Sulfones, allyl dienyl

The Ramberg-Backlund reaction has been utilized for the preparation of polyenes. 1,3-Butadienyl allyl sulfones 398 and 399 were transformed into the tri- and tetra-enes 400 and 401 by alkylcuprate addition and the Ramberg-Backlund-type S02 extrusion449. Julia and coworkers450 carried out the Michael addition of various nucleophiles such as ethanol, t-butyl acetoacetate and phenyl thioacetone to allyl dienyl sulfones 402 and then converted them to diallyl sulfones 403. The sulfones were transformed into isoprenoid, 404 by the Ramberg-Backlund reaction. 

In similar work, Julia prepared allyl dienyl sulfones from (Z)-2-methyl-1,3-butadienylsulfinate. Addition of various nucleophiles to the diene and Ramberg-BMcklund reaction then yielded isoprenoid compounds (Scheme 73). 

As far as polyenes are concerned, the Ramberg-Backlund reaction is an extremely powerful tool in putting the double bonds together. Herein just two examples are listed. Cao applied the Chan modification on a group of allylic dienylic sulfones and achieved the stereoselective synthesis of substituted all-tram-1,3,5,7-octatetraenes as exemplified by transformations 9899. 55 Polyene 101 was produced from sulfone 100 using the Chan modification as well.56... 

Entry 7 involves formation and ionization of a secondary allylic sulfonate and migration of a dienyl group. 

Interestingly, this allylation process seems to be very general. For instance, introduction of a dienyl moiety using penta-2,4-dienyl phenyl sulfone has been achieved (Scheme 47, Eq. 47a). The modest yield (50%) for the conversion is due to the instability of the dienyl sulfone which readily polymerizes. Finally, the radical nature of the process has been demonstrated by running... 

Allylic and dienyl sulfones have been prepared by conjugate addition to 1,3-dienes ". Phenylsulfonyhnercuration of conjugated dienes gives mercury adducts which can be treated with base to afford phenylsulfonyldienes. 2-(Phenylsulfonyl)-l,3-dienes can be stereo- and regioselectively functionalized via Michael addition of nucleophiles to give allylic sulfones. A key intermediate in the synthesis of a Monarch butterfly pheromone 4 was prepared by BackvaU and Juntunen by alkylation and subsequent palladium-catalyzed substitution of the allylic sulfone formed by Michael addition of dimethyl malonate to 2-(phenylsulfonyl)-l,3-butadiene (equation 10). 

ChlorosttlfenylatioH-dehydrochlorinMion. This hygroscopic reagent is conveniently prepared and used in a methylene chloride solution by the reaction of NCS with thiophenol. The coproduct succinimide does not interfere with the chlorosulfenylation of alkenes. The 1 1 adducts, -chlorophenyl sulfides, are formed in high yield. The products are converted into allyl, vinyl, or dienyl sulfides on dehydrochlorination with DBU. The last example illustrates a route to a, 3-unsaturated sulfones. 

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