Polyenes, Ramberg-Backlund reaction

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. 

Addition to x,( y,S-dienyI sulfones. Lithium dialkylcuprates react with these diunsaturated sulfones by 1,6-addition, and the new double bond formed has the (Z>-geometry. The adducts on treatment with base extrude S02(Ramberg-Backlund reaction) to give a mixture of polyenes.20... 

Incorporation of deuterium at the vinylic positions of alkenes can be carried out very efficiently by performing the Ramberg-BScklund reaction in D2O. Finally, the recently developed Michael-induced and vinylogous modifications of the Ramberg-Backlund reaction offer useful approaches to conjugated dienes and polyenes. 

The Ramberg-Backlund reaction is now widely utilized in organic synthesis. It has been applied in synthesizing cyclobutenes, cyclopentenes, cyclohexenes, phenanthrenes, large ring systems, dienes, enynes, polyenes, alkynes, and many natural products. 

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... 

Reactions.—The Ramberg-Backlund reaction provides a useful route to mediumsized ring polyenes, as illustrated by the syntheses of (80) and (81), although poor yields are obtained in the synthesis of cyclophanedienes. ... 

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