Sulfoxides, allyl thermolysis

In the reaction of 88 with /(-phenethyl bromide, l-phenethyl-3-phenylpropyl methyl sulfoxide and bis-3-phenylpropyl sulfoxide, besides 3-phenylpropyl methyl sulfoxide are obtained118. Sulfoxides, bearing a /1-hydrogen to the sulfmyl function, give olefins upon thermolysis. Utilizing this reaction, Trost and Bridges120 alkylated benzyl phenyl sulfoxide, 3,4-methylenedioxybenzyl phenyl sulfoxide, phenylthiomethyl phenyl sulfoxide, phenylsulfinylmethyl phenyl sulfoxide and cyanomethyl phenyl sulfoxide with alkyl, allyl and benzyl halides and subjected these sulfoxides to thermolysis, obtaining olefins in one-pot processes. 

In the presence of a suitably disposed /i-hydrogen—as in alkyl-substituted thiirane oxides such as 16c—an alternative, more facile pathway for thermal fragmentation is available . In such cases the thiirene oxides are thermally rearranged to the allylic sulfenic acid, 37, similarly to the thermolysis of larger cyclic and acyclic sulfoxides (see equation 9). In sharp contrast to this type of thiirane oxide, mono- and cis-disubstituted ones have no available hydrogen for abstraction and afford on thermolysis only olefins and sulfur monoxide . However, rapid thermolysis of thiirane oxides of type 16c at high temperatures (200-340 °C), rather than at room temperature or lower, afforded mixtures of cis- and trans-olefins with the concomitant extrusion of sulfur monoxide . The rationale proposed for all these observations is that thiirane oxides may thermally... 

The thermolysis of acyclic- and/or six- and larger ring sulfoxides to yield olefins and sulfenic acids is well documented . The formation of allylic sulfenic acids and thiosulfinates in the thermolysis of thiirane oxides containing hydrogen on the a-carbon of the ring substituent (which is syn to the S—O bond) has been discussed previously in terms of /i-elimination of hydrogen, which is facilitated by relief of strain in the three-membered ring (Section llI.C.l). 

A novel synthesis of a-unsaturated sulfines has been introduced by Bra-verman et al. [99]. Et3N or DABCO treatment of allylic and benzylic tri-chloromethyl sulfoxides triggered the elimination of chloroform and formation of the sulfines. It must be stressed that these sulfines are thermally relatively stable, and this stands in high contrast to the corresponding thio-carbonyl compounds unsaturated thioaldehydes cannot be monitored under the same experimental conditions and have to be used at very low temperature or trapped in situ. The first synthesis of thioacrolein S-oxide was achieved by flash vacuum thermolysis of an anthracene allyl sulfoxide [100], and both isomers in a (Z E) ratio of 78 22 were characterised by NMR spectroscopy at -60 °C. 

Asymmetric sulfinylation. The reaction of ketone enolates with this reagent (1) gives chiral sulfoxides. With the chelation assistance of the sulfinyl group the reduction of the ketones is stereoselective, and a subsequent thermolysis leads to allylic alcohols with an (/ ) configuration. 

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