NaBH3CN: A Janus Substitute for Tin-Free Radical-Based Reactions

Beside showing that thermal radical reactions (reduction, Giese reaction) are efficient if bromo-/iodosugars are treated with NaBH3CN and 2,2 ''-azobisisobutyronitrile, we explored new initiation conditions on the basis of Cu-I salts (<= 0.5 equiv.) supposed to produce radicals from organobromides through a set. This was confirmed, as at about 50 degrees C under an inert atmosphere acetobromoglucose was reduced to the rearranged 2-deoxyglucose and as N-allyl alpha-bromo-amides reacted, depending on the conditions, either by reductive cyclization or atom-transfer radical cyclization. A related cyclization occurred upon using Cu(OAc)(2). This and other assays showed the reduction by NaBH3CN of Cu-II salts, either added or formed in situ. Having both ionic and radical reactivity, NaBH3CN appears as a Janus reagent that may be useful for tin-free radical chemistry under mild and very simple conditions.