Epoxy-Ramberg-Backlund

The epoxy-Ramberg-Backlund reaction (ERBR) has been used for the conversion of a,/3-epoxy sulfones into a range of mono-, di-, and tri-substituted allylic alcohols.34 Modification of this method has permitted the preparation of enantio-enriched allylic alcohols following the diastereoselective epoxidation of enantio-enriched vinyl sulfones that were accessed efficiently from the chiral pool. 

Treatment of o ,/ -epoxysulfones with bases, such as KO-/-Bu, lithium diisopropylamide (LDA), LiHMDS, or LiO-/-Bu in THE, led to the epoxy-Ramberg-Backlund reaction and gave allyl alcohols via thiirane 1,1-dioxides (HMDS = hexamethyldisilazide). The latter lose sulfur dioxide under the reaction conditions (Scheme 22) <1997TL3055>. 

Evans, P., Taylor, R. J. The epoxy-Ramberg-Backlund reaction a new route to allylic alcohols. Tetrahedron Lett. 1997, 38, 3055-3058. Evans, P., Taylor, R. J. K. Novel tandem conjugate addition/Ramberg-Backlund rearrangements. Syniett 1997,1043-1044. 

Epoxy Ramberg-Backlund Reaction. c/j/ -Epoxy sulfones... 

One of the earliest and most important discoveries in metal-catalyzed asymmetric synthesis is Sharpless s Ti-catalyzed epoxidation of allylic alcohols. A mere mention of all the total syntheses that have used this technology would require a separate review article Here, we select Trost s masterful total synthesis of solamin (100, Scheme 14), for its beautiful and multiple use of Sharpless s asymmetric epoxidation.1161 Optically pure epoxy alcohol 95 is converted to both epoxy iodide 96 and diol 97 The latter two intermediates are then united to give 98, which is oxidized and converted to dihydrofuran 99 by a Ramberg-Backlund transformation. The Re catalyzed butenolide annulation that is used to afford the requisite unsaturated lactone only adds to the efficiency of this beautiful total synthesis. 

A novel tandem process has been reported " for the preparation of allylic amines, ethers, and sulfides from a-bromo-a, jS-unsaturated sulfones. The process is believed to proceed via an initial conjugate addition followed by proton exchange and Ramberg-Backlund rearrangement (see Scheme 75). A new variant of the Ramberg-Backlund reaction has been described in which a, /f-epoxy sulfones (319), on treatment with base, are converted into a range of mono-, di-, and tri-substituted allylic alcohols (320). 

Alfylicalcohols. Epoxy sulfones undergo the Ramberg-Backlund reaction in which the epoxide acts as the leaving group. Decomposition of hydroxylated episulfones affords the allylic alcohols. 

Numerous variants of the Ramberg-BScklund reaction exist. The most prevalent are the vinylogous and Michael-induced Ramberg-BScklund reactions. Decarboxy-lative, epoxy-, and tandem Diels-Alder Ramberg-Backlund reactions are also found in the literature. 

Epoxy-Ramberg-BScklund reaction is also uncommon. In place of iodide, sulfonate, or sulfinate leaving groups, Taylor and his colleagues chose epoxide as the leaving group in the Ramberg-Backlund reaction.28 As shown below, exposure of... 

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