Allylic sulfinamides, rearrangements

In 1996, Pyne and Dong79 reported that the thermolysis of (S,S)-121 (ee 94%) in refluxing THF for 6 h gave a mixture of the rearranged allylic sulfinamides 163a... 

In 1995 Pyne and Dong95 found that the ally lie sulfoximine 165 underwent a facile and completely regioselective and efficient rearrangement to the allylic sulfinamide 166 in the presence of tetrakis(triphenylphosphine)palladium(0) ((PPh3)4Pd) catalyst (5 mol%) at room temperature. Mild base hydrolysis of the reaction mixture (10% aqueous sodium hydroxide/methanol, 1 10, room temperature, 2 h) gave pure sulfonamide 167 after purification by column chromatography (silica gel) in 90% overall yield. 

The [2,3] sigmatropic rearrangement of sulfenate esters 3, prepared in situ on treatment of 4-morpholinesulfenyl chloride with allylic alcohols, allows easy synthesis of diastereomeric allylic sulfinamides 4 (configurations were not established)104. 

When the allylic sulfinamides are hydrolyzed under special conditions (classical methods like alkali-or acid-catalyzed hydrolysis did not work properly) the obtained allylic sulfinic acids are unstable and will fragment smoothly again with allylic rearrangement into terminal alkenes. 

By modification of the elegant method of preparation of optically active sulfinates previously reported by Mikolajczyk and coworkers , an efficient stereospecific method for the conversion of readily available optically active sulfinamides to optically active sulfinates of inverted configuration at the sulfinyl function, has been recently reported by Hiroi and coworkers . The same authors subsequently reported the thermal rearrangement of several optically active cis- and trans-y-substituted allylic p-toluenesulfinates to optically active chiral sulfones with high stereoselectivity. For example, trans and cis (S)-( — )-crotyl p-toluenesulfinates rearranged to optically active (S)-(-l-)- and (R)-( — )-a-methylallyl p-tolyl sulfone, respectively (equation 19). 

As discussed above the kinetic stability of allylic sulfoximines prevents them from going downhill to the thermodynamically favored sulfinamides, which in turn is a precondition for their successful application as solutions for asymmetric d -synthons [ 13-15,20-32]. On the other hand, if it would be possible to make them rearrange to allylic amines with 1,3-chirality transfer, this would be an interesting entry to this class of compounds (Scheme 6). ... 

An asymmetric variant of this kind of allylic amination, based on their phenylcyclohexanol-derived chiral N-sulfinyl carbamates, was developed by Whitesell et al. (see also Sect. 3.2) (Scheme 34) [85]. After the asymmetric ene reaction with Z-configured olefins (not shown) had occurred, nearly di-astereomerically pure sulfinamides 127 were obtained which were found to be prone to epimerization. Their rapid conversion via O silylation and [2,3]-a rearrangement dehvered the carbamoylated allyhc amines 128 with around 7 1 diastereoselectivity as crystalline compounds that can be recrystallized to enhance their isomeric purity to 95 5. Obviously the imiform absolute configuration at Cl in the ene products 127 was difficult to transfer completely due to the already mentioned ease of epimerization. Unhke the sulfonamides of Delerit (Scheme 33) [84], the carbonyl moiety can easily be cleaved by base treatment. 

Pd(0)-catalyzed rearrangement of allylic sulfoximines to sulfinamides has been developed recently and appears to be an efficient route to chiral allylic amines (Scheme 22). This reaction is also known to occur thermaUyt but only for y-phenyl-substituted... 

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