Tellurolate-induced 1,4-elimination of 1,4-dibromo 2-enes. Syntheses of 1,3-dienes

Abstract

Sodium 2-thienyltellurolate, generated in catalytic amounts from sodium borohydride and bis(2-thienyl) ditelluride, was found to efficiently debrominate l,4-dibromo-2-olefins to 1,3-dienes under very mild reaction conditions. The required 1,4-dibromo-2-olefins were usually synthesized by allylic , '-bromination of olefins.Terminal olefins yielded, via allylic rearrangement, a mixture of 1,4-dibromo-2-olefins and l,2-dibromo-3-olefins.Both these isomers were converted to 1,3-dienes (E/Z = 9/1) by the tellurolate reagent. The synthetic utility of the tellurolate-induced debromination reaction was demonstrated in a two-step synthesis of the main component

Organotellurium Compounds in Organic Synthesis

“…8S Catalytic debromination of l,4-dibromoalk-2-enes by sodium thiophen-2-tellurolate has been used to obtain 1,3-dienes. 86 Oxidation of allyl phenyl tellurides by the oxidants enumerated above and also by t-butyl hydroperoxides leads to allyl alochols in high yields, 87 probably via the [2,3]-sigmatropic rearrangement of the alkyl phenyl telluroxides formed as intermediates.…”

Synthetic methodologies for carbo-substituted conjugated dienes

“…In addition to the traditional zinc, 34,35 the salts of arenetellurols were recommended. 36 In the latter case, the process can be performed readily using catalytic amount of Ar 2 Te 2 that is periodically reduced by titrating the reaction mass with sodium borohydride. This method was applied to a number of linear and cyclic substrates, including those bearing additional functional groups.…”

“…N-bromosuccinimide. 36 In the latter case, the bromination occurs in a stepwise mode involving allylic rearrangement. 1,2-Dibromoalk-3-enes 26 can be prepared from the corresponding diols which, in their turn, are obtainable from allylic alcohols.…”