylimines are treated with a 4-hydroxy-cis-butenyl arsonium salt or a sulfonium salt in the presence of KOH in acetonitrile. The mechanism is believed to involve a new ylide cyclization process <00T2967>. 

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