Regioselectivity Payne rearrangement

Nucleophilic substitutions at C(2) and C(3) positions are not always as regioselective as the Payne rearrangement-opening reactions [10b] and the chemist may then utilise the C(l) hydroxyl group as a control element for inducing a... 

Under Payne rearrangement conditions, sodium /-butylthiolate provides 1 -/-butylthio-2,3-diols with very high regioselectivity. The selectivity is affected, however, by many factors including reaction temperature, base concentration, and the rate of addition of the thiol. These sulfides can then be converted to the l,2-epoxy-3-alcohols, which in turn react with a wide variety of nucleophiles specifically at the 1-position (Scheme 9.6). This methodology circumvents the problems associated with the instability of many nucleophiles under Payne conditions.85... 

A novel regioselectivity is observed with rrans-2,3-epoxy alcohols. The C-1 attack of 1,2-epoxy alcohol formed by the Payne rearrangement proceeds predominantly, and anri-p,7-dihydroxyalkynes are obtained stereospecific ly (equation 37). ° The reaction is employed in the synthesis of a pheromone, eO fA o-6-acetoxyhexadecan-5-olide. 

Schomaker et al found that the Payne rearrangement is useful for controlling the regioselectivity of the reaction of dimethylsulfoxonium ylide with the epoxy alcohol 22. Thus the rearrangement of chiral non racemic epoxy alcohol 21 led to the more sterically accessible terminal epoxide 22, which then underwent nucleophilic epoxide opening with the ylide at C-1 to afford bis alkoxide 23. The 5-exo-tet ring closure of 23 resulted in the formation of 2,3-disubstituted tetrahydrofuran ring 24. 

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