Alkenyl esters, bromination

Alkenyl boronic acids synthesized from internal alkynes fail to undergo the reaction with iodine and base. However, alkenylboronic acids and esters obtained from internal alkynes react with bromine in the presence of base to afford in excellent yields the corresponding alkenyl bromides (Eq. 112)174),... 

Bennasar also recently extended their interest in the cyclization of A -alkenyl substituted 2-indolylacyl radicals towards the annulation of larger rings [126]. A 7-endo-mg closure was observed when brotnovinyl substituted seleno ester 237 was treated with excess tin hydride in EtaB. In addition to the desired azepino[3,2-I>] indole 238, the 6-exo cyclization product 239 was observed as the minor product, with both products showing no evidence of the bromine atom in their strucmres. Previous attempts at this cyclization using a tethered allyl moiety, rather than the 2-bromo-2-propenyl tether, also gave the azepinoindole but only as the minor product. 

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